////////////////////////////////////////////////////////////////////////////////
   // 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.imports;
  
  import java.util.HashSet;
  import java.util.Set;
  
  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.FullIdent;
  import com.puppycrawl.tools.checkstyle.api.TokenTypes;
  
  /**
   * <p>
   * Checks for imports that are redundant. An import statement is
   * considered redundant if:
   * </p>
   *<ul>
   *  <li>It is a duplicate of another import. This is, when a class is imported
   *  more than once.</li>
   *  <li>The class non-statically imported is from the {@code java.lang}
   *  package. For example importing {@code java.lang.String}.</li>
   *  <li>The class non-statically imported is from the same package as the
   *  current package.</li>
   *</ul>
   * <p>
   * An example of how to configure the check is:
   * </p>
   * <pre>
   * &lt;module name="RedundantImport"/&gt;
   * </pre>
   * Compatible with Java 1.5 source.
   *
   */
  @FileStatefulCheck
  public class RedundantImportCheck
      extends AbstractCheck {
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_LANG = "import.lang";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_SAME = "import.same";
  
      /**
       * A key is pointing to the warning message text in "messages.properties"
       * file.
       */
      public static final String MSG_DUPLICATE = "import.duplicate";
  
      /** Set of the imports. */
      private final Set<FullIdent> imports = new HashSet<>();
      /** Set of static imports. */
      private final Set<FullIdent> staticImports = new HashSet<>();
  
      /** Name of package in file. */
      private String pkgName;
  
      @Override
      public void beginTree(DetailAST aRootAST) {
          pkgName = null;
          imports.clear();
          staticImports.clear();
      }
  
      @Override
      public int[] getDefaultTokens() {
          return getRequiredTokens();
      }
  
      @Override
      public int[] getAcceptableTokens() {
          return getRequiredTokens();
      }
  
     @Override
     public int[] getRequiredTokens() {
         return new int[] {
             TokenTypes.IMPORT, TokenTypes.STATIC_IMPORT, TokenTypes.PACKAGE_DEF,
         };
     }
 
     @Override
     public void visitToken(DetailAST ast) {
         if (ast.getType() == TokenTypes.PACKAGE_DEF) {
             pkgName = FullIdent.createFullIdent(
                     ast.getLastChild().getPreviousSibling()).getText();
         }
         else if (ast.getType() == TokenTypes.IMPORT) {
             final FullIdent imp = FullIdent.createFullIdentBelow(ast);
             if (isFromPackage(imp.getText(), "java.lang")) {
                 log(ast, MSG_LANG, imp.getText());
             }
             // imports from unnamed package are not allowed,
             // so we are checking SAME rule only for named packages
             else if (pkgName != null && isFromPackage(imp.getText(), pkgName)) {
                 log(ast, MSG_SAME, imp.getText());
             }
             // Check for a duplicate import
             imports.stream().filter(full -> imp.getText().equals(full.getText()))
                 .forEach(full -> log(ast,
                     MSG_DUPLICATE, full.getLineNo(),
                     imp.getText()));
 
             imports.add(imp);
         }
         else {
             // Check for a duplicate static import
             final FullIdent imp =
                 FullIdent.createFullIdent(
                     ast.getLastChild().getPreviousSibling());
             staticImports.stream().filter(full -> imp.getText().equals(full.getText()))
                 .forEach(full -> log(ast,
                     MSG_DUPLICATE, full.getLineNo(), imp.getText()));
 
             staticImports.add(imp);
         }
     }
 
     /**
      * Determines if an import statement is for types from a specified package.
      * @param importName the import name
      * @param pkg the package name
      * @return whether from the package
      */
     private static boolean isFromPackage(String importName, String pkg) {
         // imports from unnamed package are not allowed:
         // https://docs.oracle.com/javase/specs/jls/se7/html/jls-7.html#jls-7.5
         // So '.' must be present in member name and we are not checking for it
         final int index = importName.lastIndexOf('.');
         final String front = importName.substring(0, index);
         return front.equals(pkg);
     }
 
 }