/*
 ** Authored by Timothy Gerard Endres
 ** <mailto:time@gjt.org>  <http://www.trustice.com>
 ** 
 ** This work has been placed into the public domain.
 ** You may use this work in any way and for any purpose you wish.
 **
 ** THIS SOFTWARE IS PROVIDED AS-IS WITHOUT WARRANTY OF ANY KIND,
 ** NOT EVEN THE IMPLIED WARRANTY OF MERCHANTABILITY. THE AUTHOR
 ** OF THIS SOFTWARE, ASSUMES _NO_ RESPONSIBILITY FOR ANY
 ** CONSEQUENCE RESULTING FROM THE USE, MODIFICATION, OR
 ** REDISTRIBUTION OF THIS SOFTWARE. 
 ** 
 */

package com.ice.tar;

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

/**
 * The TarBuffer class implements the tar archive concept
 * of a buffered input stream. This concept goes back to the
 * days of blocked tape drives and special io devices. In the
 * Java universe, the only real function that this class
 * performs is to ensure that files have the correct "block"
 * size, or other tars will complain.
 * <p>
 * You should never have a need to access this class directly.
 * TarBuffers are created by Tar IO Streams.
 *
 * @version $Revision$
 * @author Timothy Gerard Endres,
 *  <a href="mailto:time@gjt.org">time@trustice.com</a>.
 * @see TarArchive
 */

public class TarBuffer extends Object
{
    public static final int DEFAULT_RCDSIZE = (512);
    public static final int DEFAULT_BLKSIZE = (DEFAULT_RCDSIZE * 20);

    private InputStream inStream;
    private OutputStream outStream;

    private byte[] blockBuffer;
    private int currBlkIdx;
    private int currRecIdx;
    private int blockSize;
    private int recordSize;
    private int recsPerBlock;

    private boolean debug;

    public TarBuffer(InputStream inStream)
    {
        this(inStream, TarBuffer.DEFAULT_BLKSIZE);
    }

    public TarBuffer(InputStream inStream, int blockSize)
    {
        this(inStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
    }

    public TarBuffer(InputStream inStream, int blockSize, int recordSize)
    {
        this.inStream = inStream;
        this.outStream = null;
        this.initialize(blockSize, recordSize);
    }

    public TarBuffer(OutputStream outStream)
    {
        this(outStream, TarBuffer.DEFAULT_BLKSIZE);
    }

    public TarBuffer(OutputStream outStream, int blockSize)
    {
        this(outStream, blockSize, TarBuffer.DEFAULT_RCDSIZE);
    }

    public TarBuffer(OutputStream outStream, int blockSize, int recordSize)
    {
        this.inStream = null;
        this.outStream = outStream;
        this.initialize(blockSize, recordSize);
    }

    /**
     * Initialization common to all constructors.
     */
    private void initialize(int newBlockSize, int newRecordSize)
    {
        this.debug = false;
        this.blockSize = newBlockSize;
        this.recordSize = newRecordSize;
        this.recsPerBlock = (this.blockSize / this.recordSize);
        this.blockBuffer = new byte[this.blockSize];

        if (this.inStream != null)
        {
            this.currBlkIdx = -1;
            this.currRecIdx = this.recsPerBlock;
        }
        else
        {
            this.currBlkIdx = 0;
            this.currRecIdx = 0;
        }
    }

    /**
     * Get the TAR Buffer's block size. Blocks consist of multiple records.
     */
    public int getBlockSize()
    {
        return this.blockSize;
    }

    /**
     * Get the TAR Buffer's record size.
     */
    public int getRecordSize()
    {
        return this.recordSize;
    }

    /**
     * Set the debugging flag for the buffer.
     *
     * @param debug If true, print debugging output.
     */
    public void setDebug(boolean debug)
    {
        this.debug = debug;
    }

    /**
     * Determine if an archive record indicate End of Archive. End of
     * archive is indicated by a record that consists entirely of null bytes.
     *
     * @param record The record data to check.
     */
    public boolean isEOFRecord(byte[] record)
    {
        for (int i = 0, sz = this.getRecordSize(); i < sz; ++i)
            if (record[i] != 0)
                return false;

        return true;
    }

    /**
     * Skip over a record on the input stream.
     */
    public void skipRecord() throws IOException
    {
        if (this.debug)
        {
            System.err.println("SkipRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
        }

        if (this.inStream == null)
            throw new IOException("reading (via skip) from an output buffer");

        if (this.currRecIdx >= this.recsPerBlock)
        {
            if (!this.readBlock())
                return; // UNDONE
        }

        this.currRecIdx++;
    }

    /**
     * Read a record from the input stream and return the data.
     *
     * @return The record data.
     */
    public byte[] readRecord() throws IOException
    {
        if (this.debug)
        {
            System.err.println("ReadRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
        }

        if (this.inStream == null)
            throw new IOException("reading from an output buffer");

        if (this.currRecIdx >= this.recsPerBlock)
        {
            if (!this.readBlock())
                return null;
        }

        byte[] result = new byte[this.recordSize];

        System.arraycopy(this.blockBuffer, (this.currRecIdx * this.recordSize), result, 0, this.recordSize);

        this.currRecIdx++;

        return result;
    }

    /**
     * @return false if End-Of-File, else true
     */
    private boolean readBlock() throws IOException
    {
        if (this.debug)
        {
            System.err.println("ReadBlock: blkIdx = " + this.currBlkIdx);
        }

        if (this.inStream == null)
            throw new IOException("reading from an output buffer");

        this.currRecIdx = 0;

        int offset = 0;
        int bytesNeeded = this.blockSize;
        for (; bytesNeeded > 0;)
        {
            long numBytes = this.inStream.read(this.blockBuffer, offset, bytesNeeded);

            //
            // NOTE
            // We have fit EOF, and the block is not full!
            //
            // This is a broken archive. It does not follow the standard
            // blocking algorithm. However, because we are generous, and
            // it requires little effort, we will simply ignore the error
            // and continue as if the entire block were read. This does
            // not appear to break anything upstream. We used to return
            // false in this case.
            //
            // Thanks to 'Yohann.Roussel@alcatel.fr' for this fix.
            //

            if (numBytes == -1)
                break;

            offset += numBytes;
            bytesNeeded -= numBytes;
            if (numBytes != this.blockSize)
            {
                if (this.debug)
                {
                    System.err.println("ReadBlock: INCOMPLETE READ " + numBytes + " of " + this.blockSize + " bytes read.");
                }
            }
        }

        this.currBlkIdx++;

        return true;
    }

    /**
     * Get the current block number, zero based.
     *
     * @return The current zero based block number.
     */
    public int getCurrentBlockNum()
    {
        return this.currBlkIdx;
    }

    /**
     * Get the current record number, within the current block, zero based.
     * Thus, current offset = (currentBlockNum * recsPerBlk) + currentRecNum.
     *
     * @return The current zero based record number.
     */
    public int getCurrentRecordNum()
    {
        return this.currRecIdx - 1;
    }

    /**
     * Write an archive record to the archive.
     *
     * @param record The record data to write to the archive.
     */

    public void writeRecord(byte[] record) throws IOException
    {
        if (this.debug)
        {
            System.err.println("WriteRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
        }

        if (this.outStream == null)
            throw new IOException("writing to an input buffer");

        if (record.length != this.recordSize)
            throw new IOException("record to write has length '" + record.length + "' which is not the record size of '" + this.recordSize + "'");

        if (this.currRecIdx >= this.recsPerBlock)
        {
            this.writeBlock();
        }

        System.arraycopy(record, 0, this.blockBuffer, (this.currRecIdx * this.recordSize), this.recordSize);

        this.currRecIdx++;
    }

    /**
     * Write an archive record to the archive, where the record may be
     * inside of a larger array buffer. The buffer must be "offset plus
     * record size" long.
     *
     * @param buf The buffer containing the record data to write.
     * @param offset The offset of the record data within buf.
     */

    public void writeRecord(byte[] buf, int offset) throws IOException
    {
        if (this.debug)
        {
            System.err.println("WriteRecord: recIdx = " + this.currRecIdx + " blkIdx = " + this.currBlkIdx);
        }

        if (this.outStream == null)
            throw new IOException("writing to an input buffer");

        if ((offset + this.recordSize) > buf.length)
            throw new IOException("record has length '" + buf.length + "' with offset '" + offset + "' which is less than the record size of '"
                            + this.recordSize + "'");

        if (this.currRecIdx >= this.recsPerBlock)
        {
            this.writeBlock();
        }

        System.arraycopy(buf, offset, this.blockBuffer, (this.currRecIdx * this.recordSize), this.recordSize);

        this.currRecIdx++;
    }

    /**
     * Write a TarBuffer block to the archive.
     */
    private void writeBlock() throws IOException
    {
        if (this.debug)
        {
            System.err.println("WriteBlock: blkIdx = " + this.currBlkIdx);
        }

        if (this.outStream == null)
            throw new IOException("writing to an input buffer");

        this.outStream.write(this.blockBuffer, 0, this.blockSize);
        this.outStream.flush();

        this.currRecIdx = 0;
        this.currBlkIdx++;
    }

    /**
     * Flush the current data block if it has any data in it.
     */

    private void flushBlock() throws IOException
    {
        if (this.debug)
        {
            System.err.println("TarBuffer.flushBlock() called.");
        }

        if (this.outStream == null)
            throw new IOException("writing to an input buffer");

        // Thanks to 'Todd Kofford <tkofford@bigfoot.com>' for this patch.
        // Use a buffer initialized with 0s to initialize everything in the
        // blockBuffer after the last current, complete record. This prevents
        // any previous data that might have previously existed in the
        // blockBuffer from being written to the file.

        if (this.currRecIdx > 0)
        {
            int offset = this.currRecIdx * this.recordSize;
            byte[] zeroBuffer = new byte[this.blockSize - offset];

            System.arraycopy(zeroBuffer, 0, this.blockBuffer, offset, zeroBuffer.length);

            this.writeBlock();
        }
    }

    /**
     * Close the TarBuffer. If this is an output buffer, also flush the
     * current block before closing.
     */
    public void close() throws IOException
    {
        if (this.debug)
        {
            System.err.println("TarBuffer.closeBuffer().");
        }

        if (this.outStream != null)
        {
            this.flushBlock();

            if (this.outStream != System.out && this.outStream != System.err)
            {
                this.outStream.close();
                this.outStream = null;
            }
        }
        else if (this.inStream != null)
        {
            if (this.inStream != System.in)
            {
                this.inStream.close();
                this.inStream = null;
            }
        }
    }

}