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Logic useful to read and analyze regular expressions
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/*
 * SonarSource Analyzers Regex Parsing Commons
 * Copyright (C) 2009-2024 SonarSource SA
 * mailto:info AT sonarsource DOT com
 *
 * This program 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 3 of the License, or (at your option) any later version.
 *
 * This program 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 program; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 */
package org.sonarsource.analyzer.commons.regex.helpers;

import java.util.ArrayList;
import java.util.List;
import java.util.regex.Pattern;
import org.sonarsource.analyzer.commons.regex.RegexIssueLocation;
import org.sonarsource.analyzer.commons.regex.ast.CharacterTree;
import org.sonarsource.analyzer.commons.regex.ast.RegexSyntaxElement;

public class GraphemeHelper {

  // M (Mark) is "a character intended to be combined with another character (e.g. accents, umlauts, enclosing boxes, etc.)."
  // See https://www.regular-expressions.info/unicode.html
  private static final Pattern MARK_PATTERN = Pattern.compile("\\p{M}");

  private GraphemeHelper() {
    // Helper class
  }

  public static List getGraphemeInList(List trees) {
    List result = new ArrayList<>();
    List codePoints = new ArrayList<>();
    for (RegexSyntaxElement child : trees) {
      if (child instanceof CharacterTree) {
        CharacterTree currentCharacter = (CharacterTree) child;
        if (!currentCharacter.isEscapeSequence()) {
          if (!isMark(currentCharacter)) {
            addCurrentGrapheme(result, codePoints);
            codePoints.clear();
            codePoints.add(currentCharacter);
          } else if (!codePoints.isEmpty()) {
            codePoints.add(currentCharacter);
          }
          continue;
        }
      }
      addCurrentGrapheme(result, codePoints);
      codePoints.clear();
    }
    addCurrentGrapheme(result, codePoints);
    return result;
  }

  private static boolean isMark(CharacterTree currentChar) {
    return MARK_PATTERN.matcher(currentChar.characterAsString()).matches();
  }

  private static void addCurrentGrapheme(List result, List codePoints) {
    if (codePoints.size() > 1) {
      result.add(new RegexIssueLocation(codePoints, ""));
    }
  }

}