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// Copyright 2025 Shota FUJI
//
// 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.
//
// SPDX-License-Identifier: Apache-2.0

using GLib;

namespace Sood {
	public errordomain ParseError {
		SIGNATURE_MISMATCH,
		INVALID_HEADER_SIZE,
		INVALID_PROPERTY_KEY,
		INVALID_PROPERTY_VALUE,
		DUPLICATED_PROPERTY_KEY,
	}

	public enum Kind {
		UNKNOWN = 0,
		QUERY = 1,
		RESPONSE = 2;

		internal static Kind from_byte(uint8 byte) {
			switch (byte) {
			case 'Q':
				return QUERY;
			case 'R':
				return RESPONSE;
			default:
				return UNKNOWN;
			}
		}
	}

	public const uint8[] discovery_query = {
		'S', 'O', 'O', 'D', 2, 'Q',
		16,
		// query_service_id
		'q', 'u', 'e', 'r', 'y', '_', 's', 'e', 'r', 'v', 'i', 'c', 'e', '_', 'i', 'd',
		0, 36,
		// 00720724-5143-4a9b-abac-0e50cba674bb
		'0', '0', '7', '2', '0', '7', '2', '4', '-',
		'5', '1', '4', '3', '-',
		'4', 'a', '9', 'b', '-',
		'a', 'b', 'a', 'c', '-',
		'0', 'e', '5', '0', 'c', 'b', 'a', '6', '7', '4', 'b', 'b'
	};

	private const uint8[] signature = { 'S', 'O', 'O', 'D', 2 };

	public class Message : Object {
		public Kind kind { get; set construct; }
		public Gee.HashMap<string, string> properties { get; construct; }

		public Message.from_bytes(Bytes bytes) throws ParseError {
			if (bytes.length < signature.length + 1) {
				throw new ParseError.INVALID_HEADER_SIZE("Too small header size, unlikely SOOD message.");
			}

			var properties = new Gee.HashMap<string, string>();

			int i = 0;
			for (; i < signature.length; i++) {
				if (bytes[i] != signature[i]) {
					throw new ParseError.SIGNATURE_MISMATCH("Message does not have valid SOOD signature.");
				}
			}

			var kind = Kind.from_byte(bytes[i]);
			i += 1;

			while (i < bytes.length) {
				var key = parse_property_key(bytes, ref i);

				if (i >= bytes.length) {
					throw new ParseError.INVALID_PROPERTY_VALUE("Property value is missing after key field.");
				}

				if (properties.has_key(key)) {
					throw new ParseError.DUPLICATED_PROPERTY_KEY("Found duplicated property.");
				}

				var value = parse_property_value(bytes, ref i);

				properties[key] = value;
			}

			Object(kind: kind, properties: properties);
		}

		private static string parse_property_key(Bytes bytes, ref int position) throws ParseError {
			var size = bytes[position];
			position += 1;
			if (size == 0) {
				throw new ParseError.INVALID_PROPERTY_KEY("Found property key of zero bytes.");
			}
			if ((position + size) > bytes.length) {
				throw new ParseError.INVALID_PROPERTY_KEY("Declared key size overflows byte array.");
			}

			var key = bytes.slice(position, position + size);
			for (int i = 0; i < key.length; i++) {
				if (key[i] == 0) {
					throw new ParseError.INVALID_PROPERTY_KEY("Property key contains NUL character.");
				}
			}
			var key_data = Bytes.unref_to_data(key);

			position += size;
			return "%.*s".printf(key_data.length, key_data);
		}

		private static string parse_property_value(Bytes bytes, ref int position) throws ParseError {
			// Size field is 16bit and value can be empty, so the minimum byte size is 2.
			if (position + 2 >= bytes.length) {
				throw new ParseError.INVALID_PROPERTY_VALUE("Property value size is corrupted.");
			}

			var size = uint16.from_big_endian(((uint16) bytes[position]) | ((uint16) (bytes[position + 1] << 8)));
			position += 2;
			if ((position + size) > bytes.length) {
				throw new ParseError.INVALID_PROPERTY_VALUE("Declared value size overflows byte array.");
			}

			var value = bytes.slice(position, position + size);
			for (int i = 0; i < value.length; i++) {
				if (value[i] == 0) {
					throw new ParseError.INVALID_PROPERTY_VALUE("Property value contains NUL character.");
				}
			}
			var value_data = Bytes.unref_to_data(value);

			position += size;
			return "%.*s".printf(value_data.length, value_data);
		}
	}
}