/// RTC Relay
///
/// @author Pierre Hubert

package main

import (
	"encoding/json"
	"io"
	"log"
	"sync"
	"time"

	"github.com/pion/rtcp"
	"github.com/pion/webrtc/v2"
)

const (
	// SDP This is a SDP signal
	SDP = iota

	// CANDIDATE This is a candidate
	CANDIDATE = iota

	// RequestOffer for a broadcast receiver
	RequestOffer = iota

	// CloseConnection Requests the connection to be closed
	CloseConnection = iota
)

type receivedSignal struct {
	peerID    string
	callHash  string
	sigType   uint
	sdp       webrtc.SessionDescription
	candidate webrtc.ICECandidateInit
}

type activeRelay struct {
	channel  chan receivedSignal
	callHash string
	id       uint
	closed   bool
}

/// We keep for each connection its channel
var closeChan = make(chan *activeRelay)
var connections = make(map[string]*activeRelay)

var currID uint = 0

/// Process incoming messages
func onSignal(callHash, peerID string, data map[string]interface{}) {

	// Close all the channels that requested so
	processCloseRequests()

	// Decode received signal
	newSignal := receivedSignal{
		peerID:   peerID,
		callHash: callHash,
	}

	if data["type"] == "SDP" {
		newSignal.sigType = SDP

		// I have to re-encode data to initialize SDP
		var enc []byte
		enc, err := json.Marshal(data["data"])
		if err != nil {
			log.Printf("Could not re-encode candidate ! %s", err)
			return
		}

		err = json.Unmarshal(enc, &newSignal.sdp)
		if err != nil {
			log.Printf("Discarding invalid candidate: %s", err)
			return
		}

	} else if data["type"] == "CANDIDATE" {
		newSignal.sigType = CANDIDATE

		// I have to re-encode data to initialize ICECandidate
		var enc []byte
		enc, err := json.Marshal(data["data"])
		if err != nil {
			log.Printf("Could not re-encode candidate ! %s", err)
			return
		}

		err = json.Unmarshal(enc, &newSignal.candidate)
		if err != nil {
			log.Printf("Discarding invalid candidate: %s", err)
			return
		}

	} else if data["type"] == "REQUEST_OFFER" {

		// Request an offer
		newSignal.sigType = RequestOffer

	} else if data["type"] == "CLOSE_CONN" {

		// Close connection
		newSignal.sigType = CloseConnection

	} else {
		log.Fatalf("Invalid signal type: %s !", data["type"])
	}

	// Check if we are attempting to connect as viewer to a non existing channel
	if _, ok := connections[callHash]; !ok {
		if peerID != "0" || newSignal.sigType != SDP {
			log.Printf("Attempting to connect as viewer | send candidate to a non-ready broadcast! (callhash %s / peerid %s)", callHash, peerID)
			return
		}
	}

	// Handle new offers
	if newSignal.sigType == SDP && peerID == "0" {

		// Check if we are overwriting another connection
		if val, ok := connections[callHash]; ok {
			closeConnection(val)
		}

		newRelay := activeRelay{
			id:       currID,
			callHash: callHash,
			channel:  make(chan receivedSignal, 10),
		}
		currID++
		connections[callHash] = &newRelay
		go newCall(newSignal, &newRelay)

	} else {
		// Forward the message to the channel
		connections[callHash].channel <- newSignal
	}
}

/// Request an offer for a client of a broadcast
func onRequestOffer(callHash, peerID string) {
	onSignal(callHash, peerID, map[string]interface{}{
		"type": "REQUEST_OFFER",
	})
}

/// Request connections to be closed
func onCloseConnection(callHash, peerID string) {
	onSignal(callHash, peerID, map[string]interface{}{
		"type": "CLOSE_CONN",
	})
}

/// Close a connection
func closeConnection(r *activeRelay) {

	// Close the channel
	if !r.closed {
		close(r.channel)
		r.closed = true
	}

	// Remove the channel from the list
	if val, ok := connections[r.callHash]; ok && val.id == r.id {
		delete(connections, r.callHash)
	}

	log.Printf("Closing call %s / id: %d (%d remaining open calls)", r.callHash, r.id, len(connections))
}

// Ask for a channel to be closed
func askForClose(r *activeRelay) {
	closeChan <- r
}

// Process channel close requests (in thread safe way)
func processCloseRequests() {
	for {
		select {
		case r := <-closeChan:
			closeConnection(r)
		case <-time.After(time.Millisecond * 10):
			return
		}
	}
}

/// Start new call
func newCall(mainOffer receivedSignal, r *activeRelay) {

	log.Printf("Starting new call: %s / id: %d", r.callHash, r.id)

	// Ice candidates mutex
	var candidatesMux sync.Mutex
	pendingCandidates := make([]*webrtc.ICECandidate, 0)

	// Since we are answering use PayloadTypes declared by offerer
	mediaEngine := webrtc.MediaEngine{}
	err := mediaEngine.PopulateFromSDP(mainOffer.sdp)
	if err != nil {
		log.Println("Error: invalid data in offer!", err)
		askForClose(r)
		return
	}

	// Enable trickling
	s := webrtc.SettingEngine{}
	s.SetTrickle(false) // I did not manage to make the connection trickling, sorry...

	// Create the API object with the MediaEngine
	api := webrtc.NewAPI(webrtc.WithMediaEngine(mediaEngine),
		webrtc.WithSettingEngine(s))

	// Setup config
	peerConnectionConfig := webrtc.Configuration{
		ICEServers: callConf.iceServers,
	}

	// Create a new RTCPeerConnection
	mainPeerConnection, err := api.NewPeerConnection(peerConnectionConfig)
	if err != nil {
		log.Println("Error: could not create peer connection!", err)
		askForClose(r)
		return
	}

	// Close peer connection
	defer mainPeerConnection.Close()

	// Check if the connection is closed
	mainPeerConnection.OnConnectionStateChange(func(s webrtc.PeerConnectionState) {
		if s == webrtc.PeerConnectionStateClosed {
			askForClose(r)
			return
		}
	})

	// Forward ice candidates
	mainPeerConnection.OnICECandidate(func(c *webrtc.ICECandidate) {
		if c == nil || r.closed {
			return
		}

		// Lock the list of candidates
		candidatesMux.Lock()
		defer candidatesMux.Unlock()

		desc := mainPeerConnection.RemoteDescription()

		if desc == nil {
			// Add the signal to the pending list
			pendingCandidates = append(pendingCandidates, c)
		} else {
			// Send the signal directly
			sendSignal(mainOffer.callHash, mainOffer.peerID, c.ToJSON())
		}

	})

	// Allow us to receive 1 audio & 1 video track
	if callConf.allowVideo {
		if _, err = mainPeerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeVideo,
			webrtc.RtpTransceiverInit{Direction: webrtc.RTPTransceiverDirectionRecvonly}); err != nil {
			log.Println("Error: could not prepare to receive video track!", err)
			askForClose(r)
			return
		}
	}

	if _, err = mainPeerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeAudio,
		webrtc.RtpTransceiverInit{Direction: webrtc.RTPTransceiverDirectionRecvonly}); err != nil {
		log.Println("Error: could not prepare to receive audio track!", err)
		askForClose(r)
		return
	}

	localTrackChan := make(chan *webrtc.Track)

	// Set a handler for when a new remote track starts, this just distributes all our packets
	// to connected peers
	mainPeerConnection.OnTrack(func(remoteTrack *webrtc.Track, receiver *webrtc.RTPReceiver) {

		// Send a PLI on an interval so that the publisher is pushing a keyframe every rtcpPLIInterval
		// This can be less wasteful by processing incoming RTCP events, then we would emit a NACK/PLI when a viewer requests it
		go func() {
			rtcpPLIInterval := time.Second * 3
			ticker := time.NewTicker(rtcpPLIInterval)
			for range ticker.C {

				if r.closed {
					return
				}

				if rtcpSendErr := mainPeerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: remoteTrack.SSRC()}}); rtcpSendErr != nil {
					log.Println("Write RTCP error:", rtcpSendErr)
					askForClose(r)
					return
				}
			}
		}()

		// Create a local track, all our SFU clients will be fed via this track
		trackID := "audio"
		trackLabel := "pion" // We need only one track label
		if remoteTrack.Kind() == webrtc.RTPCodecTypeVideo {

			// Check if video calls are allowed
			if !callConf.allowVideo {
				log.Printf("Blocked a video stream! Call hash: %s", r.callHash)
				return
			}

			trackID = "video" // We need two different track ids
		}

		localTrack, newTrackErr := mainPeerConnection.NewTrack(remoteTrack.PayloadType(), remoteTrack.SSRC(), trackID, trackLabel)

		if newTrackErr != nil {
			log.Println("New track error!", err)
			askForClose(r)
			return
		}

		// Send the track to the main goroutine (in order to respond correctly to SDP requests & responses)
		localTrackChan <- localTrack

		rtpBuf := make([]byte, 1400)
		for {

			if r.closed {
				return
			}

			i, readErr := remoteTrack.Read(rtpBuf)
			if readErr != nil {
				// Could not read from remote track
				log.Println("Read error!", readErr)
				askForClose(r)
				break
			}

			// ErrClosedPipe means we don't have any subscribers, this is ok if no peers have connected yet
			if _, err = localTrack.Write(rtpBuf[:i]); err != nil && err != io.ErrClosedPipe {
				log.Println("Write error!", err)
				askForClose(r)
				break
			}
		}
	})

	// Set the remote SessionDescription
	err = mainPeerConnection.SetRemoteDescription(mainOffer.sdp)
	if err != nil {
		log.Println("Set remote description error!", err)
		askForClose(r)
		return
	}

	// Create answer
	answer, err := mainPeerConnection.CreateAnswer(nil)
	if err != nil {
		log.Println("Create answer error!", err)
		askForClose(r)
		return
	}

	// Sets the LocalDescription, and starts our UDP listeners
	err = mainPeerConnection.SetLocalDescription(answer)
	if err != nil {
		log.Println("Set local description error!", err)
		askForClose(r)
		return
	}

	// Send anwser
	if !r.closed {
		sendSignal(mainOffer.callHash, mainOffer.peerID, answer)

		// Warning ! Do not put this outside a specific block
		candidatesMux.Lock()

		// Send pending ice candidates
		for _, val := range pendingCandidates {
			sendSignal(mainOffer.callHash, mainOffer.peerID, val)
		}

		candidatesMux.Unlock()
	}

	// Keep a list of active tracks
	localTracks := make([]*webrtc.Track, 0, 2)

	clients := make(map[string]*webrtc.PeerConnection, 1)

	// Close all clients connections at the end
	defer func() {
		for _, v := range clients {
			v.Close()
		}
	}()

	// Enter messags loop
	for {

		// Receive new channels
		stopCheck := len(localTracks) >= 2 // Stop check if we got all the channel
		for !stopCheck {
			select {
			case t := <-localTrackChan:
				localTracks = append(localTracks, t)
			case <-time.After(time.Millisecond * 100):
				stopCheck = true
			}
		}

		newMessage, ok := <-r.channel

		if !ok {
			log.Printf("Channel closed: call hash: %s / call id: %d", r.callHash, r.id)
			return
		}

		// Check if we are creating a new connection
		if newMessage.sigType == RequestOffer {

			// Close any previous connection of this client
			if val, ok := clients[newMessage.peerID]; ok {
				val.Close()
			}

			// Ice candidates mutex
			var newCandidatesMux sync.Mutex
			newPendingCandidates := make([]*webrtc.ICECandidate, 0)

			// Create new peer connection
			newPeerConnection, err := api.NewPeerConnection(peerConnectionConfig)
			if err != nil {
				log.Printf("Error creating new remote peer connection: %s", err)
				continue
			}
			clients[newMessage.peerID] = newPeerConnection

			defer newPeerConnection.Close()

			// Send ice candidates
			newPeerConnection.OnICECandidate(func(c *webrtc.ICECandidate) {
				if c == nil || r.closed {
					return
				}

				newCandidatesMux.Lock()
				defer newCandidatesMux.Unlock()

				// Check if we have already determined remote descprition
				desc := newPeerConnection.LocalDescription()
				if desc == nil {
					// Append signal to the queue
					newPendingCandidates = append(newPendingCandidates, c)
				} else {
					// Send the signal immedialy
					sendSignal(r.callHash, newMessage.peerID, c.ToJSON())
				}

			})

			// Add tracks
			for _, value := range localTracks {
				_, err = newPeerConnection.AddTrack(value)
				if err != nil {
					log.Printf("Error adding a track: %s", err)
					continue
				}
			}

			// Create the offer
			offer, err := newPeerConnection.CreateOffer(nil)
			if err != nil {
				log.Printf("Could not create answer: %s!", err)
				continue
			}

			err = newPeerConnection.SetLocalDescription(offer)
			if err != nil {
				log.Printf("Could not set local description: %s!", err)
				continue
			}

			// Send offer
			sendSignal(r.callHash, newMessage.peerID, offer)

			// Send pending ice candidates
			newCandidatesMux.Lock()
			for _, c := range newPendingCandidates {
				sendSignal(r.callHash, newMessage.peerID, c.ToJSON())
			}
			newCandidatesMux.Unlock()

		} else if newMessage.sigType == SDP {

			// Got an answer from the client
			if val, ok := clients[newMessage.peerID]; ok {
				// Set remote description
				if err := val.SetRemoteDescription(newMessage.sdp); err != nil {
					log.Printf("Could not set remote description! %s", err)
				}

			} else {
				log.Printf("Dropped un-usable answer: callHash %s / peer ID %s", newMessage.callHash, newMessage.peerID)
			}

		} else if newMessage.sigType == CANDIDATE {

			if newMessage.peerID == "0" {
				// Ice candidate for main peer
				if err := mainPeerConnection.AddICECandidate(newMessage.candidate); err != nil {
					log.Printf("Err Adding ICECandidate to main peer: %s", err)
				}

			} else if val, ok := clients[newMessage.peerID]; ok {
				// Ice candidate for remote peer
				if err := val.AddICECandidate(newMessage.candidate); err != nil {
					log.Printf("Err adding ice candidate for remote peer: %s", err)
				}

			} else {
				log.Printf("Err tried to add ICE Candidate for non ready peer connection!")
			}

		} else if newMessage.sigType == CloseConnection {

			// Check if we have to close the whole connection or just a client
			if newMessage.peerID == "0" {
				askForClose(r)
				return
			} else if val, ok := clients[newMessage.peerID]; ok {
				// Close a single client
				val.Close()
				delete(clients, newMessage.peerID)
			}

		}
	}
}