//
//  ModelHanlderPublisher.swift
//  VDS
//
//  Created by Matt Bruce on 8/12/22.
//

import Foundation
import Combine

extension Publishers {
    public struct ModelHandlerPublisher<ModelHandlerType: ModelHandlerable>: Publisher {
        
        public typealias Output = ModelHandlerType.ModelType
        public typealias Failure = Never

        private let modelHandler: ModelHandlerType

        public init(modelHandler: ModelHandlerType) { self.modelHandler = modelHandler }

        public func receive<S>(subscriber: S) where S : Subscriber, Never == S.Failure, ModelHandlerType.ModelType == S.Input {
            let subscription = ModelHandlerSubscription(subscriber: subscriber, modelHandler: modelHandler)
            subscriber.receive(subscription: subscription)
        }
    }

    public class ModelHandlerSubscription<S: Subscriber, ModelHandlerType: ModelHandlerable>: Subscription where S.Input == ModelHandlerType.ModelType, S.Failure == Never {

        private var subscriber: S?
        private var modelHandler: ModelHandlerType?
        public var subscribers = Set<AnyCancellable>()
        public init(subscriber: S, modelHandler: ModelHandlerType) {
            self.subscriber = subscriber
            self.modelHandler = modelHandler
            subscribe()
        }

        public func request(_ demand: Subscribers.Demand) { }

        public func cancel() {
            subscriber = nil
            modelHandler = nil
        }
        
        private func subscribe() {
            guard let publisher = modelHandler?.modelPublisher else { return }
            
            publisher
                .debounce(for: .seconds(Constants.ModelStateDebounce), scheduler: RunLoop.main)
                .sink { [weak self] viewModel in
                    _ = self?.subscriber?.receive(viewModel)
                }
                .store(in: &subscribers)
        }
    }
}

extension ModelHandlerable {
    public func handlerPublisher() -> AnyPublisher<ModelType, Never> {
        return Publishers.ModelHandlerPublisher(modelHandler: self).eraseToAnyPublisher()
    }
    
    public func createBinding(with subject: CurrentValueSubject<ModelType, Never>, storeIn subscriptions: inout Set<AnyCancellable>) {
        handlerPublisher()
            .sink { (value) in
                subject.send(value)
            }
            .store(in: &subscriptions)
    }
}