////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code for adherence to a set of rules.
// Copyright (C) 2001-2020 the original author or authors.
//
// This library is free software; you can redistribute it and/or
// modify it under the terms of the GNU Lesser General Public
// License as published by the Free Software Foundation; either
// version 2.1 of the License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
////////////////////////////////////////////////////////////////////////////////

package com.puppycrawl.tools.checkstyle.checks.coding;

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import java.util.regex.Pattern;

import com.puppycrawl.tools.checkstyle.FileStatefulCheck;
import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
import com.puppycrawl.tools.checkstyle.api.DetailAST;
import com.puppycrawl.tools.checkstyle.api.FullIdent;
import com.puppycrawl.tools.checkstyle.api.TokenTypes;
import com.puppycrawl.tools.checkstyle.utils.AnnotationUtil;
import com.puppycrawl.tools.checkstyle.utils.TokenUtil;

/**
 * <p>
 * Checks that particular classes or interfaces are never used.
 * </p>
 * <p>
 * Rationale: Helps reduce coupling on concrete classes.
 * </p>
 * <p>
 * For additional restriction of type usage see also:
 * <a href="https://checkstyle.org/config_coding.html#IllegalInstantiation">
 * IllegalInstantiation</a>,
 * <a href="https://checkstyle.org/config_imports.html#IllegalImport">IllegalImport</a>
 * </p>
 * <p>
 * It is possible to set illegal class names via short or
 * <a href="https://docs.oracle.com/javase/specs/jls/se11/html/jls-6.html#jls-6.7">canonical</a>
 * name. Specifying illegal type invokes analyzing imports and Check puts violations at
 * corresponding declarations (of variables, methods or parameters).
 * This helps to avoid ambiguous cases, e.g.: {@code java.awt.List} was set as
 * illegal class name, then, code like:
 * </p>
 * <pre>
 * import java.util.List;
 * ...
 * List list; //No violation here
 * </pre>
 * <p>
 * will be ok.
 * </p>
 * <p>
 * In most cases it's justified to put following classes to <b>illegalClassNames</b>:
 * </p>
 * <ul>
 * <li>GregorianCalendar</li>
 * <li>Hashtable</li>
 * <li>ArrayList</li>
 * <li>LinkedList</li>
 * <li>Vector</li>
 * </ul>
 * <p>
 * as methods that are differ from interface methods are rarely used, so in most cases user will
 * benefit from checking for them.
 * </p>
 * <ul>
 * <li>
 * Property {@code validateAbstractClassNames} - Control whether to validate abstract class names.
 * Type is {@code boolean}.
 * Default value is {@code false}.
 * </li>
 * <li>
 * Property {@code illegalClassNames} - Specify classes that should not be used
 * as types in variable declarations, return values or parameters.
 * Type is {@code java.lang.String[]}.
 * Default value is {@code HashMap, HashSet, LinkedHashMap, LinkedHashSet, TreeMap,
 * TreeSet, java.util.HashMap, java.util.HashSet, java.util.LinkedHashMap,
 * java.util.LinkedHashSet, java.util.TreeMap, java.util.TreeSet}.
 * </li>
 * <li>
 * Property {@code legalAbstractClassNames} - Define abstract classes that may be used as types.
 * Type is {@code java.lang.String[]}.
 * Default value is {@code ""}.
 * </li>
 * <li>
 * Property {@code ignoredMethodNames} - Specify methods that should not be checked.
 * Type is {@code java.lang.String[]}.
 * Default value is {@code getEnvironment, getInitialContext}.
 * </li>
 * <li>
 * Property {@code illegalAbstractClassNameFormat} - Specify RegExp for illegal abstract class
 * names.
 * Type is {@code java.util.regex.Pattern}.
 * Default value is {@code "^(.*[.])?Abstract.*$"}.
 * </li>
 * <li>
 * Property {@code memberModifiers} - Control whether to check only methods and fields with any
 * of the specified modifiers.
 * This property does not affect method calls nor method references.
 * Type is {@code java.lang.String[]}.
 * Validation type is {@code tokenTypesSet}.
 * Default value is {@code no tokens}.
 * </li>
 * <li>
 * Property {@code tokens} - tokens to check
 * Type is {@code java.lang.String[]}.
 * Validation type is {@code tokenSet}.
 * Default value is:
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#ANNOTATION_FIELD_DEF">
 * ANNOTATION_FIELD_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#CLASS_DEF">
 * CLASS_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#INTERFACE_DEF">
 * INTERFACE_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#METHOD_CALL">
 * METHOD_CALL</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#METHOD_DEF">
 * METHOD_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#METHOD_REF">
 * METHOD_REF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#PARAMETER_DEF">
 * PARAMETER_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#VARIABLE_DEF">
 * VARIABLE_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#PATTERN_VARIABLE_DEF">
 * PATTERN_VARIABLE_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#RECORD_DEF">
 * RECORD_DEF</a>,
 * <a href="https://checkstyle.org/apidocs/com/puppycrawl/tools/checkstyle/api/TokenTypes.html#RECORD_COMPONENT_DEF">
 * RECORD_COMPONENT_DEF</a>.
 * </li>
 * </ul>
 * <p>
 * To configure the default check:
 * </p>
 * <pre>
 * &lt;module name=&quot;IllegalType&quot;/&gt;
 * </pre>
 * <pre>
 * public class Test extends TreeSet { // violation
 *   public &lt;T extends java.util.HashSet&gt; void method() { // violation
 *
 *     LinkedHashMap&lt;Integer, String&gt; lhmap =
 *     new LinkedHashMap&lt;Integer, String&gt;(); // violation
 *     TreeMap&lt;Integer, String&gt; treemap =
 *     new TreeMap&lt;Integer, String&gt;(); // violation
 *     Test t; // OK
 *     HashMap&lt;String, String&gt; hmap; // violation
 *     Queue&lt;Integer&gt; intqueue; // OK
 *
 *     java.lang.IllegalArgumentException illegalex; // OK
 *     java.util.TreeSet treeset; // violation
 *   }
 *
 * }
 * </pre>
 * <p>
 * To configure the Check so that particular tokens are checked:
 * </p>
 * <pre>
 * &lt;module name="IllegalType"&gt;
 *   &lt;property name="tokens" value="METHOD_DEF"/&gt;
 * &lt;/module&gt;
 * </pre>
 * <pre>
 * public class Test extends TreeSet { // OK
 *   public &lt;T extends java.util.HashSet&gt; void method() { // violation
 *     LinkedHashMap&lt;Integer, String&gt; lhmap =
 *     new LinkedHashMap&lt;Integer, String&gt;(); // OK
 *
 *     java.lang.IllegalArgumentException illegalex; // OK
 *     java.util.TreeSet treeset; // Ok
 *   }
 *
 *   public &lt;T extends java.util.HashSet&gt; void typeParam(T t) {} // violation
 *
 *   public void fullName(TreeSet a) {} // OK
 *
 * }
 * </pre>
 * <p>
 * To configure the Check so that it ignores function() methods:
 * </p>
 * <pre>
 * &lt;module name=&quot;IllegalType&quot;&gt;
 *   &lt;property name=&quot;ignoredMethodNames&quot; value=&quot;function&quot;/&gt;
 * &lt;/module&gt;
 * </pre>
 * <pre>
 * public class Test {
 *   public HashMap&lt;String, String&gt; function() { // OK
 *     // code
 *   }
 *
 *   public HashMap&lt;String, String&gt; function1() { // violation
 *     // code
 *   }
 * }
 * </pre>
 * <p>
 * To configure the Check so that it validates abstract class names:
 * </p>
 * <pre>
 *  &lt;module name=&quot;IllegalType&quot;&gt;
 *    &lt;property name=&quot;validateAbstractClassNames&quot; value=&quot;true&quot;/&gt;
 *    &lt;property name=&quot;illegalAbstractClassNameFormat&quot; value=&quot;Gitt&quot;/&gt;
 *  &lt;/module&gt;
 * </pre>
 * <pre>
 * class Test extends Gitter { // violation
 * }
 *
 * class Test1 extends Github { // OK
 * }
 * </pre>
 * <p>
 * To configure the Check so that it verifies only public, protected or static methods and fields:
 * </p>
 * <pre>
 * &lt;module name=&quot;IllegalType&quot;&gt;
 *   &lt;property name=&quot;memberModifiers&quot; value=&quot;LITERAL_PUBLIC,
 *    LITERAL_PROTECTED, LITERAL_STATIC&quot;/&gt;
 * &lt;/module&gt;
 * </pre>
 * <pre>
 * public class Test {
 *   public HashMap&lt;String, String&gt; function1() { // violation
 *     // code
 *   }
 *
 *   private HashMap&lt;String, String&gt; function2() { // OK
 *     // code
 *   }
 *
 *   protected HashMap&lt;Integer, String&gt; function3() { // violation
 *     // code
 *   }
 *
 *   public static TreeMap&lt;Integer, String&gt; function4() { // violation
 *     // code
 *   }
 *
 * }
 * </pre>
 * <p>
 * To configure the check so that it verifies usage of types Boolean and Foo:
 * </p>
 * <pre>
 * &lt;module name=&quot;IllegalType&quot;&gt;
 *           &lt;property name=&quot;illegalClassNames&quot; value=&quot;Boolean, Foo&quot;/&gt;
 * &lt;/module&gt;
 * </pre>
 * <pre>
 * public class Test {
 *
 *   public Set&lt;Boolean&gt; set; // violation
 *   public java.util.List&lt;Map&lt;Boolean, Foo&gt;&gt; list; // violation
 *
 *   private void method(List&lt;Foo&gt; list, Boolean value) { // violation
 *     SomeType.&lt;Boolean&gt;foo(); // violation
 *     final Consumer&lt;Foo&gt; consumer = Foo&lt;Boolean&gt;::foo; // violation
 *   }
 *
 *   public &lt;T extends Boolean, U extends Serializable&gt; void typeParam(T a) {} // violation
 *
 *   public void fullName(java.util.ArrayList&lt;? super Boolean&gt; a) {} // violation
 *
 *   public abstract Set&lt;Boolean&gt; shortName(Set&lt;? super Boolean&gt; a); // violation
 *
 *   public Set&lt;? extends Foo&gt; typeArgument() { // violation
 *     return new TreeSet&lt;Foo&lt;Boolean&gt;&gt;();
 *   }
 *
 * }
 * </pre>
 * <p>
 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
 * </p>
 * <p>
 * Violation Message Keys:
 * </p>
 * <ul>
 * <li>
 * {@code illegal.type}
 * </li>
 * </ul>
 *
 * @since 3.2
 *
 */
@FileStatefulCheck
public final class IllegalTypeCheck extends AbstractCheck {

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_KEY = "illegal.type";

    /** Types illegal by default. */
    private static final String[] DEFAULT_ILLEGAL_TYPES = {
        "HashSet",
        "HashMap",
        "LinkedHashMap",
        "LinkedHashSet",
        "TreeSet",
        "TreeMap",
        "java.util.HashSet",
        "java.util.HashMap",
        "java.util.LinkedHashMap",
        "java.util.LinkedHashSet",
        "java.util.TreeSet",
        "java.util.TreeMap",
    };

    /** Default ignored method names. */
    private static final String[] DEFAULT_IGNORED_METHOD_NAMES = {
        "getInitialContext",
        "getEnvironment",
    };

    /**
     * Specify classes that should not be used as types in variable declarations,
     * return values or parameters.
     */
    private final Set<String> illegalClassNames = new HashSet<>();
    /** Illegal short classes. */
    private final Set<String> illegalShortClassNames = new HashSet<>();
    /** Define abstract classes that may be used as types. */
    private final Set<String> legalAbstractClassNames = new HashSet<>();
    /** Specify methods that should not be checked. */
    private final Set<String> ignoredMethodNames = new HashSet<>();
    /**
     * Control whether to check only methods and fields with any of the specified modifiers.
     * This property does not affect method calls nor method references.
     */
    private List<Integer> memberModifiers;

    /** Specify RegExp for illegal abstract class names. */
    private Pattern illegalAbstractClassNameFormat = Pattern.compile("^(.*[.])?Abstract.*$");

    /**
     * Control whether to validate abstract class names.
     */
    private boolean validateAbstractClassNames;

    /** Creates new instance of the check. */
    public IllegalTypeCheck() {
        setIllegalClassNames(DEFAULT_ILLEGAL_TYPES);
        setIgnoredMethodNames(DEFAULT_IGNORED_METHOD_NAMES);
    }

    /**
     * Setter to specify RegExp for illegal abstract class names.
     *
     * @param pattern a pattern.
     */
    public void setIllegalAbstractClassNameFormat(Pattern pattern) {
        illegalAbstractClassNameFormat = pattern;
    }

    /**
     * Setter to control whether to validate abstract class names.
     *
     * @param validateAbstractClassNames whether abstract class names must be ignored.
     */
    public void setValidateAbstractClassNames(boolean validateAbstractClassNames) {
        this.validateAbstractClassNames = validateAbstractClassNames;
    }

    @Override
    public int[] getDefaultTokens() {
        return getAcceptableTokens();
    }

    @Override
    public int[] getAcceptableTokens() {
        return new int[] {
            TokenTypes.ANNOTATION_FIELD_DEF,
            TokenTypes.CLASS_DEF,
            TokenTypes.IMPORT,
            TokenTypes.INTERFACE_DEF,
            TokenTypes.METHOD_CALL,
            TokenTypes.METHOD_DEF,
            TokenTypes.METHOD_REF,
            TokenTypes.PARAMETER_DEF,
            TokenTypes.VARIABLE_DEF,
            TokenTypes.PATTERN_VARIABLE_DEF,
            TokenTypes.RECORD_DEF,
            TokenTypes.RECORD_COMPONENT_DEF,
        };
    }

    @Override
    public void beginTree(DetailAST rootAST) {
        illegalShortClassNames.clear();

        for (String s : illegalClassNames) {
            if (s.indexOf('.') == -1) {
                illegalShortClassNames.add(s);
            }
        }
    }

    @Override
    public int[] getRequiredTokens() {
        return new int[] {TokenTypes.IMPORT};
    }

    @Override
    public void visitToken(DetailAST ast) {
        switch (ast.getType()) {
            case TokenTypes.CLASS_DEF:
            case TokenTypes.INTERFACE_DEF:
            case TokenTypes.RECORD_DEF:
                visitTypeDef(ast);
                break;
            case TokenTypes.METHOD_CALL:
            case TokenTypes.METHOD_REF:
                visitMethodCallOrRef(ast);
                break;
            case TokenTypes.METHOD_DEF:
                visitMethodDef(ast);
                break;
            case TokenTypes.VARIABLE_DEF:
            case TokenTypes.ANNOTATION_FIELD_DEF:
            case TokenTypes.PATTERN_VARIABLE_DEF:
            case TokenTypes.RECORD_COMPONENT_DEF:
                visitVariableDef(ast);
                break;
            case TokenTypes.PARAMETER_DEF:
                visitParameterDef(ast);
                break;
            case TokenTypes.IMPORT:
                visitImport(ast);
                break;
            default:
                throw new IllegalStateException(ast.toString());
        }
    }

    /**
     * Checks if current method's return type or variable's type is verifiable
     * according to <b>memberModifiers</b> option.
     *
     * @param methodOrVariableDef METHOD_DEF or VARIABLE_DEF ast node.
     * @return true if member is verifiable according to <b>memberModifiers</b> option.
     */
    private boolean isVerifiable(DetailAST methodOrVariableDef) {
        boolean result = true;
        if (memberModifiers != null) {
            final DetailAST modifiersAst = methodOrVariableDef
                    .findFirstToken(TokenTypes.MODIFIERS);
            result = isContainVerifiableType(modifiersAst);
        }
        return result;
    }

    /**
     * Checks is modifiers contain verifiable type.
     *
     * @param modifiers
     *            parent node for all modifiers
     * @return true if method or variable can be verified
     */
    private boolean isContainVerifiableType(DetailAST modifiers) {
        boolean result = false;
        if (modifiers.getFirstChild() != null) {
            for (DetailAST modifier = modifiers.getFirstChild(); modifier != null;
                     modifier = modifier.getNextSibling()) {
                if (memberModifiers.contains(modifier.getType())) {
                    result = true;
                    break;
                }
            }
        }
        return result;
    }

    /**
     * Checks the super type and implemented interfaces of a given type.
     *
     * @param typeDef class or interface for check.
     */
    private void visitTypeDef(DetailAST typeDef) {
        if (isVerifiable(typeDef)) {
            checkTypeParameters(typeDef);
            final DetailAST extendsClause = typeDef.findFirstToken(TokenTypes.EXTENDS_CLAUSE);
            if (extendsClause != null) {
                checkBaseTypes(extendsClause);
            }
            final DetailAST implementsClause = typeDef.findFirstToken(TokenTypes.IMPLEMENTS_CLAUSE);
            if (implementsClause != null) {
                checkBaseTypes(implementsClause);
            }
        }
    }

    /**
     * Checks return type of a given method.
     *
     * @param methodDef method for check.
     */
    private void visitMethodDef(DetailAST methodDef) {
        if (isCheckedMethod(methodDef)) {
            checkClassName(methodDef);
        }
    }

    /**
     * Checks type of parameters.
     *
     * @param parameterDef parameter list for check.
     */
    private void visitParameterDef(DetailAST parameterDef) {
        final DetailAST grandParentAST = parameterDef.getParent().getParent();

        if (grandParentAST.getType() == TokenTypes.METHOD_DEF && isCheckedMethod(grandParentAST)) {
            checkClassName(parameterDef);
        }
    }

    /**
     * Checks type of given variable.
     *
     * @param variableDef variable to check.
     */
    private void visitVariableDef(DetailAST variableDef) {
        if (isVerifiable(variableDef)) {
            checkClassName(variableDef);
        }
    }

    /**
     * Checks the type arguments of given method call/reference.
     *
     * @param methodCallOrRef method call/reference to check.
     */
    private void visitMethodCallOrRef(DetailAST methodCallOrRef) {
        checkTypeArguments(methodCallOrRef);
    }

    /**
     * Checks imported type (as static and star imports are not supported by Check,
     *  only type is in the consideration).<br>
     * If this type is illegal due to Check's options - puts violation on it.
     *
     * @param importAst {@link TokenTypes#IMPORT Import}
     */
    private void visitImport(DetailAST importAst) {
        if (!isStarImport(importAst)) {
            final String canonicalName = getImportedTypeCanonicalName(importAst);
            extendIllegalClassNamesWithShortName(canonicalName);
        }
    }

    /**
     * Checks if current import is star import. E.g.:
     * <p>
     * {@code
     * import java.util.*;
     * }
     * </p>
     *
     * @param importAst {@link TokenTypes#IMPORT Import}
     * @return true if it is star import
     */
    private static boolean isStarImport(DetailAST importAst) {
        boolean result = false;
        DetailAST toVisit = importAst;
        while (toVisit != null) {
            toVisit = getNextSubTreeNode(toVisit, importAst);
            if (toVisit != null && toVisit.getType() == TokenTypes.STAR) {
                result = true;
                break;
            }
        }
        return result;
    }

    /**
     * Checks type and type arguments/parameters of given method, parameter, variable or
     * method call/reference.
     *
     * @param ast node to check.
     */
    private void checkClassName(DetailAST ast) {
        final DetailAST type = ast.findFirstToken(TokenTypes.TYPE);
        checkType(type);
        checkTypeParameters(ast);
    }

    /**
     * Checks the identifier of the given type.
     *
     * @param type node to check.
     */
    private void checkIdent(DetailAST type) {
        final FullIdent ident = FullIdent.createFullIdent(type);
        if (isMatchingClassName(ident.getText())) {
            log(ident.getDetailAst(), MSG_KEY, ident.getText());
        }
    }

    /**
     * Checks the {@code extends} or {@code implements} statement.
     *
     * @param clause DetailAST for either {@link TokenTypes#EXTENDS_CLAUSE} or
     *               {@link TokenTypes#IMPLEMENTS_CLAUSE}
     */
    private void checkBaseTypes(DetailAST clause) {
        DetailAST child = clause.getFirstChild();
        while (child != null) {
            if (child.getType() == TokenTypes.IDENT) {
                checkIdent(child);
            }
            else if (child.getType() == TokenTypes.TYPE_ARGUMENTS) {
                TokenUtil.forEachChild(child, TokenTypes.TYPE_ARGUMENT, this::checkType);
            }
            child = child.getNextSibling();
        }
    }

    /**
     * Checks the given type, its arguments and parameters.
     *
     * @param type node to check.
     */
    private void checkType(DetailAST type) {
        checkIdent(type.getFirstChild());
        checkTypeArguments(type);
        checkTypeBounds(type);
    }

    /**
     * Checks the upper and lower bounds for the given type.
     *
     * @param type node to check.
     */
    private void checkTypeBounds(DetailAST type) {
        final DetailAST upperBounds = type.findFirstToken(TokenTypes.TYPE_UPPER_BOUNDS);
        if (upperBounds != null) {
            checkType(upperBounds);
        }
        final DetailAST lowerBounds = type.findFirstToken(TokenTypes.TYPE_LOWER_BOUNDS);
        if (lowerBounds != null) {
            checkType(lowerBounds);
        }
    }

    /**
     * Checks the type parameters of the node.
     *
     * @param node node to check.
     */
    private void checkTypeParameters(final DetailAST node) {
        final DetailAST typeParameters = node.findFirstToken(TokenTypes.TYPE_PARAMETERS);
        if (typeParameters != null) {
            TokenUtil.forEachChild(typeParameters, TokenTypes.TYPE_PARAMETER, this::checkType);
        }
    }

    /**
     * Checks the type arguments of the node.
     *
     * @param node node to check.
     */
    private void checkTypeArguments(final DetailAST node) {
        DetailAST typeArguments = node.findFirstToken(TokenTypes.TYPE_ARGUMENTS);
        if (typeArguments == null) {
            typeArguments = node.getFirstChild().findFirstToken(TokenTypes.TYPE_ARGUMENTS);
        }

        if (typeArguments != null) {
            TokenUtil.forEachChild(typeArguments, TokenTypes.TYPE_ARGUMENT, this::checkType);
        }
    }

    /**
     * Returns true if given class name is one of illegal classes or else false.
     *
     * @param className class name to check.
     * @return true if given class name is one of illegal classes
     *         or if it matches to abstract class names pattern.
     */
    private boolean isMatchingClassName(String className) {
        final String shortName = className.substring(className.lastIndexOf('.') + 1);
        return illegalClassNames.contains(className)
                || illegalShortClassNames.contains(shortName)
                || validateAbstractClassNames
                    && !legalAbstractClassNames.contains(className)
                    && illegalAbstractClassNameFormat.matcher(className).find();
    }

    /**
     * Extends illegal class names set via imported short type name.
     *
     * @param canonicalName
     *  <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-6.html#jls-6.7">
     *  Canonical</a> name of imported type.
     */
    private void extendIllegalClassNamesWithShortName(String canonicalName) {
        if (illegalClassNames.contains(canonicalName)) {
            final String shortName = canonicalName
                .substring(canonicalName.lastIndexOf('.') + 1);
            illegalShortClassNames.add(shortName);
        }
    }

    /**
     * Gets imported type's
     * <a href="https://docs.oracle.com/javase/specs/jls/se8/html/jls-6.html#jls-6.7">
     *  canonical name</a>.
     *
     * @param importAst {@link TokenTypes#IMPORT Import}
     * @return Imported canonical type's name.
     */
    private static String getImportedTypeCanonicalName(DetailAST importAst) {
        final StringBuilder canonicalNameBuilder = new StringBuilder(256);
        DetailAST toVisit = importAst;
        while (toVisit != null) {
            toVisit = getNextSubTreeNode(toVisit, importAst);
            if (toVisit != null && toVisit.getType() == TokenTypes.IDENT) {
                if (canonicalNameBuilder.length() > 0) {
                    canonicalNameBuilder.append('.');
                }
                canonicalNameBuilder.append(toVisit.getText());
            }
        }
        return canonicalNameBuilder.toString();
    }

    /**
     * Gets the next node of a syntactical tree (child of a current node or
     * sibling of a current node, or sibling of a parent of a current node).
     *
     * @param currentNodeAst Current node in considering
     * @param subTreeRootAst SubTree root
     * @return Current node after bypassing, if current node reached the root of a subtree
     *        method returns null
     */
    private static DetailAST
        getNextSubTreeNode(DetailAST currentNodeAst, DetailAST subTreeRootAst) {
        DetailAST currentNode = currentNodeAst;
        DetailAST toVisitAst = currentNode.getFirstChild();
        while (toVisitAst == null) {
            toVisitAst = currentNode.getNextSibling();
            if (toVisitAst == null) {
                if (currentNode.getParent().equals(subTreeRootAst)) {
                    break;
                }
                currentNode = currentNode.getParent();
            }
        }
        return toVisitAst;
    }

    /**
     * Returns true if method has to be checked or false.
     *
     * @param ast method def to check.
     * @return true if we should check this method.
     */
    private boolean isCheckedMethod(DetailAST ast) {
        final String methodName =
            ast.findFirstToken(TokenTypes.IDENT).getText();
        return isVerifiable(ast) && !ignoredMethodNames.contains(methodName)
                && !AnnotationUtil.containsAnnotation(ast, "Override");
    }

    /**
     * Setter to specify classes that should not be used as types in variable declarations,
     * return values or parameters.
     *
     * @param classNames array of illegal variable types
     * @noinspection WeakerAccess
     */
    public void setIllegalClassNames(String... classNames) {
        illegalClassNames.clear();
        Collections.addAll(illegalClassNames, classNames);
    }

    /**
     * Setter to specify methods that should not be checked.
     *
     * @param methodNames array of ignored method names
     * @noinspection WeakerAccess
     */
    public void setIgnoredMethodNames(String... methodNames) {
        ignoredMethodNames.clear();
        Collections.addAll(ignoredMethodNames, methodNames);
    }

    /**
     * Setter to define abstract classes that may be used as types.
     *
     * @param classNames array of legal abstract class names
     * @noinspection WeakerAccess
     */
    public void setLegalAbstractClassNames(String... classNames) {
        Collections.addAll(legalAbstractClassNames, classNames);
    }

    /**
     * Setter to control whether to check only methods and fields with any of
     * the specified modifiers.
     * This property does not affect method calls nor method references.
     *
     * @param modifiers String contains modifiers.
     */
    public void setMemberModifiers(String modifiers) {
        final List<Integer> modifiersList = new ArrayList<>();
        for (String modifier : modifiers.split(",")) {
            modifiersList.add(TokenUtil.getTokenId(modifier.trim()));
        }
        memberModifiers = modifiersList;
    }

}
