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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

namespace Plac {
	namespace V2 {
		public class ServerScanner : Object {
			/**
			 * Found a server.
			 *
			 * ServerScanner emits this signal everytime server returned discovery response:
			 * if a server A returned a response at t1 then returned again at t2, ServerScanner
			 * emits this signal twice (t1 and t2.)
			 */
			public signal void found(Server server);

			/**
			 * Scan has been aborted due to a socket error.
			 */
			public signal void scan_failed(GLib.Error error);

			private GLib.Cancellable? cancellable = null;

			public int64 read_timeout_us = 1000 * 1000 * 2;

			public ServerScanner() {
				Object();
			}

			public void start() {
				GLib.log("Plac", LEVEL_DEBUG, "Starting server scanner...");

				cancellable = new GLib.Cancellable();

				new GLib.Thread<void>("plac-server-scanner", () => {
					try {
						var socket = new GLib.Socket(IPV4, DATAGRAM, UDP);

						socket.set_timeout(3);

						var inet_addr = new GLib.InetAddress.from_bytes(Sood.DISCOVERY_MULTICAST_IPV4_ADDRESS, IPV4);
						var sock_addr = new GLib.InetSocketAddress(inet_addr, Sood.DISCOVERY_SERVER_UDP_PORT);

						while (true) {
							try {
								socket.send_to(sock_addr, (uint8[]) Sood.DISCOVERY_QUERY_PREBUILT, cancellable);

								GLib.log("Plac", LEVEL_DEBUG, "Sent discovery query");
							} catch (GLib.Error error) {
								if (error is GLib.IOError.CANCELLED) {
									return;
								}

								GLib.log("Plac", LEVEL_CRITICAL, "Failed to send discovery query: %s", error.message);

								var e = error.copy();
								GLib.Idle.add(() => {
									scan_failed(e);
									return false;
								});
								cancellable = null;
								return;
							}

							while (true) {
								try {
									GLib.SocketAddress addr;
									var bytes = socket.receive_bytes_from(out addr, 512, read_timeout_us, cancellable);

									if (!(addr is GLib.InetSocketAddress)) {
										GLib.log("Plac", LEVEL_WARNING, "Received discovery response from non-IP socket");
										continue;
									}

									Sood.DiscoveryResponse resp;
									var result = Sood.DiscoveryResponse.parse(out resp, (char[]) bytes.get_data());
									if (result != Sood.Result.OK) {
										GLib.log("Plac", LEVEL_WARNING, "Received malformed discovery response: %s", result.to_string());
										continue;
									}

									// String in Vala is null-terminated, without exception.
									// Using non null-terminated string or casting uint8[] to string
									// will result in out of bound reads. I found no function, class,
									// or language builtins for allocating null-terminated string from
									// non-null one. Slicing is the closest I got.
									var server = new Server(
										(GLib.InetSocketAddress) addr,
										resp.unique_id.slice(0, (long) resp.unique_id_len),
										resp.display_version.slice(0, (long) resp.display_version_len),
										resp.name.slice(0, (long) resp.name_len),
										resp.http_port
									);

									GLib.Idle.add(() => {
										found(server);
										return false;
									});
								} catch (GLib.Error error) {
									if (error is GLib.IOError.TIMED_OUT) {
										break;
									}

									if (error is GLib.IOError.CANCELLED) {
										return;
									}

									GLib.log("Plac", LEVEL_CRITICAL, "Failed to read discovery response: %s", error.message);
									cancellable = null;

									var e = error.copy();
									GLib.Idle.add(() => {
										scan_failed(e);
										return false;
									});
									return;
								}
							}
						}
					} catch (GLib.Error error) {
						GLib.log("Plac", LEVEL_CRITICAL, "Discovery aborted due to an error: %s", error.message);

						var e = error.copy();
						GLib.Idle.add(() => {
							scan_failed(e);
							return false;
						});
					}

					cancellable = null;
				});
			}

			public void stop() {
				GLib.log("Plac", LEVEL_DEBUG, "Stopping server scanner...");
				cancellable.cancel();
			}
		}
	}
}