// Go Virtual Clipboard – single-file server
//
// Features
// - Web UI + REST API + SSE for realtime sync
// - Rooms ("channels") to separate clipboards
// - Optional shared-secret token (env: CLIPBOARD_TOKEN)
// - Optional JSON persistence (env: CLIPBOARD_DATA)
// - CORS enabled for API so you can script it from anywhere
// - No external dependencies; Go standard library only
//
// Build & Run
//
//	go run .
//
// or
//
//	PORT=9090 CLIPBOARD_TOKEN=geheim CLIPBOARD_DATA=clipboard.json go run .
//
// Open http://localhost:8080 (or your chosen PORT)
//
// API examples
//
//	# put text
//	curl -X POST http://localhost:8080/api/default/clip \
//	  -H 'Content-Type: application/json' \
//	  -d '{"content":"Hallo Welt","type":"text","author":"alice"}'
//
//	# get latest
//	curl http://localhost:8080/api/default/latest
//
//	# stream updates (SSE)
//	curl http://localhost:8080/api/default/stream
package main

import (
	"context"
	"crypto/rand"
	"embed"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"log"
	"net/http"
	"os"
	"os/signal"
	"path/filepath"
	"sort"
	"strconv"
	"strings"
	"sync"
	"syscall"
	"time"
)

// ---- Data model ----

type Clip struct {
	ID        string    `json:"id"`
	Room      string    `json:"room"`
	Type      string    `json:"type"` // e.g., "text"
	Content   string    `json:"content"`
	Author    string    `json:"author,omitempty"`
	CreatedAt time.Time `json:"created_at"`
}

// For persistence
type snapshot struct {
	Version int                `json:"version"`
	Rooms   map[string][]*Clip `json:"rooms"`
}

// Room keeps a ring buffer and subscribers for SSE.
// Non-blocking fanout so slow clients don't stall writers.

type Room struct {
	name   string
	max    int
	mu     sync.RWMutex
	clips  []*Clip
	subs   map[chan *Clip]struct{}
	closed bool
}

func NewRoom(name string, max int) *Room {
	return &Room{name: name, max: max, subs: make(map[chan *Clip]struct{})}
}

func (r *Room) addClip(c *Clip) {
	r.mu.Lock()
	defer r.mu.Unlock()
	if len(r.clips) >= r.max {
		// drop oldest
		copy(r.clips, r.clips[1:])
		r.clips[len(r.clips)-1] = c
	} else {
		r.clips = append(r.clips, c)
	}
	for ch := range r.subs {
		select {
		case ch <- c:
		default:
			// drop to avoid blocking
		}
	}
}

func (r *Room) latest() (*Clip, bool) {
	r.mu.RLock()
	defer r.mu.RUnlock()
	if len(r.clips) == 0 {
		return nil, false
	}
	return r.clips[len(r.clips)-1], true
}

func (r *Room) history(limit int) []*Clip {
	r.mu.RLock()
	defer r.mu.RUnlock()
	if limit <= 0 || limit > len(r.clips) {
		limit = len(r.clips)
	}
	start := len(r.clips) - limit
	out := make([]*Clip, limit)
	copy(out, r.clips[start:])
	return out
}

// ---- Server ----

type Server struct {
	mu          sync.RWMutex
	rooms       map[string]*Room
	maxPerRoom  int
	secretToken string
	persistPath string
}

func NewServer(maxPerRoom int, token, persist string) *Server {
	var perspath string = ""
	if persist != "" {
		perspath = persist
	} else {
		perspath = "./clipboard.json" // klar als Datei
	}
	return &Server{rooms: make(map[string]*Room), maxPerRoom: maxPerRoom, secretToken: token, persistPath: perspath}
}

func (s *Server) room(name string) *Room {
	s.mu.Lock()
	defer s.mu.Unlock()
	if r, ok := s.rooms[name]; ok {
		return r
	}
	r := NewRoom(name, s.maxPerRoom)
	s.rooms[name] = r
	return r
}

func (s *Server) load() error {
	if s.persistPath == "" {
		return nil
	}
	f, err := os.Open(s.persistPath)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return nil
		}
		return err
	}
	defer f.Close()
	dec := json.NewDecoder(f)
	var snap snapshot
	if err := dec.Decode(&snap); err != nil {
		return err
	}
	if snap.Version != 1 {
		return fmt.Errorf("unsupported snapshot version: %d", snap.Version)
	}
	for name, list := range snap.Rooms {
		r := s.room(name)
		r.mu.Lock()
		// keep only up to capacity
		if len(list) > r.max {
			list = list[len(list)-r.max:]
		}
		r.clips = append([]*Clip(nil), list...)
		r.mu.Unlock()
	}
	return nil
}

func (s *Server) save() error {
	if s.persistPath == "" {
		return nil
	}
	tmp := s.persistPath + ".tmp"
	if err := os.MkdirAll(filepath.Dir(s.persistPath), 0o755); err != nil {
		return err
	}
	f, err := os.Create(tmp)
	if err != nil {
		return err
	}
	enc := json.NewEncoder(f)
	enc.SetIndent("", "  ")
	// build snapshot copy
	s.mu.RLock()
	snap := snapshot{Version: 1, Rooms: make(map[string][]*Clip, len(s.rooms))}
	for name, r := range s.rooms {
		r.mu.RLock()
		list := make([]*Clip, len(r.clips))
		copy(list, r.clips)
		r.mu.RUnlock()
		snap.Rooms[name] = list
	}
	s.mu.RUnlock()
	if err := enc.Encode(&snap); err != nil {
		_ = f.Close()
		_ = os.Remove(tmp)
		return err
	}
	if err := f.Close(); err != nil {
		_ = os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, s.persistPath)
}

// ---- HTTP helpers ----

type apiError struct {
	Error string `json:"error"`
}

func writeJSON(w http.ResponseWriter, status int, v any) {
	w.Header().Set("Content-Type", "application/json; charset=utf-8")
	w.Header().Set("Cache-Control", "no-store, no-cache, must-revalidate")
	w.Header().Set("Pragma", "no-cache")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(v)
}

func (s *Server) withCORS(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		w.Header().Set("Access-Control-Allow-Origin", "*")
		w.Header().Set("Access-Control-Allow-Headers", "Content-Type, X-Token")
		w.Header().Set("Access-Control-Allow-Methods", "GET, POST, OPTIONS")
		if r.Method == http.MethodOptions {
			w.WriteHeader(http.StatusNoContent)
			return
		}
		next.ServeHTTP(w, r)
	})
}

func (s *Server) requireToken(next http.Handler) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if s.secretToken == "" {
			next.ServeHTTP(w, r)
			return
		}
		token := r.Header.Get("X-Token")
		if token == "" {
			token = r.URL.Query().Get("token")
		}
		if token != s.secretToken {
			writeJSON(w, http.StatusUnauthorized, apiError{Error: "missing or invalid token"})
			return
		}
		next.ServeHTTP(w, r)
	})
}

// ---- Handlers ----

func (s *Server) handleStatus(w http.ResponseWriter, r *http.Request) {
	// Simple JSON status endpoint
	s.mu.RLock()
	rooms := make([]string, 0, len(s.rooms))
	for name := range s.rooms {
		rooms = append(rooms, name)
	}
	s.mu.RUnlock()
	sort.Strings(rooms)
	resp := map[string]any{
		"rooms":         rooms,
		"requiresToken": s.secretToken != "",
	}
	writeJSON(w, http.StatusOK, resp)
}

type postClipReq struct {
	Type    string `json:"type"`
	Content string `json:"content"`
	Author  string `json:"author"`
}

func (s *Server) handlePostClip(w http.ResponseWriter, r *http.Request) {
	room := strings.TrimPrefix(r.URL.Path, "/api/")

	room, _, _ = strings.Cut(room, "/") // first segment is room
	if room == "" || room == "api" || strings.ContainsRune(room, '\n') {
		writeJSON(w, http.StatusBadRequest, apiError{Error: "invalid room"})
		return
	}
	if r.Method != http.MethodPost {
		writeJSON(w, http.StatusMethodNotAllowed, apiError{Error: "use POST"})
		return
	}
	var req postClipReq
	if err := json.NewDecoder(http.MaxBytesReader(w, r.Body, 1<<20)).Decode(&req); err != nil { // 1MB
		writeJSON(w, http.StatusBadRequest, apiError{Error: "invalid JSON or payload too large"})
		return
	}
	if req.Type == "" {
		req.Type = "text"
	}
	if req.Content == "" {
		writeJSON(w, http.StatusBadRequest, apiError{Error: "content empty"})
		return
	}
	id := makeID()
	clip := &Clip{ID: id, Room: room, Type: req.Type, Content: req.Content, Author: req.Author, CreatedAt: time.Now().UTC()}
	rm := s.room(room)
	rm.addClip(clip)
	_ = s.save()
	writeJSON(w, http.StatusCreated, clip)
}

func (s *Server) handleLatest(w http.ResponseWriter, r *http.Request) {
	room := strings.TrimPrefix(r.URL.Path, "/api/")
	room, _, _ = strings.Cut(room, "/")
	rm := s.room(room)
	if c, ok := rm.latest(); ok {
		writeJSON(w, http.StatusOK, c)
		return
	}
	writeJSON(w, http.StatusNotFound, apiError{Error: "no clips yet"})
}

func (s *Server) handleHistory(w http.ResponseWriter, r *http.Request) {
	room := strings.TrimPrefix(r.URL.Path, "/api/")
	room, _, _ = strings.Cut(room, "/")
	limit := 50
	if v := r.URL.Query().Get("limit"); v != "" {
		if n, err := strconv.Atoi(v); err == nil && n > 0 && n <= 200 {
			limit = n
		}
	}
	rm := s.room(room)
	list := rm.history(limit)
	writeJSON(w, http.StatusOK, list)
}

func (s *Server) handleStream(w http.ResponseWriter, r *http.Request) {
	room := strings.TrimPrefix(r.URL.Path, "/api/")
	room, _, _ = strings.Cut(room, "/")
	rm := s.room(room)
	w.Header().Set("Content-Type", "text/event-stream")
	w.Header().Set("Cache-Control", "no-cache")
	w.Header().Set("Connection", "keep-alive")
	flusher, ok := w.(http.Flusher)
	if !ok {
		writeJSON(w, http.StatusInternalServerError, apiError{Error: "streaming unsupported"})
		return
	}
	ch, unsubscribe := rm.subscribe()
	defer unsubscribe()
	ticker := time.NewTicker(25 * time.Second) // keep-alive for proxies
	defer ticker.Stop()
	ctx := r.Context()
	enc := json.NewEncoder(w)
	// send latest immediately if present
	if latest, ok := rm.latest(); ok {
		fmt.Fprintf(w, "id: %s\n", latest.ID)
		fmt.Fprintf(w, "event: clip\n")
		fmt.Fprintf(w, "data: ")
		_ = enc.Encode(latest)
		fmt.Fprintf(w, "\n")
		flusher.Flush()
	}
	for {
		select {
		case <-ctx.Done():
			return
		case c, ok := <-ch:
			if !ok {
				// Raum wurde gelöscht -> Kanal zu -> Handler beenden
				return
			}
			fmt.Fprintf(w, "id: %s\n", c.ID)
			fmt.Fprintf(w, "event: clip\n")
			fmt.Fprintf(w, "data: ")
			_ = enc.Encode(c)
			fmt.Fprintf(w, "\n")
			flusher.Flush()
		case <-ticker.C:
			fmt.Fprintf(w, ": ping %d\n\n", time.Now().Unix())
			flusher.Flush()
		}
	}
}

// ---- Utilities ----

func makeID() string {
	var b [8]byte
	_, _ = rand.Read(b[:])
	return fmt.Sprintf("%s-%s", time.Now().UTC().Format("20060102T150405.000000000Z"), hex.EncodeToString(b[:]))
}

// ---- Router ----

//go:embed web/**
var embedded embed.FS

func (s *Server) routes() http.Handler {
	mux := http.NewServeMux()

	// --- API Handler ---
	api := http.NewServeMux()
	api.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		// parse /api/{room}/...
		path := strings.TrimPrefix(r.URL.Path, "/api/")
		room, rest, _ := strings.Cut(path, "/")

		if room == "" {
			writeJSON(w, http.StatusNotFound, apiError{Error: "not found"})
			return
		}

		// Fall 1: DELETE /api/{room} → Raum löschen
		if rest == "" {
			if r.Method == http.MethodDelete {
				if err := s.deleteRoom(room); err != nil {
					writeJSON(w, http.StatusInternalServerError, apiError{Error: err.Error()})
					return
				}
				writeJSON(w, http.StatusOK, map[string]any{"status": "deleted", "room": room})
				return
			}
			writeJSON(w, http.StatusNotFound, apiError{Error: "not found"})
			return
		}

		// Fall 2: Sub-Routen wie /clip, /latest, /history, /stream
		switch rest {
		case "clip":
			if r.Method != http.MethodPost {
				writeJSON(w, http.StatusMethodNotAllowed, apiError{Error: "use POST"})
				return
			}
			s.handlePostClip(w, r)
		case "latest":
			s.handleLatest(w, r)
		case "history":
			// Zusätzlich: DELETE /api/{room}/history -> Verlauf leeren
			if r.Method == http.MethodDelete {
				if err := s.clearRoom(room); err != nil {
					writeJSON(w, http.StatusInternalServerError, apiError{Error: err.Error()})
					return
				}
				writeJSON(w, http.StatusOK, map[string]any{"status": "cleared", "room": room})
				return
			}
			s.handleHistory(w, r)
		case "stream":
			s.handleStream(w, r)
		default:
			writeJSON(w, http.StatusNotFound, apiError{Error: "unknown endpoint"})
		}
	})

	// /api/* Routes einhängen (ggf. mit Token/CORS-Middleware umwickeln)
	mux.Handle("/api/", s.withCORS(s.requireToken(api)))

	// Status
	mux.HandleFunc("/status", s.handleStatus)

	// Static UI
	sub, _ := fs.Sub(embedded, "web")
	mux.Handle("/", http.FileServer(http.FS(sub)))

	return mux
}

func main() {
	port := getenv("PORT", ":8080")
	maxPerRoom := getenvInt("MAX_PER_ROOM", 200)
	secret := os.Getenv("CLIPBOARD_TOKEN")
	persist := os.Getenv("CLIPBOARD_DATA")

	s := NewServer(maxPerRoom, secret, persist)
	if err := s.load(); err != nil {
		log.Printf("WARN: could not load snapshot: %v", err)
	}

	srv := &http.Server{
		Addr:              port,
		Handler:           s.routes(),
		ReadHeaderTimeout: 10 * time.Second,
	}

	// Docker-/Ctrl+C-Signale abfangen
	ctx, stop := signal.NotifyContext(context.Background(), os.Interrupt, syscall.SIGTERM)
	defer stop()

	go func() {
		log.Printf("Virtual Clipboard listening on http://0.0.0.0:%s (token required: %v)", port, secret != "")
		if err := srv.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
			log.Fatalf("server error: %v", err)
		}
	}()

	<-ctx.Done()
	log.Printf("Shutdown signal received")

	shutdownCtx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
	defer cancel()
	if err := srv.Shutdown(shutdownCtx); err != nil {
		log.Printf("server shutdown error: %v", err)
	}

	// Final speichert ihr ohnehin nach jedem POST; hier optional noch ein Save:
	if err := s.save(); err != nil {
		log.Printf("final save error: %v", err)
	}
}

// nahe bei deinen Server-Methoden ergänzen
func (s *Server) clearRoom(name string) error {
	r := s.room(name)
	r.mu.Lock()
	r.clips = nil
	r.mu.Unlock()
	return s.save()
}

// Room: alle Subscriber schließen (z.B. bei Delete)
func (r *Room) closeAll() {
	r.mu.Lock()
	if r.closed {
		r.mu.Unlock()
		return
	}
	r.closed = true
	for ch := range r.subs {
		close(ch)
		delete(r.subs, ch)
	}
	r.mu.Unlock()
}

// Raum komplett löschen
func (s *Server) deleteRoom(name string) error {
	s.mu.Lock()
	r, ok := s.rooms[name]
	if ok {
		delete(s.rooms, name)
	}
	s.mu.Unlock()
	if ok && r != nil {
		r.closeAll() // <- WICHTIG: SSE-Kanäle schließen
	}
	return s.save()
}

func getenv(k, def string) string {
	if v := os.Getenv(k); v != "" {
		return v
	}
	return def
}

func getenvInt(k string, def int) int {
	if v := os.Getenv(k); v != "" {
		if n, err := strconv.Atoi(v); err == nil {
			return n
		}
	}
	return def
}

func (r *Room) subscribe() (chan *Clip, func()) {
	ch := make(chan *Clip, 8)
	r.mu.Lock()
	if r.closed {
		r.mu.Unlock()
		close(ch)
		return ch, func() {}
	}
	r.subs[ch] = struct{}{}
	r.mu.Unlock()

	unsubscribe := func() {
		r.mu.Lock()
		// Nur schließen, wenn noch registriert
		if _, ok := r.subs[ch]; ok {
			delete(r.subs, ch)
			close(ch)
		}
		r.mu.Unlock()
	}
	return ch, unsubscribe
}