////////////////////////////////////////////////////////////////////////////////
// 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.ArrayDeque;
import java.util.Deque;

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.TokenTypes;
import com.puppycrawl.tools.checkstyle.utils.TokenUtil;

/**
 * <p>
 * Checks that there is only one statement per line.
 * </p>
 * <p>
 * Rationale: It's very difficult to read multiple statements on one line.
 * </p>
 * <p>
 * In the Java programming language, statements are the fundamental unit of
 * execution. All statements except blocks are terminated by a semicolon.
 * Blocks are denoted by open and close curly braces.
 * </p>
 * <p>
 * OneStatementPerLineCheck checks the following types of statements:
 * variable declaration statements, empty statements, import statements,
 * assignment statements, expression statements, increment statements,
 * object creation statements, 'for loop' statements, 'break' statements,
 * 'continue' statements, 'return' statements, resources statements (optional).
 * </p>
 * <ul>
 * <li>
 * Property {@code treatTryResourcesAsStatement} - Enable resources processing.
 * Type is {@code boolean}.
 * Default value is {@code false}.
 * </li>
 * </ul>
 * <p>
 * To configure the check:
 * </p>
 * <pre>
 * &lt;module name=&quot;OneStatementPerLine&quot;/&gt;
 * </pre>
 * <p>
 * The following examples will be flagged as a violation:
 * </p>
 * <pre>
 * //Each line causes violation:
 * int var1; int var2;
 * var1 = 1; var2 = 2;
 * int var1 = 1; int var2 = 2;
 * var1++; var2++;
 * Object obj1 = new Object(); Object obj2 = new Object();
 * import java.io.EOFException; import java.io.BufferedReader;
 * ;; //two empty statements on the same line.
 *
 * //Multi-line statements:
 * int var1 = 1
 * ; var2 = 2; //violation here
 * int o = 1, p = 2,
 * r = 5; int t; //violation here
 * </pre>
 * <p>
 * An example of how to configure the check to treat resources
 * in a try statement as statements to require them on their own line:
 * </p>
 * <pre>
 * &lt;module name=&quot;OneStatementPerLine&quot;&gt;
 *   &lt;property name=&quot;treatTryResourcesAsStatement&quot; value=&quot;true&quot;/&gt;
 * &lt;/module&gt;
 * </pre>
 * <p>
 * Note: resource declarations can contain variable definitions
 * and variable references (from java9).
 * When property "treatTryResourcesAsStatement" is enabled,
 * this check is only applied to variable definitions.
 * If there are one or more variable references
 * and one variable definition on the same line in resources declaration,
 * there is no violation.
 * The following examples will illustrate difference:
 * </p>
 * <pre>
 * OutputStream s1 = new PipedOutputStream();
 * OutputStream s2 = new PipedOutputStream();
 * // only one statement(variable definition) with two variable references
 * try (s1; s2; OutputStream s3 = new PipedOutputStream();) // OK
 * {}
 * // two statements with variable definitions
 * try (Reader r = new PipedReader(); s2; Reader s3 = new PipedReader() // violation
 * ) {}
 * </pre>
 * <p>
 * Parent is {@code com.puppycrawl.tools.checkstyle.TreeWalker}
 * </p>
 * <p>
 * Violation Message Keys:
 * </p>
 * <ul>
 * <li>
 * {@code multiple.statements.line}
 * </li>
 * </ul>
 *
 * @since 5.3
 */
@FileStatefulCheck
public final class OneStatementPerLineCheck extends AbstractCheck {

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

    /**
     * Counts number of semicolons in nested lambdas.
     */
    private final Deque<Integer> countOfSemiInLambda = new ArrayDeque<>();

    /**
     * Hold the line-number where the last statement ended.
     */
    private int lastStatementEnd = -1;

    /**
     * Hold the line-number where the last 'for-loop' statement ended.
     */
    private int forStatementEnd = -1;

    /**
     * The for-header usually has 3 statements on one line, but THIS IS OK.
     */
    private boolean inForHeader;

    /**
     * Holds if current token is inside lambda.
     */
    private boolean isInLambda;

    /**
     * Hold the line-number where the last lambda statement ended.
     */
    private int lambdaStatementEnd = -1;

    /**
     * Hold the line-number where the last resource variable statement ended.
     */
    private int lastVariableResourceStatementEnd = -1;

    /**
     * Enable resources processing.
     */
    private boolean treatTryResourcesAsStatement;

    /**
     * Setter to enable resources processing.
     *
     * @param treatTryResourcesAsStatement user's value of treatTryResourcesAsStatement.
     */
    public void setTreatTryResourcesAsStatement(boolean treatTryResourcesAsStatement) {
        this.treatTryResourcesAsStatement = treatTryResourcesAsStatement;
    }

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

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

    @Override
    public int[] getRequiredTokens() {
        return new int[] {
            TokenTypes.SEMI,
            TokenTypes.FOR_INIT,
            TokenTypes.FOR_ITERATOR,
            TokenTypes.LAMBDA,
        };
    }

    @Override
    public void beginTree(DetailAST rootAST) {
        inForHeader = false;
        lastStatementEnd = -1;
        forStatementEnd = -1;
        isInLambda = false;
        lastVariableResourceStatementEnd = -1;
    }

    @Override
    public void visitToken(DetailAST ast) {
        switch (ast.getType()) {
            case TokenTypes.SEMI:
                checkIfSemicolonIsInDifferentLineThanPrevious(ast);
                break;
            case TokenTypes.FOR_ITERATOR:
                forStatementEnd = ast.getLineNo();
                break;
            case TokenTypes.LAMBDA:
                isInLambda = true;
                countOfSemiInLambda.push(0);
                break;
            default:
                inForHeader = true;
                break;
        }
    }

    @Override
    public void leaveToken(DetailAST ast) {
        switch (ast.getType()) {
            case TokenTypes.SEMI:
                lastStatementEnd = ast.getLineNo();
                forStatementEnd = -1;
                lambdaStatementEnd = -1;
                break;
            case TokenTypes.FOR_ITERATOR:
                inForHeader = false;
                break;
            case TokenTypes.LAMBDA:
                countOfSemiInLambda.pop();
                if (countOfSemiInLambda.isEmpty()) {
                    isInLambda = false;
                }
                lambdaStatementEnd = ast.getLineNo();
                break;
            default:
                break;
        }
    }

    /**
     * Checks if given semicolon is in different line than previous.
     *
     * @param ast semicolon to check
     */
    private void checkIfSemicolonIsInDifferentLineThanPrevious(DetailAST ast) {
        DetailAST currentStatement = ast;
        final boolean hasResourcesPrevSibling =
                currentStatement.getPreviousSibling() != null
                        && currentStatement.getPreviousSibling().getType() == TokenTypes.RESOURCES;
        if (!hasResourcesPrevSibling && isMultilineStatement(currentStatement)) {
            currentStatement = ast.getPreviousSibling();
        }
        if (isInLambda) {
            checkLambda(ast, currentStatement);
        }
        else if (isResource(ast.getParent())) {
            checkResourceVariable(ast);
        }
        else if (!inForHeader && isOnTheSameLine(currentStatement, lastStatementEnd,
                forStatementEnd, lambdaStatementEnd)) {
            log(ast, MSG_KEY);
        }
    }

    private void checkLambda(DetailAST ast, DetailAST currentStatement) {
        int countOfSemiInCurrentLambda = countOfSemiInLambda.pop();
        countOfSemiInCurrentLambda++;
        countOfSemiInLambda.push(countOfSemiInCurrentLambda);
        if (!inForHeader && countOfSemiInCurrentLambda > 1
                && isOnTheSameLine(currentStatement,
                lastStatementEnd, forStatementEnd,
                lambdaStatementEnd)) {
            log(ast, MSG_KEY);
        }
    }

    private static boolean isResource(DetailAST ast) {
        return ast != null
            && (ast.getType() == TokenTypes.RESOURCES
                 || ast.getType() == TokenTypes.RESOURCE_SPECIFICATION);
    }

    private void checkResourceVariable(DetailAST currentStatement) {
        if (treatTryResourcesAsStatement) {
            final DetailAST nextNode = currentStatement.getNextSibling();
            if (currentStatement.getPreviousSibling().findFirstToken(TokenTypes.ASSIGN) != null) {
                lastVariableResourceStatementEnd = currentStatement.getLineNo();
            }
            if (nextNode.findFirstToken(TokenTypes.ASSIGN) != null
                && nextNode.getLineNo() == lastVariableResourceStatementEnd) {
                log(currentStatement, MSG_KEY);
            }
        }
    }

    /**
     * Checks whether two statements are on the same line.
     *
     * @param ast token for the current statement.
     * @param lastStatementEnd the line-number where the last statement ended.
     * @param forStatementEnd the line-number where the last 'for-loop'
     *                        statement ended.
     * @param lambdaStatementEnd the line-number where the last lambda
     *                        statement ended.
     * @return true if two statements are on the same line.
     */
    private static boolean isOnTheSameLine(DetailAST ast, int lastStatementEnd,
                                           int forStatementEnd, int lambdaStatementEnd) {
        return lastStatementEnd == ast.getLineNo() && forStatementEnd != ast.getLineNo()
                && lambdaStatementEnd != ast.getLineNo();
    }

    /**
     * Checks whether statement is multiline.
     *
     * @param ast token for the current statement.
     * @return true if one statement is distributed over two or more lines.
     */
    private static boolean isMultilineStatement(DetailAST ast) {
        final boolean multiline;
        if (ast.getPreviousSibling() == null) {
            multiline = false;
        }
        else {
            final DetailAST prevSibling = ast.getPreviousSibling();
            multiline = !TokenUtil.areOnSameLine(prevSibling, ast)
                    && ast.getParent() != null;
        }
        return multiline;
    }

}
