using System;
using System.IO;

namespace Org.BouncyCastle.Utilities.Encoders
{
	public class Base64Encoder
		: IEncoder
	{
		protected readonly byte[] encodingTable =
		{
			(byte)'A', (byte)'B', (byte)'C', (byte)'D', (byte)'E', (byte)'F', (byte)'G',
			(byte)'H', (byte)'I', (byte)'J', (byte)'K', (byte)'L', (byte)'M', (byte)'N',
			(byte)'O', (byte)'P', (byte)'Q', (byte)'R', (byte)'S', (byte)'T', (byte)'U',
			(byte)'V', (byte)'W', (byte)'X', (byte)'Y', (byte)'Z',
			(byte)'a', (byte)'b', (byte)'c', (byte)'d', (byte)'e', (byte)'f', (byte)'g',
			(byte)'h', (byte)'i', (byte)'j', (byte)'k', (byte)'l', (byte)'m', (byte)'n',
			(byte)'o', (byte)'p', (byte)'q', (byte)'r', (byte)'s', (byte)'t', (byte)'u',
			(byte)'v',
			(byte)'w', (byte)'x', (byte)'y', (byte)'z',
			(byte)'0', (byte)'1', (byte)'2', (byte)'3', (byte)'4', (byte)'5', (byte)'6',
			(byte)'7', (byte)'8', (byte)'9',
			(byte)'+', (byte)'/'
		};

		protected byte padding = (byte)'=';

		/*
		* set up the decoding table.
		*/
		protected readonly byte[] decodingTable = new byte[128];

		protected void InitialiseDecodingTable()
		{
			for (int i = 0; i < encodingTable.Length; i++)
			{
				decodingTable[encodingTable[i]] = (byte)i;
			}
		}

		public Base64Encoder()
		{
			InitialiseDecodingTable();
		}

		/**
		* encode the input data producing a base 64 output stream.
		*
		* @return the number of bytes produced.
		*/
		public int Encode(
			byte[]	data,
			int		off,
			int		length,
			Stream	outStream)
		{
			int modulus = length % 3;
			int dataLength = (length - modulus);
			int a1, a2, a3;

			for (int i = off; i < off + dataLength; i += 3)
			{
				a1 = data[i] & 0xff;
				a2 = data[i + 1] & 0xff;
				a3 = data[i + 2] & 0xff;

				outStream.WriteByte(encodingTable[(int) ((uint) a1 >> 2) & 0x3f]);
				outStream.WriteByte(encodingTable[((a1 << 4) | (int) ((uint) a2 >> 4)) & 0x3f]);
				outStream.WriteByte(encodingTable[((a2 << 2) | (int) ((uint) a3 >> 6)) & 0x3f]);
				outStream.WriteByte(encodingTable[a3 & 0x3f]);
			}

			/*
			* process the tail end.
			*/
			int b1, b2, b3;
			int d1, d2;

			switch (modulus)
			{
				case 0:        /* nothing left to do */
					break;
				case 1:
					d1 = data[off + dataLength] & 0xff;
					b1 = (d1 >> 2) & 0x3f;
					b2 = (d1 << 4) & 0x3f;

					outStream.WriteByte(encodingTable[b1]);
					outStream.WriteByte(encodingTable[b2]);
					outStream.WriteByte(padding);
					outStream.WriteByte(padding);
					break;
				case 2:
					d1 = data[off + dataLength] & 0xff;
					d2 = data[off + dataLength + 1] & 0xff;

					b1 = (d1 >> 2) & 0x3f;
					b2 = ((d1 << 4) | (d2 >> 4)) & 0x3f;
					b3 = (d2 << 2) & 0x3f;

					outStream.WriteByte(encodingTable[b1]);
					outStream.WriteByte(encodingTable[b2]);
					outStream.WriteByte(encodingTable[b3]);
					outStream.WriteByte(padding);
					break;
			}

			return (dataLength / 3) * 4 + ((modulus == 0) ? 0 : 4);
		}

		private bool ignore(
			char c)
		{
			return (c == '\n' || c =='\r' || c == '\t' || c == ' ');
		}

		/**
		* decode the base 64 encoded byte data writing it to the given output stream,
		* whitespace characters will be ignored.
		*
		* @return the number of bytes produced.
		*/
		public int Decode(
			byte[]	data,
			int		off,
			int		length,
			Stream	outStream)
		{
			byte b1, b2, b3, b4;
			int outLen = 0;

			int end = off + length;

			while (end > off)
			{
				if (!ignore((char)data[end - 1]))
				{
					break;
				}

				end--;
			}

			int  i = off;
			int  finish = end - 4;

			i = nextI(data, i, finish);

			while (i < finish)
			{
				b1 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b2 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b3 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b4 = decodingTable[data[i++]];

				outStream.WriteByte((byte)((b1 << 2) | (b2 >> 4)));
				outStream.WriteByte((byte)((b2 << 4) | (b3 >> 2)));
				outStream.WriteByte((byte)((b3 << 6) | b4));

				outLen += 3;

				i = nextI(data, i, finish);
			}

			outLen += decodeLastBlock(outStream, (char)data[end - 4], (char)data[end - 3], (char)data[end - 2], (char)data[end - 1]);

			return outLen;
		}

		private int nextI(
			byte[]	data,
			int		i,
			int		finish)
		{
			while ((i < finish) && ignore((char)data[i]))
			{
				i++;
			}
			return i;
		}

		/**
		* decode the base 64 encoded string data writing it to the given output stream,
		* whitespace characters will be ignored.
		*
		* @return the number of bytes produced.
		*/
		public int DecodeString(
			string	data,
			Stream	outStream)
		{
			// Platform Implementation
//			byte[] bytes = Convert.FromBase64String(data);
//			outStream.Write(bytes, 0, bytes.Length);
//			return bytes.Length;

			byte b1, b2, b3, b4;
			int length = 0;

			int end = data.Length;

			while (end > 0)
			{
				if (!ignore(data[end - 1]))
				{
					break;
				}

				end--;
			}

			int  i = 0;
			int  finish = end - 4;

			i = nextI(data, i, finish);

			while (i < finish)
			{
				b1 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b2 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b3 = decodingTable[data[i++]];

				i = nextI(data, i, finish);

				b4 = decodingTable[data[i++]];

				outStream.WriteByte((byte)((b1 << 2) | (b2 >> 4)));
				outStream.WriteByte((byte)((b2 << 4) | (b3 >> 2)));
				outStream.WriteByte((byte)((b3 << 6) | b4));

				length += 3;

				i = nextI(data, i, finish);
			}

			length += decodeLastBlock(outStream, data[end - 4], data[end - 3], data[end - 2], data[end - 1]);

			return length;
		}

		private int decodeLastBlock(
			Stream	outStream,
			char	c1,
			char	c2,
			char	c3,
			char	c4)
		{
			if (c3 == padding)
			{
				byte b1 = decodingTable[c1];
				byte b2 = decodingTable[c2];

				outStream.WriteByte((byte)((b1 << 2) | (b2 >> 4)));

				return 1;
			}

			if (c4 == padding)
			{
				byte b1 = decodingTable[c1];
				byte b2 = decodingTable[c2];
				byte b3 = decodingTable[c3];

				outStream.WriteByte((byte)((b1 << 2) | (b2 >> 4)));
				outStream.WriteByte((byte)((b2 << 4) | (b3 >> 2)));

				return 2;
			}

			{
				byte b1 = decodingTable[c1];
				byte b2 = decodingTable[c2];
				byte b3 = decodingTable[c3];
				byte b4 = decodingTable[c4];

				outStream.WriteByte((byte)((b1 << 2) | (b2 >> 4)));
				outStream.WriteByte((byte)((b2 << 4) | (b3 >> 2)));
				outStream.WriteByte((byte)((b3 << 6) | b4));

				return 3;
			}
		}

		private int nextI(string data, int i, int finish)
		{
			while ((i < finish) && ignore(data[i]))
			{
				i++;
			}
			return i;
		}
	}
}
