Sesame-Server/Sources/App/DeviceManager.swift

import Foundation
import WebSocketKit
import Vapor
import Clairvoyant

final class DeviceManager {
    
    /// The connection to the device
    private var connection: WebSocket?
    
    /// The authentication token of the device for the socket connection
    private let deviceKey: Data
    
    /// The authentication token of the remote
    private let remoteKey: Data
    
    private let deviceTimeout: Int64
    
    private let deviceConnectedMetric: Metric<Bool>
    
    private let messagesToDeviceMetric: Metric<Int>
    
    let serverStatus: Metric<ServerStatus>
    
    var deviceIsConnected: Bool {
        guard let connection, !connection.isClosed else {
            return false
        }
        return true
    }
    
    /// A promise to finish the request once the device responds or times out
    private var requestInProgress: CheckedContinuation<Data, Error>?
    private var receivedMessageData: Data?
    
    var logger: Logger?
    
    private func printAndFlush(_ message: String) {
        logger?.notice(.init(stringLiteral: message))
    }
    
    init(deviceKey: Data, remoteKey: Data, deviceTimeout: Int64, serverStatus: Metric<ServerStatus>) {
        self.deviceKey = deviceKey
        self.remoteKey = remoteKey
        self.deviceTimeout = deviceTimeout
        self.deviceConnectedMetric = .init(
            "sesame.connected",
            name: "Device connection",
            description: "Shows if the device is connected via WebSocket")
        self.messagesToDeviceMetric = .init(
            "sesame.messages",
            name: "Forwarded Messages",
            description: "The number of messages transmitted to the device")
        self.serverStatus = serverStatus
    }

    func updateDeviceConnectionMetrics() async {
        let isConnected = deviceIsConnected
        _ = try? await serverStatus.update(isConnected ? .nominal : .reducedFunctionality)
        _ = try? await deviceConnectedMetric.update(isConnected)
    }
    
    private func updateMessageCountMetric() async {
        let lastValue = await messagesToDeviceMetric.lastValue()?.value ?? 0
        _ = try? await messagesToDeviceMetric.update(lastValue + 1)
    }
    
    // MARK: API
    
    func sendMessageToDevice(_ message: Data, authToken: Data, on eventLoop: EventLoop) async throws -> Data {
        guard message.count == SignedMessage.size else {
            throw MessageResult.invalidMessageSizeFromRemote
        }
        guard SHA256.hash(data: authToken) == remoteKey else {
            throw MessageResult.invalidServerAuthenticationFromRemote
        }
        guard let socket = connection, !socket.isClosed else {
            // Ensure that metric is updated
            didCloseDeviceSocket()
            throw MessageResult.deviceNotConnected
        }
        guard receivedMessageData == nil else {
            throw MessageResult.tooManyRequests
        }
        // Indicate that a message is in transit
        receivedMessageData = Data()
        do {
            try await socket.send(Array(message))
        } catch {
            throw MessageResult.deviceNotConnected
        }
        startTimeoutForDeviceRequest(on: eventLoop)
        
        // Check if a full message has already been received
        if let receivedMessageData, receivedMessageData.count == SignedMessage.size {
            self.receivedMessageData = nil
            return receivedMessageData
        }
        // Wait until a fill message is received, or a timeout occurs
        let result: Data = try await withCheckedThrowingContinuation { continuation in
            self.requestInProgress = continuation
        }
        await updateMessageCountMetric()
        return result
    }
    
    private func startTimeoutForDeviceRequest(on eventLoop: EventLoop) {
        eventLoop.scheduleTask(in: .seconds(deviceTimeout)) { [weak self] in
            guard let self else {
                log("[WARN] No reference to self after timeout of message")
                return
            }
            self.resumeDeviceRequest(with: .deviceTimedOut)
        }
    }
    
    private func resumeDeviceRequest(with data: Data) {
        guard let receivedMessageData else {
            log("[WARN] Received \(data.count) bytes after message completion")
            self.requestInProgress = nil
            return
        }
        let newData = receivedMessageData + data
        if newData.count < SignedMessage.size {
            // Wait for more data
            self.receivedMessageData = newData
            return
        }
        self.receivedMessageData = nil
        guard let requestInProgress else {
            log("[WARN] Received \(newData.count) bytes, but no continuation to resume")
            return
        }
        self.requestInProgress = nil
        guard newData.count == SignedMessage.size else {
            log("[WARN] Received \(newData.count) bytes, expected \(SignedMessage.size) for a message.")
            requestInProgress.resume(throwing: MessageResult.invalidMessageSizeFromDevice)
            return
        }
        requestInProgress.resume(returning: newData)
    }
    
    private func resumeDeviceRequest(with result: MessageResult) {
        guard let receivedMessageData else {
            self.requestInProgress = nil
            return
        }
        self.receivedMessageData = nil
        guard let requestInProgress else {
            log("[WARN] Request in progress (\(receivedMessageData.count) bytes), but no continuation found for result: \(result)")
            return
        }
        self.requestInProgress = nil
        requestInProgress.resume(throwing: result)
    }

    func authenticateRemote(_ token: Data) -> Bool {
        let hash = SHA256.hash(data: token)
        return hash == remoteKey
    }

    func processDeviceResponse(_ buffer: ByteBuffer) {
        guard let data = buffer.getData(at: 0, length: buffer.readableBytes) else {
            log("[WARN] Failed to get data buffer received from device")
            self.resumeDeviceRequest(with: .invalidMessageSizeFromDevice)
            return
        }
        self.resumeDeviceRequest(with: data)
    }
    
    func didCloseDeviceSocket() {
        connection = nil
        Task {
            await updateDeviceConnectionMetrics()
        }
    }
    
    func removeDeviceConnection() async {
        try? await connection?.close()
        connection = nil
        await updateDeviceConnectionMetrics()
    }
    
    func createNewDeviceConnection(socket: WebSocket, auth: String) async {
        guard let key = Data(fromHexEncodedString: auth),
              SHA256.hash(data: key) == self.deviceKey else {
            log("[WARN] Invalid device key while opening socket")
            try? await socket.close()
            return
        }
        await removeDeviceConnection()
        
        connection = socket
        socket.eventLoop.execute {
            socket.pingInterval = .seconds(10)
            
            socket.onText { [weak self] socket, text in
                self?.printAndFlush("[WARN] Received text over socket: \(text)")
                // Close connection to prevent spamming the log
                try? await socket.close()
                
                guard let self else {
                    log("[WARN] No reference to self to handle text over socket")
                    return
                }
                self.didCloseDeviceSocket()
            }
            
            socket.onBinary { [weak self] _, data in
                guard let self else {
                    log("[WARN] No reference to self to process binary data on socket")
                    return
                }
                self.processDeviceResponse(data)
            }
            
            socket.onClose.whenComplete { [weak self] _ in
                guard let self else {
                    log("[WARN] No reference to self to handle socket closing")
                    return
                }
                self.didCloseDeviceSocket()
            }
        }
        await updateDeviceConnectionMetrics()
    }
}