/**
 * Copyright (c) 2002, 2015 IBM Corporation and others.
 *
 * This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License 2.0
 * which accompanies this distribution, and is available at
 * https://www.eclipse.org/legal/epl-2.0/
 *
 * SPDX-License-Identifier: EPL-2.0
 *
 * Contributors:
 *   IBM - Initial API and implementation
 */
package org.eclipse.e4.ui.css.swt.helpers;

import java.io.File;
import java.lang.ref.WeakReference;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.Objects;
import java.util.Set;
import java.util.StringTokenizer;

/**
 * A representation of a Uniform Resource Identifier (URI), as specified by
 * <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>, with certain
 * enhancements.  A <code>URI</code> instance can be created by specifying
 * values for its components, or by providing a single URI string, which is
 * parsed into its components.  Static factory methods whose names begin
 * with "create" are used for both forms of object creation.  No public or
 * protected constructors are provided; this class can not be subclassed.
 *
 * <p>Like <code>String</code>, <code>URI</code> is an immutable class;
 * a <code>URI</code> instance offers several by-value methods that return a
 * new <code>URI</code> object based on its current state.  Most useful,
 * a relative <code>URI</code> can be {@link #resolve(URI) resolve}d against
 * a base absolute <code>URI</code> -- the latter typically identifies the
 * document in which the former appears.  The inverse to this is {@link
 * #deresolve(URI) deresolve}, which answers the question, "what relative
 * URI will resolve, against the given base, to this absolute URI?"
 *
 * <p>In the <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC</a>, much
 * attention is focused on a hierarchical naming system used widely to
 * locate resources via common protocols such as HTTP, FTP, and Gopher, and
 * to identify files on a local file system.  Accordingly, most of this
 * class's functionality is for handling such URIs, which can be identified
 * via {@link #isHierarchical isHierarchical}.
 *
 * <p id="device_explanation">
 * The primary enhancement beyond the RFC description is an optional
 * device component.  Instead of treating the device as just another segment
 * in the path, it can be stored as a separate component (almost a
 * sub-authority), with the root below it.  For example, resolving
 * <code>/bar</code> against <code>file:///c:/foo</code> would result in
 * <code>file:///c:/bar</code> being returned.  Also, you cannot take
 * the parent of a device, so resolving <code>..</code> against
 * <code>file:///c:/</code> would not yield <code>file:///</code>, as you
 * might expect.  This feature is useful when working with file-scheme
 * URIs, as devices do not typically occur in protocol-based ones.  A
 * device-enabled <code>URI</code> is created by parsing a string with
 * {@link #createURI(String) createURI}; if the first segment of the path
 * ends with the <code>:</code> character, it is stored (including the colon)
 * as the device, instead.  Alternately, either the {@link
 * #createHierarchicalURI(String, String, String, String, String) no-path}
 * or the {@link #createHierarchicalURI(String, String, String, String[],
 * String, String) absolute-path} form of <code>createHierarchicalURI()</code>
 * can be used, in which a non-null <code>device</code> parameter can be
 * specified.
 *
 * <p id="archive_explanation">
 * The other enhancement provides support for the almost-hierarchical
 * form used for files within archives, such as the JAR scheme, defined
 * for the Java Platform in the documentation for {@link
 * java.net.JarURLConnection}. By default, this support is enabled for
 * absolute URIs with scheme equal to "jar", "zip", or "archive" (ignoring case), and
 * is implemented by a hierarchical URI, whose authority includes the
 * entire URI of the archive, up to and including the <code>!</code>
 * character.  The URI of the archive must have no fragment.  The whole
 * archive URI must have no device and an absolute path.  Special handling
 * is supported for {@link #createURI(String) creating}, {@link
 * #validArchiveAuthority validating}, {@link #devicePath getting the path}
 * from, and {@link #toString() displaying} archive URIs. In all other
 * operations, including {@link #resolve(URI) resolving} and {@link
 * #deresolve(URI) deresolving}, they are handled like any ordinary URI.
 * The schemes that identify archive URIs can be changed from their default
 * by setting the <code>org.eclipse.emf.common.util.URI.archiveSchemes</code>
 * system property. Multiple schemes should be space separated, and the test
 * of whether a URI's scheme matches is always case-insensitive.
 *
 * <p>This implementation does not impose all of the restrictions on
 * character validity that are specified in the RFC.  Static methods whose
 * names begin with "valid" are used to test whether a given string is valid
 * value for the various URI components.  Presently, these tests place no
 * restrictions beyond what would have been required in order for {@link
 * #createURI(String) createURI} to have parsed them correctly from a single
 * URI string.  If necessary in the future, these tests may be made more
 * strict, to better conform to the RFC.
 *
 * <p>Another group of static methods, whose names begin with "encode", use
 * percent escaping to encode any characters that are not permitted in the
 * various URI components. Another static method is provided to {@link
 * #decode decode} encoded strings.  An escaped character is represented as
 * a percent symbol (<code>%</code>), followed by two hex digits that specify
 * the character code.  These encoding methods are more strict than the
 * validation methods described above.  They ensure validity according to the
 * RFC, with one exception: non-ASCII characters.
 *
 * <p>The RFC allows only characters that can be mapped to 7-bit US-ASCII
 * representations.  Non-ASCII, single-byte characters can be used only via
 * percent escaping, as described above.  This implementation uses Java's
 * Unicode <code>char</code> and <code>String</code> representations, and
 * makes no attempt to encode characters 0xA0 and above.  Characters in the
 * range 0x80-0x9F are still escaped.  In this respect, EMF's notion of a URI
 * is actually more like an IRI (Internationalized Resource Identifier), for
 * which an RFC is now in <a href="http://www.w3.org/International/iri-edit/draft-duerst-iri-09.txt">draft
 * form</a>.
 *
 * <p>Finally, note the difference between a <code>null</code> parameter to
 * the static factory methods and an empty string.  The former signifies the
 * absence of a given URI component, while the latter simply makes the
 * component blank.  This can have a significant effect when resolving.  For
 * example, consider the following two URIs: <code>/bar</code> (with no
 * authority) and <code>///bar</code> (with a blank authority).  Imagine
 * resolving them against a base with an authority, such as
 * <code>http://www.eclipse.org/</code>.  The former case will yield
 * <code>http://www.eclipse.org/bar</code>, as the base authority will be
 * preserved.  In the latter case, the empty authority will override the
 * base authority, resulting in <code>http:///bar</code>!
 */
public final class URI
{
	// Common to all URI types.
	private final int hashCode;
	private static final int HIERARICHICAL_FLAG = 0x0100;
	private final String scheme;  // null -> relative URI reference
	private final String authority;
	private final String fragment;
	private URI cachedTrimFragment;
	private String cachedToString;
	//private final boolean iri;
	//private URI cachedASCIIURI;

	// Applicable only to a hierarchical URI.
	private final String device;
	private static final int ABSOLUTE_PATH_FLAG = 0x0010;
	private final String[] segments; // empty last segment -> trailing separator
	private final String query;

	// A cache of URIs, keyed by the strings from which they were created.
	// The fragment of any URI is removed before caching it here, to minimize
	// the size of the cache in the usual case where most URIs only differ by
	// the fragment.
	private static final URICache uriCache = new URICache();

	private static class URICache extends HashMap<String,WeakReference<URI>>
	{
		private static final long serialVersionUID = 1L;

		static final int MIN_LIMIT = 1000;
		int count;
		int limit = MIN_LIMIT;

		public synchronized URI get(String key)
		{
			WeakReference<URI> reference = super.get(key);
			return reference == null ? null : reference.get();
		}

		public synchronized void put(String key, URI value)
		{
			super.put(key, new WeakReference<>(value));
			if (++count > limit)
			{
				cleanGCedValues();
			}
		}

		private void cleanGCedValues()
		{
			for (Iterator<Map.Entry<String,WeakReference<URI>>> i = entrySet().iterator(); i.hasNext(); )
			{
				Map.Entry<String,WeakReference<URI>> entry = i.next();
				WeakReference<URI> reference = entry.getValue();
				if (reference.get() == null)
				{
					i.remove();
				}
			}
			count = 0;
			limit = Math.max(MIN_LIMIT, size() / 2);
		}
	}

	// The lower-cased schemes that will be used to identify archive URIs.
	private static final Set<String> archiveSchemes;

	// Identifies a file-type absolute URI.
	private static final String SCHEME_FILE = "file";
	private static final String SCHEME_JAR = "jar";
	private static final String SCHEME_ZIP = "zip";
	private static final String SCHEME_ARCHIVE = "archive";
	private static final String SCHEME_PLATFORM = "platform";

	// Special segment values interpreted at resolve and resolve time.
	private static final String SEGMENT_EMPTY = "";
	private static final String SEGMENT_SELF = ".";
	private static final String SEGMENT_PARENT = "..";
	private static final String[] NO_SEGMENTS = new String[0];

	// Separators for parsing a URI string.
	private static final char SCHEME_SEPARATOR = ':';
	private static final String AUTHORITY_SEPARATOR = "//";
	private static final char DEVICE_IDENTIFIER = ':';
	private static final char SEGMENT_SEPARATOR = '/';
	private static final char QUERY_SEPARATOR = '?';
	private static final char FRAGMENT_SEPARATOR = '#';
	private static final char USER_INFO_SEPARATOR = '@';
	private static final char PORT_SEPARATOR = ':';
	private static final char FILE_EXTENSION_SEPARATOR = '.';
	private static final char ARCHIVE_IDENTIFIER = '!';
	private static final String ARCHIVE_SEPARATOR = "!/";

	// Characters to use in escaping.
	private static final char ESCAPE = '%';
	private static final char[] HEX_DIGITS = {
		'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F' };

	// Some character classes, as defined in RFC 2396's BNF for URI.
	// These are 128-bit bitmasks, stored as two longs, where the Nth bit is set
	// iff the ASCII character with value N is included in the set.  These are
	// created with the highBitmask() and lowBitmask() methods defined below,
	// and a character is tested against them using matches().
	//
	private static final long ALPHA_HI = highBitmask('a', 'z') | highBitmask('A', 'Z');
	private static final long ALPHA_LO = lowBitmask('a', 'z')  | lowBitmask('A', 'Z');
	private static final long DIGIT_HI = highBitmask('0', '9');
	private static final long DIGIT_LO = lowBitmask('0', '9');
	private static final long ALPHANUM_HI = ALPHA_HI | DIGIT_HI;
	private static final long ALPHANUM_LO = ALPHA_LO | DIGIT_LO;
	private static final long HEX_HI = DIGIT_HI | highBitmask('A', 'F') | highBitmask('a', 'f');
	private static final long HEX_LO = DIGIT_LO | lowBitmask('A', 'F')  | lowBitmask('a', 'f');
	private static final long UNRESERVED_HI = ALPHANUM_HI | highBitmask("-_.!~*'()");
	private static final long UNRESERVED_LO = ALPHANUM_LO | lowBitmask("-_.!~*'()");
	private static final long RESERVED_HI = highBitmask(";/?:@&=+$,");
	private static final long RESERVED_LO = lowBitmask(";/?:@&=+$,");
	private static final long URIC_HI = RESERVED_HI | UNRESERVED_HI;  // | ucschar | escaped
	private static final long URIC_LO = RESERVED_LO | UNRESERVED_LO;

	// Additional useful character classes, including characters valid in certain
	// URI components and separators used in parsing them out of a string.
	//
	private static final long SEGMENT_CHAR_HI = UNRESERVED_HI | highBitmask(";:@&=+$,");  // | ucschar | escaped
	private static final long SEGMENT_CHAR_LO = UNRESERVED_LO | lowBitmask(";:@&=+$,");
	private static final long PATH_CHAR_HI = SEGMENT_CHAR_HI | highBitmask('/');  // | ucschar | escaped
	private static final long PATH_CHAR_LO = SEGMENT_CHAR_LO | lowBitmask('/');
//  private static final long SCHEME_CHAR_HI = ALPHANUM_HI | highBitmask("+-.");
//  private static final long SCHEME_CHAR_LO = ALPHANUM_LO | lowBitmask("+-.");
	private static final long MAJOR_SEPARATOR_HI = highBitmask(":/?#");
	private static final long MAJOR_SEPARATOR_LO = lowBitmask(":/?#");
	private static final long SEGMENT_END_HI = highBitmask("/?#");
	private static final long SEGMENT_END_LO = lowBitmask("/?#");

	// The intent of this was to switch over to encoding platform resource URIs
	// by default, but allow people to use a system property to avoid this.
	// However, that caused problems for people and we had to go back to not
	// encoding and introduce yet another factory method that explicitly enables
	// encoding.
	//
	private static final boolean ENCODE_PLATFORM_RESOURCE_URIS =
		System.getProperty("org.eclipse.emf.common.util.URI.encodePlatformResourceURIs") != null &&
		!"false".equalsIgnoreCase(System.getProperty("org.eclipse.emf.common.util.URI.encodePlatformResourceURIs"));

	// Static initializer for archiveSchemes.
	static
	{
		Set<String> set = new HashSet<>();
		String propertyValue = System.getProperty("org.eclipse.emf.common.util.URI.archiveSchemes");

		if (propertyValue == null)
		{
			set.add(SCHEME_JAR);
			set.add(SCHEME_ZIP);
			set.add(SCHEME_ARCHIVE);
		}
		else
		{
			for (StringTokenizer t = new StringTokenizer(propertyValue); t.hasMoreTokens(); )
			{
				set.add(t.nextToken().toLowerCase());
			}
		}

		archiveSchemes = Collections.unmodifiableSet(set);
	}

	// Returns the lower half bitmask for the given ASCII character.
	private static long lowBitmask(char c)
	{
		return c < 64 ? 1L << c : 0L;
	}

	// Returns the upper half bitmask for the given ACSII character.
	private static long highBitmask(char c)
	{
		return c >= 64 && c < 128 ? 1L << (c - 64) : 0L;
	}

	// Returns the lower half bitmask for all ASCII characters between the two
	// given characters, inclusive.
	private static long lowBitmask(char from, char to)
	{
		long result = 0L;
		if (from < 64 && from <= to)
		{
			to = to < 64 ? to : 63;
			for (char c = from; c <= to; c++)
			{
				result |= (1L << c);
			}
		}
		return result;
	}

	// Returns the upper half bitmask for all AsCII characters between the two
	// given characters, inclusive.
	private static long highBitmask(char from, char to)
	{
		return to < 64 ? 0 : lowBitmask((char)(from < 64 ? 0 : from - 64), (char)(to - 64));
	}

	// Returns the lower half bitmask for all the ASCII characters in the given
	// string.
	private static long lowBitmask(String chars)
	{
		long result = 0L;
		for (int i = 0, len = chars.length(); i < len; i++)
		{
			char c = chars.charAt(i);
			if (c < 64) {
		result |= (1L << c);
	}
		}
		return result;
	}

	// Returns the upper half bitmask for all the ASCII characters in the given
	// string.
	private static long highBitmask(String chars)
	{
		long result = 0L;
		for (int i = 0, len = chars.length(); i < len; i++)
		{
			char c = chars.charAt(i);
			if (c >= 64 && c < 128) {
		result |= (1L << (c - 64));
	}
		}
		return result;
	}

	// Returns whether the given character is in the set specified by the given
	// bitmask.
	private static boolean matches(char c, long highBitmask, long lowBitmask)
	{
		if (c >= 128) {
		return false;
	}
		return c < 64 ?
			((1L << c) & lowBitmask) != 0 :
			((1L << (c - 64)) & highBitmask) != 0;
	}

	// Debugging method: converts the given long to a string of binary digits.
/*
	private static String toBits(long l)
	{
		StringBuilder result = new StringBuilder();
		for (int i = 0; i < 64; i++)
		{
			boolean b = (l & 1L) != 0;
			result.insert(0, b ? '1' : '0');
			l >>= 1;
		}
		return result.toString();
	}
*/

	/**
	 * Static factory method for a generic, non-hierarchical URI.  There is no
	 * concept of a relative non-hierarchical URI; such an object cannot be
	 * created.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>scheme</code> is
	 * null, if <code>scheme</code> is an <a href="#archive_explanation">archive
	 * URI</a> scheme, or if <code>scheme</code>, <code>opaquePart</code>, or
	 * <code>fragment</code> is not valid according to {@link #validScheme
	 * validScheme}, {@link #validOpaquePart validOpaquePart}, or {@link
	 * #validFragment validFragment}, respectively.
	 */
	public static URI createGenericURI(String scheme, String opaquePart,
										String fragment)
	{
		if (scheme == null)
		{
			throw new IllegalArgumentException("relative non-hierarchical URI");
		}

		if (isArchiveScheme(scheme))
		{
			throw new IllegalArgumentException("non-hierarchical archive URI");
		}

		validateURI(false, scheme, opaquePart, null, NO_SEGMENTS, null, fragment);
		return new URI(false, scheme, opaquePart, null, false, NO_SEGMENTS, null, fragment);
	}

	/**
	 * Static factory method for a hierarchical URI with no path.  The
	 * URI will be relative if <code>scheme</code> is non-null, and absolute
	 * otherwise.  An absolute URI with no path requires a non-null
	 * <code>authority</code> and/or <code>device</code>.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>scheme</code> is
	 * non-null while <code>authority</code> and <code>device</code> are null,
	 * if <code>scheme</code> is an <a href="#archive_explanation">archive
	 * URI</a> scheme, or if <code>scheme</code>, <code>authority</code>,
	 * <code>device</code>, <code>query</code>, or <code>fragment</code> is not
	 * valid according to {@link #validScheme validSheme}, {@link
	 * #validAuthority validAuthority}, {@link #validDevice validDevice},
	 * {@link #validQuery validQuery}, or {@link #validFragment validFragment},
	 * respectively.
	 */
	public static URI createHierarchicalURI(String scheme, String authority,
											String device, String query,
											String fragment)
	{
		if (scheme != null && authority == null && device == null)
		{
			throw new IllegalArgumentException(
				"absolute hierarchical URI without authority, device, path");
		}

		if (isArchiveScheme(scheme))
		{
			throw new IllegalArgumentException("archive URI with no path");
		}

		validateURI(true, scheme, authority, device, NO_SEGMENTS, query, fragment);
		return new URI(true, scheme, authority, device, false, NO_SEGMENTS, query, fragment);
	}

	/**
	 * Static factory method for a hierarchical URI with absolute path.
	 * The URI will be relative if <code>scheme</code> is non-null, and
	 * absolute otherwise.
	 *
	 * @param segments an array of non-null strings, each representing one
	 * segment of the path.  As an absolute path, it is automatically
	 * preceded by a <code>/</code> separator.  If desired, a trailing
	 * separator should be represented by an empty-string segment as the last
	 * element of the array.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>scheme</code> is
	 * an <a href="#archive_explanation">archive URI</a> scheme and
	 * <code>device</code> is non-null, or if <code>scheme</code>,
	 * <code>authority</code>, <code>device</code>, <code>segments</code>,
	 * <code>query</code>, or <code>fragment</code> is not valid according to
	 * {@link #validScheme validScheme}, {@link #validAuthority validAuthority}
	 * or {@link #validArchiveAuthority validArchiveAuthority}, {@link
	 * #validDevice validDevice}, {@link #validSegments validSegments}, {@link
	 * #validQuery validQuery}, or {@link #validFragment validFragment}, as
	 * appropriate.
	 */
	public static URI createHierarchicalURI(String scheme, String authority,
											String device, String[] segments,
											String query, String fragment)
	{
		if (isArchiveScheme(scheme) && device != null)
		{
			throw new IllegalArgumentException("archive URI with device");
		}

		segments = fix(segments);
		validateURI(true, scheme, authority, device, segments, query, fragment);
		return new URI(true, scheme, authority, device, true, segments, query, fragment);
	}

	/**
	 * Static factory method for a relative hierarchical URI with relative
	 * path.
	 *
	 * @param segments an array of non-null strings, each representing one
	 * segment of the path.  A trailing separator is represented by an
	 * empty-string segment at the end of the array.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>segments</code>,
	 * <code>query</code>, or <code>fragment</code> is not valid according to
	 * {@link #validSegments validSegments}, {@link #validQuery validQuery}, or
	 * {@link #validFragment validFragment}, respectively.
	 */
	public static URI createHierarchicalURI(String[] segments, String query,
											String fragment)
	{
		segments = fix(segments);
		validateURI(true, null, null, null, segments, query, fragment);
		return new URI(true, null, null, null, false, segments, query, fragment);
	}

	// Converts null to length-zero array, and clones array to ensure
	// immutability.
	private static String[] fix(String[] segments)
	{
		return segments == null ? NO_SEGMENTS : segments.clone();
	}

	/**
	 * Static factory method based on parsing a URI string, with
	 * <a href="#device_explanation">explicit device support</a> and handling
	 * for <a href="#archive_explanation">archive URIs</a> enabled. The
	 * specified string is parsed as described in <a
	 * href="http://www.ietf.org/rfc/rfc2396.txt">RFC 2396</a>, and an
	 * appropriate <code>URI</code> is created and returned.  Note that
	 * validity testing is not as strict as in the RFC; essentially, only
	 * separator characters are considered.  This method also does not perform
	 * encoding of invalid characters, so it should only be used when the URI
	 * string is known to have already been encoded, so as to avoid double
	 * encoding.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from <code>uri</code> is not valid according to {@link #validScheme
	 * validScheme}, {@link #validOpaquePart validOpaquePart}, {@link
	 * #validAuthority validAuthority}, {@link #validArchiveAuthority
	 * validArchiveAuthority}, {@link #validDevice validDevice}, {@link
	 * #validSegments validSegments}, {@link #validQuery validQuery}, or {@link
	 * #validFragment validFragment}, as appropriate.
	 */
	public static URI createURI(String uri)
	{
		return createURIWithCache(uri);
	}

	/**
	 * Static factory method that encodes and parses the given URI string.
	 * Appropriate encoding is performed for each component of the URI.
	 * If more than one <code>#</code> is in the string, the last one is
	 * assumed to be the fragment's separator, and any others are encoded.
	 * This method is the simplest way to safely parse an arbitrary URI string.
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  This
	 * capability is provided to allow partially encoded URIs to be "fixed",
	 * while avoiding adding double encoding; however, it is usual just to
	 * specify <code>false</code> to perform ordinary encoding.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from <code>uri</code> is not valid according to {@link #validScheme
	 * validScheme}, {@link #validOpaquePart validOpaquePart}, {@link
	 * #validAuthority validAuthority}, {@link #validArchiveAuthority
	 * validArchiveAuthority}, {@link #validDevice validDevice}, {@link
	 * #validSegments validSegments}, {@link #validQuery validQuery}, or {@link
	 * #validFragment validFragment}, as appropriate.
	 */
	public static URI createURI(String uri, boolean ignoreEscaped)
	{
		return createURIWithCache(encodeURI(uri, ignoreEscaped, FRAGMENT_LAST_SEPARATOR));
	}

	/**
	 * When specified as the last argument to {@link #createURI(String, boolean, int)
	 * createURI}, indicates that there is no fragment, so any <code>#</code> characters
	 * should be encoded.
	 * @see #createURI(String, boolean, int)
	 */
	public static final int FRAGMENT_NONE = 0;

	/**
	 * When specified as the last argument to {@link #createURI(String, boolean, int)
	 * createURI}, indicates that the first <code>#</code> character should be taken as
	 * the fragment separator, and any others should be encoded.
	 * @see #createURI(String, boolean, int)
	 */
	public static final int FRAGMENT_FIRST_SEPARATOR = 1;

	/**
	 * When specified as the last argument to {@link #createURI(String, boolean, int)
	 * createURI}, indicates that the last <code>#</code> character should be taken as
	 * the fragment separator, and any others should be encoded.
	 * @see #createURI(String, boolean, int)
	 */
	public static final int FRAGMENT_LAST_SEPARATOR = 2;

	/**
	 * Static factory method that encodes and parses the given URI string.
	 * Appropriate encoding is performed for each component of the URI.
	 * Control is provided over which, if any, <code>#</code> should be
	 * taken as the fragment separator and which should be encoded.
	 * This method is the preferred way to safely parse an arbitrary URI string
	 * that is known to contain <code>#</code> characters in the fragment or to
	 * have no fragment at all.
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  This
	 * capability is provided to allow partially encoded URIs to be "fixed",
	 * while avoiding adding double encoding; however, it is usual just to
	 * specify <code>false</code> to perform ordinary encoding.
	 *
	 * @param fragmentLocationStyle one of {@link #FRAGMENT_NONE},
	 * {@link #FRAGMENT_FIRST_SEPARATOR}, or {@link #FRAGMENT_LAST_SEPARATOR},
	 * indicating which, if any, of the <code>#</code> characters should be
	 * considered the fragment separator. Any others will be encoded.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from <code>uri</code> is not valid according to {@link #validScheme
	 * validScheme}, {@link #validOpaquePart validOpaquePart}, {@link
	 * #validAuthority validAuthority}, {@link #validArchiveAuthority
	 * validArchiveAuthority}, {@link #validDevice validDevice}, {@link
	 * #validSegments validSegments}, {@link #validQuery validQuery}, or {@link
	 * #validFragment validFragment}, as appropriate.
	 */
	public static URI createURI(String uri, boolean ignoreEscaped, int fragmentLocationStyle)
	{
		return createURIWithCache(encodeURI(uri, ignoreEscaped, fragmentLocationStyle));
	}

	/**
	 * Static factory method based on parsing a URI string, with
	 * <a href="#device_explanation">explicit device support</a> enabled.
	 * Note that validity testing is not a strict as in the RFC; essentially,
	 * only separator characters are considered.  So, for example, non-Latin
	 * alphabet characters appearing in the scheme would not be considered an
	 * error.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from <code>uri</code> is not valid according to {@link #validScheme
	 * validScheme}, {@link #validOpaquePart validOpaquePart}, {@link
	 * #validAuthority validAuthority}, {@link #validArchiveAuthority
	 * validArchiveAuthority}, {@link #validDevice validDevice}, {@link
	 * #validSegments validSegments}, {@link #validQuery validQuery}, or {@link
	 * #validFragment validFragment}, as appropriate.
	 *
	 * @deprecated Use {@link #createURI(String) createURI}, which now has explicit
	 * device support enabled. The two methods now operate identically.
	 */
	@Deprecated
	public static URI createDeviceURI(String uri)
	{
		return createURIWithCache(uri);
	}

	// Uses a cache to speed up creation of a URI from a string.  The cache
	// is consulted to see if the URI, less any fragment, has already been
	// created.  If needed, the fragment is re-appended to the cached URI,
	// which is considerably more efficient than creating the whole URI from
	// scratch.  If the URI wasn't found in the cache, it is created using
	// parseIntoURI() and then cached.  This method should always be used
	// by string-parsing factory methods, instead of parseIntoURI() directly.
	/**
	 * This method was included in the public API by mistake.
	 *
	 * @deprecated Please use {@link #createURI(String) createURI} instead.
	 */
	@Deprecated
	public static URI createURIWithCache(String uri)
	{
		int i = uri.indexOf(FRAGMENT_SEPARATOR);
		String base = i == -1 ? uri : uri.substring(0, i);
		String fragment = i == -1 ? null : uri.substring(i + 1);

		URI result = uriCache.get(base);

		if (result == null)
		{
			result = parseIntoURI(base);
			uriCache.put(base, result);
		}

		if (fragment != null)
		{
			result = result.appendFragment(fragment);
		}
		return result;
	}

	// String-parsing implementation.
	private static URI parseIntoURI(String uri)
	{
		boolean hierarchical = true;
		String scheme = null;
		String authority = null;
		String device = null;
		boolean absolutePath = false;
		String[] segments = NO_SEGMENTS;
		String query = null;
		String fragment = null;

		int i = 0;
		int j = find(uri, i, MAJOR_SEPARATOR_HI, MAJOR_SEPARATOR_LO);

		if (j < uri.length() && uri.charAt(j) == SCHEME_SEPARATOR)
		{
			scheme = uri.substring(i, j);
			i = j + 1;
		}

		boolean archiveScheme = isArchiveScheme(scheme);
		if (archiveScheme)
		{
			j = uri.lastIndexOf(ARCHIVE_SEPARATOR);
			if (j == -1)
			{
				throw new IllegalArgumentException("no archive separator");
			}
			hierarchical = true;
			authority = uri.substring(i, ++j);
			i = j;
		}
		else if (uri.startsWith(AUTHORITY_SEPARATOR, i))
		{
			i += AUTHORITY_SEPARATOR.length();
			j = find(uri, i, SEGMENT_END_HI, SEGMENT_END_LO);
			authority = uri.substring(i, j);
			i = j;
		}
		else if (scheme != null &&
						 (i == uri.length() || uri.charAt(i) != SEGMENT_SEPARATOR))
		{
			hierarchical = false;
			j = uri.indexOf(FRAGMENT_SEPARATOR, i);
			if (j == -1) {
			j = uri.length();
	}
			authority = uri.substring(i, j);
			i = j;
		}

		if (!archiveScheme && i < uri.length() && uri.charAt(i) == SEGMENT_SEPARATOR)
		{
			j = find(uri, i + 1, SEGMENT_END_HI, SEGMENT_END_LO);
			String s = uri.substring(i + 1, j);

			if (s.length() > 0 && s.charAt(s.length() - 1) == DEVICE_IDENTIFIER)
			{
				device = s;
				i = j;
			}
		}

		if (i < uri.length() && uri.charAt(i) == SEGMENT_SEPARATOR)
		{
			i++;
			absolutePath = true;
		}

		if (segmentsRemain(uri, i))
		{
			List<String> segmentList = new ArrayList<>();

			while (segmentsRemain(uri, i))
			{
				j = find(uri, i, SEGMENT_END_HI, SEGMENT_END_LO);
				segmentList.add(uri.substring(i, j));
				i = j;

				if (i < uri.length() && uri.charAt(i) == SEGMENT_SEPARATOR)
				{
					if (!segmentsRemain(uri, ++i)) {
				segmentList.add(SEGMENT_EMPTY);
			}
				}
			}
			segments = new String[segmentList.size()];
			segmentList.toArray(segments);
		}

		if (i < uri.length() && uri.charAt(i) == QUERY_SEPARATOR)
		{
			j = uri.indexOf(FRAGMENT_SEPARATOR, ++i);
			if (j == -1) {
			j = uri.length();
		}
			query = uri.substring(i, j);
			i = j;
		}

		if (i < uri.length()) // && uri.charAt(i) == FRAGMENT_SEPARATOR (implied)
		{
			fragment = uri.substring(++i);
		}

		validateURI(hierarchical, scheme, authority, device, segments, query, fragment);
		return new URI(hierarchical, scheme, authority, device, absolutePath, segments, query, fragment);
	}

	// Checks whether the string contains any more segments after the one that
	// starts at position i.
	private static boolean segmentsRemain(String uri, int i)
	{
		return i < uri.length() && uri.charAt(i) != QUERY_SEPARATOR &&
			uri.charAt(i) != FRAGMENT_SEPARATOR;
	}

	// Finds the next occurrence of one of the characters in the set represented
	// by the given bitmask in the given string, beginning at index i. The index
	// of the first found character, or s.length() if there is none, is
	// returned.  Before searching, i is limited to the range [0, s.length()].
	//
	private static int find(String s, int i, long highBitmask, long lowBitmask)
	{
		int len = s.length();
		if (i >= len) {
			return len;
		}

		for (i = i > 0 ? i : 0; i < len; i++)
		{
			if (matches(s.charAt(i), highBitmask, lowBitmask)) {
		break;
	}
		}
		return i;
	}

	/**
	 * Static factory method based on parsing a {@link java.io.File} path
	 * string.  The <code>pathName</code> is converted into an appropriate
	 * form, as follows: platform specific path separators are converted to
	 * <code>/</code>; the path is encoded; and a "file" scheme and, if missing,
	 * a leading <code>/</code>, are added to an absolute path.  The result
	 * is then parsed using {@link #createURI(String) createURI}.
	 *
	 * <p>The encoding step escapes all spaces, <code>#</code> characters, and
	 * other characters disallowed in URIs, as well as <code>?</code>, which
	 * would delimit a path from a query.  Decoding is automatically performed
	 * by {@link #toFileString toFileString}, and can be applied to the values
	 * returned by other accessors by via the static {@link #decode(String)
	 * decode} method.
	 *
	 * <p>A relative path with a specified device (something like
	 * <code>C:myfile.txt</code>) cannot be expressed as a valid URI.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>pathName</code>
	 * specifies a device and a relative path, or if any component of the path
	 * is not valid according to {@link #validAuthority validAuthority}, {@link
	 * #validDevice validDevice}, or {@link #validSegments validSegments},
	 * {@link #validQuery validQuery}, or {@link #validFragment validFragment}.
	 */
	public static URI createFileURI(String pathName)
	{
		File file = new File(pathName);
		String uri = File.separatorChar != '/' ? pathName.replace(File.separatorChar, SEGMENT_SEPARATOR) : pathName;
		uri = encode(uri, PATH_CHAR_HI, PATH_CHAR_LO, false);
		if (file.isAbsolute())
		{
			return createURI((uri.charAt(0) == SEGMENT_SEPARATOR ? "file:" : "file:/") + uri);
		}
		else
		{
			URI result = createURI(uri);
			if (result.scheme() != null)
			{
				throw new IllegalArgumentException("invalid relative pathName: " + pathName);
			}
			return result;
		}
	}

	/**
	 * Static factory method based on parsing a workspace-relative path string.
	 *
	 * <p>The <code>pathName</code> must be of the form:
	 * <pre>
	 *   /project-name/path</pre>
	 *
	 * <p>Platform-specific path separators will be converted to slashes.
	 * If not included, the leading path separator will be added.  The
	 * result will be of this form, which is parsed using {@link #createURI(String)
	 * createURI}:
	 * <pre>
	 *   platform:/resource/project-name/path</pre>
	 *
	 * <p>This scheme supports relocatable projects in Eclipse and in
	 * stand-alone EMF.
	 *
	 * <p>Path encoding is performed only if the
	 * <code>org.eclipse.emf.common.util.URI.encodePlatformResourceURIs</code>
	 * system property is set to "true". Decoding can be performed with the
	 * static {@link #decode(String) decode} method.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from the path is not valid according to {@link #validDevice validDevice},
	 * {@link #validSegments validSegments}, {@link #validQuery validQuery}, or
	 * {@link #validFragment validFragment}.
	 *
	 * @see org.eclipse.core.runtime.Platform#resolve
	 * @see #createPlatformResourceURI(String, boolean)
	 * @deprecated Use {@link #createPlatformResourceURI(String, boolean)} instead.
	 */
	@Deprecated
	public static URI createPlatformResourceURI(String pathName)
	{
		return createPlatformResourceURI(pathName, ENCODE_PLATFORM_RESOURCE_URIS);
	}

	/**
	 * Static factory method based on parsing a workspace-relative path string,
	 * with an option to encode the created URI.
	 *
	 * <p>The <code>pathName</code> must be of the form:
	 * <pre>
	 *   /project-name/path</pre>
	 *
	 * <p>Platform-specific path separators will be converted to slashes.
	 * If not included, the leading path separator will be added.  The
	 * result will be of this form, which is parsed using {@link #createURI(String)
	 * createURI}:
	 * <pre>
	 *   platform:/resource/project-name/path</pre>
	 *
	 * <p>This scheme supports relocatable projects in Eclipse and in
	 * stand-alone EMF.
	 *
	 * <p>Depending on the <code>encode</code> argument, the path may be
	 * automatically encoded to escape all spaces, <code>#</code> characters,
	 * and other characters disallowed in URIs, as well as <code>?</code>,
	 * which would delimit a path from a query.  Decoding can be performed with
	 * the static {@link #decode(String) decode} method. It is strongly
	 * recommended to specify <code>true</code> to enable encoding, unless the
	 * path string has already been encoded.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from the path is not valid according to {@link #validDevice validDevice},
	 * {@link #validSegments validSegments}, {@link #validQuery validQuery}, or
	 * {@link #validFragment validFragment}.
	 *
	 * @see org.eclipse.core.runtime.Platform#resolve
	 */
	public static URI createPlatformResourceURI(String pathName, boolean encode)
	{
		return createPlatformURI("platform:/resource", "platform:/resource/", pathName, encode);
	}

	/**
	 * Static factory method based on parsing a plug-in-based path string,
	 * with an option to encode the created URI.
	 *
	 * <p>The <code>pathName</code> must be of the form:
	 * <pre>
	 *   /plugin-id/path</pre>
	 *
	 * <p>Platform-specific path separators will be converted to slashes.
	 * If not included, the leading path separator will be added.  The
	 * result will be of this form, which is parsed using {@link #createURI(String)
	 * createURI}:
	 * <pre>
	 *   platform:/plugin/plugin-id/path</pre>
	 *
	 * <p>This scheme supports relocatable plug-in content in Eclipse.
	 *
	 * <p>Depending on the <code>encode</code> argument, the path may be
	 * automatically encoded to escape all spaces, <code>#</code> characters,
	 * and other characters disallowed in URIs, as well as <code>?</code>,
	 * which would delimit a path from a query.  Decoding can be performed with
	 * the static {@link #decode(String) decode} method. It is strongly
	 * recommended to specify <code>true</code> to enable encoding, unless the
	 * path string has already been encoded.
	 *
	 * @exception java.lang.IllegalArgumentException if any component parsed
	 * from the path is not valid according to {@link #validDevice validDevice},
	 * {@link #validSegments validSegments}, {@link #validQuery validQuery}, or
	 * {@link #validFragment validFragment}.
	 *
	 * @see org.eclipse.core.runtime.Platform#resolve
	 * @since org.eclipse.emf.common 2.3
	 */
	public static URI createPlatformPluginURI(String pathName, boolean encode)
	{
		return createPlatformURI("platform:/plugin", "platform:/plugin/", pathName, encode);
	}

	// Private constructor for use of platform factory methods.
	private static URI createPlatformURI(String unrootedBase, String rootedBase, String pathName, boolean encode)
	{
		if (File.separatorChar != SEGMENT_SEPARATOR)
		{
			pathName = pathName.replace(File.separatorChar, SEGMENT_SEPARATOR);
		}

		if (encode)
		{
			pathName = encode(pathName, PATH_CHAR_HI, PATH_CHAR_LO, false);
		}
		return createURI((pathName.charAt(0) == SEGMENT_SEPARATOR ? unrootedBase : rootedBase) + pathName);
	}

	// Private constructor for use of static factory methods.
	private URI(boolean hierarchical, String scheme, String authority,
					String device, boolean absolutePath, String[] segments,
					String query, String fragment)
	{
		int tmpHashCode = 0;
		if (scheme != null)
		{
			tmpHashCode ^= scheme.toLowerCase().hashCode();
		}
		tmpHashCode ^= Objects.hashCode(authority);
		tmpHashCode ^= Objects.hashCode(device);
		tmpHashCode ^= Objects.hashCode(query);
		tmpHashCode ^= Objects.hashCode(fragment);
		for (String segment : segments) {
			tmpHashCode ^= segment.hashCode();
		}

		if (hierarchical)
		{
			tmpHashCode |= HIERARICHICAL_FLAG;
		}
		else
		{
			tmpHashCode &= ~HIERARICHICAL_FLAG;
		}
		if (absolutePath)
		{
			tmpHashCode |= ABSOLUTE_PATH_FLAG;
		}
		else
		{
			tmpHashCode &= ~ABSOLUTE_PATH_FLAG;
		}
		this.hashCode = tmpHashCode;
		this.scheme = scheme == null ? null : scheme.intern();
		this.authority = authority;
		this.device = device;
		this.segments = segments;
		this.query = query;
		this.fragment = fragment;
	}

	// Validates all of the URI components.  Factory methods should call this
	// before using the constructor, though they must ensure that the
	// inter-component requirements described in their own Javadocs are all
	// satisfied, themselves.  If a new URI is being constructed out of
	// an existing URI, this need not be called.  Instead, just the new
	// components may be validated individually.
	private static void validateURI(boolean hierarchical, String scheme,
									String authority, String device,
									String[] segments,
									String query, String fragment)
	{
		if (!validScheme(scheme))
		{
			throw new IllegalArgumentException("invalid scheme: " + scheme);
		}
		if (!hierarchical && !validOpaquePart(authority))
		{
			throw new IllegalArgumentException("invalid opaquePart: " + authority);
		}
		if (hierarchical && !isArchiveScheme(scheme) && !validAuthority(authority))
		{
			throw new IllegalArgumentException("invalid authority: " + authority);
		}
		if (hierarchical && isArchiveScheme(scheme) && !validArchiveAuthority(authority))
		{
			throw new IllegalArgumentException("invalid authority: " + authority);
		}
		if (!validDevice(device))
		{
			throw new IllegalArgumentException("invalid device: " + device);
		}
		if (!validSegments(segments))
		{
			String s = segments == null ? "invalid segments: null" :
				"invalid segment: " + firstInvalidSegment(segments);
			throw new IllegalArgumentException(s);
		}
		if (!validQuery(query))
		{
			throw new IllegalArgumentException("invalid query: " + query);
		}
		if (!validFragment(fragment))
		{
			throw new IllegalArgumentException("invalid fragment: " + fragment);
		}
	}

	// Alternate, stricter implementations of the following validation methods
	// are provided, commented out, for possible future use...

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the scheme component of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid scheme may be null or contain any characters except for the
	 * following: <code>: / ? #</code>
	 */
	public static boolean validScheme(String value)
	{
		return value == null || !contains(value, MAJOR_SEPARATOR_HI, MAJOR_SEPARATOR_LO);

	// <p>A valid scheme may be null, or consist of a single letter followed
	// by any number of letters, numbers, and the following characters:
	// <code>+ - .</code>

		//if (value == null) return true;
		//return value.length() != 0 &&
		//  matches(value.charAt(0), ALPHA_HI, ALPHA_LO) &&
		//  validate(value, SCHEME_CHAR_HI, SCHEME_CHAR_LO, false, false);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the opaque part component of a URI; <code>false</code>
	 * otherwise.
	 *
	 * <p>A valid opaque part must be non-null, non-empty, and not contain the
	 * <code>#</code> character.  In addition, its first character must not be
	 * <code>/</code>
	 */
	public static boolean validOpaquePart(String value)
	{
		return value != null && value.indexOf(FRAGMENT_SEPARATOR) == -1 &&
		value.length() > 0 && value.charAt(0) != SEGMENT_SEPARATOR;

	// <p>A valid opaque part must be non-null and non-empty. It may contain
	// any allowed URI characters, but its first character may not be
	// <code>/</code>

		//return value != null && value.length() != 0 &&
		//  value.charAt(0) != SEGMENT_SEPARATOR &&
		//  validate(value, URIC_HI, URIC_LO, true, true);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the authority component of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid authority may be null or contain any characters except for
	 * the following: <code>/ ? #</code>
	 */
	public static boolean validAuthority(String value)
	{
		return value == null || !contains(value, SEGMENT_END_HI, SEGMENT_END_LO);

	// A valid authority may be null or contain any allowed URI characters except
	// for the following: <code>/ ?</code>

		//return value == null || validate(value, SEGMENT_CHAR_HI, SEGMENT_CHAR_LO, true, true);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the authority component of an <a
	 * href="#archive_explanation">archive URI</a>; <code>false</code>
	 * otherwise.
	 *
	 * <p>To be valid, the authority, itself, must be a URI with no fragment,
	 * followed by the character <code>!</code>.
	 */
	public static boolean validArchiveAuthority(String value)
	{
		if (value != null && value.length() > 0 &&
				value.charAt(value.length() - 1) == ARCHIVE_IDENTIFIER)
		{
			try
			{
				URI archiveURI = createURI(value.substring(0, value.length() - 1));
				return !archiveURI.hasFragment();
			}
			catch (IllegalArgumentException e)
			{
				// Ignore the exception and return false.
			}
		}
		return false;
	}

	/**
	 * Tests whether the specified <code>value</code> would be valid as the
	 * authority component of an <a href="#archive_explanation">archive
	 * URI</a>. This method has been replaced by {@link #validArchiveAuthority
	 * validArchiveAuthority} since the same form of URI is now supported
	 * for schemes other than "jar". This now simply calls that method.
	 *
	 * @deprecated As of EMF 2.0, replaced by {@link #validArchiveAuthority
	 * validArchiveAuthority}.
	 */
	@Deprecated
	public static boolean validJarAuthority(String value)
	{
		return validArchiveAuthority(value);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the device component of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid device may be null or non-empty, containing any characters
	 * except for the following: <code>/ ? #</code>  In addition, its last
	 * character must be <code>:</code>
	 */
	public static boolean validDevice(String value)
	{
		if (value == null) {
			return true;
		}
		int len = value.length();
		return len > 0 && value.charAt(len - 1) == DEVICE_IDENTIFIER &&
			!contains(value, SEGMENT_END_HI, SEGMENT_END_LO);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * a valid path segment of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid path segment must be non-null and not contain any of the
	 * following characters: <code>/ ? #</code>
	 */
	public static boolean validSegment(String value)
	{
		return value != null && !contains(value, SEGMENT_END_HI, SEGMENT_END_LO);

	// <p>A valid path segment must be non-null and may contain any allowed URI
	// characters except for the following: <code>/ ?</code>

		//return value != null && validate(value, SEGMENT_CHAR_HI, SEGMENT_CHAR_LO, true, true);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * a valid path segment array of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid path segment array must be non-null and contain only path
	 * segments that are valid according to {@link #validSegment validSegment}.
	 */
	public static boolean validSegments(String[] value)
	{
		if (value == null) {
			return false;
		}
		for (String segment : value) {
			if (!validSegment(segment)) {
			return false;
		}
		}
		return true;
	}

	// Returns null if the specified value is null or would be a valid path
	// segment array of a URI; otherwise, the value of the first invalid
	// segment.
	private static String firstInvalidSegment(String[] value)
	{
		if (value == null) {
			return null;
		}
		for (String segment : value) {
			if (!validSegment(segment)) {
			return segment;
		}
		}
		return null;
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the query component of a URI; <code>false</code> otherwise.
	 *
	 * <p>A valid query may be null or contain any characters except for
	 * <code>#</code>
	 */
	public static boolean validQuery(String value)
	{
		return value == null || value.indexOf(FRAGMENT_SEPARATOR) == -1;

	// <p>A valid query may be null or contain any allowed URI characters.

		//return value == null || validate(value, URIC_HI, URIC_LO, true, true);
}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the fragment component of a URI; <code>false</code> otherwise.
	 *
	 * <p>A fragment is taken to be unconditionally valid.
	 */
	public static boolean validFragment(String value)
	{
		return true;

	// <p>A valid fragment may be null or contain any allowed URI characters.

		//return value == null || validate(value, URIC_HI, URIC_LO, true, true);
	}

	// Searches the specified string for any characters in the set represented
	// by the 128-bit bitmask.  Returns true if any occur, or false otherwise.
	private static boolean contains(String s, long highBitmask, long lowBitmask)
	{
		for (int i = 0, len = s.length(); i < len; i++)
		{
			if (matches(s.charAt(i), highBitmask, lowBitmask)) {
		return true;
	}
		}
		return false;
	}

	// Tests the non-null string value to see if it contains only ASCII
	// characters in the set represented by the specified 128-bit bitmask,
	// as well as, optionally, non-ASCII characters 0xA0 and above, and,
	// also optionally, escape sequences of % followed by two hex digits.
	// This method is used for the new, strict URI validation that is not
	// not currently in place.
/*
	private static boolean validate(String value, long highBitmask, long lowBitmask,
									boolean allowNonASCII, boolean allowEscaped)
	{
		for (int i = 0, length = value.length(); i < length; i++)
		{
			char c = value.charAt(i);

			if (matches(c, highBitmask, lowBitmask)) continue;
			if (allowNonASCII && c >= 160) continue;
			if (allowEscaped && isEscaped(value, i))
			{
				i += 2;
				continue;
			}
			return false;
		}
		return true;
	}
*/

	/**
	 * Returns <code>true</code> if this is a relative URI, or
	 * <code>false</code> if it is an absolute URI.
	 */
	public boolean isRelative()
	{
		return scheme == null;
	}

	/**
	 * Returns <code>true</code> if this a a hierarchical URI, or
	 * <code>false</code> if it is of the generic form.
	 */
	public boolean isHierarchical()
	{
		return (hashCode & HIERARICHICAL_FLAG) != 0;
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with an authority
	 * component; <code>false</code> otherwise.
	 */
	public boolean hasAuthority()
	{
		return isHierarchical() && authority != null;
	}

	/**
	 * Returns <code>true</code> if this is a non-hierarchical URI with an
	 * opaque part component; <code>false</code> otherwise.
	 */
	public boolean hasOpaquePart()
	{
		// note: hierarchical -> authority != null
		return !isHierarchical();
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with a device
	 * component; <code>false</code> otherwise.
	 */
	public boolean hasDevice()
	{
		// note: device != null -> hierarchical
		return device != null;
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with an
	 * absolute or relative path; <code>false</code> otherwise.
	 */
	public boolean hasPath()
	{
		// note: (absolutePath || authority == null) -> hierarchical
		// (authority == null && device == null && !absolutePath) -> scheme == null
		return hasAbsolutePath() || (authority == null && device == null);
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with an
	 * absolute path, or <code>false</code> if it is non-hierarchical, has no
	 * path, or has a relative path.
	 */
	public boolean hasAbsolutePath()
	{
		// note: absolutePath -> hierarchical
		return (hashCode & ABSOLUTE_PATH_FLAG) != 0;
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with a relative
	 * path, or <code>false</code> if it is non-hierarchical, has no path, or
	 * has an absolute path.
	 */
	public boolean hasRelativePath()
	{
		// note: authority == null -> hierarchical
		// (authority == null && device == null && !absolutePath) -> scheme == null
		return authority == null && device == null && !hasAbsolutePath();
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with an empty
	 * relative path; <code>false</code> otherwise.
	 *
	 * <p>Note that <code>!hasEmpty()</code> does <em>not</em> imply that this
	 * URI has any path segments; however, <code>hasRelativePath &amp;&amp;
	 * !hasEmptyPath()</code> does.
	 */
	public boolean hasEmptyPath()
	{
		// note: authority == null -> hierarchical
		// (authority == null && device == null && !absolutePath) -> scheme == null
		return authority == null && device == null && !hasAbsolutePath() &&
			segments.length == 0;
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI with a query
	 * component; <code>false</code> otherwise.
	 */
	public boolean hasQuery()
	{
		// note: query != null -> hierarchical
		return query != null;
	}

	/**
	 * Returns <code>true</code> if this URI has a fragment component;
	 * <code>false</code> otherwise.
	 */
	public boolean hasFragment()
	{
		return fragment != null;
	}

	/**
	 * Returns <code>true</code> if this is a current document reference; that
	 * is, if it is a relative hierarchical URI with no authority, device or
	 * query components, and no path segments; <code>false</code> is returned
	 * otherwise.
	 */
	public boolean isCurrentDocumentReference()
	{
		// note: authority == null -> hierarchical
		// (authority == null && device == null && !absolutePath) -> scheme == null
		return authority == null && device == null && !hasAbsolutePath() &&
			segments.length == 0 && query == null;
	}

	/**
	 * Returns <code>true</code> if this is a {@link
	 * #isCurrentDocumentReference() current document reference} with no
	 * fragment component; <code>false</code> otherwise.
	 *
	 * @see #isCurrentDocumentReference()
	 */
	public boolean isEmpty()
	{
		// note: authority == null -> hierarchical
		// (authority == null && device == null && !absolutePath) -> scheme == null
		return authority == null && device == null && !hasAbsolutePath() &&
			segments.length == 0 && query == null && fragment == null;
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI that may refer
	 * directly to a locally accessible file.  This is considered to be the
	 * case for a file-scheme absolute URI, or for a relative URI with no query;
	 * <code>false</code> is returned otherwise.
	 */
	public boolean isFile()
	{
		return isHierarchical() &&
			((isRelative() && !hasQuery()) || SCHEME_FILE.equalsIgnoreCase(scheme));
	}

	/**
	 * Returns <code>true</code> if this is a platform URI, that is, an absolute,
	 * hierarchical URI, with "platform" scheme, no authority, and at least two
	 * segments; <code>false</code> is returned otherwise.
	 * @since org.eclipse.emf.common 2.3
	 */
	public boolean isPlatform()
	{
		return isHierarchical() && !hasAuthority() && segmentCount() >= 2 &&
			SCHEME_PLATFORM.equalsIgnoreCase(scheme);
	}

	/**
	 * Returns <code>true</code> if this is a platform resource URI, that is,
	 * a {@link #isPlatform platform URI} whose first segment is "resource";
	 * <code>false</code> is returned otherwise.
	 * @see #isPlatform
	 * @since org.eclipse.emf.common 2.3
	 */
	public boolean isPlatformResource()
	{
		return isPlatform() && "resource".equals(segments[0]);
	}

	/**
	 * Returns <code>true</code> if this is a platform plug-in URI, that is,
	 * a {@link #isPlatform platform URI} whose first segment is "plugin";
	 * <code>false</code> is returned otherwise.
	 * @see #isPlatform
	 * @since org.eclipse.emf.common 2.3
	 */
	public boolean isPlatformPlugin()
	{
		return isPlatform() && "plugin".equals(segments[0]);
	}

	/**
	 * Returns <code>true</code> if this is an archive URI.  If so, it is also
	 * hierarchical, with an authority (consisting of an absolute URI followed
	 * by "!"), no device, and an absolute path.
	 */
	public boolean isArchive()
	{
		return isArchiveScheme(scheme);
	}

	/**
	 * Returns <code>true</code> if the specified <code>value</code> would be
	 * valid as the scheme of an <a
	 * href="#archive_explanation">archive URI</a>; <code>false</code>
	 * otherwise.
	 */
	public static boolean isArchiveScheme(String value)
	{
		// Returns true if the given value is an archive scheme, as defined by
		// the org.eclipse.emf.common.util.URI.archiveSchemes system property.
		// By default, "jar", "zip", and "archive" are considered archives.
		return value != null && archiveSchemes.contains(value.toLowerCase());
	}

	/**
	 * Returns the hash code.
	 */
	@Override
	public int hashCode()
	{
		return hashCode;
	}

	/**
	 * Returns <code>true</code> if <code>object</code> is an instance of
	 * <code>URI</code> equal to this one; <code>false</code> otherwise.
	 *
	 * <p>Equality is determined strictly by comparing components, not by
	 * attempting to interpret what resource is being identified.  The
	 * comparison of schemes is case-insensitive.
	 */
	@Override
	public boolean equals(Object object)
	{
		if (this == object) {
			return true;
		}
		if (!(object instanceof URI)) {
			return false;
		}
		URI uri = (URI) object;

		return hashCode == uri.hashCode() &&
			equals(scheme, uri.scheme(), true) &&
			equals(authority, isHierarchical() ? uri.authority() : uri.opaquePart()) &&
			equals(device, uri.device()) &&
			equals(query, uri.query()) &&
			equals(fragment, uri.fragment()) &&
			segmentsEqual(uri);
	}

	// Tests whether this URI's path segment array is equal to that of the
	// given uri.
	private boolean segmentsEqual(URI uri)
	{
		if (segments.length != uri.segmentCount()) {
			return false;
		}
		for (int i = 0, len = segments.length; i < len; i++)
		{
			if (!segments[i].equals(uri.segment(i))) {
			return false;
		}
		}
		return true;
	}

	// Tests two objects for equality, tolerating nulls; null is considered
	// to be a valid value that is only equal to itself.
	private static boolean equals(Object o1, Object o2)
	{
		return o1 == null ? o2 == null : o1.equals(o2);
	}

	// Tests two strings for equality, tolerating nulls and optionally
	// ignoring case.
	private static boolean equals(String s1, String s2, boolean ignoreCase)
	{
		return s1 == null ? s2 == null :
			ignoreCase ? s1.equalsIgnoreCase(s2) : s1.equals(s2);
	}

	/**
	 * If this is an absolute URI, returns the scheme component;
	 * <code>null</code> otherwise.
	 */
	public String scheme()
	{
		return scheme;
	}

	/**
	 * If this is a non-hierarchical URI, returns the opaque part component;
	 * <code>null</code> otherwise.
	 */
	public String opaquePart()
	{
		return isHierarchical() ? null : authority;
	}

	/**
	 * If this is a hierarchical URI with an authority component, returns it;
	 * <code>null</code> otherwise.
	 */
	public String authority()
	{
		return isHierarchical() ? authority : null;
	}

	/**
	 * If this is a hierarchical URI with an authority component that has a
	 * user info portion, returns it; <code>null</code> otherwise.
	 */
	public String userInfo()
	{
		if (!hasAuthority()) {
			return null;
		}

		int i = authority.indexOf(USER_INFO_SEPARATOR);
		return i < 0 ? null : authority.substring(0, i);
	}

	/**
	 * If this is a hierarchical URI with an authority component that has a
	 * host portion, returns it; <code>null</code> otherwise.
	 */
	public String host()
	{
		if (!hasAuthority()) {
			return null;
		}

		int i = authority.indexOf(USER_INFO_SEPARATOR);
		int j = authority.indexOf(PORT_SEPARATOR);
		return j < 0 ? authority.substring(i + 1) : authority.substring(i + 1, j);
	}

	/**
	 * If this is a hierarchical URI with an authority component that has a
	 * port portion, returns it; <code>null</code> otherwise.
	 */
	public String port()
	{
		if (!hasAuthority()) {
			return null;
		}

		int i = authority.indexOf(PORT_SEPARATOR);
		return i < 0 ? null : authority.substring(i + 1);
	}

	/**
	 * If this is a hierarchical URI with a device component, returns it;
	 * <code>null</code> otherwise.
	 */
	public String device()
	{
		return device;
	}

	/**
	 * If this is a hierarchical URI with a path, returns an array containing
	 * the segments of the path; an empty array otherwise.  The leading
	 * separator in an absolute path is not represented in this array, but a
	 * trailing separator is represented by an empty-string segment as the
	 * final element.
	 */
	public String[] segments()
	{
		return segments.clone();
	}

	/**
	 * Returns an unmodifiable list containing the same segments as the array
	 * returned by {@link #segments segments}.
	 */
	public List<String> segmentsList()
	{
		return Collections.unmodifiableList(Arrays.asList(segments));
	}

	/**
	 * Returns the number of elements in the segment array that would be
	 * returned by {@link #segments segments}.
	 */
	public int segmentCount()
	{
		return segments.length;
	}

	/**
	 * Provides fast, indexed access to individual segments in the path
	 * segment array.
	 *
	 * @exception java.lang.IndexOutOfBoundsException if <code>i &lt; 0</code> or
	 * <code>i &gt;= segmentCount()</code>.
	 */
	public String segment(int i)
	{
		return segments[i];
	}

	/**
	 * Returns the last segment in the segment array, or <code>null</code>.
	 */
	public String lastSegment()
	{
		int len = segments.length;
		if (len == 0) {
			return null;
		}
		return segments[len - 1];
	}

	/**
	 * If this is a hierarchical URI with a path, returns a string
	 * representation of the path; <code>null</code> otherwise.  The path
	 * consists of a leading segment separator character (a slash), if the
	 * path is absolute, followed by the slash-separated path segments.  If
	 * this URI has a separate <a href="#device_explanation">device
	 * component</a>, it is <em>not</em> included in the path.
	 */
	public String path()
	{
		if (!hasPath()) {
			return null;
		}

		StringBuilder result = new StringBuilder();
		if (hasAbsolutePath()) {
			result.append(SEGMENT_SEPARATOR);
		}

		for (int i = 0, len = segments.length; i < len; i++)
		{
			if (i != 0) {
			result.append(SEGMENT_SEPARATOR);
		}
			result.append(segments[i]);
		}
		return result.toString();
	}

	/**
	 * If this is a hierarchical URI with a path, returns a string
	 * representation of the path, including the authority and the
	 * <a href="#device_explanation">device component</a>;
	 * <code>null</code> otherwise.
	 *
	 * <p>If there is no authority, the format of this string is:
	 * <pre>
	 *   device/pathSegment1/pathSegment2...</pre>
	 *
	 * <p>If there is an authority, it is:
	 * <pre>
	 *   //authority/device/pathSegment1/pathSegment2...</pre>
	 *
	 * <p>For an <a href="#archive_explanation">archive URI</a>, it's just:
	 * <pre>
	 *   authority/pathSegment1/pathSegment2...</pre>
	 */
	public String devicePath()
	{
		if (!hasPath()) {
			return null;
		}

		StringBuilder result = new StringBuilder();

		if (hasAuthority())
		{
			if (!isArchive()) {
			result.append(AUTHORITY_SEPARATOR);
		}
			result.append(authority);

			if (hasDevice()) {
			result.append(SEGMENT_SEPARATOR);
		}
		}

		if (hasDevice()) {
			result.append(device);
		}
		if (hasAbsolutePath()) {
			result.append(SEGMENT_SEPARATOR);
		}

		for (int i = 0, len = segments.length; i < len; i++)
		{
			if (i != 0) {
			result.append(SEGMENT_SEPARATOR);
		}
			result.append(segments[i]);
		}
		return result.toString();
	}

	/**
	 * If this is a hierarchical URI with a query component, returns it;
	 * <code>null</code> otherwise.
	 */
	public String query()
	{
		return query;
	}


	/**
	 * Returns the URI formed from this URI and the given query.
	 *
	 * @exception java.lang.IllegalArgumentException if
	 * <code>query</code> is not a valid query (portion) according
	 * to {@link #validQuery validQuery}.
	 */
	public URI appendQuery(String query)
	{
		if (!validQuery(query))
		{
			throw new IllegalArgumentException(
				"invalid query portion: " + query);
		}
		return new URI(isHierarchical(), scheme, authority, device, hasAbsolutePath(), segments, query, fragment);
	}

	/**
	 * If this URI has a non-null {@link #query query}, returns the URI
	 * formed by removing it; this URI unchanged, otherwise.
	 */
	public URI trimQuery()
	{
		if (query == null)
		{
			return this;
		}
		else
		{
			return new URI(isHierarchical(), scheme, authority, device, hasAbsolutePath(), segments, null, fragment);
		}
	}

	/**
	 * If this URI has a fragment component, returns it; <code>null</code>
	 * otherwise.
	 */
	public String fragment()
	{
		return fragment;
	}

	/**
	 * Returns the URI formed from this URI and the given fragment.
	 *
	 * @exception java.lang.IllegalArgumentException if
	 * <code>fragment</code> is not a valid fragment (portion) according
	 * to {@link #validFragment validFragment}.
	 */
	public URI appendFragment(String fragment)
	{
		if (!validFragment(fragment))
		{
			throw new IllegalArgumentException(
				"invalid fragment portion: " + fragment);
		}
		URI result = new URI(isHierarchical(), scheme, authority, device, hasAbsolutePath(), segments, query, fragment);

		if (!hasFragment())
		{
			result.cachedTrimFragment = this;
		}
		return result;
	}

	/**
	 * If this URI has a non-null {@link #fragment fragment}, returns the URI
	 * formed by removing it; this URI unchanged, otherwise.
	 */
	public URI trimFragment()
	{
		if (fragment == null)
		{
			return this;
		}
		else if (cachedTrimFragment == null)
		{
			cachedTrimFragment = new URI(isHierarchical(), scheme, authority, device, hasAbsolutePath(), segments, query, null);
		}

		return cachedTrimFragment;
	}

	/**
	 * Resolves this URI reference against a <code>base</code> absolute
	 * hierarchical URI, returning the resulting absolute URI.  If already
	 * absolute, the URI itself is returned.  URI resolution is described in
	 * detail in section 5.2 of <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC
	 * 2396</a>, "Resolving Relative References to Absolute Form."
	 *
	 * <p>During resolution, empty segments, self references ("."), and parent
	 * references ("..") are interpreted, so that they can be removed from the
	 * path.  Step 6(g) gives a choice of how to handle the case where parent
	 * references point to a path above the root: the offending segments can
	 * be preserved or discarded.  This method preserves them.  To have them
	 * discarded, please use the two-parameter form of {@link
	 * #resolve(URI, boolean) resolve}.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>base</code> is
	 * non-hierarchical or is relative.
	 */
	public URI resolve(URI base)
	{
		return resolve(base, true);
	}

	/**
	 * Resolves this URI reference against a <code>base</code> absolute
	 * hierarchical URI, returning the resulting absolute URI.  If already
	 * absolute, the URI itself is returned.  URI resolution is described in
	 * detail in section 5.2 of <a href="http://www.ietf.org/rfc/rfc2396.txt">RFC
	 * 2396</a>, "Resolving Relative References to Absolute Form."
	 *
	 * <p>During resolution, empty segments, self references ("."), and parent
	 * references ("..") are interpreted, so that they can be removed from the
	 * path.  Step 6(g) gives a choice of how to handle the case where parent
	 * references point to a path above the root: the offending segments can
	 * be preserved or discarded.  This method can do either.
	 *
	 * @param preserveRootParents <code>true</code> if segments referring to the
	 * parent of the root path are to be preserved; <code>false</code> if they
	 * are to be discarded.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>base</code> is
	 * non-hierarchical or is relative.
	 */
	public URI resolve(URI base, boolean preserveRootParents)
	{
		if (!base.isHierarchical() || base.isRelative())
		{
			throw new IllegalArgumentException(
				"resolve against non-hierarchical or relative base");
		}

		// an absolute URI needs no resolving
		if (!isRelative()) {
			return this;
		}

		// note: isRelative() -> hierarchical

		String newAuthority = authority;
		String newDevice = device;
		boolean newAbsolutePath = hasAbsolutePath();
		String[] newSegments = segments;
		String newQuery = query;
		// note: it's okay for two URIs to share a segments array, since
		// neither will ever modify it

		if (authority == null)
		{
			// no authority: use base's
			newAuthority = base.authority();

			if (device == null)
			{
				// no device: use base's
				newDevice = base.device();

				if (hasEmptyPath() && query == null)
				{
					// current document reference: use base path and query
					newAbsolutePath = base.hasAbsolutePath();
					newSegments = base.segments();
					newQuery = base.query();
				}
				else if (hasRelativePath())
				{
					// relative path: merge with base and keep query (note: if the
					// base has no path and this a non-empty relative path, there is
					// an implied root in the resulting path)
					newAbsolutePath = base.hasAbsolutePath() || !hasEmptyPath();
					newSegments = newAbsolutePath ? mergePath(base, preserveRootParents)
						: NO_SEGMENTS;
				}
				// else absolute path: keep it and query
			}
			// else keep device, path, and query
		}
		// else keep authority, device, path, and query

		// always keep fragment, even if null, and use scheme from base;
		// no validation needed since all components are from existing URIs
		return new URI(true, base.scheme(), newAuthority, newDevice,
						newAbsolutePath, newSegments, newQuery, fragment);
	}

	// Merges this URI's relative path with the base non-relative path.  If
	// base has no path, treat it as the root absolute path, unless this has
	// no path either.
	private String[] mergePath(URI base, boolean preserveRootParents)
	{
		if (base.hasRelativePath())
		{
			throw new IllegalArgumentException("merge against relative path");
		}
		if (!hasRelativePath())
		{
			throw new IllegalStateException("merge non-relative path");
		}

		int baseSegmentCount = base.segmentCount();
		int segmentCount = segments.length;
		String[] stack = new String[baseSegmentCount + segmentCount];
		int sp = 0;

		// use a stack to accumulate segments of base, except for the last
		// (i.e. skip trailing separator and anything following it), and of
		// relative path
		for (int i = 0; i < baseSegmentCount - 1; i++)
		{
			sp = accumulate(stack, sp, base.segment(i), preserveRootParents);
		}

		for (int i = 0; i < segmentCount; i++)
		{
			sp = accumulate(stack, sp, segments[i], preserveRootParents);
		}

		// if the relative path is empty or ends in an empty segment, a parent
		// reference, or a self reference, add a trailing separator to a
		// non-empty path
		if (sp > 0 &&  (segmentCount == 0 ||
							SEGMENT_EMPTY.equals(segments[segmentCount - 1]) ||
							SEGMENT_PARENT.equals(segments[segmentCount - 1]) ||
							SEGMENT_SELF.equals(segments[segmentCount - 1])))
		{
			stack[sp++] = SEGMENT_EMPTY;
		}

		// return a correctly sized result
		String[] result = new String[sp];
		System.arraycopy(stack, 0, result, 0, sp);
		return result;
	}

	// Adds a segment to a stack, skipping empty segments and self references,
	// and interpreting parent references.
	private static int accumulate(String[] stack, int sp, String segment,
																boolean preserveRootParents)
	{
		if (SEGMENT_PARENT.equals(segment))
		{
			if (sp == 0)
			{
				// special care must be taken for a root's parent reference: it is
				// either ignored or the symbolic reference itself is pushed
				if (preserveRootParents) {
				stack[sp++] = segment;
			}
			}
			else
			{
				// unless we're already accumulating root parent references,
				// parent references simply pop the last segment descended
				if (SEGMENT_PARENT.equals(stack[sp - 1])) {
				stack[sp++] = segment;
			} else {
				sp--;
			}
			}
		}
		else if (!SEGMENT_EMPTY.equals(segment) && !SEGMENT_SELF.equals(segment))
		{
			// skip empty segments and self references; push everything else
			stack[sp++] = segment;
		}
		return sp;
	}

	/**
	 * Finds the shortest relative or, if necessary, the absolute URI that,
	 * when resolved against the given <code>base</code> absolute hierarchical
	 * URI using {@link #resolve(URI) resolve}, will yield this absolute URI.
	 * If <code>base</code> is non-hierarchical or is relative,
	 * or <code>this</code> is non-hierarchical or is relative,
	 * <code>this</code> will be returned.
	 */
	public URI deresolve(URI base)
	{
		return deresolve(base, true, false, true);
	}

	/**
	 * Finds an absolute URI that, when resolved against the given
	 * <code>base</code> absolute hierarchical URI using {@link
	 * #resolve(URI, boolean) resolve}, will yield this absolute URI.
	 * If <code>base</code> is non-hierarchical or is relative,
	 * or <code>this</code> is non-hierarchical or is relative,
	 * <code>this</code> will be returned.
	 *
	 * @param preserveRootParents the boolean argument to <code>resolve(URI,
	 * boolean)</code> for which the returned URI should resolve to this URI.
	 * @param anyRelPath if <code>true</code>, the returned URI's path (if
	 * any) will be relative, if possible.  If <code>false</code>, the form of
	 * the result's path will depend upon the next parameter.
	 * @param shorterRelPath if <code>anyRelPath</code> is <code>false</code>
	 * and this parameter is <code>true</code>, the returned URI's path (if
	 * any) will be relative, if one can be found that is no longer (by number
	 * of segments) than the absolute path.  If both <code>anyRelPath</code>
	 * and this parameter are <code>false</code>, it will be absolute.
	 */
	public URI deresolve(URI base, boolean preserveRootParents,
											 boolean anyRelPath, boolean shorterRelPath)
	{
		if (!base.isHierarchical() || base.isRelative()) {
			return this;
		}

		if (isRelative()) {
			return this;
		}

		// note: these assertions imply that neither this nor the base URI has a
		// relative path; thus, both have either an absolute path or no path

		// different scheme: need complete, absolute URI
		if (!scheme.equalsIgnoreCase(base.scheme())) {
			return this;
		}

		// since base must be hierarchical, and since a non-hierarchical URI
		// must have both scheme and opaque part, the complete absolute URI is
		// needed to resolve to a non-hierarchical URI
		if (!isHierarchical()) {
			return this;
		}

		String newAuthority = authority;
		String newDevice = device;
		boolean newAbsolutePath = hasAbsolutePath();
		String[] newSegments = segments;
		String newQuery = query;

		if (equals(authority, base.authority()) &&
				(hasDevice() || hasPath() || (!base.hasDevice() && !base.hasPath())))
		{
			// matching authorities and no device or path removal
			newAuthority = null;

			if (equals(device, base.device()) && (hasPath() || !base.hasPath()))
			{
				// matching devices and no path removal
				newDevice = null;

				// exception if (!hasPath() && base.hasPath())

				if (!anyRelPath && !shorterRelPath)
				{
					// user rejects a relative path: keep absolute or no path
				}
				else if (hasPath() == base.hasPath() && segmentsEqual(base) &&
								 equals(query, base.query()))
				{
					// current document reference: keep no path or query
					newAbsolutePath = false;
					newSegments = NO_SEGMENTS;
					newQuery = null;
				}
				else if (!hasPath() && !base.hasPath())
				{
					// no paths: keep query only
					newAbsolutePath = false;
					newSegments = NO_SEGMENTS;
				}
				// exception if (!hasAbsolutePath())
				else if (hasCollapsableSegments(preserveRootParents))
				{
					// path form demands an absolute path: keep it and query
				}
				else
				{
					// keep query and select relative or absolute path based on length
					String[] rel = findRelativePath(base, preserveRootParents);
					if (anyRelPath || segments.length > rel.length)
					{
						// user demands a relative path or the absolute path is longer
						newAbsolutePath = false;
						newSegments = rel;
					}
					// else keep shorter absolute path
				}
			}
			// else keep device, path, and query
		}
		// else keep authority, device, path, and query

		// always include fragment, even if null;
		// no validation needed since all components are from existing URIs
		return new URI(true, null, newAuthority, newDevice, newAbsolutePath,
							newSegments, newQuery, fragment);
	}

	// Returns true if the non-relative path includes segments that would be
	// collapsed when resolving; false otherwise.  If preserveRootParents is
	// true, collapsible segments include any empty segments, except for the
	// last segment, as well as and parent and self references.  If
	// preserveRootsParents is false, parent references are not collapsible if
	// they are the first segment or preceded only by other parent
	// references.
	private boolean hasCollapsableSegments(boolean preserveRootParents)
	{
		if (hasRelativePath())
		{
			throw new IllegalStateException("test collapsability of relative path");
		}

		for (int i = 0, len = segments.length; i < len; i++)
		{
			String segment = segments[i];
			if ((i < len - 1 && SEGMENT_EMPTY.equals(segment)) ||
					SEGMENT_SELF.equals(segment) ||
					SEGMENT_PARENT.equals(segment) && (
						!preserveRootParents || (
							i != 0 && !SEGMENT_PARENT.equals(segments[i - 1]))))
			{
				return true;
			}
		}
		return false;
	}

	// Returns the shortest relative path between the the non-relative path of
	// the given base and this absolute path.  If the base has no path, it is
	// treated as the root absolute path.
	private String[] findRelativePath(URI base, boolean preserveRootParents)
	{
		if (base.hasRelativePath())
		{
			throw new IllegalArgumentException(
				"find relative path against base with relative path");
		}
		if (!hasAbsolutePath())
		{
			throw new IllegalArgumentException(
				"find relative path of non-absolute path");
		}

		// treat an empty base path as the root absolute path
		String[] startPath = base.collapseSegments(preserveRootParents);
		String[] endPath = segments;

		// drop last segment from base, as in resolving
		int startCount = startPath.length > 0 ? startPath.length - 1 : 0;
		int endCount = endPath.length;

		// index of first segment that is different between endPath and startPath
		int diff = 0;

		// if endPath is shorter than startPath, the last segment of endPath may
		// not be compared: because startPath has been collapsed and had its
		// last segment removed, all preceding segments can be considered non-
		// empty and followed by a separator, while the last segment of endPath
		// will either be non-empty and not followed by a separator, or just empty
		for (int count = startCount < endCount ? startCount : endCount - 1;
				 diff < count && startPath[diff].equals(endPath[diff]); diff++)
		{
			// Empty statement.
		}

		int upCount = startCount - diff;
		int downCount = endCount - diff;

		// a single separator, possibly preceded by some parent reference
		// segments, is redundant
		if (downCount == 1 && SEGMENT_EMPTY.equals(endPath[endCount - 1]))
		{
			downCount = 0;
		}

		// an empty path needs to be replaced by a single "." if there is no
		// query, to distinguish it from a current document reference
		if (upCount + downCount == 0)
		{
			if (query == null) {
			return new String[] { SEGMENT_SELF };
		}
			return NO_SEGMENTS;
		}

		// return a correctly sized result
		String[] result = new String[upCount + downCount];
		Arrays.fill(result, 0, upCount, SEGMENT_PARENT);
		System.arraycopy(endPath, diff, result, upCount, downCount);
		return result;
	}

	// Collapses non-ending empty segments, parent references, and self
	// references in a non-relative path, returning the same path that would
	// be produced from the base hierarchical URI as part of a resolve.
	String[] collapseSegments(boolean preserveRootParents)
	{
		if (hasRelativePath())
		{
			throw new IllegalStateException("collapse relative path");
		}

		if (!hasCollapsableSegments(preserveRootParents)) {
			return segments();
		}

		// use a stack to accumulate segments
		int segmentCount = segments.length;
		String[] stack = new String[segmentCount];
		int sp = 0;

		for (int i = 0; i < segmentCount; i++)
		{
			sp = accumulate(stack, sp, segments[i], preserveRootParents);
		}

		// if the path is non-empty and originally ended in an empty segment, a
		// parent reference, or a self reference, add a trailing separator
		if (sp > 0 && (SEGMENT_EMPTY.equals(segments[segmentCount - 1]) ||
							SEGMENT_PARENT.equals(segments[segmentCount - 1]) ||
							SEGMENT_SELF.equals(segments[segmentCount - 1])))
		{
			stack[sp++] = SEGMENT_EMPTY;
		}

		// return a correctly sized result
		String[] result = new String[sp];
		System.arraycopy(stack, 0, result, 0, sp);
		return result;
	}

	/**
	 * Returns the string representation of this URI.  For a generic,
	 * non-hierarchical URI, this looks like:
	 * <pre>
	 *   scheme:opaquePart#fragment</pre>
	 *
	 * <p>For a hierarchical URI, it looks like:
	 * <pre>
	 *   scheme://authority/device/pathSegment1/pathSegment2...?query#fragment</pre>
	 *
	 * <p>For an <a href="#archive_explanation">archive URI</a>, it's just:
	 * <pre>
	 *   scheme:authority/pathSegment1/pathSegment2...?query#fragment</pre>
	 * <p>Of course, absent components and their separators will be omitted.
	 */
	@Override
	public String toString()
	{
		if (cachedToString == null)
		{
			StringBuilder result = new StringBuilder();
			if (!isRelative())
			{
				result.append(scheme);
				result.append(SCHEME_SEPARATOR);
			}

			if (isHierarchical())
			{
				if (hasAuthority())
				{
					if (!isArchive()) {
				result.append(AUTHORITY_SEPARATOR);
			}
					result.append(authority);
				}

				if (hasDevice())
				{
					result.append(SEGMENT_SEPARATOR);
					result.append(device);
				}

				if (hasAbsolutePath()) {
				result.append(SEGMENT_SEPARATOR);
			}

				for (int i = 0, len = segments.length; i < len; i++)
				{
					if (i != 0) {
				result.append(SEGMENT_SEPARATOR);
			}
					result.append(segments[i]);
				}

				if (hasQuery())
				{
					result.append(QUERY_SEPARATOR);
					result.append(query);
				}
			}
			else
			{
				result.append(authority);
			}

			if (hasFragment())
			{
				result.append(FRAGMENT_SEPARATOR);
				result.append(fragment);
			}
			cachedToString = result.toString();
		}
		return cachedToString;
	}

	// Returns a string representation of this URI for debugging, explicitly
	// showing each of the components.
	String toString(boolean includeSimpleForm)
	{
		StringBuilder result = new StringBuilder();
		if (includeSimpleForm) {
			result.append(toString());
		}
		result.append("\n hierarchical: ");
		result.append(isHierarchical());
		result.append("\n       scheme: ");
		result.append(scheme);
		result.append("\n    authority: ");
		result.append(authority);
		result.append("\n       device: ");
		result.append(device);
		result.append("\n absolutePath: ");
		result.append(hasAbsolutePath());
		result.append("\n     segments: ");
		if (segments.length == 0) {
			result.append("<empty>");
		}
		for (int i = 0, len = segments.length; i < len; i++)
		{
			if (i > 0) {
			result.append("\n               ");
		}
			result.append(segments[i]);
		}
		result.append("\n        query: ");
		result.append(query);
		result.append("\n     fragment: ");
		result.append(fragment);
		return result.toString();
	}

	/**
	 * If this URI may refer directly to a locally accessible file, as
	 * determined by {@link #isFile isFile}, {@link #decode decodes} and formats
	 * the URI as a pathname to that file; returns null otherwise.
	 *
	 * <p>If there is no authority, the format of this string is:
	 * <pre>
	 *   device/pathSegment1/pathSegment2...</pre>
	 *
	 * <p>If there is an authority, it is:
	 * <pre>
	 *   //authority/device/pathSegment1/pathSegment2...</pre>
	 *
	 * <p>However, the character used as a separator is system-dependent and
	 * obtained from {@link java.io.File#separatorChar}.
	 */
	public String toFileString()
	{
		if (!isFile()) {
			return null;
		}

		StringBuilder result = new StringBuilder();
		char separator = File.separatorChar;

		if (hasAuthority())
		{
			result.append(separator);
			result.append(separator);
			result.append(authority);

			if (hasDevice()) {
			result.append(separator);
		}
		}

		if (hasDevice()) {
			result.append(device);
		}
		if (hasAbsolutePath()) {
			result.append(separator);
		}

		for (int i = 0, len = segments.length; i < len; i++)
		{
			if (i != 0) {
			result.append(separator);
		}
			result.append(segments[i]);
		}

		return decode(result.toString());
	}

	/**
	 * If this is a platform URI, as determined by {@link #isPlatform}, returns
	 * the workspace-relative or plug-in-based path to the resource, optionally
	 * {@link #decode decoding} the segments in the process.
	 * @see #createPlatformResourceURI(String, boolean)
	 * @see #createPlatformPluginURI
	 * @since org.eclipse.emf.common 2.3
	 */
	public String toPlatformString(boolean decode)
	{
		if (isPlatform())
		{
			StringBuilder result = new StringBuilder();
			for (int i = 1, len = segments.length; i < len; i++)
			{
				result.append('/').append(decode ? URI.decode(segments[i]) : segments[i]);
			}
			return result.toString();
		}
		return null;
	}

	/**
	 * Returns the URI formed by appending the specified segment on to the end
	 * of the path of this URI, if hierarchical; this URI unchanged,
	 * otherwise.  If this URI has an authority and/or device, but no path,
	 * the segment becomes the first under the root in an absolute path.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>segment</code>
	 * is not a valid segment according to {@link #validSegment}.
	 */
	public URI appendSegment(String segment)
	{
		if (!validSegment(segment))
		{
			throw new IllegalArgumentException("invalid segment: " + segment);
		}

		if (!isHierarchical()) {
			return this;
		}

		// absolute path or no path -> absolute path
		boolean newAbsolutePath = !hasRelativePath();

		int len = segments.length;
		String[] newSegments = new String[len + 1];
		System.arraycopy(segments, 0, newSegments, 0, len);
		newSegments[len] = segment;

		return new URI(true, scheme, authority, device, newAbsolutePath,
									 newSegments, query, fragment);
	}

	/**
	 * Returns the URI formed by appending the specified segments on to the
	 * end of the path of this URI, if hierarchical; this URI unchanged,
	 * otherwise.  If this URI has an authority and/or device, but no path,
	 * the segments are made to form an absolute path.
	 *
	 * @param segments an array of non-null strings, each representing one
	 * segment of the path.  If desired, a trailing separator should be
	 * represented by an empty-string segment as the last element of the
	 * array.
	 *
	 * @exception java.lang.IllegalArgumentException if <code>segments</code>
	 * is not a valid segment array according to {@link #validSegments}.
	 */
	public URI appendSegments(String[] segments)
	{
		if (!validSegments(segments))
		{
			String s = segments == null ? "invalid segments: null" :
				"invalid segment: " + firstInvalidSegment(segments);
			throw new IllegalArgumentException(s);
		}

		if (!isHierarchical()) {
			return this;
		}

		// absolute path or no path -> absolute path
		boolean newAbsolutePath = !hasRelativePath();

		int len = this.segments.length;
		int segmentsCount = segments.length;
		String[] newSegments = new String[len + segmentsCount];
		System.arraycopy(this.segments, 0, newSegments, 0, len);
		System.arraycopy(segments, 0, newSegments, len, segmentsCount);

		return new URI(true, scheme, authority, device, newAbsolutePath,
									 newSegments, query, fragment);
	}

	/**
	 * Returns the URI formed by trimming the specified number of segments
	 * (including empty segments, such as one representing a trailing
	 * separator) from the end of the path of this URI, if hierarchical;
	 * otherwise, this URI is returned unchanged.
	 *
	 * <p>Note that if all segments are trimmed from an absolute path, the
	 * root absolute path remains.
	 *
	 * @param i the number of segments to be trimmed in the returned URI.  If
	 * less than 1, this URI is returned unchanged; if equal to or greater
	 * than the number of segments in this URI's path, all segments are
	 * trimmed.
	 */
	public URI trimSegments(int i)
	{
		if (!isHierarchical() || i < 1) {
			return this;
		}

		String[] newSegments = NO_SEGMENTS;
		int len = segments.length - i;
		if (len > 0)
		{
			newSegments = new String[len];
			System.arraycopy(segments, 0, newSegments, 0, len);
		}
		return new URI(true, scheme, authority, device, hasAbsolutePath(),
									 newSegments, query, fragment);
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI that has a path
	 * that ends with a trailing separator; <code>false</code> otherwise.
	 *
	 * <p>A trailing separator is represented as an empty segment as the
	 * last segment in the path; note that this definition does <em>not</em>
	 * include the lone separator in the root absolute path.
	 */
	public boolean hasTrailingPathSeparator()
	{
		return segments.length > 0 &&
			SEGMENT_EMPTY.equals(segments[segments.length - 1]);
	}

	/**
	 * If this is a hierarchical URI whose path includes a file extension,
	 * that file extension is returned; null otherwise.  We define a file
	 * extension as any string following the last period (".") in the final
	 * path segment.  If there is no path, the path ends in a trailing
	 * separator, or the final segment contains no period, then we consider
	 * there to be no file extension.  If the final segment ends in a period,
	 * then the file extension is an empty string.
	 */
	public String fileExtension()
	{
		int len = segments.length;
		if (len == 0) {
			return null;
		}

		String lastSegment = segments[len - 1];
		int i = lastSegment.lastIndexOf(FILE_EXTENSION_SEPARATOR);
		return i < 0 ? null : lastSegment.substring(i + 1);
	}

	/**
	 * Returns the URI formed by appending a period (".") followed by the
	 * specified file extension to the last path segment of this URI, if it is
	 * hierarchical with a non-empty path ending in a non-empty segment;
	 * otherwise, this URI is returned unchanged.

	 * <p>The extension is appended regardless of whether the segment already
	 * contains an extension.
	 *
	 * @exception java.lang.IllegalArgumentException if
	 * <code>fileExtension</code> is not a valid segment (portion) according
	 * to {@link #validSegment}.
	 */
	public URI appendFileExtension(String fileExtension)
	{
		if (!validSegment(fileExtension))
		{
			throw new IllegalArgumentException(
				"invalid segment portion: " + fileExtension);
		}

		int len = segments.length;
		if (len == 0) {
			return this;
		}

		String lastSegment = segments[len - 1];
		if (SEGMENT_EMPTY.equals(lastSegment)) {
			return this;
		}
		StringBuilder newLastSegment = new StringBuilder(lastSegment);
		newLastSegment.append(FILE_EXTENSION_SEPARATOR);
		newLastSegment.append(fileExtension);

		String[] newSegments = new String[len];
		System.arraycopy(segments, 0, newSegments, 0, len - 1);
		newSegments[len - 1] = newLastSegment.toString();

		// note: segments.length > 0 -> hierarchical
		return new URI(true, scheme, authority, device, hasAbsolutePath(),
									 newSegments, query, fragment);
	}

	/**
	 * If this URI has a non-null {@link #fileExtension fileExtension},
	 * returns the URI formed by removing it; this URI unchanged, otherwise.
	 */
	public URI trimFileExtension()
	{
		int len = segments.length;
		if (len == 0) {
			return this;
		}

		String lastSegment = segments[len - 1];
		int i = lastSegment.lastIndexOf(FILE_EXTENSION_SEPARATOR);
		if (i < 0) {
			return this;
		}

		String newLastSegment = lastSegment.substring(0, i);
		String[] newSegments = new String[len];
		System.arraycopy(segments, 0, newSegments, 0, len - 1);
		newSegments[len - 1] = newLastSegment;

		// note: segments.length > 0 -> hierarchical
		return new URI(true, scheme, authority, device, hasAbsolutePath(),
									 newSegments, query, fragment);
	}

	/**
	 * Returns <code>true</code> if this is a hierarchical URI that ends in a
	 * slash; that is, it has a trailing path separator or is the root
	 * absolute path, and has no query and no fragment; <code>false</code>
	 * is returned otherwise.
	 */
	public boolean isPrefix()
	{
		return isHierarchical() && query == null && fragment == null &&
			(hasTrailingPathSeparator() || (hasAbsolutePath() && segments.length == 0));
	}

	/**
	 * If this is a hierarchical URI reference and <code>oldPrefix</code> is a
	 * prefix of it, this returns the URI formed by replacing it by
	 * <code>newPrefix</code>; <code>null</code> otherwise.
	 *
	 * <p>In order to be a prefix, the <code>oldPrefix</code>'s
	 * {@link #isPrefix isPrefix} must return <code>true</code>, and it must
	 * match this URI's scheme, authority, and device.  Also, the paths must
	 * match, up to prefix's end.
	 *
	 * @exception java.lang.IllegalArgumentException if either
	 * <code>oldPrefix</code> or <code>newPrefix</code> is not a prefix URI
	 * according to {@link #isPrefix}.
	 */
	public URI replacePrefix(URI oldPrefix, URI newPrefix)
	{
		if (!oldPrefix.isPrefix() || !newPrefix.isPrefix())
		{
			String which = oldPrefix.isPrefix() ? "new" : "old";
			throw new IllegalArgumentException("non-prefix " + which + " value");
		}

		// Get what's left of the segments after trimming the prefix.
		String[] tailSegments = getTailSegments(oldPrefix);
		if (tailSegments == null) {
			return null;
		}

		// If the new prefix has segments, it is not the root absolute path,
		// and we need to drop the trailing empty segment and append the tail
		// segments.
		String[] mergedSegments = tailSegments;
		if (newPrefix.segmentCount() != 0)
		{
			int segmentsToKeep = newPrefix.segmentCount() - 1;
			mergedSegments = new String[segmentsToKeep + tailSegments.length];
			System.arraycopy(newPrefix.segments(), 0, mergedSegments, 0,
											 segmentsToKeep);

			if (tailSegments.length != 0)
			{
				System.arraycopy(tailSegments, 0, mergedSegments, segmentsToKeep,
												 tailSegments.length);
			}
		}

		// no validation needed since all components are from existing URIs
		return new URI(true, newPrefix.scheme(), newPrefix.authority(),
									 newPrefix.device(), newPrefix.hasAbsolutePath(),
									 mergedSegments, query, fragment);
	}

	// If this is a hierarchical URI reference and prefix is a prefix of it,
	// returns the portion of the path remaining after that prefix has been
	// trimmed; null otherwise.
	private String[] getTailSegments(URI prefix)
	{
		if (!prefix.isPrefix())
		{
			throw new IllegalArgumentException("non-prefix trim");
		}

		// Don't even consider it unless this is hierarchical and has scheme,
		// authority, device and path absoluteness equal to those of the prefix.
		if (!isHierarchical() ||
				!equals(scheme, prefix.scheme(), true) ||
				!equals(authority, prefix.authority()) ||
				!equals(device, prefix.device()) ||
				hasAbsolutePath() != prefix.hasAbsolutePath())
		{
			return null;
		}

		// If the prefix has no segments, then it is the root absolute path, and
		// we know this is an absolute path, too.
		if (prefix.segmentCount() == 0) {
			return segments;
		}

		// This must have no fewer segments than the prefix.  Since the prefix
		// is not the root absolute path, its last segment is empty; all others
		// must match.
		int i = 0;
		int segmentsToCompare = prefix.segmentCount() - 1;
		if (segments.length <= segmentsToCompare) {
			return null;
		}

		for (; i < segmentsToCompare; i++)
		{
			if (!segments[i].equals(prefix.segment(i))) {
			return null;
		}
		}

		// The prefix really is a prefix of this.  If this has just one more,
		// empty segment, the paths are the same.
		if (i == segments.length - 1 && SEGMENT_EMPTY.equals(segments[i]))
		{
			return NO_SEGMENTS;
		}

		// Otherwise, the path needs only the remaining segments.
		String[] newSegments = new String[segments.length - i];
		System.arraycopy(segments, i, newSegments, 0, newSegments.length);
		return newSegments;
	}

	/**
	 * Encodes a string so as to produce a valid opaque part value, as defined
	 * by the RFC.  All excluded characters, such as space and <code>#</code>,
	 * are escaped, as is <code>/</code> if it is the first character.
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  Note that
	 * if a <code>%</code> is not followed by 2 hex digits, it will always be
	 * escaped.
	 */
	public static String encodeOpaquePart(String value, boolean ignoreEscaped)
	{
		String result = encode(value, URIC_HI, URIC_LO, ignoreEscaped);
		return result != null && result.length() > 0 && result.charAt(0) == SEGMENT_SEPARATOR ?
			"%2F" + result.substring(1) :
			result;
	}

	/**
	 * Encodes a string so as to produce a valid authority, as defined by the
	 * RFC.  All excluded characters, such as space and <code>#</code>,
	 * are escaped, as are <code>/</code> and <code>?</code>
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  Note that
	 * if a <code>%</code> is not followed by 2 hex digits, it will always be
	 * escaped.
	 */
	public static String encodeAuthority(String value, boolean ignoreEscaped)
	{
		return encode(value, SEGMENT_CHAR_HI, SEGMENT_CHAR_LO, ignoreEscaped);
	}

	/**
	 * Encodes a string so as to produce a valid segment, as defined by the
	 * RFC.  All excluded characters, such as space and <code>#</code>,
	 * are escaped, as are <code>/</code> and <code>?</code>
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  Note that
	 * if a <code>%</code> is not followed by 2 hex digits, it will always be
	 * escaped.
	 */
	public static String encodeSegment(String value, boolean ignoreEscaped)
	{
		return encode(value, SEGMENT_CHAR_HI, SEGMENT_CHAR_LO, ignoreEscaped);
	}

	/**
	 * Encodes a string so as to produce a valid query, as defined by the RFC.
	 * Only excluded characters, such as space and <code>#</code>, are escaped.
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  Note that
	 * if a <code>%</code> is not followed by 2 hex digits, it will always be
	 * escaped.
	 */
	public static String encodeQuery(String value, boolean ignoreEscaped)
	{
		return encode(value, URIC_HI, URIC_LO, ignoreEscaped);
	}

	/**
	 * Encodes a string so as to produce a valid fragment, as defined by the
	 * RFC.  Only excluded characters, such as space and <code>#</code>, are
	 * escaped.
	 *
	 * @param ignoreEscaped <code>true</code> to leave <code>%</code> characters
	 * unescaped if they already begin a valid three-character escape sequence;
	 * <code>false</code> to encode all <code>%</code> characters.  Note that
	 * if a <code>%</code> is not followed by 2 hex digits, it will always be
	 * escaped.
	 */
	public static String encodeFragment(String value, boolean ignoreEscaped)
	{
		return encode(value, URIC_HI, URIC_LO, ignoreEscaped);
	}

	// Encodes a complete URI, optionally leaving % characters unescaped when
	// beginning a valid three-character escape sequence.  We can either treat
	// the first or # as a fragment separator, or encode them all.
	private static String encodeURI(String uri, boolean ignoreEscaped, int fragmentLocationStyle)
	{
		if (uri == null) {
			return null;
		}

		StringBuilder result = new StringBuilder();

		int i = uri.indexOf(SCHEME_SEPARATOR);
		if (i != -1)
		{
			String scheme = uri.substring(0, i);
			result.append(scheme);
			result.append(SCHEME_SEPARATOR);
		}

		int j =
			fragmentLocationStyle == FRAGMENT_FIRST_SEPARATOR ? uri.indexOf(FRAGMENT_SEPARATOR) :
				fragmentLocationStyle == FRAGMENT_LAST_SEPARATOR ? uri.lastIndexOf(FRAGMENT_SEPARATOR) : -1;

		if (j != -1)
		{
			String sspart = uri.substring(++i, j);
			result.append(encode(sspart, URIC_HI, URIC_LO, ignoreEscaped));
			result.append(FRAGMENT_SEPARATOR);

			String fragment = uri.substring(++j);
			result.append(encode(fragment, URIC_HI, URIC_LO, ignoreEscaped));
		}
		else
		{
			String sspart = uri.substring(++i);
			result.append(encode(sspart, URIC_HI, URIC_LO, ignoreEscaped));
		}

		return result.toString();
	}

	// Encodes the given string, replacing each ASCII character that is not in
	// the set specified by the 128-bit bitmask and each non-ASCII character
	// below 0xA0 by an escape sequence of % followed by two hex digits.  If
	// % is not in the set but ignoreEscaped is true, then % will not be encoded
	// iff it already begins a valid escape sequence.
	private static String encode(String value, long highBitmask, long lowBitmask, boolean ignoreEscaped)
	{
		if (value == null) {
			return null;
		}

		StringBuilder result = null;

		for (int i = 0, len = value.length(); i < len; i++)
		{
			char c = value.charAt(i);

			if (!matches(c, highBitmask, lowBitmask) && c < 160 &&
					(!ignoreEscaped || !isEscaped(value, i)))
			{
				if (result == null)
				{
					result = new StringBuilder(value.substring(0, i));
				}
				appendEscaped(result, (byte)c);
			}
			else if (result != null)
			{
				result.append(c);
			}
		}
		return result == null ? value : result.toString();
	}

	// Tests whether an escape occurs in the given string, starting at index i.
	// An escape sequence is a % followed by two hex digits.
	private static boolean isEscaped(String s, int i)
	{
		return s.charAt(i) == ESCAPE && s.length() > i + 2 &&
			matches(s.charAt(i + 1), HEX_HI, HEX_LO) &&
			matches(s.charAt(i + 2), HEX_HI, HEX_LO);
	}

	// Computes a three-character escape sequence for the byte, appending
	// it to the StringBuilder.  Only characters up to 0xFF should be escaped;
	// all but the least significant byte will be ignored.
	private static void appendEscaped(StringBuilder result, byte b)
	{
		result.append(ESCAPE);

		// The byte is automatically widened into an int, with sign extension,
		// for shifting.  This can introduce 1's to the left of the byte, which
		// must be cleared by masking before looking up the hex digit.
		//
		result.append(HEX_DIGITS[(b >> 4) & 0x0F]);
		result.append(HEX_DIGITS[b & 0x0F]);
	}

	/**
	 * Decodes the given string by interpreting three-digit escape sequences as the bytes of a UTF-8 encoded character
	 * and replacing them with the characters they represent.
	 * Incomplete escape sequences are ignored and invalid UTF-8 encoded bytes are treated as extended ASCII characters.
	 */
	public static String decode(String value)
	{
		if (value == null) {
			return null;
		}

		int i = value.indexOf('%');
		if (i < 0)
		{
			return value;
		}
		else
		{
			StringBuilder result = new StringBuilder(value.substring(0, i));
			byte [] bytes = new byte[4];
			int receivedBytes = 0;
			int expectedBytes = 0;
			for (int len = value.length(); i < len; i++)
			{
				if (isEscaped(value, i))
				{
					char character = unescape(value.charAt(i + 1), value.charAt(i + 2));
					i += 2;

					if (expectedBytes > 0)
					{
						if ((character & 0xC0) == 0x80)
						{
							bytes[receivedBytes++] = (byte)character;
						}
						else
						{
							expectedBytes = 0;
						}
					}
					else if (character >= 0x80)
					{
						if ((character & 0xE0) == 0xC0)
						{
							bytes[receivedBytes++] = (byte)character;
							expectedBytes = 2;
						}
						else if ((character & 0xF0) == 0xE0)
						{
							bytes[receivedBytes++] = (byte)character;
							expectedBytes = 3;
						}
						else if ((character & 0xF8) == 0xF0)
						{
							bytes[receivedBytes++] = (byte)character;
							expectedBytes = 4;
						}
					}

					if (expectedBytes > 0)
					{
						if (receivedBytes == expectedBytes)
						{
							switch (receivedBytes)
							{
								case 2:
								{
									result.append((char)((bytes[0] & 0x1F) << 6 | bytes[1] & 0x3F));
									break;
								}
								case 3:
								{
									result.append((char)((bytes[0] & 0xF) << 12 | (bytes[1] & 0X3F) << 6 | bytes[2] & 0x3F));
									break;
								}
								case 4:
								{
									result.appendCodePoint(((bytes[0] & 0x7) << 18 | (bytes[1] & 0X3F) << 12 | (bytes[2] & 0X3F) << 6 | bytes[3] & 0x3F));
									break;
								}
							}
							receivedBytes = 0;
							expectedBytes = 0;
						}
					}
					else
					{
						for (int j = 0; j < receivedBytes; ++j)
						{
							result.append((char)bytes[j]);
						}
						receivedBytes = 0;
						result.append(character);
					}
				}
				else
				{
					for (int j = 0; j < receivedBytes; ++j)
					{
						result.append((char)bytes[j]);
					}
					receivedBytes = 0;
					result.append(value.charAt(i));
				}
			}
			return result.toString();
		}
	}

	// Returns the character encoded by % followed by the two given hex digits,
	// which is always 0xFF or less, so can safely be casted to a byte.  If
	// either character is not a hex digit, a bogus result will be returned.
	private static char unescape(char highHexDigit, char lowHexDigit)
	{
		return (char)((valueOf(highHexDigit) << 4) | valueOf(lowHexDigit));
	}

	// Returns the int value of the given hex digit.
	private static int valueOf(char hexDigit)
	{
		if (hexDigit >= 'A' && hexDigit <= 'F')
		{
			return hexDigit - 'A' + 10;
		}
		if (hexDigit >= 'a' && hexDigit <= 'f')
		{
			return hexDigit - 'a' + 10;
		}
		if (hexDigit >= '0' && hexDigit <= '9')
		{
			return hexDigit - '0';
		}
		return 0;
	}
}
