using System;

using Org.BouncyCastle.Crypto.Parameters;
using Org.BouncyCastle.Crypto.Utilities;

namespace Org.BouncyCastle.Crypto.Engines
{
	/**
	* An XTEA engine.
	*/
	public class XteaEngine
		: IBlockCipher
	{
		private const int
			rounds		= 32,
			block_size	= 8,
//			key_size	= 16,
			delta		= unchecked((int) 0x9E3779B9);

		/*
		* the expanded key array of 4 subkeys
		*/
		private uint[] _S = new uint[4],
			_sum0 = new uint[32],
			_sum1 = new uint[32];
		private bool _initialised, _forEncryption;

		/**
		* Create an instance of the TEA encryption algorithm
		* and set some defaults
		*/
		public XteaEngine()
		{
			_initialised = false;
		}

		public string AlgorithmName
		{
			get { return "XTEA"; }
		}

		public bool IsPartialBlockOkay
		{
			get { return false; }
		}

		public int GetBlockSize()
		{
			return block_size;
		}

		/**
		* initialise
		*
		* @param forEncryption whether or not we are for encryption.
		* @param params the parameters required to set up the cipher.
		* @exception ArgumentException if the params argument is
		* inappropriate.
		*/
		public void Init(
			bool				forEncryption,
			ICipherParameters	parameters)
		{
			if (!(parameters is KeyParameter))
			{
				throw new ArgumentException("invalid parameter passed to TEA init - "
					+ parameters.GetType().FullName);
			}

			_forEncryption = forEncryption;
			_initialised = true;

			KeyParameter p = (KeyParameter) parameters;

			setKey(p.GetKey());
		}

		public int ProcessBlock(
			byte[]	inBytes,
			int		inOff,
			byte[]	outBytes,
			int		outOff)
		{
			if (!_initialised)
				throw new InvalidOperationException(AlgorithmName + " not initialised");

			if ((inOff + block_size) > inBytes.Length)
				throw new DataLengthException("input buffer too short");

			if ((outOff + block_size) > outBytes.Length)
				throw new DataLengthException("output buffer too short");

			return _forEncryption
				?	encryptBlock(inBytes, inOff, outBytes, outOff)
				:	decryptBlock(inBytes, inOff, outBytes, outOff);
		}

		public void Reset()
		{
		}

		/**
		* Re-key the cipher.
		*
		* @param  key  the key to be used
		*/
		private void setKey(
			byte[] key)
		{
			int i, j;
			for (i = j = 0; i < 4; i++,j+=4)
			{
				_S[i] = Pack.BE_To_UInt32(key, j);
			}

			for (i = j = 0; i < rounds; i++)
			{
				_sum0[i] = ((uint)j + _S[j & 3]);
				j += delta;
				_sum1[i] = ((uint)j + _S[j >> 11 & 3]);
			}
		}

		private int encryptBlock(
			byte[]  inBytes,
			int     inOff,
			byte[]  outBytes,
			int     outOff)
		{
			// Pack bytes into integers
			uint v0 = Pack.BE_To_UInt32(inBytes, inOff);
			uint v1 = Pack.BE_To_UInt32(inBytes, inOff + 4);

			for (int i = 0; i < rounds; i++)
			{
				v0 += ((v1 << 4 ^ v1 >> 5) + v1) ^ _sum0[i];
				v1 += ((v0 << 4 ^ v0 >> 5) + v0) ^ _sum1[i];
			}

			Pack.UInt32_To_BE(v0, outBytes, outOff);
			Pack.UInt32_To_BE(v1, outBytes, outOff + 4);

			return block_size;
		}

		private int decryptBlock(
			byte[]	inBytes,
			int		inOff,
			byte[]	outBytes,
			int		outOff)
		{
			// Pack bytes into integers
			uint v0 = Pack.BE_To_UInt32(inBytes, inOff);
			uint v1 = Pack.BE_To_UInt32(inBytes, inOff + 4);

			for (int i = rounds-1; i >= 0; i--)
			{
				v1  -= ((v0 << 4 ^ v0 >> 5) + v0) ^ _sum1[i];
				v0  -= ((v1 << 4 ^ v1 >> 5) + v1) ^ _sum0[i];
			}

			Pack.UInt32_To_BE(v0, outBytes, outOff);
			Pack.UInt32_To_BE(v1, outBytes, outOff + 4);

			return block_size;
		}
	}
}