package com.aragost.javahg.internals;
   
   import java.io.ByteArrayOutputStream;
   import java.io.FilterOutputStream;
   import java.io.IOException;
   import java.io.OutputStream;
   import java.util.Map;
   
   public class PatternReplacingOutputStream extends FilterOutputStream {
  
      private enum State {
          /**
           * The normal state where bytes are directly written though to
           * the underlying stream
           */
          NORMAL,
          /**
           * A '%' has just been seen, so potentially a named pattern
           * will start
           */
          MAYBE_NAME_START,
          /**
           * Bytes written to the stream is part of a named pattern,
           * i.o. recently '%{' was written to the stream
           */
          READING_NAME,
          /**
           * 
           */
          WRITING_REPLACEMENT;
      };
  
      private final ByteArrayOutputStream nameBuffer = new ByteArrayOutputStream(20);
  
      private final Map<String, byte[]> replacements;
  
      private State state = State.NORMAL;
  
      public PatternReplacingOutputStream(OutputStream out, Map<String, byte[]> replacements) {
          super(out);
          this.replacements = replacements;
      }
  
      @Override
      public synchronized void write(int b) throws IOException {
          switch (this.state) {
          case NORMAL:
              if (b == '%') {
                  this.state = State.MAYBE_NAME_START;
              } else {
                  super.write(b);
              }
              break;
          case MAYBE_NAME_START:
              if (b == '{') {
                  this.state = State.READING_NAME;
              } else {
                  super.write('%');
                  if (b == '%') {
                      this.state = State.NORMAL;
                  } else {
                      super.write(b);
                  }
              }
              break;
          case READING_NAME:
              if (b == '}') {
                  this.state = State.WRITING_REPLACEMENT;
                  String name = new String(this.nameBuffer.toByteArray()); 
                  this.nameBuffer.reset();
                  byte[] replacement = this.replacements.get(name);
                  if (replacement == null) {
                      replacement = ("%{" + name + "=null}").getBytes();
                  }
                  this.out.write(replacement);
                  this.state = State.NORMAL;
              } else {
                  this.nameBuffer.write(b);
              }
              break;
          case WRITING_REPLACEMENT:
              super.write(b);
              break;
          }
      }
  }