/*
 * Copyright (c) 2001-2003 Thai Open Source Software Center Ltd
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without 
 * modification, are permitted provided that the following conditions 
 * are met:
 *
 *  * Redistributions of source code must retain the above copyright 
 *    notice, this list of conditions and the following disclaimer.
 *  * Redistributions in binary form must reproduce the above 
 *    copyright notice, this list of conditions and the following 
 *    disclaimer in the documentation and/or other materials provided 
 *    with the distribution.
 *  * Neither the name of the Thai Open Source Software Center Ltd nor 
 *    the names of its contributors may be used to endorse or promote 
 *    products derived from this software without specific prior 
 *    written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 
 * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 
 * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS 
 * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE 
 * REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, 
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, 
 * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; 
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER 
 * CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN 
 * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE 
 * POSSIBILITY OF SUCH DAMAGE.
 */

package nu.validator.htmlparser.rewindable;

import java.io.IOException;
import java.io.InputStream;

public class RewindableInputStream extends InputStream implements Rewindable {
    static class Block {
        Block next;

        final byte[] buf;

        int used = 0;

        static final int MIN_SIZE = 1024;

        Block(int minSize) {
            buf = new byte[Math.max(MIN_SIZE, minSize)];
        }

        Block() {
            this(0);
        }

        void append(byte b) {
            buf[used++] = b;
        }

        void append(byte[] b, int off, int len) {
            System.arraycopy(b, off, buf, used, len);
            used += len;
        }
    }

    private Block head;

    /**
     * If curBlockAvail > 0, then there are curBlockAvail bytes available to be
     * returned starting at curBlockPos in curBlock.buf.
     */
    private int curBlockAvail;

    private Block curBlock;

    private int curBlockPos;

    private Block lastBlock;

    /**
     * true unless willNotRewind has been called
     */
    private boolean saving = true;

    private final InputStream in;

    private boolean pretendClosed = false;

    /**
     * true if we have got an EOF from the underlying InputStream
     */
    private boolean eof;

    public RewindableInputStream(InputStream in) {
        if (in == null)
            throw new NullPointerException();
        this.in = in;
    }

    public void close() throws IOException {
        if (saving) {
            curBlockAvail = 0;
            curBlock = null;
            pretendClosed = true;
        } else {
            head = null;
            curBlock = null;
            lastBlock = null;
            saving = false;
            curBlockAvail = 0;
            in.close();
        }
    }

    public void rewind() {
        if (!saving)
            throw new IllegalStateException("rewind() after willNotRewind()");
        pretendClosed = false;
        if (head == null)
            return;
        curBlock = head;
        curBlockPos = 0;
        curBlockAvail = curBlock.used;
    }

    public boolean canRewind() {
        return saving;
    }

    public void willNotRewind() {
        saving = false;
        head = null;
        lastBlock = null;
        if (pretendClosed) {
            pretendClosed = false;
            try {
                in.close();
            } catch (IOException e) {
            }
        }
    }

    public int read() throws IOException {
        if (curBlockAvail > 0) {
            int c = curBlock.buf[curBlockPos++] & 0xFF;
            --curBlockAvail;
            if (curBlockAvail == 0) {
                curBlock = curBlock.next;
                if (curBlock != null) {
                    curBlockPos = 0;
                    curBlockAvail = curBlock.used;
                }
            }
            return c;
        }
        int c = in.read();
        if (saving && c != -1) {
            if (lastBlock == null)
                lastBlock = head = new Block();
            else if (lastBlock.used == lastBlock.buf.length)
                lastBlock = lastBlock.next = new Block();
            lastBlock.append((byte) c);
        }
        return c;
    }

    public int read(byte b[], int off, int len) throws IOException {
        if (curBlockAvail == 0 && !saving)
            return in.read(b, off, len);
        if (b == null)
            throw new NullPointerException();
        if (len < 0)
            throw new IndexOutOfBoundsException();
        int nRead = 0;
        if (curBlockAvail != 0) {
            for (;;) {
                if (len == 0)
                    return nRead;
                b[off++] = curBlock.buf[curBlockPos++];
                --len;
                nRead++;
                --curBlockAvail;
                if (curBlockAvail == 0) {
                    curBlock = curBlock.next;
                    if (curBlock == null)
                        break;
                    curBlockAvail = curBlock.used;
                    curBlockPos = 0;
                }
            }
        }
        if (len == 0)
            return nRead;
        if (eof)
            return nRead > 0 ? nRead : -1;
        try {
            int n = in.read(b, off, len);
            if (n < 0) {
                eof = true;
                return nRead > 0 ? nRead : -1;
            }
            nRead += n;
            if (saving) {
                if (lastBlock == null)
                    lastBlock = head = new Block(n);
                else if (lastBlock.buf.length - lastBlock.used < n) {
                    if (lastBlock.used != lastBlock.buf.length) {
                        int free = lastBlock.buf.length - lastBlock.used;
                        lastBlock.append(b, off, free);
                        off += free;
                        n -= free;
                    }
                    lastBlock = lastBlock.next = new Block(n);
                }
                lastBlock.append(b, off, n);
            }
        } catch (IOException e) {
            eof = true;
            if (nRead == 0)
                throw e;
        }
        return nRead;
    }

    public int available() throws IOException {
        if (curBlockAvail == 0)
            return in.available();
        int n = curBlockAvail;
        for (Block b = curBlock.next; b != null; b = b.next)
            n += b.used;
        return n + in.available();
    }

}