/*

  * #%L

  * StringDecoder.java - mongodb-async-driver - Allanbank Consulting, Inc.

  * %%

  * Copyright (C) 2011 - 2014 Allanbank Consulting, Inc.

  * %%

  * 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.

  * #L%

  */

 package com.allanbank.mongodb.bson.io;

 import java.io.EOFException;

 import java.io.StreamCorruptedException;

 import java.nio.charset.Charset;

 /**

  * StringDecoder provides a decoder for byte arrays into strings that uses a

  * trie data structure to cache recurring strings.

  * <p>

  * This class is <b>not</b> thread safe.

  * </p>

  * 

  * @api.no This class is <b>NOT</b> part of the drivers API. This class may be

  *         mutated in incompatible ways between any two releases of the driver.

  * @copyright 2013, Allanbank Consulting, Inc., All Rights Reserved

  */

 public class StringDecoder {

     /** UTF-8 Character set for encoding strings. */

     /* package */final static Charset UTF8 = Charset.forName("UTF-8");

     /** A builder for the ASCII strings. */

     private final StringBuilder myBuilder = new StringBuilder(64);

     /** The cached decoded strings. */

     private final StringDecoderCache myCache;

     /**

      * Creates a new StringDecoder.

      */

     public StringDecoder() {

         this(new StringDecoderCache());

     }

     /**

      * Creates a new StringDecoder.

      * 

      * @param cache

      *            The cache for the decoder.

      */

     public StringDecoder(final StringDecoderCache cache) {

         super();

         myCache = cache;

     }

     /**

      * Decode a string of a known length. The last byte should be a zero byte

      * and will not be included in the decoded string.

      * 

      * @param source

      *            The source of the bytes in the string.

      * @param offset

      *            The offset of the first byte to decode.

      * @param length

      *            The length of the string to decode with a terminal zero byte.

      * @return The decoded string.

      * @throws StreamCorruptedException

      *             On the decoding of the string failing.

      * @throws EOFException

      *             On the array not containing enough bytes to decoded.

      */

     public String decode(final byte[] source, final int offset, final int length)

             throws StreamCorruptedException, EOFException {

         String result = myCache.find(source, offset, length);

         if (result == null) {

             result = fastDecode(source, offset, length - 1);

         }

         myCache.used(result, source, offset, length);

         return result;

     }

     /**

      * Returns the cache value.

      * 

      * @return The cache value.

      * @deprecated The cache {@link StringDecoderCache} should be controlled

      *             directly. This method will be removed after the 2.1.0

      *             release.

      */

     @Deprecated

     public StringDecoderCache getCache() {

         return myCache;

     }

     /**

      * Retrieves or caches the decoded string for the Trie.

      * 

      * @param source

      *            The source of the bytes in the string.

      * @param offset

      *            The offset of the first byte to decode.

      * @param length

      *            The length of the string to decode without a terminal zero

      *            byte.

      * @return The value for the string.

      */

     private String fastDecode(final byte[] source, final int offset,

             final int length) {

         // Try to decode as ASCII.

         boolean isAscii = true;

         for (int i = 0; isAscii && (i < length); ++i) {

             final int b = (source[offset + i] & 0xFF);

             if (b < 0x80) {

                 myBuilder.append((char) b);

             }

             else {

                 isAscii = false;

             }

         }

         String result;

         if (!isAscii) {

             final int encodedLength = myBuilder.length();

             final String remaining = new String(source, offset + encodedLength,

                     length - encodedLength, UTF8);

             myBuilder.append(remaining);

         }

         result = myBuilder.toString();

         // Clear the string builder.

         myBuilder.setLength(0);

         return result;

     }

 }