zunda-bot/Sources/DiscordKit/GatewayClient.swift

import Foundation
#if canImport(FoundationNetworking)
import FoundationNetworking
#endif

actor GatewayClient {
    private var ws: URLSessionWebSocketTask
    private let token: String
    private(set) var open = false
    private var sequenceNum: Int? = nil
    private var sessionID: String? = nil
    private var resumeURL: URL? = nil
    private let intents: Intents
    private let gatewayURL: URL
    private var hbTask: Task<(), any Error>? = nil


    init(gatewayURL: URL, token: String, intents: Intents) {
        self.intents = intents
        self.token = token
        self.gatewayURL = gatewayURL
        let queryItems = [URLQueryItem(name: "v", value: "10"), URLQueryItem(name: "encoding", value: "json")]
        ws = URLSession.shared.webSocketTask(with: gatewayURL.appending(queryItems: queryItems))
    }

    func openConnection() async throws {
        ws.resume()
        try await setupHeartbeat()

        try await sendIdentify(intents: intents)
        guard case .ready(let readyMessage) = try await getMessage().d else { throw GatewayError.connectionFailure }
        open = true
        sessionID = readyMessage.session_id
        resumeURL = readyMessage.resume_gateway_url
    }

    func setupHeartbeat() async throws {
        guard case .hello(let helloMessage) = try await getMessage().d else { throw GatewayError.connectionFailure }

        self.hbTask = Task.detached { [self] in
            do {
                try await Task.sleep(for: .milliseconds(Int.random(in: 0...helloMessage.heartbeat_interval)))
                try await sendHeartbeat()

                while !Task.isCancelled {
                    try await Task.sleep(for: .milliseconds(helloMessage.heartbeat_interval))
                    try await sendHeartbeat()
                }
            } catch {
                print("Heartbeat task canceled")
            }
        }
    }

    func sendIdentify(intents: Intents) async throws {
        let payload = """
        {
          "op": 2,
          "d": {
            "token": "\(token)",
            "intents": \(intents.rawValue),
            "properties": {
              "os": "linux",
              "browser": "discordkit",
              "device": "discordkit"
            }
          }
        }
        """ // Im lazy
        try await ws.send(.string(payload))
    }

    func getMessage() async throws -> GatewayMessage {
        var strBuffer = ""
        var gwMessage: GatewayMessage? = nil
        let json = JSONDecoder()
        while gwMessage == nil {
            do {
                let wsMessage = try await ws.receive()
#if DEBUG
                //print(wsMessage)
#endif
                guard case .string(let str) = wsMessage else { throw GatewayError.invalidMessage }
                strBuffer.append(str)
                gwMessage = try json.decode(GatewayMessage.self, from: Data(strBuffer.utf8))
            } catch URLError.networkConnectionLost {
                self.open = false
                try await reconnect()
            } catch DecodingError.dataCorrupted {
                continue
            }
        }
        guard let gwMessage = gwMessage else { throw GatewayError.invalidMessage }
        sequenceNum = gwMessage.s ?? sequenceNum
        return gwMessage
    }

    private func reconnect() async throws {
        hbTask?.cancel()
        do {
            try await attemptResume()
        } catch {
            print(error)
            ws.cancel()
            let queryItems = [URLQueryItem(name: "v", value: "10"), URLQueryItem(name: "encoding", value: "json")]
            ws = URLSession.shared.webSocketTask(with: gatewayURL.appending(queryItems: queryItems))
            try await openConnection()
        }
    }

    private func attemptResume() async throws {
        guard
            ws.closeCode.rawValue != 4004 && ws.closeCode.rawValue < 4010,
            let resumeURL = resumeURL,
            let sessionID = sessionID,
            let sequenceNum = sequenceNum
        else {
            if let closeReason = ws.closeReason {
                throw GatewayError.disconected(code: ws.closeCode.rawValue, message: String(data: closeReason, encoding: .utf8))
            } else {
                throw GatewayError.disconected(code: ws.closeCode.rawValue, message: "unknown")
            }
        }
        ws.cancel()
        let queryItems = [URLQueryItem(name: "v", value: "10"), URLQueryItem(name: "encoding", value: "json")]
        ws = URLSession.shared.webSocketTask(with: resumeURL.appending(queryItems: queryItems))
        ws.resume()
        try await setupHeartbeat()

        let payload = """
        {
            "op": 6,
            "d": {
                "token": "\(token)",
                "session_id": "\(sessionID)",
                "seq": \(sequenceNum)
            }
        }
        """ // Im lazy
        try await ws.send(.string(payload))
        self.open = true
    }

    private func sendHeartbeat() async throws {
        guard self.open else { print("conn closed, skipping hb"); return }
        let hbMessage = "{\"op\":1,\"d\":\(sequenceNum == nil ? "null" : String(sequenceNum!))}"
        try await ws.send(.string(hbMessage))
    }

    var events: AsyncStream<GatewayPayload> {
        AsyncStream { [self] in
            var payload: GatewayPayload? = nil
            while payload == nil {
                do {
                    while await !self.open {
                        try await Task.sleep(for: .seconds(1))
                    }
                    let event = try await getMessage()
#if DEBUG
                    dump(event)
#endif
                    if event.op == 1 { try await sendHeartbeat() }
                    payload = event.d
                } catch {
                    print("Error listening to gateway: \(error)")
                }
            }
            return payload!
        }
    }

}

public enum GatewayError: Error {
    case invalidMessage
    case invalidOpcode
    case mismatchedOpcode
    case disconected(code: Int, message: String?)
    case connectionFailure
}