conversations-classic-ios/ConversationsClassic/AppCore/AppStore.swift

// This file declare global state object for whole app
// and reducers/actions/middleware types. Core of app.
import Combine
import Foundation

typealias Stateable = Codable & Equatable
typealias AppStore = Store<AppState, AppAction>
typealias Reducer<State: Stateable, Action: Codable> = (inout State, Action) -> Void
typealias Middleware<State: Stateable, Action: Codable> = (State, Action) -> AnyPublisher<Action, Never>?

final class Store<State: Stateable, Action: Codable>: ObservableObject {
    // Fake variable for be able to trigger SwiftUI redraw after app state completely changed
    // this hack is needed because @Published wrapper sends signals on "willSet:"
    @Published private var dumbVar: UUID = .init()

    // State is read-only (changes only over reducers)
    private(set) var state: State {
        didSet {
            DispatchQueue.main.async { [weak self] in
                self?.dumbVar = UUID()
            }
        } // signal to SwiftUI only when new state did set
    }

    // Serial queue for performing any actions sequentially
    private let serialQueue = DispatchQueue(label: "im.narayana.conversations.classic.serial.queue", qos: .userInteractive)

    private let reducer: Reducer<State, Action>
    private let middlewares: [Middleware<State, Action>]
    private var middlewareCancellables: Set<AnyCancellable> = []

    // Init
    init(
        initialState: State,
        reducer: @escaping Reducer<State, Action>,
        middlewares: [Middleware<State, Action>] = []
    ) {
        state = initialState
        self.reducer = reducer
        self.middlewares = middlewares
    }

    // Run reducers/middlewares
    func dispatch(_ action: Action) {
        serialQueue.sync { [weak self] in
            guard let wSelf = self else { return }
            let newState = wSelf.dispatch(wSelf.state, action)
            wSelf.state = newState
        }
    }

    private func dispatch(_ currentState: State, _ action: Action) -> State {
        // Do reducing
        var startTime = CFAbsoluteTimeGetCurrent()
        var newState = currentState
        reducer(&newState, action)
        var timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
        if timeElapsed > 0.05 {
            #if DEBUG
                print(
                    """
                    --
                    (Ignore this warning ONLY in case, when execution is paused by your breakpoint)
                    🕐Execution time: \(timeElapsed)
                    ❌WARNING! Some reducers work too long! It will lead to issues in production build!
                    Because of execution each action is synchronous the any stuck will reduce performance dramatically.
                    Probably you need check which part of reducer/middleware should be async (wrapped with Futures, as example)
                    --
                    """
                )
            #else
            #endif
        }

        // Dispatch all middleware functions
        for middleware in middlewares {
            guard let middleware = middleware(newState, action) else {
                break
            }
            startTime = CFAbsoluteTimeGetCurrent()
            middleware
                .receive(on: DispatchQueue.main)
                .sink(receiveValue: dispatch)
                .store(in: &middlewareCancellables)
            timeElapsed = CFAbsoluteTimeGetCurrent() - startTime
            if timeElapsed > 0.05 {
                #if DEBUG
                    print(
                        """
                        --
                        (Ignore this warning ONLY in case, when execution is paused by your breakpoint)
                        🕐Execution time: \(timeElapsed)
                        ❌WARNING! Middleware work too long! It will lead to issues in production build!
                        Because of execution each action is synchronous the any stuck will reduce performance dramatically.
                        Probably you need check which part of reducer/middleware should be async (wrapped with Futures, as example)
                        --
                        """
                    )
                #else
                #endif
            }
        }

        return newState
    }
}