package main

import (
	"bufio"
	"encoding/base64"
	"fmt"
	"io"
	"math/rand"
	"os"
	"time"

	"github.com/pions/webrtc"
	"github.com/pions/webrtc/pkg/datachannel"
	"github.com/pions/webrtc/pkg/ice"
)

func main() {
	// Wait for the offer to be pasted
	sd := mustReadStdin()

	/* Everything below is the pion-WebRTC API, thanks for using it! */

	// Prepare the configuration
	config := webrtc.RTCConfiguration{
		IceServers: []webrtc.RTCIceServer{
			{
				URLs: []string{"stun:stun.l.google.com:19302"},
			},
		},
	}

	// Create a new RTCPeerConnection
	peerConnection, err := webrtc.New(config)
	check(err)

	// Set the handler for ICE connection state
	// This will notify you when the peer has connected/disconnected
	peerConnection.OnICEConnectionStateChange = func(connectionState ice.ConnectionState) {
		fmt.Printf("ICE Connection State has changed: %s\n", connectionState.String())
	}

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

		d.Lock()
		defer d.Unlock()

		// Register channel opening handling
		d.OnOpen = func() {
			fmt.Printf("Data channel '%s'-'%d' open. Random messages will now be sent to any connected DataChannels every 5 seconds\n", d.Label, d.ID)
			for {
				time.Sleep(5 * time.Second)
				message := randSeq(15)
				fmt.Printf("Sending %s \n", message)

				err := d.Send(datachannel.PayloadString{Data: []byte(message)})
				check(err)
			}
		}

		// Register message handling
		d.Onmessage = func(payload datachannel.Payload) {
			switch p := payload.(type) {
			case *datachannel.PayloadString:
				fmt.Printf("Message '%s' from DataChannel '%s' payload '%s'\n", p.PayloadType().String(), d.Label, string(p.Data))
			case *datachannel.PayloadBinary:
				fmt.Printf("Message '%s' from DataChannel '%s' payload '% 02x'\n", p.PayloadType().String(), d.Label, p.Data)
			default:
				fmt.Printf("Message '%s' from DataChannel '%s' no payload \n", p.PayloadType().String(), d.Label)
			}
		}
	}

	// Set the remote SessionDescription
	offer := webrtc.RTCSessionDescription{
		Type: webrtc.RTCSdpTypeOffer,
		Sdp:  string(sd),
	}

	err = peerConnection.SetRemoteDescription(offer)
	check(err)

	// Sets the LocalDescription, and starts our UDP listeners
	answer, err := peerConnection.CreateAnswer(nil)
	check(err)

	// Get the LocalDescription and take it to base64 so we can paste in browser
	fmt.Println(base64.StdEncoding.EncodeToString([]byte(answer.Sdp)))

	// Block forever
	select {}
}

func randSeq(n int) string {
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	letters := []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ")
	b := make([]rune, n)
	for i := range b {
		b[i] = letters[r.Intn(len(letters))]
	}
	return string(b)
}

// mustReadStdin blocks untill input is received from stdin
func mustReadStdin() string {
	reader := bufio.NewReader(os.Stdin)
	rawSd, err := reader.ReadString('\n')
	if err != io.EOF {
		check(err)
	}

	fmt.Println("")

	sd, err := base64.StdEncoding.DecodeString(rawSd)
	check(err)

	return string(sd)
}

// check is used to panic in an error occurs.
func check(err error) {
	if err != nil {
		panic(err)
	}
}