//
//  FollowingListViewModel+State.swift
//  Mastodon
//
//  Created by Cirno MainasuK on 2021-11-2.
//

import os.log
import Foundation
import GameplayKit
import MastodonSDK

extension FollowingListViewModel {
    class State: GKState {
        
        let logger = Logger(subsystem: "FollowingListViewModel.State", category: "StateMachine")

        let id = UUID()
        
        weak var viewModel: FollowingListViewModel?
        
        init(viewModel: FollowingListViewModel) {
            self.viewModel = viewModel
        }
        
        override func didEnter(from previousState: GKState?) {
            super.didEnter(from: previousState)
            
            let from = previousState.flatMap { String(describing: $0) } ?? "nil"
            let to = String(describing: self)
            logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): \(from) -> \(to)")
        }
        
        @MainActor
        func enter(state: State.Type) {
            stateMachine?.enter(state)
        }
        
        deinit {
            logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): [\(self.id.uuidString)] \(String(describing: self))")
        }
    }
}

extension FollowingListViewModel.State {
    class Initial: FollowingListViewModel.State {
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            guard let viewModel = viewModel else { return false }
            switch stateClass {
            case is Reloading.Type:
                return viewModel.userID != nil
            default:
                return false
            }
        }
    }
    
    class Reloading: FollowingListViewModel.State {
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            switch stateClass {
            case is Loading.Type:
                return true
            default:
                return false
            }
        }
        
        override func didEnter(from previousState: GKState?) {
            super.didEnter(from: previousState)
            guard let viewModel = viewModel, let stateMachine = stateMachine else { return }
            
            // reset
            viewModel.userFetchedResultsController.userIDs = []
            
            stateMachine.enter(Loading.self)
        }
    }
    
    class Fail: FollowingListViewModel.State {
        
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            switch stateClass {
            case is Loading.Type:
                return true
            default:
                return false
            }
        }
        
        override func didEnter(from previousState: GKState?) {
            super.didEnter(from: previousState)
            guard let _ = viewModel, let stateMachine = stateMachine else { return }
            
            os_log(.info, log: .debug, "%{public}s[%{public}ld], %{public}s: retry loading 3s later…", ((#file as NSString).lastPathComponent), #line, #function)
            DispatchQueue.main.asyncAfter(deadline: .now() + 3) {
                os_log(.info, log: .debug, "%{public}s[%{public}ld], %{public}s: retry loading", ((#file as NSString).lastPathComponent), #line, #function)
                stateMachine.enter(Loading.self)
            }
        }
    }
    
    class Idle: FollowingListViewModel.State {
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            switch stateClass {
            case is Reloading.Type, is Loading.Type:
                return true
            default:
                return false
            }
        }
    }
    
    class Loading: FollowingListViewModel.State {
        
        var maxID: String?
        
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            switch stateClass {
            case is Fail.Type:
                return true
            case is Idle.Type:
                return true
            case is NoMore.Type:
                return true
            default:
                return false
            }
        }
        
        override func didEnter(from previousState: GKState?) {
            super.didEnter(from: previousState)
            
            if previousState is Reloading {
                maxID = nil
            }
            
            guard let viewModel = viewModel, let stateMachine = stateMachine else { return }
            
            guard let userID = viewModel.userID, !userID.isEmpty else {
                stateMachine.enter(Fail.self)
                return
            }
            
            Task {
                do {
                    let response = try await viewModel.context.apiService.following(
                        userID: userID,
                        maxID: maxID,
                        authenticationBox: viewModel.authContext.mastodonAuthenticationBox
                    )
                    
                    logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch \(response.value.count)")
                    
                    var hasNewAppend = false
                    var userIDs = viewModel.userFetchedResultsController.userIDs
                    for user in response.value {
                        guard !userIDs.contains(user.id) else { continue }
                        userIDs.append(user.id)
                        hasNewAppend = true
                    }
                    
                    let maxID = response.link?.maxID
                    
                    if hasNewAppend, maxID != nil {
                        await enter(state: Idle.self)
                    } else {
                        await enter(state: NoMore.self)
                    }
                    self.maxID = maxID
                    viewModel.userFetchedResultsController.userIDs = userIDs
                    
                } catch {
                    logger.log(level: .debug, "\((#file as NSString).lastPathComponent, privacy: .public)[\(#line, privacy: .public)], \(#function, privacy: .public): fetch following fail: \(error.localizedDescription)")
                    await enter(state: Fail.self)
                }
            }   // end Task
        }   // end func didEnter
    }
    
    class NoMore: FollowingListViewModel.State {
        override func isValidNextState(_ stateClass: AnyClass) -> Bool {
            switch stateClass {
            case is Reloading.Type:
                return true
            default:
                return false
            }
        }
        
        override func didEnter(from previousState: GKState?) {
            super.didEnter(from: previousState)
        }
    }
}