// SPDX-FileCopyrightText: 2023 The Pion community <https://pion.ly>
// SPDX-License-Identifier: MIT

//go:build !js
// +build !js

// rtp-to-webrtc demonstrates how to consume a RTP stream video UDP, and then send to a WebRTC client.
package main

import (
	"bufio"
	"encoding/base64"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"net"
	"os"
	"strings"

	"github.com/pion/webrtc/v4"
)

// nolint:cyclop
func main() {
	peerConnection, err := webrtc.NewPeerConnection(webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	})
	if err != nil {
		panic(err)
	}

	// Open a UDP Listener for RTP Packets on port 5004
	listener, err := net.ListenUDP("udp", &net.UDPAddr{IP: net.ParseIP("127.0.0.1"), Port: 5004})
	if err != nil {
		panic(err)
	}

	// Increase the UDP receive buffer size
	// Default UDP buffer sizes vary on different operating systems
	bufferSize := 300000 // 300KB
	err = listener.SetReadBuffer(bufferSize)
	if err != nil {
		panic(err)
	}

	defer func() {
		if err = listener.Close(); err != nil {
			panic(err)
		}
	}()

	// Create a video track
	videoTrack, err := webrtc.NewTrackLocalStaticRTP(
		webrtc.RTPCodecCapability{MimeType: webrtc.MimeTypeVP8}, "video", "pion",
	)
	if err != nil {
		panic(err)
	}
	rtpSender, err := peerConnection.AddTrack(videoTrack)
	if err != nil {
		panic(err)
	}

	// Read incoming RTCP packets
	// Before these packets are returned they are processed by interceptors. For things
	// like NACK this needs to be called.
	go func() {
		rtcpBuf := make([]byte, 1500)
		for {
			if _, _, rtcpErr := rtpSender.Read(rtcpBuf); rtcpErr != nil {
				return
			}
		}
	}()

	// Set the handler for ICE connection state
	// This will notify you when the peer has connected/disconnected
	peerConnection.OnICEConnectionStateChange(func(connectionState webrtc.ICEConnectionState) {
		fmt.Printf("Connection State has changed %s \n", connectionState.String())

		if connectionState == webrtc.ICEConnectionStateFailed {
			if closeErr := peerConnection.Close(); closeErr != nil {
				panic(closeErr)
			}
		}
	})

	// Wait for the offer to be pasted
	offer := webrtc.SessionDescription{}
	decode(readUntilNewline(), &offer)

	// Set the remote SessionDescription
	if err = peerConnection.SetRemoteDescription(offer); err != nil {
		panic(err)
	}

	// Create answer
	answer, err := peerConnection.CreateAnswer(nil)
	if err != nil {
		panic(err)
	}

	// Create channel that is blocked until ICE Gathering is complete
	gatherComplete := webrtc.GatheringCompletePromise(peerConnection)

	// Sets the LocalDescription, and starts our UDP listeners
	if err = peerConnection.SetLocalDescription(answer); err != nil {
		panic(err)
	}

	// Block until ICE Gathering is complete, disabling trickle ICE
	// we do this because we only can exchange one signaling message
	// in a production application you should exchange ICE Candidates via OnICECandidate
	<-gatherComplete

	// Output the answer in base64 so we can paste it in browser
	fmt.Println(encode(peerConnection.LocalDescription()))

	// Read RTP packets forever and send them to the WebRTC Client
	inboundRTPPacket := make([]byte, 1600) // UDP MTU
	for {
		n, _, err := listener.ReadFrom(inboundRTPPacket)
		if err != nil {
			panic(fmt.Sprintf("error during read: %s", err))
		}

		if _, err = videoTrack.Write(inboundRTPPacket[:n]); err != nil {
			if errors.Is(err, io.ErrClosedPipe) {
				// The peerConnection has been closed.
				return
			}

			panic(err)
		}
	}
}

// Read from stdin until we get a newline.
func readUntilNewline() (in string) {
	var err error

	r := bufio.NewReader(os.Stdin)
	for {
		in, err = r.ReadString('\n')
		if err != nil && !errors.Is(err, io.EOF) {
			panic(err)
		}

		if in = strings.TrimSpace(in); len(in) > 0 {
			break
		}
	}

	fmt.Println("")

	return
}

// JSON encode + base64 a SessionDescription.
func encode(obj *webrtc.SessionDescription) string {
	b, err := json.Marshal(obj)
	if err != nil {
		panic(err)
	}

	return base64.StdEncoding.EncodeToString(b)
}

// Decode a base64 and unmarshal JSON into a SessionDescription.
func decode(in string, obj *webrtc.SessionDescription) {
	b, err := base64.StdEncoding.DecodeString(in)
	if err != nil {
		panic(err)
	}

	if err = json.Unmarshal(b, obj); err != nil {
		panic(err)
	}
}