// 
// 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 Foundation
import Combine


enum TemplateRoomChatRoomIntializationStatus{
    case notInitialized
    case initialized
    case failedToInitialize
}

@available(iOS 14.0, *)
class TemplateRoomChatService: TemplateRoomChatServiceProtocol {
    
    // MARK: - Properties
    
    // MARK: Private
    
    private let room: MXRoom
    private let eventFormatter: EventFormatter
    private var roomState: MXRoomState?
    private var roomListenerReference: Any?
    
    // MARK: Public
    private(set) var chatMessagesSubject: CurrentValueSubject<[TemplateRoomChatMessage], Never>
    private(set) var roomInitialized: CurrentValueSubject<TemplateRoomChatRoomIntializationStatus, Never>
    
    var roomName: String? {
        self.room.summary.displayname
    }
    // MARK: - Setup
    
    init(room: MXRoom) {
        self.room = room
        self.eventFormatter = EventFormatter(matrixSession: room.mxSession)
        self.chatMessagesSubject = CurrentValueSubject([])
        self.roomInitialized = CurrentValueSubject(.notInitialized)
        
        initalizeRoom()
    }
    
    deinit {
        guard let reference = roomListenerReference else { return }
        room.removeListener(reference)
    }
    
    // MARK: Public
    func send(message: String) {
        var localEcho: MXEvent? = nil
        room.sendTextMessage(message, localEcho: &localEcho, completion: { _ in }) 
    }
    
    // MARK: Private
    
    private func initalizeRoom(){
        room.state { [weak self] roomState in
            guard let self = self else { return }
            if let roomState = roomState {
                self.roomState = roomState
                self.roomInitialized.value = .initialized
                self.loadInitialMessages()
                self.startListeningToRoomEvents()
            } else {
                self.roomInitialized.value = .failedToInitialize
            }
        }
    }
    
    private func loadInitialMessages() {
        let batch = room.enumeratorForStoredMessages.nextEventsBatch(200)
        let messageBatch = self.mapChatMessages(from: batch ?? [])
        self.chatMessagesSubject.value = messageBatch
    }
    
    private func startListeningToRoomEvents(){
        roomListenerReference = room.listen { [weak self] event, directionId, roomState in
            let direction = MXTimelineDirection(identifer: directionId)
            guard let self = self,
                  let event = event else { return }
            if let roomState = roomState {
                self.roomState = roomState
            }
            if direction == .forwards &&  event.type == kMXEventTypeStringRoomMessage {
                self.appendNewMessage(event: event)
            }
        }
    }
    
    private func mapChatMessages(from events: [MXEvent]) -> [TemplateRoomChatMessage] {
        return events
            .filter({ event in
                event.type == kMXEventTypeStringRoomMessage
                    && event.content["msgtype"] as? String == kMXMessageTypeText
            })
            .compactMap({ event -> TemplateRoomChatMessage?  in
                guard let eventId = event.eventId,
                      let eventBody = event.content["body"] as? String,
                      let sender = senderForMessage(event: event)
                else { return nil }
                
                return TemplateRoomChatMessage(
                    id: eventId,
                    body: eventBody,
                    sender: sender,
                    timestamp: Date(timeIntervalSince1970: TimeInterval(event.originServerTs / 1000))
                )
            })
    }
    
    private func senderForMessage(event: MXEvent) -> TemplateRoomChatMember? {
        guard let sender = event.sender, let roomState = roomState else {
            return nil
        }
        let displayName = eventFormatter.senderDisplayName(for: event, with: roomState)
        let avatarUrl = eventFormatter.senderAvatarUrl(for: event, with: roomState)
        return TemplateRoomChatMember(id: sender, avatarUrl: avatarUrl, displayName: displayName)
    }
    
    private func appendNewMessage(event: MXEvent) {
        chatMessagesSubject.value += mapChatMessages(from: [event])
    }
    
}