/**
    * Logback: the reliable, generic, fast and flexible logging framework.
    * Copyright (C) 1999-2015, QOS.ch. All rights reserved.
    *
    * This program and the accompanying materials are dual-licensed under
    * either the terms of the Eclipse Public License v1.0 as published by
    * the Eclipse Foundation
    *
    *   or (per the licensee's choosing)
   *
   * under the terms of the GNU Lesser General Public License version 2.1
   * as published by the Free Software Foundation.
   */
  package ch.qos.logback.core.util;
  
  import java.text.SimpleDateFormat;
  import java.util.ArrayList;
  import java.util.List;
  
  /**
   * This class is concerned with computing a regex corresponding to a date
   * pattern (in {@link SimpleDateFormat} format).
   *
   * @author Ceki Gülcü
   */
  public class DatePatternToRegexUtil {
  
      final String datePattern;
      final int datePatternLength;
      final CharSequenceToRegexMapper regexMapper = new CharSequenceToRegexMapper();
  
      public DatePatternToRegexUtil(String datePattern) {
          this.datePattern = datePattern;
          datePatternLength = datePattern.length();
      }
  
      public String toRegex() {
          List<CharSequenceState> charSequenceList = tokenize();
          StringBuilder sb = new StringBuilder();
          for (CharSequenceState seq : charSequenceList) {
              sb.append(regexMapper.toRegex(seq));
          }
          return sb.toString();
      }
  
      private List<CharSequenceState> tokenize() {
          List<CharSequenceState> sequenceList = new ArrayList<CharSequenceState>();
  
          CharSequenceState lastCharSequenceState = null;
  
          for (int i = 0; i < datePatternLength; i++) {
              char t = datePattern.charAt(i);
              if (lastCharSequenceState == null || lastCharSequenceState.c != t) {
                  lastCharSequenceState = new CharSequenceState(t);
                  sequenceList.add(lastCharSequenceState);
              } else {
                  lastCharSequenceState.incrementOccurrences();
              }
          }
          return sequenceList;
      }
  }