/* ====================================================================
   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.poi.poifs.crypt.xor;

import java.io.File;
import java.io.IOException;
import java.io.OutputStream;
import java.security.GeneralSecurityException;
import java.util.BitSet;

import javax.crypto.Cipher;
import javax.crypto.spec.SecretKeySpec;

import org.apache.poi.poifs.crypt.ChunkedCipherOutputStream;
import org.apache.poi.poifs.crypt.CryptoFunctions;
import org.apache.poi.poifs.crypt.Encryptor;
import org.apache.poi.poifs.filesystem.DirectoryNode;
import org.apache.poi.util.LittleEndian;

public class XOREncryptor extends Encryptor implements Cloneable {
    protected XOREncryptor() {
    }

    @Override
    public void confirmPassword(String password) {
        int keyComp      = CryptoFunctions.createXorKey1(password);
        int verifierComp = CryptoFunctions.createXorVerifier1(password);
        byte xorArray[]  = CryptoFunctions.createXorArray1(password);
        
        byte shortBuf[] = new byte[2];
        XOREncryptionVerifier ver = (XOREncryptionVerifier)getEncryptionInfo().getVerifier();
        LittleEndian.putUShort(shortBuf, 0, keyComp);
        ver.setEncryptedKey(shortBuf);
        LittleEndian.putUShort(shortBuf, 0, verifierComp);
        ver.setEncryptedVerifier(shortBuf);
        setSecretKey(new SecretKeySpec(xorArray, "XOR"));
    }

    @Override
    public void confirmPassword(String password, byte keySpec[],
            byte keySalt[], byte verifier[], byte verifierSalt[],
            byte integritySalt[]) {
        confirmPassword(password);
    }

    @Override
    public OutputStream getDataStream(DirectoryNode dir)
    throws IOException, GeneralSecurityException {
        return new XORCipherOutputStream(dir);
    }

    @Override
    public XORCipherOutputStream getDataStream(OutputStream stream, int initialOffset)
    throws IOException, GeneralSecurityException {
        return new XORCipherOutputStream(stream, initialOffset);
    }

    protected int getKeySizeInBytes() {
        return -1;
    }

    @Override
    public void setChunkSize(int chunkSize) {
        // chunkSize is irrelevant
    }

    protected void createEncryptionInfoEntry(DirectoryNode dir) throws IOException {
    }

    @Override
    public XOREncryptor clone() throws CloneNotSupportedException {
        return (XOREncryptor)super.clone();
    }

    private class XORCipherOutputStream extends ChunkedCipherOutputStream {
        private int recordStart = 0;
        private int recordEnd = 0;

        public XORCipherOutputStream(OutputStream stream, int initialPos) throws IOException, GeneralSecurityException {
            super(stream, -1);
        }

        public XORCipherOutputStream(DirectoryNode dir) throws IOException, GeneralSecurityException {
            super(dir, -1);
        }

        @Override
        protected Cipher initCipherForBlock(Cipher cipher, int block, boolean lastChunk)
        throws GeneralSecurityException {
            return XORDecryptor.initCipherForBlock(cipher, block, getEncryptionInfo(), getSecretKey(), Cipher.ENCRYPT_MODE);
        }

        @Override
        protected void calculateChecksum(File file, int i) {
        }

        @Override
        protected void createEncryptionInfoEntry(DirectoryNode dir, File tmpFile)
        throws IOException, GeneralSecurityException {
            XOREncryptor.this.createEncryptionInfoEntry(dir);
        }

        @Override
        public void setNextRecordSize(int recordSize, boolean isPlain) {
            if (recordEnd > 0 && !isPlain) {
                // encrypt last record
                invokeCipher((int)getPos(), true);
            }
            recordStart = (int)getTotalPos()+4;
            recordEnd = recordStart+recordSize;
        }

        @Override
        public void flush() throws IOException {
            setNextRecordSize(0, true);
            super.flush();
        }

        @Override
        protected int invokeCipher(int posInChunk, boolean doFinal) {
            if (posInChunk == 0) {
                return 0;
            }

            final int start = Math.max(posInChunk-(recordEnd-recordStart), 0);

            final BitSet plainBytes = getPlainByteFlags();
            final byte xorArray[] = getEncryptionInfo().getEncryptor().getSecretKey().getEncoded();
            final byte chunk[] = getChunk();
            final byte plain[] = (plainBytes.isEmpty()) ? null : chunk.clone();

            /*
             * From: http://social.msdn.microsoft.com/Forums/en-US/3dadbed3-0e68-4f11-8b43-3a2328d9ebd5
             *
             * The initial value for XorArrayIndex is as follows:
             * XorArrayIndex = (FileOffset + Data.Length) % 16
             *
             * The FileOffset variable in this context is the stream offset into the Workbook stream at
             * the time we are about to write each of the bytes of the record data.
             * This (the value) is then incremented after each byte is written.
             */
            // ... also need to handle invocation in case of a filled chunk
            int xorArrayIndex = recordEnd+(start-recordStart);

            for (int i=start; i < posInChunk; i++) {
                byte value = chunk[i];
                value ^= xorArray[(xorArrayIndex++) & 0x0F];
                value = rotateLeft(value, 8-3);
                chunk[i] = value;
            }

            for (int i = plainBytes.nextSetBit(start); i >= 0 && i < posInChunk; i = plainBytes.nextSetBit(i+1)) {
                chunk[i] = plain[i];
            }

            return posInChunk;
        }

        private byte rotateLeft(byte bits, int shift) {
            return (byte)(((bits & 0xff) << shift) | ((bits & 0xff) >>> (8 - shift)));
        }


    }
}