GenericWhitespaceCheck

///////////////////////////////////////////////////////////////////////////////////////////////
// checkstyle: Checks Java source code and other text files for adherence to a set of rules.
// Copyright (C) 2001-2026 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.whitespace;

import java.util.stream.IntStream;

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.CodePointUtil;
import com.puppycrawl.tools.checkstyle.utils.CommonUtil;

/**
 * <div>
 * Checks that the whitespace around the Generic tokens (angle brackets)
 * "{@literal <}" and "{@literal >}" are correct to the <i>typical</i> convention.
 * The convention is not configurable.
 * </div>
 *
 * <p>
 * Whitespace is defined by implementation of
 * java.lang.Character.isWhitespace(char)
 * </p>
 *
 * <p>
 * Left angle bracket ("{@literal <}"):
 * </p>
 * <ul>
 * <li> should be preceded with whitespace only
 *   in generic methods definitions.</li>
 * <li> should not be preceded with whitespace
 *   when it is preceded method name or constructor.</li>
 * <li> should not be preceded with whitespace when following type name.</li>
 * <li> should not be followed with whitespace in all cases.</li>
 * </ul>
 *
 * <p>
 * Right angle bracket ("{@literal >}"):
 * </p>
 * <ul>
 * <li> should not be preceded with whitespace in all cases.</li>
 * <li> should be followed with whitespace in almost all cases,
 *   except diamond operators and when preceding a method name, constructor, or record header.</li>
 * </ul>
 *
 * @since 5.0
 */
@FileStatefulCheck
public class GenericWhitespaceCheck extends AbstractCheck {

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_WS_PRECEDED = "ws.preceded";

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_WS_FOLLOWED = "ws.followed";

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_WS_NOT_PRECEDED = "ws.notPreceded";

    /**
     * A key is pointing to the warning message text in "messages.properties"
     * file.
     */
    public static final String MSG_WS_ILLEGAL_FOLLOW = "ws.illegalFollow";

    /** Open angle bracket literal. */
    private static final String OPEN_ANGLE_BRACKET = "<";

    /** Close angle bracket literal. */
    private static final String CLOSE_ANGLE_BRACKET = ">";

    /** Used to count the depth of a Generic expression. */
    private int depth;

    /**
     * Creates a new {@code GenericWhitespaceCheck} instance.
     */
    public GenericWhitespaceCheck() {
        // no code by default
    }

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

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

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

    @Override
    public void beginTree(DetailAST rootAST) {
        // Reset for each tree, just increase there are violations in preceding
        // trees.
        depth = 0;
    }

    @Override
    public void visitToken(DetailAST ast) {
        switch (ast.getType()) {
            case TokenTypes.GENERIC_START -> {
                processStart(ast);
                depth++;
            }
            case TokenTypes.GENERIC_END -> {
                processEnd(ast);
                depth--;
            }
            default -> throw new IllegalArgumentException("Unknown type " + ast);
        }
    }

    /**
     * Checks the token for the end of Generics.
     *
     * @param ast the token to check
     */
    private void processEnd(DetailAST ast) {
        final int[] line = getLineCodePoints(ast.getLineNo() - 1);
        final int before = ast.getColumnNo() - 1;
        final int after = ast.getColumnNo() + 1;

        if (before >= 0 && CommonUtil.isCodePointWhitespace(line, before)
                && !containsWhitespaceBefore(before, line)) {
            log(ast, MSG_WS_PRECEDED, CLOSE_ANGLE_BRACKET);
        }

        if (after < line.length) {
            // Check if the last Generic, in which case must be a whitespace
            // or a '(),[.'.
            if (depth == 1) {
                processSingleGeneric(ast, line, after);
            }
            else {
                processNestedGenerics(ast, line, after);
            }
        }
    }

    /**
     * Process Nested generics.
     *
     * @param ast token
     * @param line unicode code points array of line
     * @param after position after
     */
    private void processNestedGenerics(DetailAST ast, int[] line, int after) {
        // In a nested Generic type, so can only be a '>' or ',' or '&'

        // In case of several extends definitions:
        //
        //   class IntEnumValueType<E extends Enum<E> & IntEnum>
        //                                          ^
        //   should be whitespace if followed by & -+
        //
        final int indexOfAmp = IntStream.range(after, line.length)
                .filter(index -> line[index] == '&')
                .findFirst()
                .orElse(-1);
        if (indexOfAmp >= 1
            && containsWhitespaceBetween(after, indexOfAmp, line)) {
            if (indexOfAmp - after == 0) {
                log(ast, MSG_WS_NOT_PRECEDED, "&");
            }
            else if (indexOfAmp - after != 1) {
                log(ast, MSG_WS_FOLLOWED, CLOSE_ANGLE_BRACKET);
            }
        }
        else if (line[after] == ' ') {
            log(ast, MSG_WS_FOLLOWED, CLOSE_ANGLE_BRACKET);
        }
    }

    /**
     * Process Single-generic.
     *
     * @param ast token
     * @param line unicode code points array of line
     * @param after position after
     */
    private void processSingleGeneric(DetailAST ast, int[] line, int after) {
        final char charAfter = Character.toChars(line[after])[0];
        if (isGenericBeforeMethod(ast)
                || isGenericBeforeCtorInvocation(ast)
                || isGenericBeforeRecordHeader(ast)) {
            if (Character.isWhitespace(charAfter)) {
                log(ast, MSG_WS_FOLLOWED, CLOSE_ANGLE_BRACKET);
            }
        }
        else if (!isCharacterValidAfterGenericEnd(charAfter)) {
            log(ast, MSG_WS_ILLEGAL_FOLLOW, CLOSE_ANGLE_BRACKET);
        }
    }

    /**
     * Checks if generic is before record header. Identifies two cases:
     * <ol>
     *     <li>In record def, eg: {@code record Session<T>()}</li>
     *     <li>In record pattern def, eg: {@code o instanceof Session<String>(var s)}</li>
     * </ol>
     *
     * @param ast ast
     * @return true if generic is before record header
     */
    private static boolean isGenericBeforeRecordHeader(DetailAST ast) {
        DetailAST typeNode = ast.getParent().getParent();
        if (typeNode.getType() == TokenTypes.DOT) {
            typeNode = typeNode.getParent();
        }
        return typeNode.getType() == TokenTypes.RECORD_DEF
                || typeNode.getParent().getType() == TokenTypes.RECORD_PATTERN_DEF;
    }

    /**
     * Checks if generic is before constructor invocation. Identifies two cases:
     * <ol>
     *     <li>{@code new ArrayList<>();}</li>
     *     <li>{@code new Outer.Inner<>();}</li>
     * </ol>
     *
     * @param ast ast
     * @return true if generic is before constructor invocation
     */
    private static boolean isGenericBeforeCtorInvocation(DetailAST ast) {
        final DetailAST grandParent = ast.getParent().getParent();
        return grandParent.getType() == TokenTypes.LITERAL_NEW
                || grandParent.getParent().getType() == TokenTypes.LITERAL_NEW;
    }

    /**
     * Checks if generic is after {@code LITERAL_NEW}. Identifies three cases:
     * <ol>
     *     <li>{@code new <String>Object();}</li>
     *     <li>{@code new <String>Outer.Inner();}</li>
     *     <li>{@code new <@A Outer>@B Inner();}</li>
     * </ol>
     *
     * @param ast ast
     * @return true if generic after {@code LITERAL_NEW}
     */
    private static boolean isGenericAfterNew(DetailAST ast) {
        final DetailAST parent = ast.getParent();
        return parent.getParent().getType() == TokenTypes.LITERAL_NEW
                && (parent.getNextSibling().getType() == TokenTypes.IDENT
                    || parent.getNextSibling().getType() == TokenTypes.DOT
                    || parent.getNextSibling().getType() == TokenTypes.ANNOTATIONS);
    }

    /**
     * Is generic before method reference.
     *
     * @param ast ast
     * @return true if generic before a method ref
     */
    private static boolean isGenericBeforeMethod(DetailAST ast) {
        return ast.getParent().getParent().getParent().getType() == TokenTypes.METHOD_CALL
                || isAfterMethodReference(ast);
    }

    /**
     * Checks if current generic end ('{@literal >}') is located after
     * {@link TokenTypes#METHOD_REF method reference operator}.
     *
     * @param genericEnd {@link TokenTypes#GENERIC_END}
     * @return true if '{@literal >}' follows after method reference.
     */
    private static boolean isAfterMethodReference(DetailAST genericEnd) {
        return genericEnd.getParent().getParent().getType() == TokenTypes.METHOD_REF;
    }

    /**
     * Checks the token for the start of Generics.
     *
     * @param ast the token to check
     */
    private void processStart(DetailAST ast) {
        final int[] line = getLineCodePoints(ast.getLineNo() - 1);
        final int before = ast.getColumnNo() - 1;
        final int after = ast.getColumnNo() + 1;

        // Checks if generic needs to be preceded by a whitespace or not.
        // Handles 3 cases as in:
        //
        //   public static <T> Callable<T> callable(Runnable task, T result)
        //                 ^           ^
        //   1. ws reqd ---+        2. +--- whitespace NOT required
        //
        //   new <String>Object()
        //       ^
        //    3. +--- ws required
        if (before >= 0) {
            final DetailAST parent = ast.getParent();
            final DetailAST grandparent = parent.getParent();
            // cases (1, 3) where whitespace is required:
            if (grandparent.getType() == TokenTypes.CTOR_DEF
                    || grandparent.getType() == TokenTypes.METHOD_DEF
                    || isGenericAfterNew(ast)) {

                if (!CommonUtil.isCodePointWhitespace(line, before)) {
                    log(ast, MSG_WS_NOT_PRECEDED, OPEN_ANGLE_BRACKET);
                }
            }
            // case 2 where whitespace is not required:
            else if (CommonUtil.isCodePointWhitespace(line, before)
                && !containsWhitespaceBefore(before, line)) {
                log(ast, MSG_WS_PRECEDED, OPEN_ANGLE_BRACKET);
            }
        }

        if (after < line.length
                && CommonUtil.isCodePointWhitespace(line, after)) {
            log(ast, MSG_WS_FOLLOWED, OPEN_ANGLE_BRACKET);
        }
    }

    /**
     * Returns whether the specified string contains only whitespace between
     * specified indices.
     *
     * @param fromIndex the index to start the search from. Inclusive
     * @param toIndex the index to finish the search. Exclusive
     * @param line the unicode code points array of line to check
     * @return whether there are only whitespaces (or nothing)
     */
    private static boolean containsWhitespaceBetween(int fromIndex, int toIndex, int... line) {
        boolean result = true;
        for (int i = fromIndex; i < toIndex; i++) {
            if (!CommonUtil.isCodePointWhitespace(line, i)) {
                result = false;
                break;
            }
        }
        return result;
    }

    /**
     * Returns whether the specified string contains only whitespace up to specified index.
     *
     * @param before the index to finish the search. Exclusive
     * @param line   the unicode code points array of line to check
     * @return {@code true} if there are only whitespaces,
     *     false if there is nothing before or some other characters
     */
    private static boolean containsWhitespaceBefore(int before, int... line) {
        return before != 0 && CodePointUtil.hasWhitespaceBefore(before, line);
    }

    /**
     * Checks whether given character is valid to be right after generic ends.
     *
     * @param charAfter character to check
     * @return checks if given character is valid
     */
    private static boolean isCharacterValidAfterGenericEnd(char charAfter) {
        return charAfter == ')' || charAfter == ','
            || charAfter == '[' || charAfter == '.'
            || charAfter == ':' || charAfter == ';'
            || Character.isWhitespace(charAfter);
    }

}