package main

import (
	"crypto/rand"
	"fmt"
	"log"
	"os"
	"time"

	"github.com/bluenviron/gortsplib/v4"
	"github.com/bluenviron/gortsplib/v4/pkg/description"
	"github.com/bluenviron/gortsplib/v4/pkg/format"
	"github.com/bluenviron/mediacommon/pkg/formats/mpegts"
)

// This example shows how to
// 1. read H264 frames from a video file in MPEG-TS format
// 2. connect to a RTSP server, announce a H264 format
// 3. wrap frames into RTP packets
// 4. write packets to the server

func findTrack(r *mpegts.Reader) (*mpegts.Track, error) {
	for _, track := range r.Tracks() {
		if _, ok := track.Codec.(*mpegts.CodecH264); ok {
			return track, nil
		}
	}
	return nil, fmt.Errorf("H264 track not found")
}

func randUint32() (uint32, error) {
	var b [4]byte
	_, err := rand.Read(b[:])
	if err != nil {
		return 0, err
	}
	return uint32(b[0])<<24 | uint32(b[1])<<16 | uint32(b[2])<<8 | uint32(b[3]), nil
}

func main() {
	// open a file in MPEG-TS format
	f, err := os.Open("myvideo.ts")
	if err != nil {
		panic(err)
	}
	defer f.Close()

	// setup MPEG-TS parser
	r, err := mpegts.NewReader(f)
	if err != nil {
		panic(err)
	}

	// find the H264 track inside the file
	track, err := findTrack(r)
	if err != nil {
		panic(err)
	}

	// create a RTSP description that contains a H264 format
	forma := &format.H264{
		PayloadTyp:        96,
		PacketizationMode: 1,
	}
	desc := &description.Session{
		Medias: []*description.Media{{
			Type:    description.MediaTypeVideo,
			Formats: []format.Format{forma},
		}},
	}

	// connect to the server, announce the format and start recording
	c := gortsplib.Client{}
	err = c.StartRecording("rtsp://localhost:8554/mystream", desc)
	if err != nil {
		panic(err)
	}
	defer c.Close()

	// setup H264 -> RTP encoder
	rtpEnc, err := forma.CreateEncoder()
	if err != nil {
		panic(err)
	}

	randomStart, err := randUint32()
	if err != nil {
		panic(err)
	}

	timeDecoder := mpegts.NewTimeDecoder2()
	var firstDTS *int64
	var startTime time.Time

	// setup a callback that is called whenever a H264 access unit is read from the file
	r.OnDataH264(track, func(pts, dts int64, au [][]byte) error {
		dts = timeDecoder.Decode(dts)
		pts = timeDecoder.Decode(pts)

		// sleep between access units
		if firstDTS != nil {
			timeDrift := time.Duration(dts-*firstDTS)*time.Second/90000 - time.Since(startTime)
			if timeDrift > 0 {
				time.Sleep(timeDrift)
			}
		} else {
			startTime = time.Now()
			firstDTS = &dts
		}

		log.Printf("writing access unit with pts=%d dts=%d", pts, dts)

		// wrap the access unit into RTP packets
		packets, err := rtpEnc.Encode(au)
		if err != nil {
			return err
		}

		// set packet timestamp
		// we don't have to perform any conversion
		// since H264 clock rate is the same in both MPEG-TS and RTSP
		for _, packet := range packets {
			packet.Timestamp = randomStart + uint32(pts)
		}

		// write packets to the server
		for _, packet := range packets {
			err := c.WritePacketRTP(desc.Medias[0], packet)
			if err != nil {
				return err
			}
		}

		return nil
	})

	// start reading the MPEG-TS file
	for {
		err := r.Read()
		if err != nil {
			panic(err)
		}
	}
}