////////////////////////////////////////////////////////////////////////////////
   // checkstyle: Checks Java source code for adherence to a set of rules.
   // Copyright (C) 2001-2019 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.coding;
  
  import com.puppycrawl.tools.checkstyle.StatelessCheck;
  import com.puppycrawl.tools.checkstyle.api.AbstractCheck;
  import com.puppycrawl.tools.checkstyle.api.DetailAST;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Checks for overly complicated boolean return statements.
   * Idea shamelessly stolen from the equivalent PMD rule (pmd.sourceforge.net).
   * </p>
   * <p>
   * An example of how to configure the check is:
   * </p>
   * <pre>
   * &lt;module name="SimplifyBooleanReturn"/&gt;
   * </pre>
   */
  @StatelessCheck
  public class SimplifyBooleanReturnCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "simplify.boolReturn";
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getRequiredTokens() {
          return new int[] {TokenTypes.LITERAL_IF};
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          // LITERAL_IF has the following four or five children:
          // '('
          // condition
          // ')'
          // thenStatement
          // [ LITERAL_ELSE (with the elseStatement as a child) ]
  
          // don't bother if this is not if then else
          final DetailAST elseLiteral =
              ast.findFirstToken(TokenTypes.LITERAL_ELSE);
          if (elseLiteral != null) {
              final DetailAST elseStatement = elseLiteral.getFirstChild();
  
              // skip '(' and ')'
              final DetailAST condition = ast.getFirstChild().getNextSibling();
              final DetailAST thenStatement = condition.getNextSibling().getNextSibling();
  
              if (canReturnOnlyBooleanLiteral(thenStatement)
                  && canReturnOnlyBooleanLiteral(elseStatement)) {
                  log(ast, MSG_KEY);
              }
          }
      }
  
      /**
       * Returns if an AST is a return statement with a boolean literal
       * or a compound statement that contains only such a return statement.
       *
       * <p>Returns {@code true} iff ast represents
       * <br/>
       * <pre>
       * return true/false;
       * </pre>
       * or
      * <br/>
      * <pre>
      * {
      *   return true/false;
      * }
      * </pre>
      *
      * @param ast the syntax tree to check
      * @return if ast is a return statement with a boolean literal.
      */
     private static boolean canReturnOnlyBooleanLiteral(DetailAST ast) {
         boolean result = true;
         if (!isBooleanLiteralReturnStatement(ast)) {
             final DetailAST firstStatement = ast.getFirstChild();
             result = isBooleanLiteralReturnStatement(firstStatement);
         }
         return result;
     }
 
     /**
      * Returns if an AST is a return statement with a boolean literal.
      *
      * <p>Returns {@code true} iff ast represents
      * <br/>
      * <pre>
      * return true/false;
      * </pre>
      *
      * @param ast the syntax tree to check
      * @return if ast is a return statement with a boolean literal.
      */
     private static boolean isBooleanLiteralReturnStatement(DetailAST ast) {
         boolean booleanReturnStatement = false;
 
         if (ast != null && ast.getType() == TokenTypes.LITERAL_RETURN) {
             final DetailAST expr = ast.getFirstChild();
 
             if (expr.getType() != TokenTypes.SEMI) {
                 final DetailAST value = expr.getFirstChild();
                 booleanReturnStatement = isBooleanLiteralType(value.getType());
             }
         }
         return booleanReturnStatement;
     }
 
     /**
      * Checks if a token type is a literal true or false.
      * @param tokenType the TokenType
      * @return true iff tokenType is LITERAL_TRUE or LITERAL_FALSE
      */
     private static boolean isBooleanLiteralType(final int tokenType) {
         final boolean isTrue = tokenType == TokenTypes.LITERAL_TRUE;
         final boolean isFalse = tokenType == TokenTypes.LITERAL_FALSE;
         return isTrue || isFalse;
     }
 
 }