SideStore/SideStoreApp/Sources/Shared/Connections/Connection.swift

//
//  Connection.swift
//  AltKit
//
//  Created by Riley Testut on 6/1/20.
//  Copyright © 2020 Riley Testut. All rights reserved.
//

import Foundation
import Network
import SideKit
import os.log

public protocol SideConnection: Connection {
    func __send(_ data: Data, completionHandler: @escaping (Bool, Error?) -> Void)
    func __receiveData(expectedSize: Int, completionHandler: @escaping (Data?, Error?) -> Void)
}

public extension SideConnection {
    func send(_ data: Data, completionHandler: @escaping (Result<Void, ALTServerError>) -> Void) {
        __send(data) { success, error in
            let result = Result(success, error).mapError { (failure: Error) -> ALTServerError in
                guard let nwError = failure as? NWError else { return ALTServerError(failure) }
                return ALTServerError.lostConnection(underlyingError: nwError)
            }

            completionHandler(result)
        }
    }

    func receiveData(expectedSize: Int, completionHandler: @escaping (Result<Data, ALTServerError>) -> Void) {
        __receiveData(expectedSize: expectedSize) { data, error in
            let result = Result(data, error).mapError { (failure: Error) -> ALTServerError in
                guard let nwError = failure as? NWError else { return ALTServerError(failure) }
                return ALTServerError.lostConnection(underlyingError: nwError)
            }

            completionHandler(result)
        }
    }

    func send<T: Encodable>(_ response: T, shouldDisconnect: Bool = false, completionHandler: @escaping (Result<Void, ALTServerError>) -> Void) {
        func finish(_ result: Result<Void, ALTServerError>) {
            completionHandler(result)

            if shouldDisconnect {
                // Add short delay to prevent us from dropping connection too quickly.
                DispatchQueue.global().asyncAfter(deadline: .now() + 1.0) {
                    self.disconnect()
                }
            }
        }

        do {
            let data = try JSONEncoder().encode(response)
            let responseSize = withUnsafeBytes(of: Int32(data.count)) { Data($0) }

            send(responseSize) { result in
                switch result {
                case let .failure(error): finish(.failure(error))
                case .success:
                    self.send(data) { result in
                        switch result {
                        case let .failure(error): finish(.failure(error))
                        case .success: finish(.success(()))
                        }
                    }
                }
            }
        } catch {
            finish(.failure(.invalidResponse(underlyingError: error)))
        }
    }

    func receiveRequest(completionHandler: @escaping (Result<ServerRequest, ALTServerError>) -> Void) {
        let size = MemoryLayout<Int32>.size

        os_log("Receiving request size from connection: %@", type: .info , String(describing: self))
        receiveData(expectedSize: size) { result in
            do {
                let data = try result.get()

                let expectedSize = Int(data.withUnsafeBytes { $0.load(as: Int32.self) })
                print("Receiving request from connection: \(self)... (\(expectedSize) bytes)")

                self.receiveData(expectedSize: expectedSize) { result in
                    do {
                        let data = try result.get()
                        let request = try JSONDecoder().decode(ServerRequest.self, from: data)

						os_log("Received request: %@", type: .info , String(describing: request))
                        completionHandler(.success(request))
                    } catch {
                        completionHandler(.failure(ALTServerError(error)))
                    }
                }
            } catch {
                completionHandler(.failure(ALTServerError(error)))
            }
        }
    }
}