/*
    * Licensed to the Apache Software Foundation (ASF) under one
    * or more contributor license agreements.  See the NOTICE file
    * distributed with this work for additional information
    * regarding copyright ownership.  The ASF licenses this file
    * to you under the Apache License, Version 2.0 (the
    * "License"); you may not use this file except in compliance
    * with the License.  You may obtain a copy of the License at
    *
   *     http://www.apache.org/licenses/LICENSE-2.0
   *
   * Unless required by applicable law or agreed to in writing, software
   * distributed under the License is distributed on an "AS IS" BASIS,
   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   * See the License for the specific language governing permissions and
   * limitations under the License.
   */
  
  package org.apache.hadoop.chukwa.util;
  
  import java.util.regex.Pattern;
  import java.util.regex.PatternSyntaxException;
  
  /*>>>
  import checkers.nullness.quals.*;
  import checkers.regex.quals.*;
  */
  
  /**
   * Utility methods for regular expressions, most notably for testing whether
   * a string is a regular expression.
   */
  public class RegexUtil {
  
    /**
     * A checked version of {@link PatternSyntaxException}.
     * <p>
     * This exception is useful when an illegal regex is detected but the
     * contextual information to report a helpful error message is not available
     * at the current depth in the call stack. By using a checked
     * PatternSyntaxException the error must be handled up the call stack where
     * a better error message can be reported.
     * <p>
     *
     * Typical usage is:
     * <pre>
     * void myMethod(...) throws CheckedPatternSyntaxException {
     *   ...
     *   if (! isRegex(myString)) {
     *     throw new CheckedPatternSyntaxException(...);
     *   }
     *   ... Pattern.compile(myString) ...
     * </pre>
     *
     * Simply calling <tt>Pattern.compile</tt> would have a similar effect,
     * in that <tt>PatternSyntaxException</tt> would be thrown at run time if
     * <tt>myString</tt> is not a regular expression.  There are two problems
     * with such an approach.  First, a client of <tt>myMethod</tt> might
     * forget to handle the exception, since <tt>PatternSyntaxException</tt>
     * is not checked.  Also, the Regex Checker would issue a warning about
     * the call to <tt>Pattern.compile</tt> that might throw an exception.
     * The above usage pattern avoids both problems.
     *
     * @see PatternSyntaxException
     */
    public static class CheckedPatternSyntaxException extends Exception {
  
      private static final long serialVersionUID = 6266881831979001480L;
  
      private final PatternSyntaxException pse;
  
      /**
       * Constructs a new CheckedPatternSyntaxException equivalent to the
       * given {@link PatternSyntaxException}.
       * <p>
       * Consider calling this constructor with the result of
       * {@link RegexUtil#regexError}.
       * @param pse is PatternSyntaxException object
       */
      public CheckedPatternSyntaxException(PatternSyntaxException pse) {
        this.pse = pse;
      }
  
      /**
       * Constructs a new CheckedPatternSyntaxException.
       *
       * @param desc A description of the error
       * @param regex The erroneous pattern
       * @param index The approximate index in the pattern of the error,
       *              or {@code -1} if the index is not known
       */
      public CheckedPatternSyntaxException(String desc, String regex, int index) {
        this(new PatternSyntaxException(desc, regex, index));
      }
  
      /**
       * Retrieves the description of the error.
       *
       * @return The description of the error
      */
     public String getDescription() {
       return pse.getDescription();
     }
 
     /**
      * Retrieves the error index.
      *
      * @return The approximate index in the pattern of the error, or {@code -1}
      *         if the index is not known
      */
     public int getIndex() {
       return pse.getIndex();
     }
 
     /**
      * Returns a multi-line string containing the description of the syntax
      * error and its index, the erroneous regular-expression pattern, and a
      * visual indication of the error index within the pattern.
      *
      * @return The full detail message
      */
     public String getMessage() {
       return pse.getMessage();
     }
 
     /**
      * Retrieves the erroneous regular-expression pattern.
      *
      * @return The erroneous pattern
      */
     public String getPattern() {
       return pse.getPattern();
     }
   }
 
   private RegexUtil() {
     throw new AssertionError("Class RegexUtil shouldn't be instantiated");
   }
 
   /**
    * Returns true if the argument is a syntactically valid regular
    * expression.
    * @param s is regular expression
    * @return true if there is a match
    */
   public static boolean isRegex(String s) {
     return isRegex(s, 0);
   }
 
   /**
    * Returns true if the argument is a syntactically valid regular
    * expression with at least the given number of groups.
    * @param s is regular expression
    * @param groups is number of groups to match
    * @return true if there is a match
    */
   /*>>>
   @SuppressWarnings("regex")    // RegexUtil
   */
   /*@Pure*/
   public static boolean isRegex(String s, int groups) {
     Pattern p;
     try {
       p = Pattern.compile(s);
     } catch (PatternSyntaxException e) {
       return false;
     }
     return getGroupCount(p) >= groups;
   }
 
   /**
    * Returns true if the argument is a syntactically valid regular
    * expression.
    * @param c is a character
    * @return true if there is a match
    */
   public static boolean isRegex(char c) {
     return isRegex(Character.toString(c));
   }
 
   /**
    * Returns null if the argument is a syntactically valid regular
    * expression. Otherwise returns a string describing why the argument is
    * not a regex.
    * @param s is regular expression
    * @return null if s is a regular expression
    */
   public static String regexError(String s) {
     return regexError(s, 0);
   }
 
   /**
    * Returns null if the argument is a syntactically valid regular
    * expression with at least the given number of groups. Otherwise returns
    * a string describing why the argument is not a regex.
    * @param s is regular expression
    * @param groups is number of groups to match
    * @return null if s is a regular expression
    */
   public static String regexError(String s, int groups) {
     try {
       Pattern p = Pattern.compile(s);
       int actualGroups = getGroupCount(p);
       if (actualGroups < groups) {
         return regexErrorMessage(s, groups, actualGroups);
       }
     } catch (PatternSyntaxException e) {
       return e.getMessage();
     }
     return null;
   }
 
   /**
    * Returns null if the argument is a syntactically valid regular
    * expression. Otherwise returns a PatternSyntaxException describing
    * why the argument is not a regex.
    * @param s is regular expression
    * @return null if s is a regular expression
    */
   public static PatternSyntaxException regexException(String s) {
     return regexException(s, 0);
   }
 
   /**
    * Returns null if the argument is a syntactically valid regular
    * expression with at least the given number of groups. Otherwise returns a
    * PatternSyntaxException describing why the argument is not a regex.
    * @param s is regular expression
    * @param groups is number of groups to match
    * @return null if s is a regular expression
    */
   public static PatternSyntaxException regexException(String s, int groups) {
     try {
       Pattern p = Pattern.compile(s);
       int actualGroups = getGroupCount(p);
       if (actualGroups < groups) {
         return new PatternSyntaxException(regexErrorMessage(s, groups, actualGroups), s, -1);
       }
     } catch (PatternSyntaxException pse) {
       return pse;
     }
     return null;
   }
 
   /**
    * Returns the argument as a {@code @Regex String} if it is a regex,
    * otherwise throws an error. The purpose of this method is to suppress Regex
    * Checker warnings. Once the the Regex Checker supports flow-sensitivity, it
    * should be very rarely needed.
    * @param s is a regular expression
    * @return null if s is a regular expression
    */
   public static String asRegex(String s) {
     return asRegex(s, 0);
   }
 
   /**
    * Returns the argument as a {@code @Regex(groups) String} if it is a regex
    * with at least the given number of groups, otherwise throws an error. The
    * purpose of this method is to suppress Regex Checker warnings. Once the the
    * Regex Checker supports flow-sensitivity, it should be very rarely needed.
    * @param s is a regular expression
    * @param groups is number of group to match
    * @return null if s is a regular expression
    */
   public static String asRegex(String s, int groups) {
     try {
       Pattern p = Pattern.compile(s);
       int actualGroups = getGroupCount(p);
       if (actualGroups < groups) {
         throw new Error(regexErrorMessage(s, groups, actualGroups));
       }
       return s;
     } catch (PatternSyntaxException e) {
       throw new Error(e);
     }
   }
 
   /**
    * Generates an error message for s when expectedGroups are needed, but s
    * only has actualGroups.
    */
   private static String regexErrorMessage(String s, int expectedGroups, int actualGroups) {
     return "regex \"" + s + "\" has " + actualGroups + " groups, but " +
         expectedGroups + " groups are needed.";
   }
 
   /**
    * Returns the count of groups in the argument.
    */
   private static int getGroupCount(Pattern p) {
     return p.matcher("").groupCount();
   }
 }