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

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

// play-from-disk demonstrates how to send video and/or audio to your browser from files saved to disk.
package main

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

	"github.com/pion/webrtc/v4"
	"github.com/pion/webrtc/v4/pkg/media"
	"github.com/pion/webrtc/v4/pkg/media/ivfreader"
	"github.com/pion/webrtc/v4/pkg/media/oggreader"
)

const (
	audioFileName   = "output.ogg"
	videoFileName   = "output.ivf"
	oggPageDuration = time.Millisecond * 20
)

func main() { //nolint:gocognit,cyclop,gocyclo,maintidx
	// Assert that we have an audio or video file
	_, err := os.Stat(videoFileName)
	haveVideoFile := !os.IsNotExist(err)

	_, err = os.Stat(audioFileName)
	haveAudioFile := !os.IsNotExist(err)

	if !haveAudioFile && !haveVideoFile {
		panic("Could not find `" + audioFileName + "` or `" + videoFileName + "`")
	}

	// Create a new RTCPeerConnection
	peerConnection, err := webrtc.NewPeerConnection(webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	})
	if err != nil {
		panic(err)
	}
	defer func() {
		if cErr := peerConnection.Close(); cErr != nil {
			fmt.Printf("cannot close peerConnection: %v\n", cErr)
		}
	}()

	iceConnectedCtx, iceConnectedCtxCancel := context.WithCancel(context.Background())

	if haveVideoFile { //nolint:nestif
		file, openErr := os.Open(videoFileName)
		if openErr != nil {
			panic(openErr)
		}

		_, header, openErr := ivfreader.NewWith(file)
		if openErr != nil {
			panic(openErr)
		}

		// Determine video codec
		var trackCodec string
		switch header.FourCC {
		case "AV01":
			trackCodec = webrtc.MimeTypeAV1
		case "VP90":
			trackCodec = webrtc.MimeTypeVP9
		case "VP80":
			trackCodec = webrtc.MimeTypeVP8
		default:
			panic(fmt.Sprintf("Unable to handle FourCC %s", header.FourCC))
		}

		// Create a video track
		videoTrack, videoTrackErr := webrtc.NewTrackLocalStaticSample(
			webrtc.RTPCodecCapability{MimeType: trackCodec}, "video", "pion",
		)
		if videoTrackErr != nil {
			panic(videoTrackErr)
		}

		rtpSender, videoTrackErr := peerConnection.AddTrack(videoTrack)
		if videoTrackErr != nil {
			panic(videoTrackErr)
		}

		// 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
				}
			}
		}()

		go func() {
			// Open a IVF file and start reading using our IVFReader
			file, ivfErr := os.Open(videoFileName)
			if ivfErr != nil {
				panic(ivfErr)
			}

			ivf, header, ivfErr := ivfreader.NewWith(file)
			if ivfErr != nil {
				panic(ivfErr)
			}

			// Wait for connection established
			<-iceConnectedCtx.Done()

			// Send our video file frame at a time. Pace our sending so we send it at the same speed it should be played back as.
			// This isn't required since the video is timestamped, but we will such much higher loss if we send all at once.
			//
			// It is important to use a time.Ticker instead of time.Sleep because
			// * avoids accumulating skew, just calling time.Sleep didn't compensate for the time spent parsing the data
			// * works around latency issues with Sleep (see https://github.com/golang/go/issues/44343)
			ticker := time.NewTicker(
				time.Millisecond * time.Duration((float32(header.TimebaseNumerator)/float32(header.TimebaseDenominator))*1000),
			)
			defer ticker.Stop()
			for ; true; <-ticker.C {
				frame, _, ivfErr := ivf.ParseNextFrame()
				if errors.Is(ivfErr, io.EOF) {
					fmt.Printf("All video frames parsed and sent")
					os.Exit(0)
				}

				if ivfErr != nil {
					panic(ivfErr)
				}

				if ivfErr = videoTrack.WriteSample(media.Sample{Data: frame, Duration: time.Second}); ivfErr != nil {
					panic(ivfErr)
				}
			}
		}()
	}

	if haveAudioFile { //nolint:nestif
		// Create a audio track
		audioTrack, audioTrackErr := webrtc.NewTrackLocalStaticSample(
			webrtc.RTPCodecCapability{MimeType: webrtc.MimeTypeOpus}, "audio", "pion",
		)
		if audioTrackErr != nil {
			panic(audioTrackErr)
		}

		rtpSender, audioTrackErr := peerConnection.AddTrack(audioTrack)
		if audioTrackErr != nil {
			panic(audioTrackErr)
		}

		// 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
				}
			}
		}()

		go func() {
			// Open a OGG file and start reading using our OGGReader
			file, oggErr := os.Open(audioFileName)
			if oggErr != nil {
				panic(oggErr)
			}

			// Open on oggfile in non-checksum mode.
			ogg, _, oggErr := oggreader.NewWith(file)
			if oggErr != nil {
				panic(oggErr)
			}

			// Wait for connection established
			<-iceConnectedCtx.Done()

			// Keep track of last granule, the difference is the amount of samples in the buffer
			var lastGranule uint64

			// It is important to use a time.Ticker instead of time.Sleep because
			// * avoids accumulating skew, just calling time.Sleep didn't compensate for the time spent parsing the data
			// * works around latency issues with Sleep (see https://github.com/golang/go/issues/44343)
			ticker := time.NewTicker(oggPageDuration)
			defer ticker.Stop()
			for ; true; <-ticker.C {
				pageData, pageHeader, oggErr := ogg.ParseNextPage()
				if errors.Is(oggErr, io.EOF) {
					fmt.Printf("All audio pages parsed and sent")
					os.Exit(0)
				}

				if oggErr != nil {
					panic(oggErr)
				}

				// The amount of samples is the difference between the last and current timestamp
				sampleCount := float64(pageHeader.GranulePosition - lastGranule)
				lastGranule = pageHeader.GranulePosition
				sampleDuration := time.Duration((sampleCount/48000)*1000) * time.Millisecond

				if oggErr = audioTrack.WriteSample(media.Sample{Data: pageData, Duration: sampleDuration}); oggErr != nil {
					panic(oggErr)
				}
			}
		}()
	}

	// 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.ICEConnectionStateConnected {
			iceConnectedCtxCancel()
		}
	})

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

		if state == webrtc.PeerConnectionStateFailed {
			// Wait until PeerConnection has had no network activity for 30 seconds or another failure.
			// It may be reconnected using an ICE Restart.
			// Use webrtc.PeerConnectionStateDisconnected if you are interested in detecting faster timeout.
			// Note that the PeerConnection may come back from PeerConnectionStateDisconnected.
			fmt.Println("Peer Connection has gone to failed exiting")
			os.Exit(0)
		}

		if state == webrtc.PeerConnectionStateClosed {
			// PeerConnection was explicitly closed. This usually happens from a DTLS CloseNotify
			fmt.Println("Peer Connection has gone to closed exiting")
			os.Exit(0)
		}
	})

	// 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()))

	// Block forever
	select {}
}

// 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)
	}
}
