/*
    * SPDX-FileCopyrightText: Copyright (c) 2011-2026 Yegor Bugayenko
    * SPDX-License-Identifier: MIT
    */
   package com.qulice.checkstyle;
   
   import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
   import com.puppycrawl.tools.checkstyle.api.DetailAST;
   import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * Checks if possible to use Diamond operator in generic instances creation.
   *
   * <p>Check is performed for variable declarations. Since parameterized types are invariant
   * in generics, Diamond operator should always be used in variable declarations.</p>
   *
   * <p>For example,
   * <pre>
   *     private List&lt;Number&gt; numbers = new ArrayList&lt;Integer&gt;(); // error
   * </pre>
   * will return compilation error (because <code>ArrayList&lt;Integer&gt;</code> is not
   * a subclass of <code>List&lt;Number&gt;</code>).
   * </p>
   * <p>Hence, the only possible way to create a generic instance is copying type arguments from
   * the variable declaration.
   * <pre>
   *     private List&lt;Number&gt; numbers = new ArrayList&lt;Number&gt;();
   * </pre>
   * In that case, Diamond Operator should always be used.
   * <pre>
   *     private List&lt;Number&gt; numbers = new ArrayList&lt;&gt;();
   * </pre>
   * </p>
   * <p>Exceptions to the rule above are wildcards, with them it's possible
   * to have different type parameters for left and right parts of variable declaration.
   * <pre>
   *     // will compile
   *     private List&lt;? extends Number&gt; numbers = new ArrayList&lt;Integer&gt;();
   *     private List&lt;? super Integer&gt; list = new ArrayList&lt;Number&gt;();
   *</pre>
   * Although, this is not considered as good codestyle,
   * so it's better to use diamond operator here either.
   * </p>
   *
   * @since 0.17
   */
  public final class DiamondOperatorCheck extends AbstractCheck {
  
      @Override
      public int[] getDefaultTokens() {
          return new int[]{TokenTypes.VARIABLE_DEF};
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return this.getDefaultTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return this.getDefaultTokens();
      }
  
      @Override
      public void visitToken(final DetailAST node) {
          final DetailAST generic = DiamondOperatorCheck.findFirstChildNodeOfType(
              node.findFirstToken(TokenTypes.TYPE), TokenTypes.TYPE_ARGUMENTS
          );
          final DetailAST assign = node.findFirstToken(TokenTypes.ASSIGN);
          final DetailAST instance;
          if (assign == null || generic == null) {
              instance = null;
          } else {
              instance = assign.getFirstChild().getFirstChild();
          }
          if (instance != null && instance.getType() == TokenTypes.LITERAL_NEW
              && DiamondOperatorCheck.validUsage(instance)) {
              final DetailAST type =
                  DiamondOperatorCheck.findFirstChildNodeOfType(
                      instance, TokenTypes.TYPE_ARGUMENTS
                  );
              if (type != null && !DiamondOperatorCheck.isDiamondOperatorUsed(type)) {
                  log(type, "Use diamond operator");
              }
          }
      }
  
      /**
       * Checks if diamond is not required.
       * @param node Node
       * @return True if not array
       */
      private static boolean validUsage(final DetailAST node) {
          return DiamondOperatorCheck.isNotObjectBlock(node)
              && DiamondOperatorCheck.isNotArray(node)
              && !DiamondOperatorCheck.isInitUsingDiamond(node);
      }
  
      /**
      * Checks if node is not array.
      * @param node Node
      * @return True if not array
      */
     private static boolean isNotArray(final DetailAST node) {
         return node.findFirstToken(TokenTypes.ARRAY_DECLARATOR) == null;
     }
 
     /**
      * Checks if node is object block.
      * @param node Node
      * @return True if not object block
      */
     private static boolean isNotObjectBlock(final DetailAST node) {
         return node.getLastChild().getType() != TokenTypes.OBJBLOCK;
     }
 
     /**
      * Checks if node has initialization with diamond operator.
      * @param node Node
      * @return True if not object block
      */
     private static boolean isInitUsingDiamond(final DetailAST node) {
         final DetailAST init = node.findFirstToken(TokenTypes.ELIST);
         boolean typed = false;
         if (init != null) {
             final DetailAST inst = DiamondOperatorCheck.secondChild(init);
             if (inst != null && inst.getType() == TokenTypes.LITERAL_NEW) {
                 typed =
                     DiamondOperatorCheck.isDiamondOperatorUsed(
                         inst.findFirstToken(TokenTypes.TYPE_ARGUMENTS)
                     );
             }
         }
         return typed;
     }
 
     /**
      * Checks if node has initialization with diamond operator.
      * @param node Node
      * @return True if not object block
      */
     private static DetailAST secondChild(final DetailAST node) {
         DetailAST result = null;
         if (node != null) {
             final DetailAST first = node.getFirstChild();
             if (first != null) {
                 result = first.getFirstChild();
             }
         }
         return result;
     }
 
     /**
      * Checks if node contains empty set of type parameters and
      * comprises angle brackets only (<>).
      * @param node Node of type arguments
      * @return True if node contains angle brackets only
      */
     private static boolean isDiamondOperatorUsed(final DetailAST node) {
         return node != null && node.getChildCount() == 2
             && node.getFirstChild().getType() == TokenTypes.GENERIC_START
             && node.getLastChild().getType() == TokenTypes.GENERIC_END;
     }
 
     /**
      * Returns the first child node of a specified type.
      * @param node AST subtree to process
      * @param type Type of token
      * @return Child node of specified type OR NULL!
      */
     private static DetailAST findFirstChildNodeOfType(
         final DetailAST node, final int type
     ) {
         DetailAST result = node.findFirstToken(type);
         if (result == null) {
             final DetailAST child = node.getFirstChild();
             if (child != null) {
                 result = DiamondOperatorCheck
                     .findFirstChildNodeOfType(child, type);
             }
         }
         return result;
     }
 }