// Copyright © 2022 Rangeproof Pty Ltd. All rights reserved.

import Foundation
import Combine
import GRDB
import WebRTC
import SessionUtilitiesKit
import SessionSnodeKit

public protocol WebRTCSessionDelegate: AnyObject {
    var videoCapturer: RTCVideoCapturer { get }
    
    func webRTCIsConnected()
    func isRemoteVideoDidChange(isEnabled: Bool)
    func dataChannelDidOpen()
    func didReceiveHangUpSignal()
    func reconnectIfNeeded()
}

/// See https://webrtc.org/getting-started/overview for more information.
public final class WebRTCSession : NSObject, RTCPeerConnectionDelegate {
    public weak var delegate: WebRTCSessionDelegate?
    public let uuid: String
    private let contactSessionId: String
    private var queuedICECandidates: [RTCIceCandidate] = []
    private var iceCandidateSendTimer: Timer?
    
    private lazy var defaultICEServer: TurnServerInfo? = {
        let url = Bundle.main.url(forResource: "Session-Turn-Server", withExtension: nil)!
        let data = try! Data(contentsOf: url)
        let json = try! JSONSerialization.jsonObject(with: data, options: [ .fragmentsAllowed ]) as! JSON
        return TurnServerInfo(attributes: json, random: 2)
    }()
    
    internal lazy var factory: RTCPeerConnectionFactory = {
        RTCInitializeSSL()
        let videoEncoderFactory = RTCDefaultVideoEncoderFactory()
        let videoDecoderFactory = RTCDefaultVideoDecoderFactory()
        return RTCPeerConnectionFactory(encoderFactory: videoEncoderFactory, decoderFactory: videoDecoderFactory)
    }()
    
    /// Represents a WebRTC connection between the user and a remote peer. Provides methods to connect to a
    /// remote peer, maintain and monitor the connection, and close the connection once it's no longer needed.
    internal lazy var peerConnection: RTCPeerConnection? = {
        let configuration = RTCConfiguration()
        if let defaultICEServer = defaultICEServer {
            configuration.iceServers = [ RTCIceServer(urlStrings: defaultICEServer.urls, username: defaultICEServer.username, credential: defaultICEServer.password) ]
        }
        configuration.sdpSemantics = .unifiedPlan
        let constraints = RTCMediaConstraints(mandatoryConstraints: [:], optionalConstraints: [:])
        return factory.peerConnection(with: configuration, constraints: constraints, delegate: self)
    }()
    
    // Audio
    internal lazy var audioSource: RTCAudioSource = {
        let constraints = RTCMediaConstraints(mandatoryConstraints: [:], optionalConstraints: [:])
        return factory.audioSource(with: constraints)
    }()
    
    internal lazy var audioTrack: RTCAudioTrack = {
        return factory.audioTrack(with: audioSource, trackId: "ARDAMSa0")
    }()
    
    // Video
    public lazy var localVideoSource: RTCVideoSource = {
        let result = factory.videoSource()
        result.adaptOutputFormat(toWidth: 360, height: 780, fps: 30)
        return result
    }()
    
    internal lazy var localVideoTrack: RTCVideoTrack = {
        return factory.videoTrack(with: localVideoSource, trackId: "ARDAMSv0")
    }()
    
    internal lazy var remoteVideoTrack: RTCVideoTrack? = {
        return peerConnection?.transceivers.first { $0.mediaType == .video }?.receiver.track as? RTCVideoTrack
    }()
    
    // Data Channel
    internal var dataChannel: RTCDataChannel?
    
    // MARK: - Error
    
    public enum WebRTCSessionError: LocalizedError {
        case noThread
        
        public var errorDescription: String? {
            switch self {
                case .noThread: return "Couldn't find thread for contact."
            }
        }
    }
    
    // MARK: Initialization
    public static var current: WebRTCSession?
    
    public init(for contactSessionId: String, with uuid: String) {
        RTCAudioSession.sharedInstance().useManualAudio = true
        RTCAudioSession.sharedInstance().isAudioEnabled = false
        
        self.contactSessionId = contactSessionId
        self.uuid = uuid
        
        super.init()
        
        let mediaStreamTrackIDS = ["ARDAMS"]
        
        peerConnection?.add(audioTrack, streamIds: mediaStreamTrackIDS)
        peerConnection?.add(localVideoTrack, streamIds: mediaStreamTrackIDS)
        
        // Configure audio session
        configureAudioSession()
        
        // Data channel
        if let dataChannel = createDataChannel() {
            dataChannel.delegate = self
            self.dataChannel = dataChannel
        }
    }
    
    // MARK: - Signaling
    
    public func sendPreOffer(
        _ db: Database,
        message: CallMessage,
        interactionId: Int64?,
        in thread: SessionThread
    ) throws -> AnyPublisher<Void, Error> {
        SNLog("[Calls] Sending pre-offer message.")
        
        return MessageSender
            .sendImmediate(
                preparedSendData: try MessageSender
                    .preparedSendData(
                        db,
                        message: message,
                        to: try Message.Destination.from(db, threadId: thread.id, threadVariant: thread.variant),
                        namespace: try Message.Destination
                            .from(db, threadId: thread.id, threadVariant: thread.variant)
                            .defaultNamespace,
                        interactionId: interactionId
                    )
            )
            .handleEvents(receiveOutput: { _ in SNLog("[Calls] Pre-offer message has been sent.") })
            .eraseToAnyPublisher()
    }
    
    public func sendOffer(
        _ db: Database,
        to sessionId: String,
        isRestartingICEConnection: Bool = false
    ) -> AnyPublisher<Void, Error> {
        SNLog("[Calls] Sending offer message.")
        let uuid: String = self.uuid
        let mediaConstraints: RTCMediaConstraints = mediaConstraints(isRestartingICEConnection)
        
        guard let thread: SessionThread = try? SessionThread.fetchOne(db, id: sessionId) else {
            return Fail(error: WebRTCSessionError.noThread)
                .eraseToAnyPublisher()
        }
        
        return Deferred {
            Future<Void, Error> { [weak self] resolver in
                self?.peerConnection?.offer(for: mediaConstraints) { sdp, error in
                    if let error = error {
                        return
                    }
                    
                    guard let sdp: RTCSessionDescription = self?.correctSessionDescription(sdp: sdp) else {
                        preconditionFailure()
                    }
                    
                    self?.peerConnection?.setLocalDescription(sdp) { error in
                        if let error = error {
                            print("Couldn't initiate call due to error: \(error).")
                            resolver(Result.failure(error))
                            return
                        }
                    }
                    
                    Storage.shared
                        .writePublisher { db in
                            try MessageSender
                                .preparedSendData(
                                    db,
                                    message: CallMessage(
                                        uuid: uuid,
                                        kind: .offer,
                                        sdps: [ sdp.sdp ],
                                        sentTimestampMs: UInt64(SnodeAPI.currentOffsetTimestampMs())
                                    ),
                                    to: try Message.Destination
                                        .from(db, threadId: thread.id, threadVariant: thread.variant),
                                    namespace: try Message.Destination
                                        .from(db, threadId: thread.id, threadVariant: thread.variant)
                                        .defaultNamespace,
                                    interactionId: nil
                                )
                        }
                        .flatMap { MessageSender.sendImmediate(preparedSendData: $0) }
                        .subscribe(on: DispatchQueue.global(qos: .userInitiated))
                        .sinkUntilComplete(
                            receiveCompletion: { result in
                                switch result {
                                    case .finished: resolver(Result.success(()))
                                    case .failure(let error): resolver(Result.failure(error))
                                }
                            }
                        )
                }
            }
        }
        .eraseToAnyPublisher()
    }
    
    public func sendAnswer(to sessionId: String) -> AnyPublisher<Void, Error> {
        SNLog("[Calls] Sending answer message.")
        let uuid: String = self.uuid
        let mediaConstraints: RTCMediaConstraints = mediaConstraints(false)
        
        return Storage.shared
            .readPublisher { db -> SessionThread in
                guard let thread: SessionThread = try? SessionThread.fetchOne(db, id: sessionId) else {
                    throw WebRTCSessionError.noThread
                }
                
                return thread
            }
            .flatMap { [weak self] thread in
                Future<Void, Error> { resolver in
                    self?.peerConnection?.answer(for: mediaConstraints) { [weak self] sdp, error in
                        if let error = error {
                            resolver(Result.failure(error))
                            return
                        }
                        
                        guard let sdp: RTCSessionDescription = self?.correctSessionDescription(sdp: sdp) else {
                            preconditionFailure()
                        }
                        
                        self?.peerConnection?.setLocalDescription(sdp) { error in
                            if let error = error {
                                print("Couldn't accept call due to error: \(error).")
                                return resolver(Result.failure(error))
                            }
                        }
                        
                        Storage.shared
                            .writePublisher { db in
                                try MessageSender
                                    .preparedSendData(
                                        db,
                                        message: CallMessage(
                                            uuid: uuid,
                                            kind: .answer,
                                            sdps: [ sdp.sdp ]
                                        ),
                                        to: try Message.Destination
                                            .from(db, threadId: thread.id, threadVariant: thread.variant),
                                        namespace: try Message.Destination
                                            .from(db, threadId: thread.id, threadVariant: thread.variant)
                                            .defaultNamespace,
                                        interactionId: nil
                                    )
                            }
                            .flatMap { MessageSender.sendImmediate(preparedSendData: $0) }
                            .subscribe(on: DispatchQueue.global(qos: .userInitiated))
                            .sinkUntilComplete(
                                receiveCompletion: { result in
                                    switch result {
                                        case .finished: resolver(Result.success(()))
                                        case .failure(let error): resolver(Result.failure(error))
                                    }
                                }
                            )
                    }
                }
            }
            .eraseToAnyPublisher()
    }
    
    private func queueICECandidateForSending(_ candidate: RTCIceCandidate) {
        queuedICECandidates.append(candidate)
        DispatchQueue.main.async {
            self.iceCandidateSendTimer?.invalidate()
            self.iceCandidateSendTimer = Timer.scheduledTimer(withTimeInterval: 1, repeats: false) { _ in
                self.sendICECandidates()
            }
        }
    }
    
    private func sendICECandidates() {
        let candidates: [RTCIceCandidate] = self.queuedICECandidates
        let uuid: String = self.uuid
        let contactSessionId: String = self.contactSessionId
        
        // Empty the queue
        self.queuedICECandidates.removeAll()
        
        Storage.shared
            .writePublisher { db in
                guard let thread: SessionThread = try SessionThread.fetchOne(db, id: contactSessionId) else {
                    throw WebRTCSessionError.noThread
                }
                
                SNLog("[Calls] Batch sending \(candidates.count) ICE candidates.")
                
                return try MessageSender
                    .preparedSendData(
                        db,
                        message: CallMessage(
                            uuid: uuid,
                            kind: .iceCandidates(
                                sdpMLineIndexes: candidates.map { UInt32($0.sdpMLineIndex) },
                                sdpMids: candidates.map { $0.sdpMid! }
                            ),
                            sdps: candidates.map { $0.sdp }
                        ),
                        to: try Message.Destination
                            .from(db, threadId: thread.id, threadVariant: thread.variant),
                        namespace: try Message.Destination
                            .from(db, threadId: thread.id, threadVariant: thread.variant)
                            .defaultNamespace,
                        interactionId: nil
                    )
            }
            .subscribe(on: DispatchQueue.global(qos: .userInitiated))
            .flatMap { MessageSender.sendImmediate(preparedSendData: $0) }
            .sinkUntilComplete()
    }
    
    public func endCall(_ db: Database, with sessionId: String) throws {
        guard let thread: SessionThread = try SessionThread.fetchOne(db, id: sessionId) else { return }
        
        SNLog("[Calls] Sending end call message.")
        
        let preparedSendData: MessageSender.PreparedSendData = try MessageSender
            .preparedSendData(
                db,
                message: CallMessage(
                    uuid: self.uuid,
                    kind: .endCall,
                    sdps: []
                ),
                to: try Message.Destination.from(db, threadId: thread.id, threadVariant: thread.variant),
                namespace: try Message.Destination
                    .from(db, threadId: thread.id, threadVariant: thread.variant)
                    .defaultNamespace,
                interactionId: nil
            )
        
        MessageSender
            .sendImmediate(preparedSendData: preparedSendData)
            .subscribe(on: DispatchQueue.global(qos: .userInitiated))
            .sinkUntilComplete()
    }
    
    public func dropConnection() {
        peerConnection?.close()
    }
    
    private func mediaConstraints(_ isRestartingICEConnection: Bool) -> RTCMediaConstraints {
        var mandatory: [String:String] = [
            kRTCMediaConstraintsOfferToReceiveAudio : kRTCMediaConstraintsValueTrue,
            kRTCMediaConstraintsOfferToReceiveVideo : kRTCMediaConstraintsValueTrue,
        ]
        if isRestartingICEConnection { mandatory[kRTCMediaConstraintsIceRestart] = kRTCMediaConstraintsValueTrue }
        let optional: [String:String] = [:]
        return RTCMediaConstraints(mandatoryConstraints: mandatory, optionalConstraints: optional)
    }
    
    private func correctSessionDescription(sdp: RTCSessionDescription?) -> RTCSessionDescription? {
        guard let sdp = sdp else { return nil }
        let cbrSdp = sdp.sdp.description.replace(regex: "(a=fmtp:111 ((?!cbr=).)*)\r?\n", with: "$1;cbr=1\r\n")
        let finalSdp = cbrSdp.replace(regex: ".+urn:ietf:params:rtp-hdrext:ssrc-audio-level.*\r?\n", with: "")
        return RTCSessionDescription(type: sdp.type, sdp: finalSdp)
    }
    
    // MARK: Peer connection delegate
    public func peerConnection(_ peerConnection: RTCPeerConnection, didChange state: RTCSignalingState) {
        SNLog("[Calls] Signaling state changed to: \(state).")
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didAdd stream: RTCMediaStream) {
        SNLog("[Calls] Peer connection did add stream.")
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didRemove stream: RTCMediaStream) {
        SNLog("[Calls] Peer connection did remove stream.")
    }
    
    public func peerConnectionShouldNegotiate(_ peerConnection: RTCPeerConnection) {
        SNLog("[Calls] Peer connection should negotiate.")
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didChange state: RTCIceConnectionState) {
        SNLog("[Calls] ICE connection state changed to: \(state).")
        if state == .connected {
            delegate?.webRTCIsConnected()
        } else if state == .disconnected {
            if self.peerConnection?.signalingState == .stable {
                delegate?.reconnectIfNeeded()
            }
        }
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didChange state: RTCIceGatheringState) {
        SNLog("[Calls] ICE gathering state changed to: \(state).")
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didGenerate candidate: RTCIceCandidate) {
        queueICECandidateForSending(candidate)
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didRemove candidates: [RTCIceCandidate]) {
        SNLog("[Calls] \(candidates.count) ICE candidate(s) removed.")
    }
    
    public func peerConnection(_ peerConnection: RTCPeerConnection, didOpen dataChannel: RTCDataChannel) {
        SNLog("[Calls] Data channel opened.")
    }
}

extension WebRTCSession {
    public func configureAudioSession(outputAudioPort: AVAudioSession.PortOverride = .none) {
        let audioSession = RTCAudioSession.sharedInstance()
        audioSession.lockForConfiguration()
        do {
            try audioSession.setCategory(AVAudioSession.Category.playAndRecord.rawValue)
            try audioSession.setMode(AVAudioSession.Mode.voiceChat.rawValue)
            try audioSession.overrideOutputAudioPort(outputAudioPort)
            try audioSession.setActive(true)
        } catch let error {
            SNLog("Couldn't set up WebRTC audio session due to error: \(error)")
        }
        audioSession.unlockForConfiguration()
    }
    
    public func audioSessionDidActivate(_ audioSession: AVAudioSession) {
        RTCAudioSession.sharedInstance().audioSessionDidActivate(audioSession)
        RTCAudioSession.sharedInstance().isAudioEnabled = true
        configureAudioSession()
    }
    
    public func audioSessionDidDeactivate(_ audioSession: AVAudioSession) {
        RTCAudioSession.sharedInstance().audioSessionDidDeactivate(audioSession)
        RTCAudioSession.sharedInstance().isAudioEnabled = false
    }
    
    public func mute() {
        audioTrack.isEnabled = false
    }
    
    public func unmute() {
        audioTrack.isEnabled = true
    }
    
    public func turnOffVideo() {
        localVideoTrack.isEnabled = false
        sendJSON(["video": false])
    }
    
    public func turnOnVideo() {
        localVideoTrack.isEnabled = true
        sendJSON(["video": true])
    }
    
    public func hangUp() {
        sendJSON(["hangup": true])
    }
}