package org.bouncycastle.crypto.paddings;

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.DataLengthException;
import org.bouncycastle.crypto.DefaultBufferedBlockCipher;
import org.bouncycastle.crypto.InvalidCipherTextException;
import org.bouncycastle.crypto.OutputLengthException;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.util.Arrays;

/**
 * A wrapper class that allows block ciphers to be used to process data in
 * a piecemeal fashion with padding. The PaddedBufferedBlockCipher
 * outputs a block only when the buffer is full and more data is being added,
 * or on a doFinal (unless the current block in the buffer is a pad block).
 * The default padding mechanism used is the one outlined in PKCS5/PKCS7.
 */
public class PaddedBufferedBlockCipher
    extends DefaultBufferedBlockCipher
{
    BlockCipherPadding  padding;

    /**
     * Create a buffered block cipher with the desired padding.
     *
     * @param cipher the underlying block cipher this buffering object wraps.
     * @param padding the padding type.
     */
    public PaddedBufferedBlockCipher(
        BlockCipher         cipher,
        BlockCipherPadding  padding)
    {
        this.cipher = cipher;
        this.padding = padding;

        buf = new byte[cipher.getBlockSize()];
        bufOff = 0;
    }

    /**
     * Create a buffered block cipher PKCS7 padding
     *
     * @param cipher the underlying block cipher this buffering object wraps.
     */
    public PaddedBufferedBlockCipher(
        BlockCipher     cipher)
    {
        this(cipher, new PKCS7Padding());
    }

    /**
     * initialise the cipher.
     *
     * @param forEncryption if true the cipher is initialised for
     *  encryption, if false for decryption.
     * @param params the key and other data required by the cipher.
     * @exception IllegalArgumentException if the params argument is
     * inappropriate.
     */
    public void init(
        boolean             forEncryption,
        CipherParameters    params)
        throws IllegalArgumentException
    {
        this.forEncryption = forEncryption;

        reset();

        if (params instanceof ParametersWithRandom)
        {
            ParametersWithRandom    p = (ParametersWithRandom)params;

            padding.init(p.getRandom());

            cipher.init(forEncryption, p.getParameters());
        }
        else
        {
            padding.init(null);

            cipher.init(forEncryption, params);
        }
    }

    /**
     * return the minimum size of the output buffer required for an update
     * plus a doFinal with an input of len bytes.
     *
     * @param len the length of the input.
     * @return the space required to accommodate a call to update and doFinal
     * with len bytes of input.
     */
    public int getOutputSize(
        int len)
    {
        int total       = len + bufOff;
        int leftOver    = total % buf.length;

        if (leftOver == 0)
        {
            if (forEncryption)
            {
                return total + buf.length;
            }

            return total;
        }

        return total - leftOver + buf.length;
    }

    /**
     * return the size of the output buffer required for an update 
     * an input of len bytes.
     *
     * @param len the length of the input.
     * @return the space required to accommodate a call to update
     * with len bytes of input.
     */
    public int getUpdateOutputSize(
        int len)
    {
        int total       = len + bufOff;
        int leftOver    = total % buf.length;

        if (leftOver == 0)
        {
            return Math.max(0, total - buf.length);
        }

        return total - leftOver;
    }

    /**
     * process a single byte, producing an output block if neccessary.
     *
     * @param in the input byte.
     * @param out the space for any output that might be produced.
     * @param outOff the offset from which the output will be copied.
     * @return the number of output bytes copied to out.
     * @exception DataLengthException if there isn't enough space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     */
    public int processByte(
        byte        in,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        int         resultLen = 0;

        if (bufOff == buf.length)
        {
            resultLen = cipher.processBlock(buf, 0, out, outOff);
            bufOff = 0;
        }

        buf[bufOff++] = in;

        return resultLen;
    }

    /**
     * process an array of bytes, producing output if necessary.
     *
     * @param in the input byte array.
     * @param inOff the offset at which the input data starts.
     * @param len the number of bytes to be copied out of the input array.
     * @param out the space for any output that might be produced.
     * @param outOff the offset from which the output will be copied.
     * @return the number of output bytes copied to out.
     * @exception DataLengthException if there isn't enough space in out.
     * @exception IllegalStateException if the cipher isn't initialised.
     */
    public int processBytes(
        byte[]      in,
        int         inOff,
        int         len,
        byte[]      out,
        int         outOff)
        throws DataLengthException, IllegalStateException
    {
        if (len < 0)
        {
            throw new IllegalArgumentException("Can't have a negative input length!");
        }

        int blockSize   = getBlockSize();
        int length      = getUpdateOutputSize(len);
        
        if (length > 0)
        {
            if ((outOff + length) > out.length)
            {
                throw new OutputLengthException("output buffer too short");
            }
        }

        int resultLen = 0;
        int gapLen = buf.length - bufOff;

        if (len > gapLen)
        {
            System.arraycopy(in, inOff, buf, bufOff, gapLen);
            inOff += gapLen;
            len -= gapLen;
            if (in == out && Arrays.segmentsOverlap(inOff, len, outOff, length))
            {
                in = new byte[len];
                System.arraycopy(out, inOff, in, 0, len);
                inOff = 0;
            }

            resultLen += cipher.processBlock(buf, 0, out, outOff);

            bufOff = 0;

            while (len > buf.length)
            {
                resultLen += cipher.processBlock(in, inOff, out, outOff + resultLen);

                len -= blockSize;
                inOff += blockSize;
            }
        }

        System.arraycopy(in, inOff, buf, bufOff, len);

        bufOff += len;

        return resultLen;
    }

    /**
     * Process the last block in the buffer. If the buffer is currently
     * full and padding needs to be added a call to doFinal will produce
     * 2 * getBlockSize() bytes.
     *
     * @param out the array the block currently being held is copied into.
     * @param outOff the offset at which the copying starts.
     * @return the number of output bytes copied to out.
     * @exception DataLengthException if there is insufficient space in out for
     * the output or we are decrypting and the input is not block size aligned.
     * @exception IllegalStateException if the underlying cipher is not
     * initialised.
     * @exception InvalidCipherTextException if padding is expected and not found.
     */
    public int doFinal(
        byte[]  out,
        int     outOff)
        throws DataLengthException, IllegalStateException, InvalidCipherTextException
    {
        int blockSize = cipher.getBlockSize();
        int resultLen = 0;

        if (forEncryption)
        {
            if (bufOff == blockSize)
            {
                if ((outOff + 2 * blockSize) > out.length)
                {
                    reset();

                    throw new OutputLengthException("output buffer too short");
                }

                resultLen = cipher.processBlock(buf, 0, out, outOff);
                bufOff = 0;
            }

            padding.addPadding(buf, bufOff);

            resultLen += cipher.processBlock(buf, 0, out, outOff + resultLen);

            reset();
        }
        else
        {
            if (bufOff == blockSize)
            {
                resultLen = cipher.processBlock(buf, 0, buf, 0);
                bufOff = 0;
            }
            else
            {
                reset();

                throw new DataLengthException("last block incomplete in decryption");
            }

            try
            {
                resultLen -= padding.padCount(buf);

                System.arraycopy(buf, 0, out, outOff, resultLen);
            }
            finally
            {
                reset();
            }
        }

        return resultLen;
    }
}
