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/*
 *  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.
 */
/**
 * @author Alexander Y. Kleymenov
 */
package com.chimerapps.niddler.util;

import java.io.UnsupportedEncodingException;

final class Base64 {
	private Base64() {
	}

	public static byte[] decode(String in) {
		// Ignore trailing '=' padding and whitespace from the input.
		int limit = in.length();
		for (; limit > 0; limit--) {
			char c = in.charAt(limit - 1);
			if (c != '=' && c != '\n' && c != '\r' && c != ' ' && c != '\t') {
				break;
			}
		}

		// If the input includes whitespace, this output array will be longer than necessary.
		byte[] out = new byte[(int) (limit * 6L / 8L)];
		int outCount = 0;
		int inCount = 0;

		int word = 0;
		for (int pos = 0; pos < limit; pos++) {
			char c = in.charAt(pos);

			int bits;
			if (c >= 'A' && c <= 'Z') {
				// char ASCII value
				//  A    65    0
				//  Z    90    25 (ASCII - 65)
				bits = c - 65;
			} else if (c >= 'a' && c <= 'z') {
				// char ASCII value
				//  a    97    26
				//  z    122   51 (ASCII - 71)
				bits = c - 71;
			} else if (c >= '0' && c <= '9') {
				// char ASCII value
				//  0    48    52
				//  9    57    61 (ASCII + 4)
				bits = c + 4;
			} else if (c == '+' || c == '-') {
				bits = 62;
			} else if (c == '/' || c == '_') {
				bits = 63;
			} else if (c == '\n' || c == '\r' || c == ' ' || c == '\t') {
				continue;
			} else {
				return null;
			}

			// Append this char's 6 bits to the word.
			word = (word << 6) | (byte) bits;

			// For every 4 chars of input, we accumulate 24 bits of output. Emit 3 bytes.
			inCount++;
			if (inCount % 4 == 0) {
				out[outCount++] = (byte) (word >> 16);
				out[outCount++] = (byte) (word >> 8);
				out[outCount++] = (byte) word;
			}
		}

		int lastWordChars = inCount % 4;
		if (lastWordChars == 1) {
			// We read 1 char followed by "===". But 6 bits is a truncated byte! Fail.
			return null;
		} else if (lastWordChars == 2) {
			// We read 2 chars followed by "==". Emit 1 byte with 8 of those 12 bits.
			word = word << 12;
			out[outCount++] = (byte) (word >> 16);
		} else if (lastWordChars == 3) {
			// We read 3 chars, followed by "=". Emit 2 bytes for 16 of those 18 bits.
			word = word << 6;
			out[outCount++] = (byte) (word >> 16);
			out[outCount++] = (byte) (word >> 8);
		}

		// If we sized our out array perfectly, we're done.
		if (outCount == out.length) {
			return out;
		}

		// Copy the decoded bytes to a new, right-sized array.
		byte[] prefix = new byte[outCount];
		System.arraycopy(out, 0, prefix, 0, outCount);
		return prefix;
	}

	private static final byte[] MAP = new byte[]{
			'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
			'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
			'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
			'5', '6', '7', '8', '9', '+', '/'
	};

	private static final byte[] URL_MAP = new byte[]{
			'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S',
			'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l',
			'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', '0', '1', '2', '3', '4',
			'5', '6', '7', '8', '9', '-', '_'
	};

	public static String encode(byte[] in) {
		return encode(in, MAP);
	}

	public static String encodeUrl(byte[] in) {
		return encode(in, URL_MAP);
	}

	private static String encode(byte[] in, byte[] map) {
		int length = (in.length + 2) / 3 * 4;
		byte[] out = new byte[length];
		int index = 0, end = in.length - in.length % 3;
		for (int i = 0; i < end; i += 3) {
			out[index++] = map[(in[i] & 0xff) >> 2];
			out[index++] = map[((in[i] & 0x03) << 4) | ((in[i + 1] & 0xff) >> 4)];
			out[index++] = map[((in[i + 1] & 0x0f) << 2) | ((in[i + 2] & 0xff) >> 6)];
			out[index++] = map[(in[i + 2] & 0x3f)];
		}
		switch (in.length % 3) {
			case 1:
				out[index++] = map[(in[end] & 0xff) >> 2];
				out[index++] = map[(in[end] & 0x03) << 4];
				out[index++] = '=';
				out[index++] = '=';
				break;
			case 2:
				out[index++] = map[(in[end] & 0xff) >> 2];
				out[index++] = map[((in[end] & 0x03) << 4) | ((in[end + 1] & 0xff) >> 4)];
				out[index++] = map[((in[end + 1] & 0x0f) << 2)];
				out[index++] = '=';
				break;
		}
		try {
			return new String(out, "US-ASCII");
		} catch (UnsupportedEncodingException e) {
			throw new AssertionError(e);
		}
	}
}