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/*
 * Copyright 2008 CoreMedia AG
 * 
 * Licensed 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 net.jangaroo.jooc;

import java.io.IOException;
import java.io.Writer;

/**
 * An SubstitutingWriter is a FilterWriter that replaces
 * each character in the output stream
 * with the String obtained by calling the abstract method substitute
 * on the characters.
 * Characters for which substitute returns null are output verbatim.
 * The implementation is fairly efficient in the number of calls to
 * the various out.write methods.
 *
 * @author Axel Wienberg
 */
public abstract class SubstitutingWriter extends java.io.FilterWriter {

  public SubstitutingWriter(Writer out) {
    super(out);
  }

  /**
   * What should be printed instead of character c?
   * This method is always called synchronized on out.
   * Changes to the substitution function should therefore also be synchronized on out.
   *
   * @param c the character
   * @return the string to be printed, or null for "no change", i.e. just c
   */
  protected abstract String substitute(char c);

  protected void writeReplacement(String replacement) throws java.io.IOException {
    out.write(replacement);
  }

  /**
   * Write a single character, applying the substitution.
   *
   * @throws java.io.IOException If an I/O error occurs
   */
  public void write(int c) throws IOException {
    char ch = (char) c;
    String replacement = substitute(ch);
    if (replacement == null) {
      out.write(c);
    } else {
      writeReplacement(replacement);
    }
  }

  /**
   * Write a portion of an array of characters, applying the substitution.
   *
   * @param cbuf Buffer of characters to be written
   * @param off  Offset from which to start reading characters
   * @param len  Number of characters to be written
   * @throws java.io.IOException If an I/O error occurs
   */
  public void write(char cbuf[], int off, int len) throws IOException {
    int nextToWrite = off;
    int guard = off + len;
    for (; off < guard; ++off) {
      String replacement = substitute(cbuf[off]);
      if (replacement != null) {
        if (nextToWrite < off) {
          out.write(cbuf, nextToWrite, off - nextToWrite);
        }
        writeReplacement(replacement);
        nextToWrite = off + 1;
      }
    }
    if (nextToWrite < off) {
      out.write(cbuf, nextToWrite, off - nextToWrite);
    }
  }

  /**
   * Write a portion of a string, applying the substitution.
   *
   * @param str String to be written
   * @param off Offset from which to start reading characters
   * @param len Number of characters to be written
   * @throws java.io.IOException If an I/O error occurs
   */
  public void write(String str, int off, int len) throws IOException {
    int nextToWrite = off;
    int guard = off + len;
    for (; off < guard; ++off) {
      String replacement = substitute(str.charAt(off));
      if (replacement != null) {
        if (nextToWrite < off) {
          out.write(str, nextToWrite, off - nextToWrite);
        }
        writeReplacement(replacement);
        nextToWrite = off + 1;
      }
    }
    if (nextToWrite < off) {
      out.write(str, nextToWrite, off - nextToWrite);
    }
  }
}