ServerClient1.swift

// This is our delegate protocol for everything that happens on the server
protocol ServerClient: class {
    func serverDidStart(_ server: Server)
    func serverDidEnd(_ server: Server)
    func server(_ server: Server, didReceive packet: Server.Packet)
}

// This is our server which will handle the socket connection with FreeCrypto socket service
class Server {

    // Our imaginary FreeCrypto service drops data in a dictionary
    struct Key {
        static let amount = "amount"
    }

    // A packet of data containing amount of crypto
    struct Packet {
        var amount: Int
    }

    weak var client: ServerClient?;

    // Connect to FreeCrypto socket service
    func start() {
        guard let client = client else { return }
        client.serverDidStart(self)
    }

    // Disconnect from FreeCrypto socket service
    func end() {
        guard let client = client else { return }
        client.serverDidEnd(self)
    }

    // Receive data from FreeCrypto socket service
    func didReceive(data: [String:Int]) {
        guard let client = client,
            let amount = data[Server.Key.amount] else { return }

        let packet = Packet(amount: amount)

        client.server(self, didReceive: packet)
    }
}

// This is our client of the FreeCrypto server, watching as the BTC rolls in.
class BitcoinWatcher: ServerClient {

    func serverDidStart(_ server: Server) {
        print("BTC here I come 😎")
    }

    func serverDidEnd(_ server: Server) {
        print("Where be my BTC 🤔")
    }

    func server(_ server: Server, didReceive packet: Server.Packet) {
        print("Yay received \(packet.amount) BTC 🔥")
    }
}

// Setting up the machinery
let server = Server()
let bitcoinWatcher = BitcoinWatcher()

// We need to set the bitcoin watcher as the client here to receive events
server.client = bitcoinWatcher

// Simulation of server events...
server.start()
server.didReceive(data:["amount":10])
server.end()

// Prints:
// BTC here I come 😎
// Yay received 10 BTC 🔥
// Where be my BTC 🤔