package main

import (
	"fmt"
	"time"

	"github.com/pions/datachannel"
	"github.com/pions/webrtc"
	"github.com/pions/webrtc/examples/util"
)

const messageSize = 15

func main() {
	// Since this behavior diverges from the WebRTC API it has to be
	// enabled using global switch.
	// Mixing both behaviors is not supported.
	webrtc.DetachDataChannels()

	// 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)
	util.Check(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 data channel creation handling
	peerConnection.OnDataChannel(func(d *webrtc.DataChannel) {
		fmt.Printf("New DataChannel %s %d\n", d.Label, d.ID)

		// Register channel opening handling
		d.OnOpen(func() {
			fmt.Printf("Data channel '%s'-'%d' open.\n", d.Label, d.ID)

			// Detach the data channel
			raw, dErr := d.Detach()
			util.Check(dErr)

			// Handle reading from the data channel
			go ReadLoop(raw)

			// Handle writing to the data channel
			go WriteLoop(raw)
		})
	})

	// Wait for the offer to be pasted
	offer := webrtc.SessionDescription{}
	util.Decode(util.MustReadStdin(), offer)

	// Set the remote SessionDescription
	err = peerConnection.SetRemoteDescription(offer)
	util.Check(err)

	// Create answer
	answer, err := peerConnection.CreateAnswer(nil)
	util.Check(err)

	// Sets the LocalDescription, and starts our UDP listeners
	err = peerConnection.SetLocalDescription(answer)
	util.Check(err)

	// Output the answer in base64 so we can paste it in browser
	fmt.Println(util.Encode(answer))

	// Block forever
	select {}
}

// ReadLoop shows how to read from the datachannel directly
func ReadLoop(d *datachannel.DataChannel) {
	for {
		buffer := make([]byte, messageSize)
		n, err := d.Read(buffer)
		if err != nil {
			fmt.Println("Datachannel closed; Exit the readloop:", err)
			return
		}

		fmt.Printf("Message from DataChannel '%s': %s\n", d.Label, string(buffer[:n]))
	}
}

// WriteLoop shows how to write to the datachannel directly
func WriteLoop(d *datachannel.DataChannel) {
	for range time.NewTicker(5 * time.Second).C {
		message := util.RandSeq(messageSize)
		fmt.Printf("Sending %s \n", message)

		_, err := d.Write([]byte(message))
		util.Check(err)
	}
}