/*
 * 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.xerces.impl.io;

import java.io.IOException;
import java.io.InputStream;
import java.io.Reader;
import java.util.Locale;

import org.apache.xerces.impl.msg.XMLMessageFormatter;
import org.apache.xerces.util.MessageFormatter;

/**
 * <p>A UTF-16 reader. Can also be used for UCS-2 (i.e. ISO-10646-UCS-2).</p>
 * 
 * @xerces.internal
 * 
 * @author Michael Glavassevich, IBM
 *
 * @version $Id$
 */
public final class UTF16Reader 
    extends Reader {
    
    //
    // Constants
    //

    /** Default byte buffer size (4096). */
    public static final int DEFAULT_BUFFER_SIZE = 4096;
    
    //
    // Data
    //

    /** Input stream. */
    protected final InputStream fInputStream;

    /** Byte buffer. */
    protected final byte[] fBuffer;
    
    /** Endianness. */
    protected final boolean fIsBigEndian;
    
    // message formatter; used to produce localized exception messages
    private final MessageFormatter fFormatter;

    // Locale to use for messages
    private final Locale fLocale;
    
    //
    // Constructors
    //

    /** 
     * Constructs a UTF-16 reader from the specified input stream 
     * using the default buffer size. Primarily for testing.
     *
     * @param inputStream The input stream.
     * @param isBigEndian The byte order.
     */
    public UTF16Reader(InputStream inputStream, boolean isBigEndian) {
        this(inputStream, DEFAULT_BUFFER_SIZE, isBigEndian, 
                new XMLMessageFormatter(), Locale.getDefault());
    } // <init>(InputStream, boolean)
    
    /** 
     * Constructs a UTF-16 reader from the specified input stream 
     * using the default buffer size and the given MessageFormatter.
     *
     * @param inputStream The input stream.
     * @param isBigEndian The byte order.
     */
    public UTF16Reader(InputStream inputStream, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        this(inputStream, DEFAULT_BUFFER_SIZE, isBigEndian, messageFormatter, locale);
    } // <init>(InputStream, boolean, MessageFormatter, Locale)
    
    /** 
     * Constructs a UTF-16 reader from the specified input stream 
     * and buffer size and given MessageFormatter.
     *
     * @param inputStream       The input stream.
     * @param size              The initial buffer size.
     * @param isBigEndian       The byte order.
     * @param messageFormatter  Given MessageFormatter
     * @param locale            Locale to use for messages
     */
    public UTF16Reader(InputStream inputStream, int size, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        this(inputStream, new byte[size], isBigEndian, messageFormatter, locale);
    } // <init>(InputStream, int, boolean, MessageFormatter, Locale)
    
    /** 
     * Constructs a UTF-16 reader from the specified input stream, 
     * buffer and MessageFormatter.
     *
     * @param inputStream       The input stream.
     * @param buffer            The byte buffer.
     * @param isBigEndian       The byte order.
     * @param messageFormatter  Given MessageFormatter
     * @param locale            Locale to use for messages
     */
    public UTF16Reader(InputStream inputStream, byte [] buffer, boolean isBigEndian, 
            MessageFormatter messageFormatter, Locale locale) {
        fInputStream = inputStream;
        fBuffer = buffer;
        fIsBigEndian = isBigEndian;
        fFormatter = messageFormatter;
        fLocale = locale;
    } // <init>(InputStream, byte[], boolean, MessageFormatter, Locale)
    
    //
    // Reader methods
    //
    
    /**
     * Read a single character.  This method will block until a character is
     * available, an I/O error occurs, or the end of the stream is reached.
     *
     * <p> Subclasses that intend to support efficient single-character input
     * should override this method.
     *
     * @return     The character read, as an integer in the range 0 to 65535
     *             (<tt>0x00-0xffff</tt>), or -1 if the end of the stream has
     *             been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read() throws IOException {
        final int b0 = fInputStream.read();
        if (b0 == -1) {
            return -1;
        }
        final int b1 = fInputStream.read();
        if (b1 == -1) {
            expectedTwoBytes();
        }
        // UTF-16BE
        if (fIsBigEndian) {
            return (b0 << 8) | b1;
        }
        // UTF-16LE
        return (b1 << 8) | b0;
    } // read():int

    /**
     * Read characters into a portion of an array.  This method will block
     * until some input is available, an I/O error occurs, or the end of the
     * stream is reached.
     *
     * @param      ch     Destination buffer
     * @param      offset Offset at which to start storing characters
     * @param      length Maximum number of characters to read
     *
     * @return     The number of characters read, or -1 if the end of the
     *             stream has been reached
     *
     * @exception  IOException  If an I/O error occurs
     */
    public int read(char ch[], int offset, int length) throws IOException {
        int byteLength = length << 1;
        if (byteLength > fBuffer.length) {
            byteLength = fBuffer.length;
        }
        int byteCount = fInputStream.read(fBuffer, 0, byteLength);
        if (byteCount == -1) {
            return -1;
        }
        // If an odd number of bytes were read, we still need to read one more.
        if ((byteCount & 1) != 0) {
            int b = fInputStream.read();
            if (b == -1) {
                expectedTwoBytes();
            }
            fBuffer[byteCount++] = (byte) b;
        }
        final int charCount = byteCount >> 1;
        if (fIsBigEndian) {
            processBE(ch, offset, charCount);
        }
        else {
            processLE(ch, offset, charCount);
        }
        return charCount;
    } // read(char[],int,int)

    /**
     * Skip characters.  This method will block until some characters are
     * available, an I/O error occurs, or the end of the stream is reached.
     *
     * @param  n  The number of characters to skip
     *
     * @return    The number of characters actually skipped
     *
     * @exception  IOException  If an I/O error occurs
     */
    public long skip(long n) throws IOException {
        long bytesSkipped = fInputStream.skip(n << 1);
        if ((bytesSkipped & 1) != 0) {
            int b = fInputStream.read();
            if (b == -1) {
                expectedTwoBytes();
            }
            ++bytesSkipped;
        }
        return bytesSkipped >> 1;
    } // skip(long):long

    /**
     * Tell whether this stream is ready to be read.
     *
     * @return True if the next read() is guaranteed not to block for input,
     * false otherwise.  Note that returning false does not guarantee that the
     * next read will block.
     *
     * @exception  IOException  If an I/O error occurs
     */
    public boolean ready() throws IOException {
        return false;
    } // ready()

    /**
     * Tell whether this stream supports the mark() operation.
     */
    public boolean markSupported() {
        return false;
    } // markSupported()

    /**
     * Mark the present position in the stream.  Subsequent calls to reset()
     * will attempt to reposition the stream to this point.  Not all
     * character-input streams support the mark() operation.
     *
     * @param  readAheadLimit  Limit on the number of characters that may be
     *                         read while still preserving the mark.  After
     *                         reading this many characters, attempting to
     *                         reset the stream may fail.
     *
     * @exception  IOException  If the stream does not support mark(),
     *                          or if some other I/O error occurs
     */
    public void mark(int readAheadLimit) throws IOException {
        throw new IOException(fFormatter.formatMessage(fLocale, "OperationNotSupported", new Object[]{"mark()", "UTF-16"}));
    } // mark(int)

    /**
     * Reset the stream.  If the stream has been marked, then attempt to
     * reposition it at the mark.  If the stream has not been marked, then
     * attempt to reset it in some way appropriate to the particular stream,
     * for example by repositioning it to its starting point.  Not all
     * character-input streams support the reset() operation, and some support
     * reset() without supporting mark().
     *
     * @exception  IOException  If the stream has not been marked,
     *                          or if the mark has been invalidated,
     *                          or if the stream does not support reset(),
     *                          or if some other I/O error occurs
     */
    public void reset() throws IOException {
    } // reset()

    /**
     * Close the stream.  Once a stream has been closed, further read(),
     * ready(), mark(), or reset() invocations will throw an IOException.
     * Closing a previously-closed stream, however, has no effect.
     *
     * @exception  IOException  If an I/O error occurs
     */
     public void close() throws IOException {
         fInputStream.close();
     } // close()
     
     //
     // Private methods
     //
     
     /** Decodes UTF-16BE **/
     private void processBE(final char ch[], int offset, final int count) {
         int curPos = 0;
         for (int i = 0; i < count; ++i) {
             final int b0 = fBuffer[curPos++] & 0xff;
             final int b1 = fBuffer[curPos++] & 0xff;
             ch[offset++] = (char) ((b0 << 8) | b1);
         }
     } // processBE(char[],int,int)
     
     /** Decodes UTF-16LE **/
     private void processLE(final char ch[], int offset, final int count) {
         int curPos = 0;
         for (int i = 0; i < count; ++i) {
             final int b0 = fBuffer[curPos++] & 0xff;
             final int b1 = fBuffer[curPos++] & 0xff;
             ch[offset++] = (char) ((b1 << 8) | b0);
         }
     } // processLE(char[],int,int)

     /** Throws an exception for expected byte. */
     private void expectedTwoBytes()
         throws MalformedByteSequenceException {
         throw new MalformedByteSequenceException(fFormatter,
             fLocale,
             XMLMessageFormatter.XML_DOMAIN,
             "ExpectedByte",
             new Object[] {"2", "2"});
     } // expectedTwoBytes()

} // class UTF16Reader
