////////////////////////////////////////////////////////////////////////////////
   // 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;
  import com.puppycrawl.tools.checkstyle.utils.CheckUtil;
  import com.puppycrawl.tools.checkstyle.utils.ScopeUtil;
  
  /**
   * <p>
   * Checks if any class or object member explicitly initialized
   * to default for its type value ({@code null} for object
   * references, zero for numeric types and {@code char}
   * and {@code false} for {@code boolean}.
   * </p>
   * <p>
   * Rationale: each instance variable gets
   * initialized twice, to the same value. Java
   * initializes each instance variable to its default
   * value (0 or null) before performing any
   * initialization specified in the code.
   * So there is a minor inefficiency.
   * </p>
   *
   */
  @StatelessCheck
  public class ExplicitInitializationCheck extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_KEY = "explicit.init";
  
      /** Whether only explicit initialization made to null should be checked.**/
      private boolean onlyObjectReferences;
  
      @Override
      public final int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public final int[] getRequiredTokens() {
          return new int[] {TokenTypes.VARIABLE_DEF};
      }
  
      @Override
      public final int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
      /**
       * Sets whether only explicit initialization made to null should be checked.
       * @param onlyObjectReferences whether only explicit initialization made to null
       *                             should be checked
       */
      public void setOnlyObjectReferences(boolean onlyObjectReferences) {
          this.onlyObjectReferences = onlyObjectReferences;
      }
  
      @Override
      public void visitToken(DetailAST ast) {
          if (!isSkipCase(ast)) {
              final DetailAST assign = ast.findFirstToken(TokenTypes.ASSIGN);
              final DetailAST exprStart =
                  assign.getFirstChild().getFirstChild();
              if (exprStart.getType() == TokenTypes.LITERAL_NULL) {
                  final DetailAST ident = ast.findFirstToken(TokenTypes.IDENT);
                  log(ident, MSG_KEY, ident.getText(), "null");
              }
              if (!onlyObjectReferences) {
                  validateNonObjects(ast);
              }
          }
      }
  
      /**
       * Checks for explicit initializations made to 'false', '0' and '\0'.
      * @param ast token being checked for explicit initializations
      */
     private void validateNonObjects(DetailAST ast) {
         final DetailAST ident = ast.findFirstToken(TokenTypes.IDENT);
         final DetailAST assign = ast.findFirstToken(TokenTypes.ASSIGN);
         final DetailAST exprStart =
                 assign.getFirstChild().getFirstChild();
         final DetailAST type = ast.findFirstToken(TokenTypes.TYPE);
         final int primitiveType = type.getFirstChild().getType();
         if (primitiveType == TokenTypes.LITERAL_BOOLEAN
                 && exprStart.getType() == TokenTypes.LITERAL_FALSE) {
             log(ident, MSG_KEY, ident.getText(), "false");
         }
         if (isNumericType(primitiveType) && isZero(exprStart)) {
             log(ident, MSG_KEY, ident.getText(), "0");
         }
         if (primitiveType == TokenTypes.LITERAL_CHAR
                 && isZeroChar(exprStart)) {
             log(ident, MSG_KEY, ident.getText(), "\\0");
         }
     }
 
     /**
      * Examine char literal for initializing to default value.
      * @param exprStart expression
      * @return true is literal is initialized by zero symbol
      */
     private static boolean isZeroChar(DetailAST exprStart) {
         return isZero(exprStart)
             || exprStart.getType() == TokenTypes.CHAR_LITERAL
             && "'\\0'".equals(exprStart.getText());
     }
 
     /**
      * Checks for cases that should be skipped: no assignment, local variable, final variables.
      * @param ast Variable def AST
      * @return true is that is a case that need to be skipped.
      */
     private static boolean isSkipCase(DetailAST ast) {
         boolean skipCase = true;
 
         // do not check local variables and
         // fields declared in interface/annotations
         if (!ScopeUtil.isLocalVariableDef(ast)
                 && !ScopeUtil.isInInterfaceOrAnnotationBlock(ast)) {
             final DetailAST assign = ast.findFirstToken(TokenTypes.ASSIGN);
 
             if (assign != null) {
                 final DetailAST modifiers = ast.findFirstToken(TokenTypes.MODIFIERS);
                 skipCase = modifiers.findFirstToken(TokenTypes.FINAL) != null;
             }
         }
         return skipCase;
     }
 
     /**
      * Determine if a given type is a numeric type.
      * @param type code of the type for check.
      * @return true if it's a numeric type.
      * @see TokenTypes
      */
     private static boolean isNumericType(int type) {
         return type == TokenTypes.LITERAL_BYTE
                 || type == TokenTypes.LITERAL_SHORT
                 || type == TokenTypes.LITERAL_INT
                 || type == TokenTypes.LITERAL_FLOAT
                 || type == TokenTypes.LITERAL_LONG
                 || type == TokenTypes.LITERAL_DOUBLE;
     }
 
     /**
      * Checks if given node contains numeric constant for zero.
      *
      * @param expr node to check.
      * @return true if given node contains numeric constant for zero.
      */
     private static boolean isZero(DetailAST expr) {
         final int type = expr.getType();
         final boolean isZero;
         switch (type) {
             case TokenTypes.NUM_FLOAT:
             case TokenTypes.NUM_DOUBLE:
             case TokenTypes.NUM_INT:
             case TokenTypes.NUM_LONG:
                 final String text = expr.getText();
                 isZero = Double.compare(CheckUtil.parseDouble(text, type), 0.0) == 0;
                 break;
             default:
                 isZero = false;
         }
         return isZero;
     }
 
 }