///////////////////////////////////////////////////////////////////////////////////////////////
   // 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.Comparator;
  import java.util.Deque;
  import java.util.HashMap;
  import java.util.LinkedHashMap;
  import java.util.Map;
  import java.util.Optional;
  import java.util.function.Function;
  import java.util.function.ToIntFunction;
  
  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.CheckUtil;
  import com.puppycrawl.tools.checkstyle.utils.CommonUtil;
  import com.puppycrawl.tools.checkstyle.utils.ScopeUtil;
  import com.puppycrawl.tools.checkstyle.utils.TokenUtil;
  
  /**
   * <div>
   * Ensures that identifies classes that can be effectively declared as final are explicitly
   * marked as final. The following are different types of classes that can be identified:
   * </div>
   * <ol>
   *   <li>
   *       Private classes with no declared constructors.
   *   </li>
   *   <li>
   *       Classes with any modifier, and contains only private constructors.
   *   </li>
   * </ol>
   *
   * <p>
   * Classes are skipped if:
   * </p>
   * <ol>
   *   <li>
   *       Class is Super class of some Anonymous inner class.
   *   </li>
   *   <li>
   *       Class is extended by another class in the same file.
   *   </li>
   * </ol>
   *
   * @since 3.1
   */
  @FileStatefulCheck
  public class FinalClassCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "final.class";
  
      /**
       * Character separate package names in qualified name of java class.
       */
      private static final String PACKAGE_SEPARATOR = ".";
  
      /** Keeps ClassDesc objects for all inner classes. */
      private Map<String, ClassDesc> innerClasses;
  
      /**
       * Maps anonymous inner class's {@link TokenTypes#LITERAL_NEW} node to
       * the outer type declaration's fully qualified name.
       */
      private Map<DetailAST, String> anonInnerClassToOuterTypeDecl;
  
      /** Keeps TypeDeclarationDescription object for stack of declared type descriptions. */
      private Deque<TypeDeclarationDescription> typeDeclarations;
  
      /** Full qualified name of the package. */
      private String packageName;
  
      /**
      * Creates a new {@code FinalClassCheck} instance.
      */
     public FinalClassCheck() {
         // no code by default
     }
 
     @Override
     public int[] getDefaultTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getAcceptableTokens() {
         return getRequiredTokens();
     }
 
     @Override
     public int[] getRequiredTokens() {
         return new int[] {
             TokenTypes.ANNOTATION_DEF,
             TokenTypes.CLASS_DEF,
             TokenTypes.ENUM_DEF,
             TokenTypes.INTERFACE_DEF,
             TokenTypes.RECORD_DEF,
             TokenTypes.CTOR_DEF,
             TokenTypes.PACKAGE_DEF,
             TokenTypes.LITERAL_NEW,
         };
     }
 
     @Override
     public void beginTree(DetailAST rootAST) {
         typeDeclarations = new ArrayDeque<>();
         innerClasses = new LinkedHashMap<>();
         anonInnerClassToOuterTypeDecl = new HashMap<>();
         packageName = "";
     }
 
     @Override
     public void visitToken(DetailAST ast) {
         switch (ast.getType()) {
             case TokenTypes.PACKAGE_DEF ->
                 packageName = CheckUtil.extractQualifiedName(ast.getFirstChild().getNextSibling());
 
             case TokenTypes.ANNOTATION_DEF,
                  TokenTypes.ENUM_DEF,
                  TokenTypes.INTERFACE_DEF,
                  TokenTypes.RECORD_DEF -> {
                 final TypeDeclarationDescription description = new TypeDeclarationDescription(
                     extractQualifiedTypeName(ast), 0, ast);
                 typeDeclarations.push(description);
             }
 
             case TokenTypes.CLASS_DEF -> visitClass(ast);
 
             case TokenTypes.CTOR_DEF -> visitCtor(ast);
 
             case TokenTypes.LITERAL_NEW -> {
                 if (ast.getFirstChild() != null
                         && ast.getLastChild().getType() == TokenTypes.OBJBLOCK) {
 
                     String outerTypeName = packageName;
                     if (!typeDeclarations.isEmpty()) {
                         outerTypeName = typeDeclarations.peek().getQualifiedName();
                     }
                     anonInnerClassToOuterTypeDecl.put(ast, outerTypeName);
                 }
             }
 
             default -> throw new IllegalStateException(ast.toString());
         }
     }
 
     /**
      * Called to process a type definition.
      *
      * @param ast the token to process
      */
     private void visitClass(DetailAST ast) {
         final String qualifiedClassName = extractQualifiedTypeName(ast);
         final ClassDesc currClass = new ClassDesc(qualifiedClassName, typeDeclarations.size(), ast);
         typeDeclarations.push(currClass);
         innerClasses.put(qualifiedClassName, currClass);
     }
 
     /**
      * Called to process a constructor definition.
      *
      * @param ast the token to process
      */
     private void visitCtor(DetailAST ast) {
         if (!ScopeUtil.isInEnumBlock(ast) && !ScopeUtil.isInRecordBlock(ast)) {
             final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
             if (modifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) == null) {
                 // Can be only of type ClassDesc, preceding if statements guarantee it.
                 final ClassDesc desc = (ClassDesc) typeDeclarations.getFirst();
                 desc.registerNonPrivateCtor();
             }
         }
     }
 
     @Override
     public void leaveToken(DetailAST ast) {
         if (TokenUtil.isTypeDeclaration(ast.getType())) {
             typeDeclarations.pop();
         }
     }
 
     @Override
     public void finishTree(DetailAST rootAST) {
         anonInnerClassToOuterTypeDecl.forEach(this::registerAnonymousInnerClassToSuperClass);
         innerClasses.forEach(this::registerExtendedClass);
         innerClasses.forEach((qualifiedClassName, classDesc) -> {
             if (shouldBeDeclaredAsFinal(classDesc)) {
                 final String className = CommonUtil.baseClassName(qualifiedClassName);
                 log(classDesc.getTypeDeclarationAst(), MSG_KEY, className);
             }
         });
     }
 
     /**
      * Checks whether a class should be declared as final or not.
      *
      * @param classDesc description of the class
      * @return true if given class should be declared as final otherwise false
      */
     private static boolean shouldBeDeclaredAsFinal(ClassDesc classDesc) {
         final boolean shouldBeFinal;
 
         final boolean skipClass = classDesc.isDeclaredAsFinal()
                     || classDesc.isDeclaredAsAbstract()
                     || classDesc.isSuperClassOfAnonymousInnerClass()
                     || classDesc.isWithNestedSubclass();
 
         if (skipClass) {
             shouldBeFinal = false;
         }
         else if (classDesc.isHasDeclaredConstructor()) {
             shouldBeFinal = classDesc.isDeclaredAsPrivate();
         }
         else {
             shouldBeFinal = !classDesc.isWithNonPrivateCtor();
         }
         return shouldBeFinal;
     }
 
     /**
      * Register to outer super class of given classAst that
      * given classAst is extending them.
      *
      * @param qualifiedClassName qualifies class name(with package) of the current class
      * @param currentClass class which outer super class will be informed about nesting subclass
      */
     private void registerExtendedClass(String qualifiedClassName,
                                        ClassDesc currentClass) {
         final String superClassName = getSuperClassName(currentClass.getTypeDeclarationAst());
         if (superClassName != null) {
             final ToIntFunction<ClassDesc> nestedClassCountProvider = classDesc -> {
                 return CheckUtil.typeDeclarationNameMatchingCount(qualifiedClassName,
                                                                   classDesc.getQualifiedName());
             };
             getNearestClassWithSameName(superClassName, nestedClassCountProvider)
                 .or(() -> Optional.ofNullable(innerClasses.get(superClassName)))
                 .ifPresent(ClassDesc::registerNestedSubclass);
         }
     }
 
     /**
      * Register to the super class of anonymous inner class that the given class is instantiated
      * by an anonymous inner class.
      *
      * @param literalNewAst ast node of {@link TokenTypes#LITERAL_NEW} representing anonymous inner
      *                      class
      * @param outerTypeDeclName Fully qualified name of the outer type declaration of anonymous
      *                          inner class
      */
     private void registerAnonymousInnerClassToSuperClass(DetailAST literalNewAst,
                                                          String outerTypeDeclName) {
         final String superClassName = CheckUtil.getShortNameOfAnonInnerClass(literalNewAst);
 
         final ToIntFunction<ClassDesc> anonClassCountProvider = classDesc -> {
             return getAnonSuperTypeMatchingCount(outerTypeDeclName, classDesc.getQualifiedName());
         };
         getNearestClassWithSameName(superClassName, anonClassCountProvider)
             .or(() -> Optional.ofNullable(innerClasses.get(superClassName)))
             .ifPresent(ClassDesc::registerSuperClassOfAnonymousInnerClass);
     }
 
     /**
      * Get the nearest class with same name.
      *
      * <p>The parameter {@code countProvider} exists because if the class being searched is the
      * super class of anonymous inner class, the rules of evaluation are a bit different,
      * consider the following example-
      * {@snippet lang="text" :
      * public class Main {
      *     static class One {
      *         static class Two {
      *         }
      *     }
      *
      *     class Three {
      *         One.Two object = new One.Two() { // Object of Main.Three.One.Two
      *                                          // and not of Main.One.Two
      *         };
      *
      *         static class One {
      *             static class Two {
      *             }
      *         }
      *     }
      * }
      * }
      * If the {@link Function} {@code countProvider} hadn't used
      * {@link FinalClassCheck#getAnonSuperTypeMatchingCount} to
      * calculate the matching count then the logic would have falsely evaluated
      * {@code Main.One.Two} to be the super class of the anonymous inner class.
      *
      * @param className name of the class
      * @param countProvider the function to apply to calculate the name matching count
      * @return {@link Optional} of {@link ClassDesc} object of the nearest class with the same name.
      * @noinspection CallToStringConcatCanBeReplacedByOperator
      * @noinspectionreason CallToStringConcatCanBeReplacedByOperator - operator causes
      *      pitest to fail
      */
     private Optional<ClassDesc> getNearestClassWithSameName(String className,
         ToIntFunction<ClassDesc> countProvider) {
         final String dotAndClassName = PACKAGE_SEPARATOR.concat(className);
         final Comparator<ClassDesc> longestMatch = Comparator.comparingInt(countProvider);
         return innerClasses.entrySet().stream()
                 .filter(entry -> entry.getKey().endsWith(dotAndClassName))
                 .map(Map.Entry::getValue)
                 .min(longestMatch.reversed().thenComparingInt(ClassDesc::getDepth));
     }
 
     /**
      * Extract the qualified type declaration name from given type declaration Ast.
      *
      * @param typeDeclarationAst type declaration for which qualified name is being fetched
      * @return qualified name of a type declaration
      */
     private String extractQualifiedTypeName(DetailAST typeDeclarationAst) {
         final String className = typeDeclarationAst.findFirstToken(TokenTypes.IDENT).getText();
         String outerTypeDeclarationQualifiedName = null;
         if (!typeDeclarations.isEmpty()) {
             outerTypeDeclarationQualifiedName = typeDeclarations.peek().getQualifiedName();
         }
         return CheckUtil.getQualifiedTypeDeclarationName(packageName,
                                                          outerTypeDeclarationQualifiedName,
                                                          className);
     }
 
     /**
      * Get super class name of given class.
      *
      * @param classAst class
      * @return super class name or null if super class is not specified
      */
     private static String getSuperClassName(DetailAST classAst) {
         String superClassName = null;
         final DetailAST classExtend = classAst.findFirstToken(TokenTypes.EXTENDS_CLAUSE);
         if (classExtend != null) {
             superClassName = CheckUtil.extractQualifiedName(classExtend.getFirstChild());
         }
         return superClassName;
     }
 
     /**
      * Calculates and returns the type declaration matching count when {@code classToBeMatched} is
      * considered to be super class of an anonymous inner class.
      *
      * <p>
      * Suppose our pattern class is {@code Main.ClassOne} and class to be matched is
      * {@code Main.ClassOne.ClassTwo.ClassThree} then type declaration name matching count would
      * be calculated by comparing every character, and updating main counter when we hit "." or
      * when it is the last character of the pattern class and certain conditions are met. This is
      * done so that matching count is 13 instead of 5. This is due to the fact that pattern class
      * can contain anonymous inner class object of a nested class which isn't true in case of
      * extending classes as you can't extend nested classes.
      * </p>
      *
      * @param patternTypeDeclaration type declaration against which the given type declaration has
      *                               to be matched
      * @param typeDeclarationToBeMatched type declaration to be matched
      * @return type declaration matching count
      */
     private static int getAnonSuperTypeMatchingCount(String patternTypeDeclaration,
                                                     String typeDeclarationToBeMatched) {
         final int typeDeclarationToBeMatchedLength = typeDeclarationToBeMatched.length();
         final int minLength = Math
             .min(typeDeclarationToBeMatchedLength, patternTypeDeclaration.length());
         final char packageSeparator = PACKAGE_SEPARATOR.charAt(0);
         final boolean shouldCountBeUpdatedAtLastCharacter =
             typeDeclarationToBeMatchedLength > minLength
                 && typeDeclarationToBeMatched.charAt(minLength) == packageSeparator;
 
         int result = 0;
         for (int idx = 0;
              idx < minLength
                  && patternTypeDeclaration.charAt(idx) == typeDeclarationToBeMatched.charAt(idx);
              idx++) {
 
             if (idx == minLength - 1 && shouldCountBeUpdatedAtLastCharacter
                 || patternTypeDeclaration.charAt(idx) == packageSeparator) {
                 result = idx;
             }
         }
         return result;
     }
 
     /**
      * Maintains information about the type of declaration.
      * Any ast node of type {@link TokenTypes#CLASS_DEF} or {@link TokenTypes#INTERFACE_DEF}
      * or {@link TokenTypes#ENUM_DEF} or {@link TokenTypes#ANNOTATION_DEF}
      * or {@link TokenTypes#RECORD_DEF} is considered as a type declaration.
      * It does not maintain information about classes, a subclass called {@link ClassDesc}
      * does that job.
      */
     private static class TypeDeclarationDescription {
 
         /**
          * Complete type declaration name with package name and outer type declaration name.
          */
         private final String qualifiedName;
 
         /**
          * Depth of nesting of type declaration.
          */
         private final int depth;
 
         /**
          * Type declaration ast node.
          */
         private final DetailAST typeDeclarationAst;
 
         /**
          * Create an instance of TypeDeclarationDescription.
          *
          * @param qualifiedName Complete type declaration name with package name and outer type
          *                      declaration name.
          * @param depth Depth of nesting of type declaration
          * @param typeDeclarationAst Type declaration ast node
          */
         private TypeDeclarationDescription(String qualifiedName, int depth,
                                           DetailAST typeDeclarationAst) {
             this.qualifiedName = qualifiedName;
             this.depth = depth;
             this.typeDeclarationAst = typeDeclarationAst;
         }
 
         /**
          * Get the complete type declaration name i.e. type declaration name with package name
          * and outer type declaration name.
          *
          * @return qualified class name
          */
         /* package */ String getQualifiedName() {
             return qualifiedName;
         }
 
         /**
          * Get the depth of type declaration.
          *
          * @return the depth of nesting of type declaration
          */
         /* package */ int getDepth() {
             return depth;
         }
 
         /**
          * Get the type declaration ast node.
          *
          * @return ast node of the type declaration
          */
 
         /* package */ DetailAST getTypeDeclarationAst() {
             return typeDeclarationAst;
         }
     }
 
     /**
      * Maintains information about the class.
      */
     private static final class ClassDesc extends TypeDeclarationDescription {
 
         /** Is class declared as final. */
         private final boolean declaredAsFinal;
 
         /** Is class declared as abstract. */
         private final boolean declaredAsAbstract;
 
         /** Is class contains private modifier. */
         private final boolean declaredAsPrivate;
 
         /** Does class have implicit constructor. */
         private final boolean hasDeclaredConstructor;
 
         /** Does class have non-private ctors. */
         private boolean withNonPrivateCtor;
 
         /** Does class have nested subclass. */
         private boolean withNestedSubclass;
 
         /** Whether the class is the super class of an anonymous inner class. */
         private boolean superClassOfAnonymousInnerClass;
 
         /**
          *  Create a new ClassDesc instance.
          *
          *  @param qualifiedName qualified class name(with package)
          *  @param depth class nesting level
          *  @param classAst classAst node
          */
         private ClassDesc(String qualifiedName, int depth, DetailAST classAst) {
             super(qualifiedName, depth, classAst);
             final DetailAST modifiers = classAst.findFirstToken(TokenTypes.MODIFIERS);
             declaredAsFinal = modifiers.findFirstToken(TokenTypes.FINAL) != null;
             declaredAsAbstract = modifiers.findFirstToken(TokenTypes.ABSTRACT) != null;
             declaredAsPrivate = modifiers.findFirstToken(TokenTypes.LITERAL_PRIVATE) != null;
             hasDeclaredConstructor =
                     classAst.getLastChild().findFirstToken(TokenTypes.CTOR_DEF) == null;
         }
 
         /** Adds non-private ctor. */
         private void registerNonPrivateCtor() {
             withNonPrivateCtor = true;
         }
 
         /** Adds nested subclass. */
         private void registerNestedSubclass() {
             withNestedSubclass = true;
         }
 
         /** Adds anonymous inner class. */
         private void registerSuperClassOfAnonymousInnerClass() {
             superClassOfAnonymousInnerClass = true;
         }
 
         /**
          *  Does class have non-private ctors.
          *
          *  @return true if class has non-private ctors
          */
         private boolean isWithNonPrivateCtor() {
             return withNonPrivateCtor;
         }
 
         /**
          * Does class have nested subclass.
          *
          * @return true if class has nested subclass
          */
         private boolean isWithNestedSubclass() {
             return withNestedSubclass;
         }
 
         /**
          *  Is class declared as final.
          *
          *  @return true if class is declared as final
          */
         private boolean isDeclaredAsFinal() {
             return declaredAsFinal;
         }
 
         /**
          *  Is class declared as abstract.
          *
          *  @return true if class is declared as final
          */
         private boolean isDeclaredAsAbstract() {
             return declaredAsAbstract;
         }
 
         /**
          * Whether the class is the super class of an anonymous inner class.
          *
          * @return {@code true} if the class is the super class of an anonymous inner class.
          */
         private boolean isSuperClassOfAnonymousInnerClass() {
             return superClassOfAnonymousInnerClass;
         }
 
         /**
          * Does class have implicit constructor.
          *
          * @return true if class have implicit constructor
          */
         private boolean isHasDeclaredConstructor() {
             return hasDeclaredConstructor;
         }
 
         /**
          * Does class is private.
          *
          * @return true if class is private
          */
         private boolean isDeclaredAsPrivate() {
             return declaredAsPrivate;
         }
     }
 
 }