// tether-client v0.3: SSE listener with optional WebRTC peer.
//
// Default flow (SSE only): subscribe to /api/stream, write incoming
// clipboard messages to the OS clipboard. Works on Win/Linux/macOS.
//
// With -rtc: also act as a WebRTC peer (Pion). Sends an SDP offer via
// the signaling bus, accepts the browser's answer, then receives
// clipboard payloads over a DataChannel — true P2P after ICE.
package main

import (
	"bufio"
	"bytes"
	"context"
	"encoding/json"
	"flag"
	"fmt"
	"io"
	"log"
	"net/http"
	"os"
	"runtime"
	"strings"
	"sync"
	"time"

	"github.com/atotto/clipboard"
	"github.com/pion/webrtc/v4"
)

const peerID = "tether-client"

func defaultLabel(role string) string {
	return fmt.Sprintf("%s-%s-%s", runtime.GOOS, "sse", role)
}

// Message envelope (must match server).
type Message struct {
	Type    string          `json:"type,omitempty"`
	Text    string          `json:"text,omitempty"`
	Signal  json.RawMessage `json:"signal,omitempty"`
	From    string          `json:"from,omitempty"`
	Source  string          `json:"source,omitempty"`
	TS      int64           `json:"ts"`
}

// Signal payload carried in Message.Signal.
type SignalPayload struct {
	Kind      string                  `json:"kind"` // "offer" | "answer" | "ice"
	SDP       *webrtc.SessionDescription `json:"sdp,omitempty"`
	Candidate *webrtc.ICECandidateInit   `json:"candidate,omitempty"`
}

var (
	noClipboard bool
	myLabel     string
	useRTC      bool
)

func main() {
	server := flag.String("server", "https://tether.pecord.io", "tether-server base URL")
	label := flag.String("label", "", "X-Tether-Client label (default: <os>-sse-<role>)")
	sendText := flag.String("send", "", "send this text and exit (otherwise listen)")
	flag.BoolVar(&noClipboard, "no-clipboard", false, "don't write incoming messages to the OS clipboard")
	flag.BoolVar(&useRTC, "rtc", false, "enable WebRTC peer (uses signaling bus to negotiate)")
	flag.Parse()

	if *label == "" {
		if *sendText != "" {
			*label = defaultLabel("sender")
		} else if useRTC {
			*label = fmt.Sprintf("%s-rtc-listener", runtime.GOOS)
		} else {
			*label = defaultLabel("listener")
		}
	}
	myLabel = *label

	if *sendText != "" {
		send(*server, *label, *sendText, "clipboard", nil)
		return
	}

	if !noClipboard && clipboard.Unsupported {
		fmt.Fprintln(os.Stderr, "tether-client: OS clipboard unsupported on this platform; falling back to stdout-only")
		noClipboard = true
	}

	if useRTC {
		go runRTCPeer(*server)
	}

	for {
		if err := listen(*server, *label); err != nil {
			log.Printf("stream error: %v — reconnecting in 3s", err)
			time.Sleep(3 * time.Second)
		}
	}
}

func send(server, label, text, msgType string, signal json.RawMessage) {
	m := Message{Type: msgType, Text: text, Source: label, From: peerID, Signal: signal}
	body, _ := json.Marshal(m)
	req, _ := http.NewRequest("POST", server+"/api/send", bytes.NewReader(body))
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("X-Tether-Source", label)
	r, err := http.DefaultClient.Do(req)
	if err != nil {
		log.Printf("send: %v", err)
		return
	}
	defer r.Body.Close()
	if r.StatusCode >= 300 {
		log.Printf("send: HTTP %d", r.StatusCode)
		return
	}
	if msgType != "signal" {
		fmt.Println("sent.")
	}
}

// listen subscribes to the SSE stream. Clipboard messages → OS clipboard.
// Signal messages → forwarded to the WebRTC peer (if enabled).
func listen(server, label string) error {
	req, _ := http.NewRequest("GET", server+"/api/stream", nil)
	req.Header.Set("X-Tether-Client", label)
	r, err := http.DefaultClient.Do(req)
	if err != nil {
		return err
	}
	defer r.Body.Close()
	if r.StatusCode != 200 {
		return fmt.Errorf("HTTP %d", r.StatusCode)
	}
	fmt.Fprintf(os.Stderr, "tether-client: connected to %s as %q (rtc=%v)\n", server, label, useRTC)
	sc := bufio.NewScanner(r.Body)
	sc.Buffer(make([]byte, 1<<20), 1<<20)
	var ev, data string
	for sc.Scan() {
		line := sc.Text()
		switch {
		case strings.HasPrefix(line, "event: "):
			ev = strings.TrimPrefix(line, "event: ")
		case strings.HasPrefix(line, "data: "):
			data = strings.TrimPrefix(line, "data: ")
		case line == "":
			if data != "" {
				var m Message
				if err := json.Unmarshal([]byte(data), &m); err == nil {
					handleMessage(ev, m)
				}
			}
			ev, data = "", ""
		}
	}
	if err := sc.Err(); err != nil && err != io.EOF {
		return err
	}
	return nil
}

func handleMessage(ev string, m Message) {
	switch m.Type {
	case "", "clipboard":
		ts := time.UnixMilli(m.TS).Format("15:04:05")
		fmt.Printf("\n──────  %s  from %s  ──────\n%s\n", ts, m.Source, m.Text)
		if !noClipboard && m.Source != myLabel {
			if err := clipboard.WriteAll(m.Text); err != nil {
				fmt.Fprintf(os.Stderr, "  ! clipboard write error: %v\n", err)
			} else {
				fmt.Fprintln(os.Stderr, "  → clipboard updated")
			}
		}
	case "signal":
		if useRTC && m.From != peerID {
			incomingSignal <- m
		}
	}
}

// ── WebRTC ────────────────────────────────────────────────────────────────

var (
	incomingSignal = make(chan Message, 16)
	rtcConnected   = make(chan struct{})
)

func runRTCPeer(server string) {
	api := webrtc.NewAPI()
	config := webrtc.Configuration{
		ICEServers: []webrtc.ICEServer{
			{URLs: []string{"stun:stun.l.google.com:19302"}},
		},
	}
	pc, err := api.NewPeerConnection(config)
	if err != nil {
		log.Printf("rtc: new peer connection: %v", err)
		return
	}

	dc, err := pc.CreateDataChannel("tether", nil)
	if err != nil {
		log.Printf("rtc: create datachannel: %v", err)
		return
	}

	var once sync.Once
	dc.OnOpen(func() {
		fmt.Fprintln(os.Stderr, "rtc: DataChannel OPEN — P2P live")
		once.Do(func() { close(rtcConnected) })
	})
	dc.OnMessage(func(msg webrtc.DataChannelMessage) {
		text := string(msg.Data)
		fmt.Printf("\n[rtc]  %s\n", text)
		if !noClipboard {
			if err := clipboard.WriteAll(text); err == nil {
				fmt.Fprintln(os.Stderr, "  → clipboard updated (via rtc)")
			}
		}
	})

	pc.OnICECandidate(func(c *webrtc.ICECandidate) {
		if c == nil {
			return
		}
		init := c.ToJSON()
		payload, _ := json.Marshal(SignalPayload{Kind: "ice", Candidate: &init})
		send(server, myLabel, "", "signal", payload)
	})
	pc.OnConnectionStateChange(func(s webrtc.PeerConnectionState) {
		fmt.Fprintf(os.Stderr, "rtc: state=%s\n", s)
	})

	// Create offer + post once immediately
	offer, err := pc.CreateOffer(nil)
	if err != nil {
		log.Printf("rtc: create offer: %v", err)
		return
	}
	if err := pc.SetLocalDescription(offer); err != nil {
		log.Printf("rtc: set local desc: %v", err)
		return
	}
	payload, _ := json.Marshal(SignalPayload{Kind: "offer", SDP: &offer})
	send(server, myLabel, "", "signal", payload)
	fmt.Fprintln(os.Stderr, "rtc: offer posted, will chirp every 5s until paired...")

	// "Chirp": re-post the offer every 5s until DataChannel opens. Catches
	// late-joining browsers without needing server-side history of signals.
	go func() {
		t := time.NewTicker(5 * time.Second)
		defer t.Stop()
		for {
			select {
			case <-rtcConnected:
				fmt.Fprintln(os.Stderr, "rtc: paired — chirping stopped")
				return
			case <-t.C:
				p, _ := json.Marshal(SignalPayload{Kind: "offer", SDP: &offer})
				send(server, myLabel, "", "signal", p)
			}
		}
	}()

	// Process incoming signals
	for {
		select {
		case msg := <-incomingSignal:
			var sp SignalPayload
			if err := json.Unmarshal(msg.Signal, &sp); err != nil {
				continue
			}
			switch sp.Kind {
			case "answer":
				if sp.SDP != nil {
					if err := pc.SetRemoteDescription(*sp.SDP); err != nil {
						log.Printf("rtc: set remote desc: %v", err)
					} else {
						fmt.Fprintln(os.Stderr, "rtc: answer applied")
					}
				}
			case "ice":
				if sp.Candidate != nil {
					if err := pc.AddICECandidate(*sp.Candidate); err != nil {
						log.Printf("rtc: add ice: %v", err)
					}
				}
			}
		case <-context.Background().Done():
			return
		}
	}
}