package main

import (
	"fmt"
	"time"

	"github.com/pion/webrtc/v3"
	"github.com/pion/webrtc/v3/examples/internal/signal"
)

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

	// Prepare the configuration
	config := webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	}

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

	// Create a datachannel with label 'data'
	dataChannel, err := peerConnection.CreateDataChannel("data", nil)
	if err != nil {
		panic(err)
	}

	// 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("ICE Connection State has changed: %s\n", connectionState.String())
	})

	// Register channel opening handling
	dataChannel.OnOpen(func() {
		fmt.Printf("Data channel '%s'-'%d' open. Random messages will now be sent to any connected DataChannels every 5 seconds\n", dataChannel.Label(), dataChannel.ID())

		for range time.NewTicker(5 * time.Second).C {
			message := signal.RandSeq(15)
			fmt.Printf("Sending '%s'\n", message)

			// Send the message as text
			sendErr := dataChannel.SendText(message)
			if sendErr != nil {
				panic(sendErr)
			}
		}
	})

	// Register text message handling
	dataChannel.OnMessage(func(msg webrtc.DataChannelMessage) {
		fmt.Printf("Message from DataChannel '%s': '%s'\n", dataChannel.Label(), string(msg.Data))
	})

	// Create an offer to send to the browser
	offer, err := peerConnection.CreateOffer(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(offer)
	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(signal.Encode(*peerConnection.LocalDescription()))

	// Wait for the answer to be pasted
	answer := webrtc.SessionDescription{}
	signal.Decode(signal.MustReadStdin(), &answer)

	// Apply the answer as the remote description
	err = peerConnection.SetRemoteDescription(answer)
	if err != nil {
		panic(err)
	}

	// Block forever
	select {}
}