//
//  MAWebSocketClient.swift
//  Mobile Music Assistant
//
//  Created by Sven Hanold on 26.03.26.
//

import Foundation
import OSLog

private let logger = Logger(subsystem: "com.musicassistant.mobile", category: "WebSocket")

/// WebSocket client for Music Assistant server communication
@Observable
final class MAWebSocketClient {
    enum ConnectionState: Equatable {
        case disconnected
        case connecting
        case connected
        case reconnecting(attempt: Int)
        
        var description: String {
            switch self {
            case .disconnected: return "Disconnected"
            case .connecting: return "Connecting..."
            case .connected: return "Connected"
            case .reconnecting(let attempt): return "Reconnecting (attempt \(attempt))..."
            }
        }
    }
    
    enum ClientError: LocalizedError {
        case notConnected
        case invalidURL
        case timeout
        case serverError(String)
        case decodingError(Error)
        
        var errorDescription: String? {
            switch self {
            case .notConnected:
                return "Not connected to server"
            case .invalidURL:
                return "Invalid server URL"
            case .timeout:
                return "Request timeout"
            case .serverError(let message):
                return "Server error: \(message)"
            case .decodingError(let error):
                return "Failed to decode response: \(error.localizedDescription)"
            }
        }
    }
    
    // MARK: - Properties
    
    private(set) var connectionState: ConnectionState = .disconnected
    private var webSocketTask: URLSessionWebSocketTask?
    private let session: URLSession
    
    // Request-Response matching
    private var pendingRequests: [String: CheckedContinuation<MAResponse, Error>] = [:]
    private let requestQueue = DispatchQueue(label: "com.musicassistant.requests")
    
    // Event stream
    private var eventContinuation: AsyncStream<MAEvent>.Continuation?
    private(set) var eventStream: AsyncStream<MAEvent>
    
    // Reconnection
    private var reconnectTask: Task<Void, Never>?
    private var shouldReconnect = false
    private let maxReconnectDelay: TimeInterval = 30.0
    private let initialReconnectDelay: TimeInterval = 3.0
    
    // Configuration
    private var serverURL: URL?
    private var authToken: String?
    
    // MARK: - Initialization
    
    init() {
        let configuration = URLSessionConfiguration.default
        configuration.timeoutIntervalForRequest = 30
        configuration.timeoutIntervalForResource = 300
        self.session = URLSession(configuration: configuration)
        
        // Initialize event stream
        var continuation: AsyncStream<MAEvent>.Continuation?
        self.eventStream = AsyncStream { cont in
            continuation = cont
        }
        self.eventContinuation = continuation
    }
    
    deinit {
        disconnect()
    }
    
    // MARK: - Connection Management
    
    /// Connect to Music Assistant server
    func connect(serverURL: URL, authToken: String?) async throws {
        guard connectionState == .disconnected else {
            logger.info("Already connected or connecting")
            return
        }
        
        self.serverURL = serverURL
        self.authToken = authToken
        self.shouldReconnect = true
        
        try await performConnect()
    }
    
    private func performConnect() async throws {
        guard let serverURL else {
            throw ClientError.invalidURL
        }
        
        connectionState = .connecting
        logger.info("Connecting to \(serverURL.absoluteString)")
        
        // Build WebSocket URL (ws:// or wss://)
        var components = URLComponents(url: serverURL, resolvingAgainstBaseURL: false)!
        components.scheme = components.scheme == "https" ? "wss" : "ws"
        components.path = "/ws"
        
        guard let wsURL = components.url else {
            throw ClientError.invalidURL
        }
        
        logger.debug("WebSocket URL: \(wsURL.absoluteString)")
        
        let task = session.webSocketTask(with: URLRequest(url: wsURL))
        self.webSocketTask = task
        task.resume()
        
        do {
            // MA sends a server-info message immediately on connect; receive and discard it
            _ = try await task.receive()
            logger.debug("Received server info")
            
            // Send auth command and wait for confirmation
            if let authToken {
                try await performAuth(task: task, token: authToken)
                logger.info("Authenticated successfully")
            }
            
            // Now safe to start the regular message loop
            startReceiving()
            connectionState = .connected
            logger.info("Connected successfully")
            
        } catch {
            task.cancel(with: .goingAway, reason: nil)
            webSocketTask = nil
            connectionState = .disconnected
            throw error
        }
    }
    
    private func performAuth(task: URLSessionWebSocketTask, token: String) async throws {
        let messageId = UUID().uuidString
        let cmd = MACommand(
            messageId: messageId,
            command: "auth",
            args: ["token": AnyCodable(token)]
        )
        let data = try JSONEncoder().encode(cmd)
        guard let json = String(data: data, encoding: .utf8) else {
            throw ClientError.decodingError(NSError(domain: "Encoding", code: -1))
        }
        
        try await task.send(.string(json))
        
        // Receive the auth response
        let result = try await task.receive()
        guard case .string(let responseText) = result,
              let responseData = responseText.data(using: .utf8) else {
            throw ClientError.serverError("Invalid auth response format")
        }
        
        if let response = try? JSONDecoder().decode(MAResponse.self, from: responseData),
           let errorCode = response.errorCode {
            throw ClientError.serverError(response.details ?? "Authentication failed (code \(errorCode))")
        }
        // Non-error response means auth succeeded
    }
    
    /// Disconnect from server
    func disconnect() {
        logger.info("Disconnecting")
        shouldReconnect = false
        reconnectTask?.cancel()
        reconnectTask = nil

        // Nil out BEFORE cancel so any in-flight receive callbacks see nil and exit early
        let task = webSocketTask
        webSocketTask = nil
        connectionState = .disconnected
        task?.cancel(with: .goingAway, reason: nil)

        // Cancel all pending requests
        requestQueue.sync {
            for (_, continuation) in pendingRequests {
                continuation.resume(throwing: ClientError.notConnected)
            }
            pendingRequests.removeAll()
        }

        eventContinuation?.finish()
    }
    
    // MARK: - Message Receiving
    
    private func startReceiving() {
        guard let task = webSocketTask else { return }

        task.receive { [weak self] result in
            guard let self else { return }

            switch result {
            case .success(let message):
                self.handleMessage(message)
                // Only continue if we are still connected to this same task
                if self.webSocketTask === task {
                    self.startReceiving()
                }

            case .failure(let error):
                // URLError.cancelled is expected during a clean disconnect — not a real error
                let nsError = error as NSError
                guard nsError.code != URLError.cancelled.rawValue else { return }
                logger.error("WebSocket receive error: \(error.localizedDescription)")
                self.handleDisconnection()
            }
        }
    }
    
    private func handleMessage(_ message: URLSessionWebSocketTask.Message) {
        guard case .string(let text) = message else {
            logger.warning("Received non-text message")
            return
        }
        
        guard let data = text.data(using: .utf8) else {
            logger.error("Failed to convert message to data")
            return
        }
        
        // Try to decode as response (has message_id)
        if let response = try? JSONDecoder().decode(MAResponse.self, from: data),
           let messageId = response.messageId {
            handleResponse(messageId: messageId, response: response)
            return
        }
        
        // Try to decode as event
        if let event = try? JSONDecoder().decode(MAEvent.self, from: data) {
            handleEvent(event)
            return
        }
        
        logger.warning("Received unknown message format: \(text)")
    }
    
    private func handleResponse(messageId: String, response: MAResponse) {
        requestQueue.sync {
            guard let continuation = pendingRequests.removeValue(forKey: messageId) else {
                logger.warning("Received response for unknown message ID: \(messageId)")
                return
            }
            
            // Check for error
            if let errorCode = response.errorCode {
                let errorMsg = response.details ?? "Error code: \(errorCode)"
                logger.error("Server error \(errorCode) for message \(messageId): \(errorMsg)")
                continuation.resume(throwing: ClientError.serverError(errorMsg))
            } else {
                continuation.resume(returning: response)
            }
        }
    }
    
    private func handleEvent(_ event: MAEvent) {
        logger.debug("Received event: \(event.event)")
        eventContinuation?.yield(event)
    }
    
    private func handleDisconnection() {
        // Idempotency guard — can be called from receive callback and disconnect() simultaneously
        guard connectionState != .disconnected else { return }

        connectionState = .disconnected
        let task = webSocketTask
        webSocketTask = nil
        task?.cancel(with: .goingAway, reason: nil)

        // Cancel pending requests
        requestQueue.sync {
            for (_, continuation) in pendingRequests {
                continuation.resume(throwing: ClientError.notConnected)
            }
            pendingRequests.removeAll()
        }

        // Attempt reconnection if needed
        if shouldReconnect {
            scheduleReconnect(attempt: 1)
        }
    }
    
    // MARK: - Reconnection
    
    private func scheduleReconnect(attempt: Int) {
        connectionState = .reconnecting(attempt: attempt)
        
        // Exponential backoff: 3s, 10s, 30s, 30s, ...
        let delay = min(
            initialReconnectDelay * pow(2.0, Double(attempt - 1)),
            maxReconnectDelay
        )
        
        logger.info("Scheduling reconnect attempt \(attempt) in \(delay)s")
        
        reconnectTask = Task {
            try? await Task.sleep(for: .seconds(delay))
            
            guard !Task.isCancelled, shouldReconnect else { return }
            
            do {
                try await performConnect()
            } catch {
                logger.error("Reconnect attempt \(attempt) failed: \(error.localizedDescription)")
                scheduleReconnect(attempt: attempt + 1)
            }
        }
    }
    
    // MARK: - Sending Commands
    
    /// Send a command and wait for response
    func sendCommand(
        _ command: String,
        args: [String: Any]? = nil
    ) async throws -> MAResponse {
        guard webSocketTask != nil, connectionState == .connected else {
            throw ClientError.notConnected
        }
        
        let messageId = UUID().uuidString
        
        // Convert args to AnyCodable
        let encodableArgs = args?.mapValues { AnyCodable($0) }
        
        let cmd = MACommand(
            messageId: messageId,
            command: command,
            args: encodableArgs
        )
        
        let data = try JSONEncoder().encode(cmd)
        guard let json = String(data: data, encoding: .utf8) else {
            throw ClientError.decodingError(NSError(domain: "Encoding", code: -1))
        }
        
        logger.debug("Sending command: \(command) (ID: \(messageId)) payload: \(json)")
        
        // Send message and wait for response
        return try await withCheckedThrowingContinuation { continuation in
            requestQueue.sync {
                pendingRequests[messageId] = continuation
            }
            
            webSocketTask?.send(.string(json)) { [weak self] error in
                if let error {
                    self?.requestQueue.sync {
                        _ = self?.pendingRequests.removeValue(forKey: messageId)
                    }
                    continuation.resume(throwing: error)
                }
            }
            
            // Timeout after 30 seconds
            Task {
                try? await Task.sleep(for: .seconds(30))
                self.requestQueue.sync {
                    if let cont = self.pendingRequests.removeValue(forKey: messageId) {
                        cont.resume(throwing: ClientError.timeout)
                    }
                }
            }
        }
    }
    
    /// Convenience method to send command and decode result
    func sendCommand<T: Decodable>(
        _ command: String,
        args: [String: Any]? = nil,
        resultType: T.Type
    ) async throws -> T {
        let response = try await sendCommand(command, args: args)
        
        guard let result = response.result else {
            throw ClientError.serverError("No result in response")
        }
        
        do {
            // Debug: Log the raw result before decoding
            if let jsonData = try? JSONEncoder().encode(result),
               let jsonString = String(data: jsonData, encoding: .utf8) {
                logger.debug("📦 Response result for '\(command)': \(jsonString)")
            }
            
            return try result.decode(as: T.self)
        } catch {
            logger.error("❌ Failed to decode result for '\(command)': \(error.localizedDescription)")
            
            // Log more details about the decoding error
            if let decodingError = error as? DecodingError {
                switch decodingError {
                case .dataCorrupted(let context):
                    logger.error("Data corrupted: \(context.debugDescription)")
                case .keyNotFound(let key, let context):
                    logger.error("Key '\(key.stringValue)' not found: \(context.debugDescription)")
                case .typeMismatch(let type, let context):
                    logger.error("Type mismatch for \(type): \(context.debugDescription)")
                case .valueNotFound(let type, let context):
                    logger.error("Value not found for \(type): \(context.debugDescription)")
                @unknown default:
                    logger.error("Unknown decoding error")
                }
            }
            
            throw ClientError.decodingError(error)
        }
    }
}