catie/internal/api/preview.go

package api

import (
	"encoding/json"
	"fmt"
	"github.com/go-gst/go-glib/glib"
	"github.com/go-gst/go-gst/gst"
	"github.com/go-gst/go-gst/gst/gstsdp"
	"github.com/go-gst/go-gst/gst/gstwebrtc"
	"github.com/gorilla/websocket"
	"github.com/labstack/echo/v4"
	"github.com/rs/zerolog/log"
	"net/http"
)

const (
	previewWidth   = 640
	previewHeight  = 360
	previewBitrate = 600 // in kbps
	previewFPS     = 25
)

var upgrader = websocket.Upgrader{
	CheckOrigin: func(r *http.Request) bool {
		return true
	},
}

type PreviewPipeline struct {
	outputID string

	pipeline  *gst.Pipeline
	webrtcbin *gst.Element
}

type SignalMessage struct {
	Type string        `json:"type"`
	SDP  string        `json:"sdp,omitempty"`
	ICE  *IceCandidate `json:"ice,omitempty"`
}

type IceCandidate struct {
	Candidate     string `json:"candidate"`
	SDPMid        string `json:"sdpMid"`
	SDPMLineIndex uint16 `json:"sdpMLineIndex"`
}

func (api *API) previewHandler(c echo.Context) error {
	devicemonitorId := c.Param("devicemonitor-id")
	source := c.Param("source")
	streamID := fmt.Sprintf("%s_%s", devicemonitorId, source)

	//debug
	for id, _ := range api.deviceMonitors {
		devicemonitorId = id
	}

	log.Debug().Str("streamID", streamID).Msg("Preview stream requested")

	deviceMonitor, ok := api.deviceMonitors[devicemonitorId]
	if !ok {
		return echo.NewHTTPError(http.StatusNotFound, fmt.Sprintf("Device monitor with ID %s not found", devicemonitorId))
	}

	sourceDevice := deviceMonitor.GetDevice(source)
	if sourceDevice == nil {
		return echo.NewHTTPError(http.StatusNotFound, fmt.Sprintf("Device with name %s not found", source))
	}

	previewPipeline, ok := api.previewPipelines[streamID]
	var err error
	if !ok {
		previewPipeline, err = api.createPreviewPipeline(sourceDevice)
		if err != nil {
			log.Error().Err(err).Msg("Failed to create preview pipeline")
			return echo.NewHTTPError(http.StatusInternalServerError, "Failed to create preview pipeline")
		}

		// TODO lock map while writing
		api.previewPipelines[streamID] = previewPipeline
	}
	if err := previewPipeline.pipeline.SetState(gst.StatePlaying); err != nil {
		log.Error().Err(err).Msg("Failed to set pipeline to playing")
		return echo.NewHTTPError(http.StatusInternalServerError, "Failed to set pipeline to playing")
	}

	conn, err := upgrader.Upgrade(c.Response(), c.Request(), nil)
	if err != nil {
		log.Error().Err(err).Msg("Upgrade error")
		return err
	}
	defer conn.Close()

	// --- WebRTC Signal Handling ---

	// on-negotiation-needed: Triggered when webrtcbin needs to create an offer or answer.
	// In our case (server receiving an offer), this fires after the remote description is set.
	previewPipeline.webrtcbin.Connect("on-negotiation-needed", func(self *gst.Element) {
		log.Info().Msg("Negotiation needed, creating answer")

		// Create Answer
		promise, err := self.Emit("create-answer")
		if err != nil {
			log.Error().Err(err).Msg("Failed to emit create-answer")
			return
		}
		if promise == nil {
			log.Error().Msg("Emit create-answer returned nil promise")
			return
		}

		// Handle the promise result (asynchronously)
		promise.(*gst.Promise).Interrupt()                  // Interrupt any previous waits
		promise.(*gst.Promise).Await(c.Request().Context()) // Wait for the answer to be created
		reply := promise.(*gst.Promise).GetReply()
		if reply == nil {
			log.Error().Msg("Promise reply for create-answer was nil")
			return
		}

		answerValue, err := reply.GetValue("answer")
		if err != nil || answerValue == nil {
			log.Error().Msg("Failed to get answer from promise reply")
			return
		}
		answer, ok := answerValue.(*gstwebrtc.SessionDescription)
		if !ok || answer == nil {
			log.Error().Msg("Answer value is not a WebRTCSessionDescription")
			return
		}

		log.Debug().Str("sdp", answer.SDP().String()).Msg("Answer created")

		// Set Local Description
		promise, err = self.Emit("set-local-description", answer)
		if err != nil {
			log.Error().Err(err).Msg("Failed to emit set-local-description")
			return
		}
		if promise == nil {
			log.Error().Msg("Emit set-local-description returned nil promise")
			return
		}
		promise.(*gst.Promise).Interrupt() // Interrupt any previous waits

		log.Info().Msg("Set local description (answer)")

		// Send Answer back to the client
		log.Info().Msg("Sending SDP answer back to browser")
		response := SignalMessage{
			Type: "answer",
			SDP:  answer.SDP().String(),
		}
		msg, err := json.Marshal(response)
		if err != nil {
			log.Error().Err(err).Msg("Failed to marshal answer")
			return
		}
		if err := conn.WriteMessage(websocket.TextMessage, msg); err != nil {
			log.Error().Err(err).Msg("Failed to send answer over WebSocket")
		}
	})

	// on-ice-candidate: Triggered when webrtcbin generates a new ICE candidate.
	previewPipeline.webrtcbin.Connect("on-ice-candidate", func(self *gst.Element, mlineindex uint, candidate string) {
		log.Debug().Uint("mlineindex", mlineindex).Str("candidate", candidate).Msg("🧊 Generated ICE candidate")
		// Note: The 'sdpMid' is often derived from the mlineindex or context,
		// but the signal itself only provides mlineindex and candidate string directly.
		// The JS side seems to handle this structure correctly.
		ice := SignalMessage{
			Type: "ice",
			ICE: &IceCandidate{
				Candidate:     candidate,
				SDPMLineIndex: uint16(mlineindex), // Assuming JS expects uint16
				// sdpMid might need to be derived if required, but often index is enough
			},
		}
		msg, err := json.Marshal(ice)
		if err != nil {
			log.Error().Err(err).Msg("Failed to marshal ICE candidate")
			return
		}
		if err := conn.WriteMessage(websocket.TextMessage, msg); err != nil {
			log.Error().Err(err).Msg("Failed to send ICE candidate over WebSocket")
		}
	})

	// --- WebSocket Message Loop ---
	for {
		_, message, err := conn.ReadMessage()
		if err != nil {
			log.Error().Err(err).Msg("WebSocket read error")
			break
		}
		var signal SignalMessage
		if err := json.Unmarshal(message, &signal); err != nil {
			log.Warn().Err(err).Msg("Failed to unmarshal signal message")
			log.Warn().Err(err).Str("message", string(message)).Msg("Failed to unmarshal signal message")
			continue
		}

		switch signal.Type {
		case "offer":
			log.Info().Msg("Received SDP offer from browser")
			//log.Debug().Str("sdp", signal.SDP).Msg("Offer SDP")

			// Create WebRTCSessionDescription for the offer
			offerMsg, err := gstsdp.ParseSDPMessage(signal.SDP)
			if err != nil {
				log.Error().Err(err).Msg("Failed to parse SDP message")
				continue
			}
			offerDesc := gstwebrtc.NewSessionDescription(gstwebrtc.SDP_TYPE_OFFER, offerMsg)

			promise := gst.NewPromise()
			// Set Remote Description
			// This will trigger on-negotiation-needed if successful and state allows
			if _, err := previewPipeline.webrtcbin.Emit("set-remote-description", offerDesc, promise); err != nil {
				log.Error().Err(err).Msg("Failed to emit set-remote-description")
				continue
			}
			if promise == nil {
				log.Error().Msg("Emit set-remote-description returned nil promise")
				continue
			}
			//promise.Interrupt() // Interrupt previous waits if any
			promise.Await(c.Request().Context()) // Wait for the remote description to be set

			log.Info().Msg("Set remote description (offer)")
			// Answer creation is now handled in on-negotiation-needed

		case "ice":
			if signal.ICE == nil {
				log.Warn().Msg("Received ICE signal with nil ICE field")
				continue
			}
			log.Debug().Str("candidate", signal.ICE.Candidate).Uint16("mlineindex", signal.ICE.SDPMLineIndex).Str("sdpMid", signal.ICE.SDPMid).Msg("Received ICE candidate from browser")

			// Add ICE Candidate
			// Note: The signal takes mlineindex (uint) and candidate (string).
			// sdpMid is usually associated but not directly passed here.
			_, err := previewPipeline.webrtcbin.Emit("add-ice-candidate", uint(signal.ICE.SDPMLineIndex), signal.ICE.Candidate)
			if err != nil {
				log.Error().Err(err).Msg("Failed to emit add-ice-candidate")
			} else {
				log.Debug().Msg("Added ICE candidate")
			}

		default:
			log.Warn().Str("type", signal.Type).Msg("Received unknown signal type")
		}
	}

	return nil
}

func (api *API) createPreviewPipeline(d Device) (*PreviewPipeline, error) {
	pipeline, err := gst.NewPipeline(fmt.Sprintf("preview-pipeline_%s", d.GetDisplayName()))
	if err != nil {
		return nil, fmt.Errorf("creating pipeline: %w", err)
	}

	videoProxySrc, err := gst.NewElementWithName("proxysrc", "video-proxy-src")
	if err != nil {
		return nil, fmt.Errorf("creating video proxy src: %w", err)
	}
	if err := pipeline.Add(videoProxySrc); err != nil {
		return nil, fmt.Errorf("adding video proxy src to pipeline: %w", err)
	}

	videoConvertScale, err := gst.NewElement("videoconvertscale")
	if err != nil {
		return nil, fmt.Errorf("creating video convert scale: %w", err)
	}
	if err := pipeline.Add(videoConvertScale); err != nil {
		return nil, fmt.Errorf("adding video convert scale to pipeline: %w", err)
	}

	if err := videoProxySrc.Link(videoConvertScale); err != nil {
		return nil, fmt.Errorf("linking video proxy src to convert scale: %w", err)
	}

	videoRate, err := gst.NewElement("videorate")
	if err != nil {
		return nil, fmt.Errorf("creating video rate: %w", err)
	}
	if err := pipeline.Add(videoRate); err != nil {
		return nil, fmt.Errorf("adding video rate to pipeline: %w", err)
	}

	if err := videoConvertScale.Link(videoRate); err != nil {
		return nil, fmt.Errorf("linking video convert scale to rate: %w", err)
	}

	convertCaps := gst.NewCapsFromString(fmt.Sprintf("video/x-raw,format=I420,width=%d,height=%d,framerate=%d/1", previewWidth, previewHeight, previewFPS))
	log.Debug().Str("caps", convertCaps.String()).Msg("Video convert caps")

	videoEncoder, err := gst.NewElementWithProperties("x264enc", map[string]interface{}{
		"bitrate":      previewBitrate,
		"speed-preset": 1,          // ultrafast
		"tune":         0x00000004, // zero-latency
	})
	if err != nil {
		return nil, fmt.Errorf("creating video encoder: %w", err)
	}
	if err := pipeline.Add(videoEncoder); err != nil {
		return nil, fmt.Errorf("adding video encoder to pipeline: %w", err)
	}

	if err := videoRate.LinkFiltered(videoEncoder, convertCaps); err != nil {
		return nil, fmt.Errorf("linking filtered video rate to encoder: %w", err)
	}

	videoPayloader, err := gst.NewElementWithProperties("rtph264pay", map[string]interface{}{
		"aggregate-mode": 1, // "zero-latency"
		"pt":             96,
	})
	if err != nil {
		return nil, fmt.Errorf("creating video payloader: %w", err)
	}
	if err := pipeline.Add(videoPayloader); err != nil {
		return nil, fmt.Errorf("adding video payloader to pipeline: %w", err)
	}

	if err := videoEncoder.Link(videoPayloader); err != nil {
		return nil, fmt.Errorf("linking video encoder to payloader: %w", err)
	}

	multiQueue, err := gst.NewElement("multiqueue")
	if err != nil {
		return nil, fmt.Errorf("creating multiqueue: %w", err)
	}
	if err := pipeline.Add(multiQueue); err != nil {
		return nil, fmt.Errorf("adding multiqueue to pipeline: %w", err)
	}

	videoPayloaderSrcPad := videoPayloader.GetStaticPad("src")
	videoQueueSinkPad := multiQueue.GetRequestPad("sink_%u")

	if plr := videoPayloaderSrcPad.Link(videoQueueSinkPad); plr != gst.PadLinkOK {
		return nil, fmt.Errorf("linking video encoder src pad to multiqueue sink pad: %s", plr.String())
	}

	webRtcBin, err := gst.NewElementWithProperties("webrtcbin", map[string]interface{}{
		"stun-server": "stun://stun.l.google.com:19302",
	})
	if err != nil {
		return nil, fmt.Errorf("creating webrtcbin: %w", err)
	}
	if err := pipeline.Add(webRtcBin); err != nil {
		return nil, fmt.Errorf("adding webrtcbin to pipeline: %w", err)
	}

	audioProxySrc, err := gst.NewElementWithName("proxysrc", "audio-proxy-src")
	if err != nil {
		return nil, fmt.Errorf("creating audio proxy src: %w", err)
	}
	if err := pipeline.Add(audioProxySrc); err != nil {
		return nil, fmt.Errorf("adding audio proxy src to pipeline: %w", err)
	}

	audioConvert, err := gst.NewElement("audioconvert")
	if err != nil {
		return nil, fmt.Errorf("creating audio convert: %w", err)
	}
	if err := pipeline.Add(audioConvert); err != nil {
		return nil, fmt.Errorf("adding audio convert to pipeline: %w", err)
	}

	if err := audioProxySrc.Link(audioConvert); err != nil {
		return nil, fmt.Errorf("linking audio proxy src to convert: %w", err)
	}

	audioRate, err := gst.NewElement("audiorate")
	if err != nil {
		return nil, fmt.Errorf("creating audio rate: %w", err)
	}
	if err := pipeline.Add(audioRate); err != nil {
		return nil, fmt.Errorf("adding audio rate to pipeline: %w", err)
	}

	if err := audioConvert.Link(audioRate); err != nil {
		return nil, fmt.Errorf("linking audio convert to rate: %w", err)
	}

	audioCaps := gst.NewCapsFromString("audio/x-raw,format=S16LE,channels=2,rate=48000")

	audioEncoder, err := gst.NewElement("opusenc")
	if err != nil {
		return nil, fmt.Errorf("creating audio encoder: %w", err)
	}
	if err := pipeline.Add(audioEncoder); err != nil {
		return nil, fmt.Errorf("adding audio encoder to pipeline: %w", err)
	}

	if err := audioRate.LinkFiltered(audioEncoder, audioCaps); err != nil {
		return nil, fmt.Errorf("linking filtered audio rate to encoder: %w", err)
	}

	audioPayloader, err := gst.NewElementWithProperties("rtpopuspay", map[string]interface{}{
		"pt": 97,
	})
	if err != nil {
		return nil, fmt.Errorf("creating audio payloader: %w", err)
	}
	if err := pipeline.Add(audioPayloader); err != nil {
		return nil, fmt.Errorf("adding audio payloader to pipeline: %w", err)
	}

	if err := audioEncoder.Link(audioPayloader); err != nil {
		return nil, fmt.Errorf("linking audio encoder to payloader: %w", err)
	}

	audioQueueSinkPad := multiQueue.GetRequestPad("sink_%u")
	audioPayloaderSrcPad := audioPayloader.GetStaticPad("src")
	if plr := audioPayloaderSrcPad.Link(audioQueueSinkPad); plr != gst.PadLinkOK {
		return nil, fmt.Errorf("linking audio encoder src pad to multiqueue sink pad: %s", plr.String())
	}

	outputID, videoSrc, audioSrc, err := d.GetOutput()
	if err != nil {
		return nil, fmt.Errorf("getting output: %w", err)
	}
	if err := linkProxySink(videoProxySrc, videoSrc); err != nil {
		return nil, fmt.Errorf("setting video proxy src proxysink: %w", err)
	}
	if err := linkProxySink(audioProxySrc, audioSrc); err != nil {
		return nil, fmt.Errorf("setting audio proxy src proxysink: %w", err)
	}

	if err := pipeline.SetState(gst.StatePlaying); err != nil {
		return nil, fmt.Errorf("setting pipeline state: %w", err)
	}
	previewPipeline := &PreviewPipeline{
		outputID:  outputID,
		pipeline:  pipeline,
		webrtcbin: webRtcBin,
	}

	if _, err := multiQueue.Connect("pad-added", previewPipeline.onMultiqueuePadAdded); err != nil {
		return nil, fmt.Errorf("connecting multiqueue pad-added signal: %w", err)
	}

	return previewPipeline, nil
}

func (pipeline *PreviewPipeline) onMultiqueuePadAdded(element *gst.Element, pad *gst.Pad) {
	log.Debug().Msg("Multiqueue pad added")
	if plr := pipeline.webrtcbin.GetRequestPad("sink_%u").Link(pad); plr != gst.PadLinkOK {
		log.Error().Str("pad-link-return", plr.String()).Msg("Failed to link multiqueue pad")
		return
	}
}

// https://github.com/go-gst/go-gst/issues/165
func linkProxySink(src, sink *gst.Element) error {
	propType, err := src.GetPropertyType("proxysink")
	if err != nil {
		return fmt.Errorf("failed to get proxysink property type: %w", err)
	}

	val, err := glib.ValueInit(propType)
	if err != nil {
		return fmt.Errorf("failed to init proxysink property value: %w", err)
	}

	val.SetInstance(sink.GetPrivate())

	return src.SetPropertyValue("proxysink", val)
}