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

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

// save-to-disk-av1 is a simple application that shows how to save a video to disk using AV1.
package main

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

	"github.com/pion/interceptor"
	"github.com/pion/interceptor/pkg/intervalpli"
	"github.com/pion/webrtc/v4"
	"github.com/pion/webrtc/v4/pkg/media"
	"github.com/pion/webrtc/v4/pkg/media/ivfwriter"
)

func saveToDisk(writer media.Writer, track *webrtc.TrackRemote) {
	defer func() {
		if err := writer.Close(); err != nil {
			panic(err)
		}
	}()

	for {
		rtpPacket, _, err := track.ReadRTP()
		if err != nil {
			fmt.Println(err)

			return
		}
		if err := writer.WriteRTP(rtpPacket); err != nil {
			fmt.Println(err)

			return
		}
	}
}

// nolint:cyclop
func main() {
	// Everything below is the Pion WebRTC API! Thanks for using it ❤️.

	// Create a MediaEngine object to configure the supported codec
	mediaEngine := &webrtc.MediaEngine{}

	if err := mediaEngine.RegisterCodec(webrtc.RTPCodecParameters{
		RTPCodecCapability: webrtc.RTPCodecCapability{
			MimeType:     webrtc.MimeTypeAV1,
			ClockRate:    90000,
			Channels:     0,
			SDPFmtpLine:  "",
			RTCPFeedback: nil,
		},
		PayloadType: 96,
	}, webrtc.RTPCodecTypeVideo); err != nil {
		panic(err)
	}

	// Create a InterceptorRegistry. This is the user configurable RTP/RTCP Pipeline.
	// This provides NACKs, RTCP Reports and other features. If you use `webrtc.NewPeerConnection`
	// this is enabled by default. If you are manually managing You MUST create a InterceptorRegistry
	// for each PeerConnection.
	interceptorRegistry := &interceptor.Registry{}

	// Register a intervalpli factory
	// This interceptor sends a PLI every 3 seconds. A PLI causes a video keyframe to be generated by the sender.
	// This makes our video seekable and more error resilent, but at a cost of lower picture quality and higher bitrates
	// A real world application should process incoming RTCP packets from viewers and forward them to senders
	intervalPliFactory, err := intervalpli.NewReceiverInterceptor()
	if err != nil {
		panic(err)
	}
	interceptorRegistry.Add(intervalPliFactory)

	// Use the default set of Interceptors
	if err = webrtc.RegisterDefaultInterceptors(mediaEngine, interceptorRegistry); err != nil {
		panic(err)
	}

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

	// Prepare the configuration
	config := webrtc.Configuration{}

	// Create a new RTCPeerConnection
	peerConnection, err := api.NewPeerConnection(config)
	if err != nil {
		panic(err)
	}

	// Allow us to receive 1 video track
	if _, err = peerConnection.AddTransceiverFromKind(webrtc.RTPCodecTypeVideo); err != nil {
		panic(err)
	}

	ivfFile, err := ivfwriter.New("output.ivf", ivfwriter.WithCodec(webrtc.MimeTypeAV1))
	if err != nil {
		panic(err)
	}

	// Set a handler for when a new remote track starts, this handler saves buffers to disk as
	// an ivf file, since we could have multiple video tracks we provide a counter.
	// In your application this is where you would handle/process video
	peerConnection.OnTrack(func(track *webrtc.TrackRemote, receiver *webrtc.RTPReceiver) { //nolint: revive
		if strings.EqualFold(track.Codec().MimeType, webrtc.MimeTypeAV1) {
			fmt.Println("Got AV1 track, saving to disk as output.ivf")
			saveToDisk(ivfFile, track)
		}
	})

	// 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 {
			fmt.Println("Ctrl+C the remote client to stop the demo")
		} else if connectionState == webrtc.ICEConnectionStateFailed || connectionState == webrtc.ICEConnectionStateClosed {
			if closeErr := ivfFile.Close(); closeErr != nil {
				panic(closeErr)
			}

			fmt.Println("Done writing media files")

			// Gracefully shutdown the peer connection
			if closeErr := peerConnection.Close(); closeErr != nil {
				panic(closeErr)
			}

			os.Exit(0)
		}
	})

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

	// Set the remote SessionDescription
	err = peerConnection.SetRemoteDescription(offer)
	if 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
	err = peerConnection.SetLocalDescription(answer)
	if 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)
	}
}