/*
 * Copyright 2024-2025 OmniOne.
 *
 * Licensed 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.
 */

package org.omnione.did.sdk.utility.Encodings;
import java.io.UnsupportedEncodingException;

/**
 * Utilities for encoding and decoding the Base64 representation of binary data. See RFCs
 * <a href="http://www.ietf.org/rfc/rfc2045.txt">2045</a> and
 * <a href="http://www.ietf.org/rfc/rfc3548.txt">3548</a>.
 */
public class Base64 {

	/* package */static abstract class Coder {

		public byte[] output;

		public int op;

		/**
		 * @return the maximum number of bytes a call to process() could produce for the
		 * given number of input bytes. This may be an overestimate.
		 */
		public abstract int maxOutputSize(int len);

		/**
		 * Encode/decode another block of input data. this.output is provided by the
		 * caller, and must be big enough to hold all the coded data. On exit, this.opwill
		 * be set to the length of the coded data.
		 * @param finish true if this is the final call to process for this object. Will
		 * finalize the coder state and include any final bytes in the output.
		 * @return true if the input so far is good; false if some error has been detected
		 * in the input stream..
		 */
		public abstract boolean process(byte[] input, int offset, int len,
				boolean finish);

	}

	/* package */static class Decoder extends Coder {

		/**
		 * Lookup table for turning bytes into their position in the Base64 alphabet.
		 */
		private static final int DECODE[] = { -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, -2, -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, };

		/**
		 * Decode lookup table for the "web safe" variant (RFC 3548 sec. 4) where - and _
		 * replace + and /.
		 */
		private static final int DECODE_WEBSAFE[] = { -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,
				62, -1, -1, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, -1, -1, -1, -2, -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, 63, -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, };

		/** Non-data values in the DECODE arrays. */
		private static final int SKIP = -1;

		private static final int EQUALS = -2;

		/**
		 * States 0-3 are reading through the next input tuple. State 4 is having read one
		 * '=' and expecting exactly one more. State 5 is expecting no more data or
		 * padding characters in the input. State 6 is the error state; an error has been
		 * detected in the input and no future input can "fix" it.
		 */
		private int state; // state number (0 to 6)

		private int value;

		final private int[] alphabet;

		public Decoder(int flags, byte[] output) {
			this.output = output;

			alphabet = ((flags & URL_SAFE) == 0) ? DECODE : DECODE_WEBSAFE;
			state = 0;
			value = 0;
		}

		/**
		 * @return an overestimate for the number of bytes {@code len} bytes could decode
		 * to.
		 */
		@Override
		public int maxOutputSize(int len) {
			return len * 3 / 4 + 10;
		}

		/**
		 * Decode another block of input data.
		 * @return true if the state machine is still healthy. false if bad base-64 data
		 * has been detected in the input stream.
		 */
		@Override
		public boolean process(byte[] input, int offset, int len, boolean finish) {
			if (this.state == 6)
				return false;

			int p = offset;
			len += offset;

			// Using local variables makes the decoder about 12%
			// faster than if we manipulate the member variables in
			// the loop. (Even alphabet makes a measurable
			// difference, which is somewhat surprising to me since
			// the member variable is final.)
			int state = this.state;
			int value = this.value;
			int op = 0;
			final byte[] output = this.output;
			final int[] alphabet = this.alphabet;

			while (p < len) {
				// Try the fast path: we're starting a new tuple and the
				// next four bytes of the input stream are all data
				// bytes. This corresponds to going through states
				// 0-1-2-3-0. We expect to use this method for most of
				// the data.
				//
				// If any of the next four bytes of input are non-data
				// (whitespace, etc.), value will end up negative. (All
				// the non-data values in decode are small negative
				// numbers, so shifting any of them up and or'ing them
				// together will result in a value with its top bit set.)
				//
				// You can remove this whole block and the output should
				// be the same, just slower.
				if (state == 0) {
					while (p + 4 <= len && (value = ((alphabet[input[p] & 0xff] << 18)
							| (alphabet[input[p + 1] & 0xff] << 12)
							| (alphabet[input[p + 2] & 0xff] << 6)
							| (alphabet[input[p + 3] & 0xff]))) >= 0) {
						output[op + 2] = (byte) value;
						output[op + 1] = (byte) (value >> 8);
						output[op] = (byte) (value >> 16);
						op += 3;
						p += 4;
					}
					if (p >= len)
						break;
				}

				// The fast path isn't available -- either we've read a
				// partial tuple, or the next four input bytes aren't all
				// data, or whatever. Fall back to the slower state
				// machine implementation.

				int d = alphabet[input[p++] & 0xff];

				switch (state) {
				case 0:
					if (d >= 0) {
						value = d;
						++state;
					}
					else if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;

				case 1:
					if (d >= 0) {
						value = (value << 6) | d;
						++state;
					}
					else if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;

				case 2:
					if (d >= 0) {
						value = (value << 6) | d;
						++state;
					}
					else if (d == EQUALS) {
						// Emit the last (partial) output tuple;
						// expect exactly one more padding character.
						output[op++] = (byte) (value >> 4);
						state = 4;
					}
					else if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;

				case 3:
					if (d >= 0) {
						// Emit the output triple and return to state 0.
						value = (value << 6) | d;
						output[op + 2] = (byte) value;
						output[op + 1] = (byte) (value >> 8);
						output[op] = (byte) (value >> 16);
						op += 3;
						state = 0;
					}
					else if (d == EQUALS) {
						// Emit the last (partial) output tuple;
						// expect no further data or padding characters.
						output[op + 1] = (byte) (value >> 2);
						output[op] = (byte) (value >> 10);
						op += 2;
						state = 5;
					}
					else if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;

				case 4:
					if (d == EQUALS) {
						++state;
					}
					else if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;

				case 5:
					if (d != SKIP) {
						this.state = 6;
						return false;
					}
					break;
				}
			}

			if (!finish) {
				// We're out of input, but a future call could provide
				// more.
				this.state = state;
				this.value = value;
				this.op = op;
				return true;
			}

			// Done reading input. Now figure out where we are left in
			// the state machine and finish up.

			switch (state) {
			case 0:
				// Output length is a multiple of three. Fine.
				break;
			case 1:
				// Read one extra input byte, which isn't enough to
				// make another output byte. Illegal.
				this.state = 6;
				return false;
			case 2:
				// Read two extra input bytes, enough to emit 1 more
				// output byte. Fine.
				output[op++] = (byte) (value >> 4);
				break;
			case 3:
				// Read three extra input bytes, enough to emit 2 more
				// output bytes. Fine.
				output[op++] = (byte) (value >> 10);
				output[op++] = (byte) (value >> 2);
				break;
			case 4:
				// Read one padding '=' when we expected 2. Illegal.
				this.state = 6;
				return false;
			case 5:
				// Read all the padding '='s we expected and no more.
				// Fine.
				break;
			}

			this.state = state;
			this.op = op;
			return true;
		}

	}

	/* package */static class Encoder extends Coder {

		/**
		 * Emit a new line every this many output tuples. Corresponds to a 76-character
		 * line length (the maximum allowable according to
		 * <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>).
		 */
		public static final int LINE_GROUPS = 19;

		/**
		 * Lookup table for turning Base64 alphabet positions (6 bits) into output bytes.
		 */
		private static final byte ENCODE[] = { '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', '+', '/', };

		/**
		 * Lookup table for turning Base64 alphabet positions (6 bits) into output bytes.
		 */
		private static final byte ENCODE_WEBSAFE[] = { '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', '-', '_', };

		final private byte[] tail;

		/* package */int tailLen;

		private int count;

		final public boolean do_padding;

		final public boolean do_newline;

		final public boolean do_cr;

		final private byte[] alphabet;

		public Encoder(int flags, byte[] output) {
			this.output = output;

			do_padding = (flags & NO_PADDING) == 0;
			do_newline = (flags & NO_WRAP) == 0;
			do_cr = (flags & CRLF) != 0;
			alphabet = ((flags & URL_SAFE) == 0) ? ENCODE : ENCODE_WEBSAFE;

			tail = new byte[2];
			tailLen = 0;

			count = do_newline ? LINE_GROUPS : -1;
		}

		/**
		 * @return an overestimate for the number of bytes {@code len} bytes could encode
		 * to.
		 */
		@Override
		public int maxOutputSize(int len) {
			return len * 8 / 5 + 10;
		}

		@Override
		public boolean process(byte[] input, int offset, int len, boolean finish) {
			// Using local variables makes the encoder about 9% faster.
			final byte[] alphabet = this.alphabet;
			final byte[] output = this.output;
			int op = 0;
			int count = this.count;

			int p = offset;
			len += offset;
			int v = -1;

			// First we need to concatenate the tail of the previous call
			// with any input bytes available now and see if we can empty
			// the tail.

			switch (tailLen) {
			case 0:
				// There was no tail.
				break;

			case 1:
				if (p + 2 <= len) {
					// A 1-byte tail with at least 2 bytes of
					// input available now.
					v = ((tail[0] & 0xff) << 16) | ((input[p++] & 0xff) << 8)
							| (input[p++] & 0xff);
					tailLen = 0;
				}
				;
				break;

			case 2:
				if (p + 1 <= len) {
					// A 2-byte tail with at least 1 byte of input.
					v = ((tail[0] & 0xff) << 16) | ((tail[1] & 0xff) << 8)
							| (input[p++] & 0xff);
					tailLen = 0;
				}
				break;
			}

			if (v != -1) {
				output[op++] = alphabet[(v >> 18) & 0x3f];
				output[op++] = alphabet[(v >> 12) & 0x3f];
				output[op++] = alphabet[(v >> 6) & 0x3f];
				output[op++] = alphabet[v & 0x3f];
				if (--count == 0) {
					if (do_cr)
						output[op++] = '\r';
					output[op++] = '\n';
					count = LINE_GROUPS;
				}
			}

			// At this point either there is no tail, or there are fewer
			// than 3 bytes of input available.

			// The main loop, turning 3 input bytes into 4 output bytes on
			// each iteration.
			while (p + 3 <= len) {
				v = ((input[p] & 0xff) << 16) | ((input[p + 1] & 0xff) << 8)
						| (input[p + 2] & 0xff);
				output[op] = alphabet[(v >> 18) & 0x3f];
				output[op + 1] = alphabet[(v >> 12) & 0x3f];
				output[op + 2] = alphabet[(v >> 6) & 0x3f];
				output[op + 3] = alphabet[v & 0x3f];
				p += 3;
				op += 4;
				if (--count == 0) {
					if (do_cr)
						output[op++] = '\r';
					output[op++] = '\n';
					count = LINE_GROUPS;
				}
			}

			if (finish) {
				// Finish up the tail of the input. Note that we need to
				// consume any bytes in tail before any bytes
				// remaining in input; there should be at most two bytes
				// total.

				if (p - tailLen == len - 1) {
					int t = 0;
					v = ((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 4;
					tailLen -= t;
					output[op++] = alphabet[(v >> 6) & 0x3f];
					output[op++] = alphabet[v & 0x3f];
					if (do_padding) {
						output[op++] = '=';
						output[op++] = '=';
					}
					if (do_newline) {
						if (do_cr)
							output[op++] = '\r';
						output[op++] = '\n';
					}
				}
				else if (p - tailLen == len - 2) {
					int t = 0;
					v = (((tailLen > 1 ? tail[t++] : input[p++]) & 0xff) << 10)
							| (((tailLen > 0 ? tail[t++] : input[p++]) & 0xff) << 2);
					tailLen -= t;
					output[op++] = alphabet[(v >> 12) & 0x3f];
					output[op++] = alphabet[(v >> 6) & 0x3f];
					output[op++] = alphabet[v & 0x3f];
					if (do_padding) {
						output[op++] = '=';
					}
					if (do_newline) {
						if (do_cr)
							output[op++] = '\r';
						output[op++] = '\n';
					}
				}
				else if (do_newline && op > 0 && count != LINE_GROUPS) {
					if (do_cr)
						output[op++] = '\r';
					output[op++] = '\n';
				}

				assert tailLen == 0;
				assert p == len;
			}
			else {
				// Save the leftovers in tail to be consumed on the next
				// call to encodeInternal.

				if (p == len - 1) {
					tail[tailLen++] = input[p];
				}
				else if (p == len - 2) {
					tail[tailLen++] = input[p];
					tail[tailLen++] = input[p + 1];
				}
			}

			this.op = op;
			this.count = count;

			return true;
		}

	}

	/**
	 * Default values for encoder/decoder flags.
	 */
	public static final int DEFAULT = 0;

	/**
	 * Encoder flag bit to omit the padding '=' characters at the end of the output (if
	 * any).
	 */
	public static final int NO_PADDING = 1;

	/**
	 * Encoder flag bit to omit all line terminators (i.e., the output will be on one long
	 * line).
	 */
	public static final int NO_WRAP = 2;

	// --------------------------------------------------------
	// shared code
	// --------------------------------------------------------

	/**
	 * Encoder flag bit to indicate lines should be terminated with a CRLF pair instead of
	 * just an LF. Has no effect if {@code NO_WRAP} is specified as well.
	 */
	public static final int CRLF = 4;

	// --------------------------------------------------------
	// decoding
	// --------------------------------------------------------

	/**
	 * Encoder/decoder flag bit to indicate using the "URL and filename safe" variant of
	 * Base64 (see RFC 3548 section 4) where {@code -} and {@code _} are used in place of
	 * {@code +} and {@code /}.
	 */
	public static final int URL_SAFE = 8;

	/**
	 * Decode the Base64-encoded data in input and return the data in a new byte array.
	 *
	 * <p>
	 * The padding '=' characters at the end are considered optional, but if any are
	 * present, there must be the correct number of them.
	 * @param input the input array to decode
	 * @param flags controls certain features of the decoded output. Pass {@code DEFAULT}
	 * to decode standard Base64.
	 * @throws IllegalArgumentException if the input contains incorrect padding
	 */
	public static byte[] decode(byte[] input, int flags) {
		return decode(input, 0, input.length, flags);
	}

	/**
	 * Decode the Base64-encoded data in input and return the data in a new byte array.
	 *
	 * <p>
	 * The padding '=' characters at the end are considered optional, but if any are
	 * present, there must be the correct number of them.
	 * @param input the data to decode
	 * @param offset the position within the input array at which to start
	 * @param len the number of bytes of input to decode
	 * @param flags controls certain features of the decoded output. Pass {@code DEFAULT}
	 * to decode standard Base64.
	 * @throws IllegalArgumentException if the input contains incorrect padding
	 */
	public static byte[] decode(byte[] input, int offset, int len, int flags) {
		// Allocate space for the most data the input could represent.
		// (It could contain less if it contains whitespace, etc.)
		Decoder decoder = new Decoder(flags, new byte[len * 3 / 4]);

		if (!decoder.process(input, offset, len, true)) {
			throw new IllegalArgumentException("bad base-64");
		}

		// Maybe we got lucky and allocated exactly enough output space.
		if (decoder.op == decoder.output.length) {
			return decoder.output;
		}

		// Need to shorten the array, so allocate a new one of the
		// right size and copy.
		byte[] temp = new byte[decoder.op];
		System.arraycopy(decoder.output, 0, temp, 0, decoder.op);
		return temp;
	}

	// --------------------------------------------------------
	// encoding
	// --------------------------------------------------------

	/**
	 * Decode the Base64-encoded data in input and return the data in a new byte array.
	 *
	 * <p>
	 * The padding '=' characters at the end are considered optional, but if any are
	 * present, there must be the correct number of them.
	 * @param str the input String to decode, which is converted to bytes using the
	 * default charset
	 * @param flags controls certain features of the decoded output. Pass {@code DEFAULT}
	 * to decode standard Base64.
	 * @throws IllegalArgumentException if the input contains incorrect padding
	 */
	public static byte[] decode(String str, int flags) {
		return decode(str.getBytes(), flags);
	}

	/**
	 * Base64-encode the given data and return a newly allocated byte[] with the result.
	 * @param input the data to encode
	 * @param flags controls certain features of the encoded output. Passing
	 * {@code DEFAULT} results in output that adheres to RFC 2045.
	 */
	public static byte[] encode(byte[] input, int flags) {
		return encode(input, 0, input.length, flags);
	}

	/**
	 * Base64-encode the given data and return a newly allocated byte[] with the result.
	 * @param input the data to encode
	 * @param offset the position within the input array at which to start
	 * @param len the number of bytes of input to encode
	 * @param flags controls certain features of the encoded output. Passing
	 * {@code DEFAULT} results in output that adheres to RFC 2045.
	 */
	public static byte[] encode(byte[] input, int offset, int len, int flags) {
		Encoder encoder = new Encoder(flags, null);

		// Compute the exact length of the array we will produce.
		int output_len = len / 3 * 4;

		// Account for the tail of the data and the padding bytes, if any.
		if (encoder.do_padding) {
			if (len % 3 > 0) {
				output_len += 4;
			}
		}
		else {
			switch (len % 3) {
			case 0:
				break;
			case 1:
				output_len += 2;
				break;
			case 2:
				output_len += 3;
				break;
			}
		}

		// Account for the newlines, if any.
		if (encoder.do_newline && len > 0) {
			output_len += (((len - 1) / (3 * Encoder.LINE_GROUPS)) + 1)
					* (encoder.do_cr ? 2 : 1);
		}

		encoder.output = new byte[output_len];
		encoder.process(input, offset, len, true);

		assert encoder.op == output_len;

		return encoder.output;
	}

	/**
	 * Base64-encode the given data and return a newly allocated String with the result.
	 * @param input the data to encode
	 * @param flags controls certain features of the encoded output. Passing
	 * {@code DEFAULT} results in output that adheres to RFC 2045.
	 */
	public static String encodeToString(byte[] input, int flags) {
		try {
			return new String(encode(input, flags), "US-ASCII");
		}
		catch (UnsupportedEncodingException e) {
			// US-ASCII is guaranteed to be available.
			throw new AssertionError(e);
		}
	}

	public static String encodeUrlString(byte[] input) {
		String output = Base64.encodeToString(input,
				Base64.URL_SAFE | Base64.NO_WRAP | Base64.NO_PADDING);

		return output;
	}

	public static byte[] decodeUrl(String input) {
		byte[] output = Base64.decode(input, Base64.URL_SAFE);

		return output;
	}

}
