import Foundation
import Combine

/// Manages multiple Navidrome server connections with automatic failover.
/// When one server is unreachable (e.g. public domain on local WiFi),
/// it automatically tries the next server with the same credentials.
class ServerManager: ObservableObject {
    
    static let shared = ServerManager()
    
    @Published var servers: [ServerConfig] = []
    @Published var activeServer: ServerConfig?
    @Published var connectionState: ConnectionState = .disconnected
    @Published var lastFailoverMessage: String?
    
    private let storageKey = "navidrome_servers"
    private let activeServerKey = "navidrome_active_server"
    private var failoverTask: Task<Void, Never>?
    
    enum ConnectionState: Equatable {
        case disconnected
        case connecting
        case connected
        case error(String)
    }
    
    let client = SubsonicClient()
    
    private init() {
        loadServers()
    }
    
    // MARK: - Server CRUD
    
    func addServer(_ server: ServerConfig) {
        var srv = server
        srv.url = srv.url.trimmingCharacters(in: CharacterSet(charactersIn: "/"))
        servers.append(srv)
        saveServers()
    }
    
    func updateServer(_ server: ServerConfig) {
        if let idx = servers.firstIndex(where: { $0.id == server.id }) {
            servers[idx] = server
            saveServers()
            if activeServer?.id == server.id {
                activeServer = server
                client.currentServer = server
            }
        }
    }
    
    func removeServer(at offsets: IndexSet) {
        let removedIds = offsets.map { servers[$0].id }
        servers.remove(atOffsets: offsets)
        if let active = activeServer, removedIds.contains(active.id) {
            activeServer = servers.first
            client.currentServer = activeServer
        }
        saveServers()
    }
    
    func removeServer(_ server: ServerConfig) {
        servers.removeAll { $0.id == server.id }
        if activeServer?.id == server.id {
            activeServer = servers.first
            client.currentServer = activeServer
        }
        saveServers()
    }
    
    // MARK: - Connection with Auto-Failover
    
    /// Connects to a specific server. On failure, tries other servers
    /// with the same username (likely the same Navidrome instance).
    func connect(to server: ServerConfig) async -> Bool {
        await MainActor.run {
            connectionState = .connecting
            lastFailoverMessage = nil
        }
        
        // Try the requested server first
        if await tryConnect(server) {
            return true
        }
        
        // Failed — try other servers with same username (same Navidrome instance)
        let alternatives = servers.filter { $0.id != server.id && $0.username == server.username }
        for alt in alternatives {
            await MainActor.run {
                lastFailoverMessage = "Trying \(alt.name)..."
            }
            if await tryConnect(alt) {
                await MainActor.run {
                    lastFailoverMessage = "Connected via \(alt.name)"
                }
                return true
            }
        }
        
        // Also try servers with different usernames as last resort
        let others = servers.filter { $0.id != server.id && $0.username != server.username }
        for other in others {
            await MainActor.run {
                lastFailoverMessage = "Trying \(other.name)..."
            }
            if await tryConnect(other) {
                await MainActor.run {
                    lastFailoverMessage = "Connected via \(other.name)"
                }
                return true
            }
        }
        
        // All failed
        await MainActor.run {
            connectionState = .error("All servers unreachable")
            lastFailoverMessage = nil
        }
        return false
    }
    
    /// Low-level connect attempt with short timeout
    private func tryConnect(_ server: ServerConfig) async -> Bool {
        client.currentServer = server
        
        do {
            let ok = try await withTimeout(seconds: 5) {
                try await self.client.ping(server: server)
            }
            if ok {
                await MainActor.run {
                    self.activeServer = server
                    self.connectionState = .connected
                    self.client.isAuthenticated = true
                    self.saveActiveServer()
                }
                return true
            }
        } catch {
            // Connection failed — will try next
        }
        return false
    }
    
    /// Timeout wrapper for network calls
    private func withTimeout<T>(seconds: TimeInterval, operation: @escaping () async throws -> T) async throws -> T {
        try await withThrowingTaskGroup(of: T.self) { group in
            group.addTask {
                try await operation()
            }
            group.addTask {
                try await Task.sleep(nanoseconds: UInt64(seconds * 1_000_000_000))
                throw URLError(.timedOut)
            }
            let result = try await group.next()!
            group.cancelAll()
            return result
        }
    }
    
    func connectToActive() async {
        guard let server = activeServer else {
            // No active server — try all
            if let first = servers.first {
                _ = await connect(to: first)
            }
            return
        }
        _ = await connect(to: server)
    }
    
    /// Called when an API request fails — triggers background failover
    func handleConnectionFailure() {
        guard failoverTask == nil else { return }
        failoverTask = Task {
            if let active = activeServer {
                _ = await connect(to: active)
            }
            failoverTask = nil
        }
    }
    
    func switchServer(_ server: ServerConfig) async -> Bool {
        return await connect(to: server)
    }
    
    func disconnect() {
        connectionState = .disconnected
        client.isAuthenticated = false
    }
    
    // MARK: - Persistence
    
    private func saveServers() {
        if let data = try? JSONEncoder().encode(servers) {
            UserDefaults.standard.set(data, forKey: storageKey)
        }
        syncToWatch()
    }
    
    private func saveActiveServer() {
        if let data = try? JSONEncoder().encode(activeServer) {
            UserDefaults.standard.set(data, forKey: activeServerKey)
        }
    }
    
    private func loadServers() {
        if let data = UserDefaults.standard.data(forKey: storageKey),
           let decoded = try? JSONDecoder().decode([ServerConfig].self, from: data) {
            servers = decoded
        }
        
        if let data = UserDefaults.standard.data(forKey: activeServerKey),
           let decoded = try? JSONDecoder().decode(ServerConfig.self, from: data) {
            activeServer = decoded
            client.currentServer = decoded
        } else {
            activeServer = servers.first
            client.currentServer = servers.first
        }
    }
    
    private func syncToWatch() {
        #if os(iOS)
        WatchConnectivityManager.shared.sendServersToWatch(servers)
        #endif
    }
}