/*
    * 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.doxia.module.markdown;
  
  import java.io.IOException;
  import java.io.Writer;
  
  import org.apache.commons.lang3.StringUtils;
  
  /**
   * Decorates an existing writer to additionally temporarily buffer the last two lines written.
   * Useful to collapse subsequent new lines or blank lines by evaluating {@link #isWriterAfterBlankLine()} and {@link #isWriterAfterBlankLine()}.
   * The buffering does not affect or defer delegation to the underlying writer, though.
   */
  public class LastTwoLinesBufferingWriter extends Writer {
  
      private final Writer out;
      private String previousLine;
      private StringBuilder currentLine;
      private final String lineSeparator;
  
      public LastTwoLinesBufferingWriter(Writer out) {
          // don't use System.lineSeparator, as overwritten in AbstractModuleTest
          this(out, System.getProperty("line.separator"));
      }
  
      LastTwoLinesBufferingWriter(Writer out, String lineSeparator) {
          super();
          this.out = out;
          this.previousLine = "";
          this.currentLine = new StringBuilder();
          this.lineSeparator = lineSeparator;
      }
  
      public boolean isWriterAtStartOfNewLine() {
          return currentLine.length() == 0;
      }
  
      public boolean isWriterAfterBlankLine() {
          return StringUtils.isAllBlank(currentLine) && StringUtils.isAllBlank(previousLine);
      }
  
      @Override
      public void write(char[] cbuf, int off, int len) throws IOException {
          int offsetWrittenInLineBuffer = off;
          int index = 0;
          while (index < len) {
              // potentially a line break...
              if (cbuf[off + index] == '\r' || cbuf[off + index] == '\n') {
                  int lenToWrite = index + 1 - (offsetWrittenInLineBuffer - off);
                  flushLine(cbuf, offsetWrittenInLineBuffer, lenToWrite);
                  offsetWrittenInLineBuffer += lenToWrite;
              }
              index++;
          }
          flushLine(cbuf, offsetWrittenInLineBuffer, index - (offsetWrittenInLineBuffer - off));
          out.write(cbuf, off, len);
      }
  
      private void flushLine(char[] cbuf, int off, int len) {
          this.currentLine.append(cbuf, off, len);
          // really a line break?
          if (currentLine.toString().endsWith(lineSeparator)) {
              previousLine = currentLine.toString();
              currentLine.setLength(0);
          }
      }
  
      @Override
      public void flush() throws IOException {
          out.flush();
      }
  
      @Override
      public void close() throws IOException {
          out.close();
      }
  }