// 
// 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 TemplateUserProfileViewModel: ObservableObject, TemplateUserProfileViewModelProtocol {
    
    // MARK: - Properties
    
    // MARK: Private
    private let templateUserProfileService: TemplateUserProfileServiceProtocol
    private var cancellables = Set<AnyCancellable>()
    
    // MARK: Public
    @Published private(set) var viewState: TemplateUserProfileViewState
    
    var completion: ((TemplateUserProfileViewModelResult) -> Void)?
    
    // MARK: - Setup
    init(templateUserProfileService: TemplateUserProfileServiceProtocol, initialState: TemplateUserProfileViewState? = nil) {
        self.templateUserProfileService = templateUserProfileService
        self.viewState = initialState ?? Self.defaultState(templateUserProfileService: templateUserProfileService)
        
        templateUserProfileService.presenceSubject
            .map(TemplateUserProfileStateAction.updatePresence)
            .receive(on: DispatchQueue.main)
            .sink(receiveValue: { [weak self] action in
                self?.dispatch(action:action)
            })
            .store(in: &cancellables)
    }
    
    private static func defaultState(templateUserProfileService: TemplateUserProfileServiceProtocol) -> TemplateUserProfileViewState {
        return TemplateUserProfileViewState(
            avatar: templateUserProfileService.avatarData,
            displayName: templateUserProfileService.displayName,
            presence: templateUserProfileService.presenceSubject.value
        )
    }
    
    // MARK: - Public
    func process(viewAction: TemplateUserProfileViewAction) {
        switch viewAction {
        case .cancel:
            cancel()
        case .done:
            done()
        }
    }
    
    // MARK: - Private
    /// Send state actions to mutate the state.
    /// - Parameter action: The `TemplateUserProfileStateAction` to trigger the state change.
    private func dispatch(action: TemplateUserProfileStateAction) {
        Self.reducer(state: &self.viewState, action: action)
    }
      
    /// A redux style reducer
    ///
    /// All modifications to state happen here.
    /// - Parameters:
    ///   - state: The `inout` state to be modified,
    ///   - action: The action that defines which state modification should take place.
    private static func reducer(state: inout TemplateUserProfileViewState, action: TemplateUserProfileStateAction) {
        switch action {
        case .updatePresence(let presence):
            state.presence = presence
        }
        UILog.debug("[TemplateUserProfileViewModel] reducer with action \(action) produced state: \(state)")
    }
    
    private func done() {
        completion?(.done)
    }
    
    private func cancel() {
        completion?(.cancel)
    }
}