//
//  ServerMultiplex.swift
//  XIONControlPanel
//
//  Created by James Magahern on 3/14/20.
//  Copyright © 2020 XION. All rights reserved.
//

import Foundation

protocol ServerMultiplexDelegate
{
    func serverMultiplex(_ multiplex: ServerMultiplex, didAddDevices devices: [AnyDevice])
    func serverMultiplex(_ multiplex: ServerMultiplex, devicesStateChanged devices: [AnyDevice])
    func serverMultiplex(_ multiplex: ServerMultiplex, didReceiveAcknowledgementFromServer server: Server)
    func serverMultiplex(_ multiplex: ServerMultiplex, didEncounterError error: Error)
}

enum ServerMultiplexError : Error
{
    case unknownDevice
}

class ServerMultiplex
{
    public var delegate: ServerMultiplexDelegate?
    public private(set) var devices = Set<AnyDevice>()
    
    private var servers: [Server] = []
    public var numServers: Int { return servers.count }
    
    public func addServer(_ server: Server)
    {
        servers.append(server)
    }
    
    /// Returns a status that best represents the status of the whole group, as if it were one device
    public func groupConnectionStatus() -> ConnectionStatus
    {
        let relevancyRank: (ConnectionStatus) -> Int = { status in
            switch status {
            case .disconnected: return 0
            case .connected:    return 1
            case .connecting:   return 2
            case .error:        return 3
            }
        }
        
        var groupStatus = ConnectionStatus.connected
        servers.forEach { server in
            if relevancyRank(server.connectionStatus) > relevancyRank(groupStatus) {
                groupStatus = server.connectionStatus
            }
        }
        
        return groupStatus
    }
    
    public func toggleDeviceState(_ device: AnyDevice, state: DeviceState, completion: @escaping (Error?) -> Void)
    {
        if let server = (servers.first { $0.responsibleForDevice(device) }) {
            server.toggleDevice(device, state: state, completion: completion)
            
            // Update internal state
            if let index = devices.firstIndex(of: device) {
                devices[index].state = state
            }
        } else {
            completion(ServerMultiplexError.unknownDevice)
        }
    }
    
    public func refreshDevices()
    {
        self.servers.forEach { server in
            server.connect { error in
                if let error {
                    print("Multiplexer: error connecting server \(server): \(error)")
                }
            }
        }
        
        self.servers.forEach { (server: Server) in
            server.fetchDevices { (result: Result<[AnyDevice], Error>) in
                self.handleServerFetchResult(forServer: server, result: result)
            }
        }
    }
}

extension ServerMultiplex
{
    private func handleServerFetchResult(forServer server: Server, result: Result<[AnyDevice], Error>)
    {
        switch result {
        case .success(let devices):
            handleDevicesChanged(forServer: server, devicesChanged: devices)
        case .failure(let error):
            handleError(forServer: server, error: error)
        }
    }
    
    private func handleDevicesChanged(forServer server: Server, devicesChanged: [AnyDevice])
    {
        // First send server acknowledgement
        self.delegate?.serverMultiplex(self, didReceiveAcknowledgementFromServer: server)
        
        // Then, optionally notify about new devices or device state changes
        let newDevicesSet = Set<AnyDevice>(devicesChanged)
        let additions = newDevicesSet.subtracting(self.devices)
        let changed = newDevicesSet.filter { (device: AnyDevice) in
            if let existing = (devices.first { $0.hashValue == device.hashValue }) {
                return existing.state != device.state
            }
            
            return false
        }
        
        self.devices = self.devices.union(newDevicesSet)
        
        if additions.count > 0 {
            DispatchQueue.main.async {
                self.delegate?.serverMultiplex(self, didAddDevices: Array(additions))
            }
        }
        
        if changed.count > 0 {
            DispatchQueue.main.async {
                self.delegate?.serverMultiplex(self, devicesStateChanged: Array(changed))
            }
        }
    }
    
    private func handleError(forServer server: Server, error: Error)
    {
        DispatchQueue.main.async {
            self.delegate?.serverMultiplex(self, didEncounterError: error)
        }
    }
}