/*
 * Copyright (c) 1999,2009 Declarative Engineering LLC.
 * All rights reserved.  This program and the accompanying materials
 * are made available under the terms of the Declarative Engineering LLC
 * verson 1 which accompanies this distribution, and is available at
 * http://declarativeengineering.com/legal/DE_Developer_License_v1.txt
 */
package com.common.io;

import java.io.InputStream;
import java.io.IOException;
import com.common.security.*;

/*
 * This class allows an symmetricly encrypted stream to be plugged into an input stream so that read bytes are decrypted using the private key.
 */
public abstract class CryptoInputStream extends java.io.InputStream implements IInputStream {
	protected InputStream stream = null;
	protected int decryptionCount;
	protected byte[] encryptedBuffer = null;
	protected byte[] decryptedBuffer = null;
	protected int decryptedBufferOffset = 0;
	protected int decryptionLength = 0;
	protected boolean stopFlag = false;  //Used to notify the read methods that the encrypted segments have ended and that wrappering streams attempting to buffer should be told there are no more bytes at this time.//
/**
 * CryptoInputStream constructor.
 */
public CryptoInputStream(InputStream stream, IAlgorithm algorithm) {
	super();

	if(stream == null) {
		throw new IllegalArgumentException("Must provide a valid output stream.");
	}//if//
	else if(algorithm == null) {
		throw new IllegalArgumentException("Must provide a valid algorithm.");
	}//if//

	this.stream = stream;
}//CryptoInputStream()//
/* (non-Javadoc)
 * @see java.io.InputStream#available()
 */
public int available() throws IOException {
	return stream.available();
}//available()//
/* (non-Javadoc)
 * @see com.common.io.IInputStream#canDecrypt()
 */
public boolean canDecrypt() {
	return true;
}//canDecrypt()//
/* (non-Javadoc)
 * @see java.io.InputStream#close()
 */
public void close() throws IOException {
	super.close();
	stream.close();
}//close()//
/**
 * Decrypts or verifies (unsigns) data and strips all padding.
 * @param data The buffer containing encrypted data.
 * @param dataOffset The index of the first encrypted byte.
 * @param dataLength The number of encrypted data bytes.
 * @param output A buffer to contain the decrypted data.
 * @param outputOffset The location of the first decrypted byte in the output buffer.
 * @return The number of bytes decrypted.
 */
protected abstract int decrypt(byte[] data, int dataOffset, int dataLength, byte[] output, int outputOffset);
/* (non-Javadoc)
 * @see com.common.io.IInputStream#decrypt(boolean)
 */
public void decrypt(boolean decrypt) throws IOException {
	if(decrypt) {
		if(decryptionCount == 0) {
			refillBuffer();
		}//if//
		
		decryptionCount++;
	}//if//
	else {
		decryptionCount--;

		if(decryptionCount == 0) {
			if(stopFlag) {
				stopFlag = false;
			}//if//
			else if((stream.read() & 0xFF) != 0xF0) {
				throw new java.io.StreamCorruptedException("Error: Premature decryption completion.");
			}//else if//
		}//if//
	}//else//
}//decrypt()//
/* (non-Javadoc)
 * @see com.common.io.IInputStream#isDecrypting()
 */
public boolean isDecrypting() {
	return decryptionCount > 0;
}//isDecrypting()//
/* (non-Javadoc)
 * @see java.io.InputStream#read()
 */
public int read() throws IOException {
	int result = -1;

	if(!stopFlag) {
		if(decryptionCount > 0) {
			if(decryptedBufferOffset == decryptionLength) {
				refillBuffer();
			}//if//

			//The stop flag may be set when we refilled the buffer.//
			if(!stopFlag) {
				result = decryptedBuffer[decryptedBufferOffset++];
			}//if//
		}//if//
		else {
			result = stream.read();
		}//else//
	}//if//
	
	return result;
}//read()//
/* (non-Javadoc)
 * @see java.io.InputStream#read(byte[], int, int)
 */
public int read(byte[] buffer, int offset, int length) throws IOException {
	int result = -1;

	if(!stopFlag) {
		if(decryptionCount > 0) {
			result = 0;
			
			while((!stopFlag) && (result != length)) {
				int size = 0;
				
				if(decryptedBufferOffset == decryptionLength) {
					refillBuffer();
				}//if//

				//The stop flag may be set when we refilled the buffer.//
				if(!stopFlag) {
					size = decryptionLength - decryptedBufferOffset;

					if(size > length - result) {
						size = length - result;
					}//if//

					System.arraycopy(decryptedBuffer, decryptedBufferOffset, buffer, offset + result, size);
					result += size;
					decryptedBufferOffset += size;
				}//if//
			}//while//
			
			if(result == 0) {
				result = -1;
			}//if//
		}//if//
		else {
			result = stream.read(buffer, offset, length);
		}//else//
	}//if//
	
	return result;
}//read()//
/* (non-Javadoc)
 * @see com.common.io.IInputStream#read(java.io.OutputStream, int)
 */
public int read(java.io.OutputStream out, int length) throws IOException {
	int result = 0;
	byte[] bytes = new byte[length];

	result = stream.read(bytes, 0, bytes.length);
	out.write(bytes, 0, result);

	return result;
}//read()//
/* (non-Javadoc)
 * @see java.io.InputStream#read()
 */
private boolean refillBuffer() throws IOException {
	boolean result = !stopFlag;

	if(!stopFlag) {
		int flag = (stream.read() & 0xFF);
		
		if(flag == 0xF0) {
			//Sometimes a wrappering stream will try to buffer beyond the encrypted segment.  In such cases we will stop reading until the decryption flag is turned off.//
			stopFlag = true;
			result = false;
		}//if//
		else if(flag == 0xFF) {
			int size = StreamSupport.readInt(stream);
			int count = stream.read(encryptedBuffer, 0, size);
			
			if(count != size) {
				throw new IOException("Error: Invalid read length.");
			}//if//
			
			decryptionLength = decrypt(encryptedBuffer, 0, count, decryptedBuffer, 0);
			decryptedBufferOffset = 0;
		}//else if//
		else {
			throw new IOException("Stream corruption found while decrypting.");
		}//else//
	}//if//

	return result;
}//refillBuffer()//
}//CryptoInputStream//