///////////////////////////////////////////////////////////////////////////////////////////////
   // 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.design;
  
  import java.util.ArrayDeque;
  import java.util.Deque;
  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.TokenTypes;
  
  /**
   * <div>
   * Ensures that exception classes (classes with names conforming to some pattern
   * and explicitly extending classes with names conforming to other
   * pattern) are immutable, that is, that they have only final fields.
   * </div>
   *
   * <p>
   * The current algorithm is very simple: it checks that all members of exception are final.
   * The user can still mutate an exception's instance (e.g. Throwable has a method called
   * {@code setStackTrace} which changes the exception's stack trace). But, at least, all
   * information provided by this exception type is unchangeable.
   * </p>
   *
   * <p>
   * Rationale: Exception instances should represent an error
   * condition. Having non-final fields not only allows the state to be
   * modified by accident and therefore mask the original condition but
   * also allows developers to accidentally forget to set the initial state.
   * In both cases, code catching the exception could draw incorrect
   * conclusions based on the state.
   * </p>
   *
   * @since 3.2
   */
  @FileStatefulCheck
  public final class MutableExceptionCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "mutable.exception";
  
      /** Default value for format and extendedClassNameFormat properties. */
      private static final String DEFAULT_FORMAT = "^.*Exception$|^.*Error$|^.*Throwable$";
      /** Stack of checking information for classes. */
      private final Deque<Boolean> checkingStack = new ArrayDeque<>();
      /** Specify pattern for extended class names. */
      private Pattern extendedClassNameFormat = Pattern.compile(DEFAULT_FORMAT);
      /** Should we check current class or not. */
      private boolean checking;
      /** Specify pattern for exception class names. */
      private Pattern format = extendedClassNameFormat;
  
      /**
       * Creates a new {@code MutableExceptionCheck} instance.
       */
      public MutableExceptionCheck() {
          // no code by default
      }
  
      /**
       * Setter to specify pattern for extended class names.
       *
       * @param extendedClassNameFormat a {@code String} value
       * @since 6.2
       */
      public void setExtendedClassNameFormat(Pattern extendedClassNameFormat) {
          this.extendedClassNameFormat = extendedClassNameFormat;
      }
  
      /**
       * Setter to specify pattern for exception class names.
       *
       * @param pattern the new pattern
       * @since 3.2
       */
      public void setFormat(Pattern pattern) {
         format = pattern;
     }
 
     @Override
     public int[] getDefaultTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getRequiredTokens() {
         return new int[] {TokenTypes.CLASS_DEF, TokenTypes.VARIABLE_DEF};
     }
 
     @Override
     public int[] getAcceptableTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public void visitToken(DetailAST ast) {
         switch (ast.getType()) {
             case TokenTypes.CLASS_DEF -> visitClassDef(ast);
             case TokenTypes.VARIABLE_DEF -> visitVariableDef(ast);
             default -> throw new IllegalStateException(ast.toString());
         }
     }
 
     @Override
     public void leaveToken(DetailAST ast) {
         if (ast.getType() == TokenTypes.CLASS_DEF) {
             leaveClassDef();
         }
     }
 
     /**
      * Called when we start processing class definition.
      *
      * @param ast class definition node
      */
     private void visitClassDef(DetailAST ast) {
         checkingStack.push(checking);
         checking = isNamedAsException(ast) && isExtendedClassNamedAsException(ast);
     }
 
     /** Called when we leave class definition. */
     private void leaveClassDef() {
         checking = checkingStack.pop();
     }
 
     /**
      * Checks variable definition.
      *
      * @param ast variable def node for check
      */
     private void visitVariableDef(DetailAST ast) {
         if (checking && ast.getParent().getType() == TokenTypes.OBJBLOCK) {
             final DetailAST modifiersAST =
                 ast.findFirstToken(TokenTypes.MODIFIERS);
 
             if (modifiersAST.findFirstToken(TokenTypes.FINAL) == null) {
                 log(ast, MSG_KEY, ast.findFirstToken(TokenTypes.IDENT).getText());
             }
         }
     }
 
     /**
      * Checks that a class name conforms to specified format.
      *
      * @param ast class definition node
      * @return true if a class name conforms to specified format
      */
     private boolean isNamedAsException(DetailAST ast) {
         final String className = ast.findFirstToken(TokenTypes.IDENT).getText();
         return format.matcher(className).find();
     }
 
     /**
      * Checks that if extended class name conforms to specified format.
      *
      * @param ast class definition node
      * @return true if extended class name conforms to specified format
      */
     private boolean isExtendedClassNamedAsException(DetailAST ast) {
         boolean result = false;
         final DetailAST extendsClause = ast.findFirstToken(TokenTypes.EXTENDS_CLAUSE);
         if (extendsClause != null) {
             DetailAST currentNode = extendsClause;
             while (currentNode.getLastChild() != null) {
                 currentNode = currentNode.getLastChild();
             }
             final String extendedClassName = currentNode.getText();
             result = extendedClassNameFormat.matcher(extendedClassName).matches();
         }
         return result;
     }
 
 }