/*
 * 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;

Reader for UCS-2 and UCS-4 encodings.
(i.e., encodings from ISO-10646-UCS-(2|4)).
Author:
Neil Graham, IBM
@xerces.internal
Version:
$Id: UCSReader.java 718095 2008-11-16 20:00:14Z mrglavas $/** 
 * Reader for UCS-2 and UCS-4 encodings.
 * (i.e., encodings from ISO-10646-UCS-(2|4)).
 * 
 * @xerces.internal

 *
 * @author Neil Graham, IBM
 *
 * @version $Id: UCSReader.java 718095 2008-11-16 20:00:14Z mrglavas $
 */
public final class UCSReader extends Reader {

    //
    // Constants
    //

    
Default byte buffer size (8192, larger than that of ASCIIReader
since it's reasonable to surmise that the average UCS-4-encoded
file should be 4 times as large as the average ASCII-encoded file). 
/** 
     * Default byte buffer size (8192, larger than that of ASCIIReader
     * since it's reasonable to surmise that the average UCS-4-encoded
     * file should be 4 times as large as the average ASCII-encoded file). 
     */
    public static final int DEFAULT_BUFFER_SIZE = 8192;

    public static final short UCS2LE = 1;
    public static final short UCS2BE = 2;
    public static final short UCS4LE = 4;
    public static final short UCS4BE = 8;

    //
    // Data
    //

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

    
Byte buffer. /** Byte buffer. */
    protected final byte[] fBuffer;

    // what kind of data we're dealing with
    protected final short fEncoding;

    //
    // Constructors
    //

    
Constructs a UCS reader from the specified input stream 
using the default buffer size.  The Endian-ness and whether this is
UCS-2 or UCS-4 needs also to be known in advance.
Params:
inputStream – The input stream.
encoding – One of UCS2LE, UCS2BE, UCS4LE or UCS4BE./** 
     * Constructs a UCS reader from the specified input stream 
     * using the default buffer size.  The Endian-ness and whether this is
     * UCS-2 or UCS-4 needs also to be known in advance.
     *
     * @param inputStream The input stream.
     * @param encoding One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
     */
    public UCSReader(InputStream inputStream, short encoding) {
        this(inputStream, DEFAULT_BUFFER_SIZE, encoding);
    } // <init>(InputStream, short)

    
Constructs a UCS reader from the specified input stream 
and buffer size.  The Endian-ness and whether this is
UCS-2 or UCS-4 needs also to be known in advance.
Params:
inputStream – The input stream.
size –        The initial buffer size.
encoding – One of UCS2LE, UCS2BE, UCS4LE or UCS4BE./** 
     * Constructs a UCS reader from the specified input stream 
     * and buffer size.  The Endian-ness and whether this is
     * UCS-2 or UCS-4 needs also to be known in advance.
     *
     * @param inputStream The input stream.
     * @param size        The initial buffer size.
     * @param encoding One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
     */
    public UCSReader(InputStream inputStream, int size, short encoding) {
        this(inputStream, new byte[size], encoding);
    } // <init>(InputStream,int,short)
    
    
Constructs a UCS reader from the specified input stream 
and buffer.  The Endian-ness and whether this is
UCS-2 or UCS-4 needs also to be known in advance.
Params:
inputStream – The input stream.
buffer –      The byte buffer.
encoding – One of UCS2LE, UCS2BE, UCS4LE or UCS4BE./** 
     * Constructs a UCS reader from the specified input stream 
     * and buffer.  The Endian-ness and whether this is
     * UCS-2 or UCS-4 needs also to be known in advance.
     *
     * @param inputStream The input stream.
     * @param buffer      The byte buffer.
     * @param encoding One of UCS2LE, UCS2BE, UCS4LE or UCS4BE.
     */
    public UCSReader(InputStream inputStream, byte [] buffer, short encoding) {
        fInputStream = inputStream;
        fBuffer = buffer;
        fEncoding = encoding;
    } // <init>(InputStream,int,short)

    //
    // 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.
 Subclasses that intend to support efficient single-character input
should override this method.
Throws:
IOException –  If an I/O error occurs
Returns:
    The character read, as an integer in the range 0 to 127
            (0x00-0x7f), or -1 if the end of the stream has
            been reached/**
     * 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 127
     *             (<tt>0x00-0x7f</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 { 
        int b0 = fInputStream.read() & 0xff;
        if (b0 == 0xff) {
            return -1;
        }
        int b1 = fInputStream.read() & 0xff;
        if (b1 == 0xff) {
            return -1;
        }
        // UCS-4
        if (fEncoding >= 4) {
            int b2 = fInputStream.read() & 0xff;
            if (b2 == 0xff) {
                return -1;
            }
            int b3 = fInputStream.read() & 0xff;
            if (b3 == 0xff) {
                return -1;
            }
            if (fEncoding == UCS4BE) {
                return (b0<<24)+(b1<<16)+(b2<<8)+b3;
            }
            return (b3<<24)+(b2<<16)+(b1<<8)+b0;
        }
        // UCS-2
        if (fEncoding == UCS2BE) {
            return (b0<<8)+b1;
        }
        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.
Params:
ch –     Destination buffer
offset – Offset at which to start storing characters
length – Maximum number of characters to read
Throws:
IOException –  If an I/O error occurs
Returns:
    The number of characters read, or -1 if the end of the
            stream has been reached/**
     * 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 << ((fEncoding >= 4)?2:1);
        if (byteLength > fBuffer.length) {
            byteLength = fBuffer.length;
        }
        int count = fInputStream.read(fBuffer, 0, byteLength);
        if (count == -1) return -1;
        // try and make count be a multiple of the number of bytes we're looking for
        if (fEncoding >= 4) { // BigEndian
            // this looks ugly, but it avoids an if at any rate...
            int numToRead = (4 - (count & 3) & 3);
            for (int i = 0; i < numToRead; i++) {
                int charRead = fInputStream.read();
                if (charRead == -1) { // end of input; something likely went wrong!A  Pad buffer with nulls.
                    for (int j = i; j < numToRead; j++) {
                        fBuffer[count+j] = 0;
                    }
                    break;
                }
                fBuffer[count+i] = (byte)charRead;
            }
            count += numToRead;
        } 
        else {
            int numToRead = count & 1;
            if (numToRead != 0) {
                count++;
                int charRead = fInputStream.read();
                if (charRead == -1) { // end of input; something likely went wrong!A  Pad buffer with nulls.
                    fBuffer[count] = 0;
                } 
                else {
                    fBuffer[count] = (byte)charRead;
                }
            }
        }

        // now count is a multiple of the right number of bytes
        int numChars = count >> ((fEncoding >= 4)?2:1);
        int curPos = 0;
        for (int i = 0; i < numChars; i++) {
            int b0 = fBuffer[curPos++] & 0xff;
            int b1 = fBuffer[curPos++] & 0xff;
            // UCS-4
            if (fEncoding >= 4) {
                int b2 = fBuffer[curPos++] & 0xff;
                int b3 = fBuffer[curPos++] & 0xff;
                if (fEncoding == UCS4BE) {
                    ch[offset+i] = (char)((b0<<24)+(b1<<16)+(b2<<8)+b3);
                }
                else {
                    ch[offset+i] = (char)((b3<<24)+(b2<<16)+(b1<<8)+b0);
                }
            } 
            else { // UCS-2
                if (fEncoding == UCS2BE) {
                    ch[offset+i] = (char)((b0<<8)+b1);
                }
                else {
                    ch[offset+i] = (char)((b1<<8)+b0);
                }
            }
        }
        return numChars;
    } // 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.
Params:
n –  The number of characters to skip
Throws:
IOException –  If an I/O error occurs
Returns:
   The number of characters actually skipped/**
     * 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 {
        // charWidth will represent the number of bits to move
        // n leftward to get num of bytes to skip, and then move the result rightward
        // to get num of chars effectively skipped.
        // The trick with &'ing, as with elsewhere in this dcode, is
        // intended to avoid an expensive use of / that might not be optimized
        // away.
        int charWidth = (fEncoding >=4)?2:1;
        long bytesSkipped = fInputStream.skip(n<<charWidth);
        if((bytesSkipped & (charWidth | 1)) == 0) return bytesSkipped >> charWidth;
        return (bytesSkipped >> charWidth) + 1;
    } // skip(long):long

    
Tell whether this stream is ready to be read.
Throws:
IOException –  If an I/O error occurs
Returns:
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./**
     * 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.
/**
     * Tell whether this stream supports the mark() operation.
     */
    public boolean markSupported() {
	    return fInputStream.markSupported();
    } // 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.
Params:
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.
Throws:
IOException –  If the stream does not support mark(),
                         or if some other I/O error occurs/**
     * 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 {
	    fInputStream.mark(readAheadLimit);
    } // 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().
Throws:
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/**
     * 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 {
        fInputStream.reset();
    } // 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.
Throws:
IOException –  If an I/O error occurs/**
     * 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()

} // class UCSReader