/**
 * 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.
 */

using System;

namespace Thrift.Protocol
{
	internal static class TBase64Utils
	{
		internal const string ENCODE_TABLE =
			"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

		internal static void encode(byte[] src, int srcOff, int len, byte[] dst,
								int dstOff)
		{
			dst[dstOff] = (byte)ENCODE_TABLE[(src[srcOff] >> 2) & 0x3F];
			if (len == 3)
			{
				dst[dstOff + 1] =
					(byte)ENCODE_TABLE[
						((src[srcOff] << 4) + (src[srcOff + 1] >> 4)) & 0x3F];
				dst[dstOff + 2] =
					(byte)ENCODE_TABLE[
						((src[srcOff + 1] << 2) + (src[srcOff + 2] >> 6)) & 0x3F];
				dst[dstOff + 3] =
					(byte)ENCODE_TABLE[src[srcOff + 2] & 0x3F];
			}
			else if (len == 2)
			{
				dst[dstOff + 1] =
					(byte)ENCODE_TABLE[
						((src[srcOff] << 4) + (src[srcOff + 1] >> 4)) & 0x3F];
				dst[dstOff + 2] =
					(byte)ENCODE_TABLE[(src[srcOff + 1] << 2) & 0x3F];

			}
			else
			{ // len == 1) {
				dst[dstOff + 1] =
					(byte)ENCODE_TABLE[(src[srcOff] << 4) & 0x3F];
			}
		}

		private static int[] DECODE_TABLE = {
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,62,-1,-1,-1,63,
			52,53,54,55,56,57,58,59,60,61,-1,-1,-1,-1,-1,-1,
			-1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9,10,11,12,13,14,
			15,16,17,18,19,20,21,22,23,24,25,-1,-1,-1,-1,-1,
			-1,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,
			41,42,43,44,45,46,47,48,49,50,51,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
			-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,-1,
		};

		internal static void decode(byte[] src, int srcOff, int len, byte[] dst,
								 int dstOff)
		{
			dst[dstOff] = (byte)
				((DECODE_TABLE[src[srcOff] & 0x0FF] << 2) |
				(DECODE_TABLE[src[srcOff + 1] & 0x0FF] >> 4));
			if (len > 2)
			{
				dst[dstOff + 1] = (byte)
					(((DECODE_TABLE[src[srcOff + 1] & 0x0FF] << 4) & 0xF0) |
					(DECODE_TABLE[src[srcOff + 2] & 0x0FF] >> 2));
				if (len > 3)
				{
					dst[dstOff + 2] = (byte)
						(((DECODE_TABLE[src[srcOff + 2] & 0x0FF] << 6) & 0xC0) |
						DECODE_TABLE[src[srcOff + 3] & 0x0FF]);
				}
			}
		}

	}
}
