/*
    * 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.maven.enforcer.rules.checksum;
  
  import java.io.FilterReader;
  import java.io.IOException;
  import java.io.Reader;
  
  /**
   * Converts Unix line separators to Windows ones and vice-versa.
   */
  class NormalizeLineSeparatorReader extends FilterReader {
  
      private static final int EOL = -1;
  
      /**
       * Type representing either Unix or Windows line separators
       */
      public enum LineSeparator {
          WINDOWS("\r\n", null),
          UNIX("\n", '\r');
  
          private final char[] separatorChars;
  
          private final Character notPrecededByChar;
  
          LineSeparator(String separator, Character notPrecededByChar) {
              separatorChars = separator.toCharArray();
              this.notPrecededByChar = notPrecededByChar;
          }
  
          enum MatchResult {
              NO_MATCH,
              POTENTIAL_MATCH,
              MATCH;
          }
  
          /**
           * Checks if two given characters match the line separator represented by this object.
           * @param currentCharacter the character to check against
           * @param previousCharacter optional previous character (may be {@code null})
           * @return one of {@link MatchResult}
           */
          public MatchResult matches(char currentCharacter, Character previousCharacter) {
              int len = separatorChars.length;
              if (currentCharacter == separatorChars[len - 1]) {
                  if (len > 1) {
                      if (previousCharacter == null || previousCharacter != separatorChars[len - 1]) {
                          return MatchResult.NO_MATCH;
                      }
                  }
                  if (notPrecededByChar != null) {
                      if (previousCharacter != null && notPrecededByChar == previousCharacter) {
                          return MatchResult.NO_MATCH;
                      }
                  }
                  return MatchResult.MATCH;
              } else if (len > 1 && currentCharacter == separatorChars[len - 2]) {
                  return MatchResult.POTENTIAL_MATCH;
              }
              return MatchResult.NO_MATCH;
          }
      }
  
      final LineSeparator lineSeparator;
  
      Character bufferedCharacter;
  
      Character previousCharacter;
  
      NormalizeLineSeparatorReader(Reader reader, LineSeparator lineSeparator) {
          super(reader);
          this.lineSeparator = lineSeparator;
          bufferedCharacter = null;
      }
  
      @Override
      public int read(char[] cbuf, int off, int len) throws IOException {
          int n;
          for (n = off; n < off + len; n++) {
              int readResult = read();
              if (readResult == EOL) {
                  return n == 0 ? EOL : n;
             } else {
                 cbuf[n] = (char) readResult;
             }
         }
         return n;
     }
 
     @Override
     public int read() throws IOException {
         // spool buffered characters, if any
         if (bufferedCharacter != null) {
             char localBuffer = bufferedCharacter;
             bufferedCharacter = null;
             return localBuffer;
         }
         int readResult = super.read();
         if (readResult == EOL) {
             return readResult;
         }
         char currentCharacter = (char) readResult;
         if (lineSeparator == LineSeparator.UNIX) {
             switch (LineSeparator.WINDOWS.matches(currentCharacter, previousCharacter)) {
                 case MATCH:
                     return lineSeparator.separatorChars[0];
                 case POTENTIAL_MATCH:
                     previousCharacter = currentCharacter;
                     return read();
                 default:
                     // fall-through
             }
         } else { // WINDOWS
             // if current is unix, convert
             switch (LineSeparator.UNIX.matches(currentCharacter, previousCharacter)) {
                 case MATCH:
                     bufferedCharacter = lineSeparator.separatorChars[1];
                     // set buffered character and return current
                     return lineSeparator.separatorChars[0];
                 case POTENTIAL_MATCH:
                     // invalid option
                     throw new IllegalStateException("No potential matches expected for Unix line separator");
                 default:
                     // fall-through
             }
         }
         previousCharacter = currentCharacter;
         return currentCharacter;
     }
 }