// 
// Copyright 2021 New Vector Ltd
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
//

import SwiftUI
import Combine
    
@available(iOS 14.0, *)
class TemplateRoomListViewModel: ObservableObject, TemplateRoomListViewModelProtocol {
    
    // MARK: - Properties
    
    // MARK: Private
    private let templateRoomListService: TemplateRoomListServiceProtocol
    private var cancellables = Set<AnyCancellable>()
    
    // MARK: Public
    @Published private(set) var viewState: TemplateRoomListViewState
    
    var completion: ((TemplateRoomListViewModelResult) -> Void)?
    
    // MARK: - Setup
    init(templateRoomListService: TemplateRoomListServiceProtocol, initialState: TemplateRoomListViewState? = nil) {
        self.templateRoomListService = templateRoomListService
        self.viewState = initialState ?? Self.defaultState(templateRoomListService: templateRoomListService)
        
        templateRoomListService.roomsSubject
            .map(TemplateRoomListStateAction.updateRooms)
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { [weak self] action in
                self?.dispatch(action:action)
            })
            .store(in: &cancellables)
    }
    
    private static func defaultState(templateRoomListService: TemplateRoomListServiceProtocol) -> TemplateRoomListViewState {
        return TemplateRoomListViewState(rooms: templateRoomListService.roomsSubject.value)
    }
    
    // MARK: - Public
    func process(viewAction: TemplateRoomListViewAction) {
        switch viewAction {
        case .cancel:
            cancel()
        case .done:
            done()
        }
    }
    
    // MARK: - Private
    /**
     Send state actions to mutate the state.
     */
    private func dispatch(action: TemplateRoomListStateAction) {
        Self.reducer(state: &self.viewState, action: action)
    }
    
    /**
     A redux style reducer, all modifications to state happen here. Receives a state and a state action and produces a new state.
     */
    private static func reducer(state: inout TemplateRoomListViewState, action: TemplateRoomListStateAction) {
        switch action {
        case .updateRooms(let rooms):
            state.rooms = rooms
        }
        UILog.debug("[TemplateRoomListViewModel] reducer with action \(action) produced state: \(state)")
    }
    
    private func done() {
        completion?(.done)
    }
    
    private func cancel() {
        completion?(.cancel)
    }
}