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

package main

import (
	"encoding/json"
	"fmt"
	"io"
	"log"
	"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
)

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

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

/// 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
		newSignal.offer.Type = webrtc.SDPTypeOffer
		newSignal.offer.SDP = data["data"].(map[string]interface{})["sdp"].(string)

	} 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 {
		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 {
			println("Attempting to connect as viewer | send candidate to a non-ready broadcast!")
			return
		}
	}

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

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

		connections[callHash] = make(chan receivedSignal, 10)
		go newCall(newSignal, connections[callHash])

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

/// Close a connection
func closeConnection(callHash string) {
	log.Printf("Closing call %s", callHash)
	if val, ok := connections[callHash]; ok {
		close(val)
		delete(connections, callHash)
	}
}

// Ask for a channel to be closed
func askForClose(callHash string) {
	closeChan <- callHash
}

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

/// Start new call
func newCall(mainOffer receivedSignal, ch chan receivedSignal) {

	log.Printf("Starting new call: %s", mainOffer.callHash)

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

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

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

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

	// Allow us to receive 1 audio & 1 video track
	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeVideo); err != nil {
		log.Println("Error: could not prepare to receive video track!", err)
		askForClose(mainOffer.callHash)
		return
	}

	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeAudio); err != nil {
		log.Println("Error: could not prepare to receive audio track!", err)
		askForClose(mainOffer.callHash)
		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
	peerConnection.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 rtcpSendErr := peerConnection.WriteRTCP([]rtcp.Packet{&rtcp.PictureLossIndication{MediaSSRC: remoteTrack.SSRC()}}); rtcpSendErr != nil {
					fmt.Println(rtcpSendErr)
				}
			}
		}()

		// Create a local track, all our SFU clients will be fed via this track
		localTrack, newTrackErr := peerConnection.NewTrack(remoteTrack.PayloadType(), remoteTrack.SSRC(), remoteTrack.ID(), remoteTrack.Label())
		if newTrackErr != nil {
			log.Println("New track error!", err)
			askForClose(mainOffer.callHash)
			return
		}

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

		rtpBuf := make([]byte, 1400)
		for {
			i, readErr := remoteTrack.Read(rtpBuf)
			if readErr != nil {

				// Could not read from remote track
				log.Println("Read error!", err)
				askForClose(mainOffer.callHash)
				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(mainOffer.callHash)
				break
			}
		}
	})

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

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

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

	// Forward ice candidates
	peerConnection.OnICECandidate(func(c *webrtc.ICECandidate) {
		if c != nil {
			sendSignal(mainOffer.callHash, mainOffer.peerID, c.ToJSON())
		}
	})

	// Send anwser
	sendSignal(mainOffer.callHash, mainOffer.peerID, answer)
}