// backend/sse.go
package main

import (
	"encoding/json"
	"fmt"
	"io"
	"net/http"
	"sort"
	"sync"
	"sync/atomic"
	"time"
)

// -------------------- SSE primitives --------------------

type sseHub struct {
	mu      sync.Mutex
	clients map[chan []byte]struct{}
}

func newSSEHub() *sseHub {
	return &sseHub{clients: map[chan []byte]struct{}{}}
}

func (h *sseHub) add(ch chan []byte) {
	h.mu.Lock()
	h.clients[ch] = struct{}{}
	h.mu.Unlock()
}

func (h *sseHub) remove(ch chan []byte) {
	h.mu.Lock()
	delete(h.clients, ch)
	h.mu.Unlock()
	close(ch)
}

func (h *sseHub) broadcast(b []byte) {
	h.mu.Lock()
	defer h.mu.Unlock()
	for ch := range h.clients {
		// Non-blocking: langsame Clients droppen Updates (holen sich beim nächsten Update wieder ein)
		select {
		case ch <- b:
		default:
		}
	}
}

// -------------------- SSE channels + notify --------------------

var (
	// done changed stream (Client soll nur "refetch done" machen)
	doneHub    = newSSEHub()
	doneNotify = make(chan struct{}, 1)
	doneSeq    uint64

	// record jobs stream
	recordJobsHub    = newSSEHub()
	recordJobsNotify = make(chan struct{}, 1)

	// assets task stream
	assetsHub    = newSSEHub()
	assetsNotify = make(chan struct{}, 1)
)

func notifyDoneChanged() {
	select {
	case doneNotify <- struct{}{}:
	default:
	}
}

func notifyJobsChanged() {
	select {
	case recordJobsNotify <- struct{}{}:
	default:
	}
}

func notifyAssetsChanged() {
	select {
	case assetsNotify <- struct{}{}:
	default:
	}
}

// initSSE startet die Debounce-Broadcaster.
// Wichtig: wird aus main.go init() aufgerufen.
func initSSE() {
	// Debounced broadcaster (jobs)
	go func() {
		for range recordJobsNotify {
			time.Sleep(40 * time.Millisecond)
			for {
				select {
				case <-recordJobsNotify:
				default:
					goto SEND
				}
			}
		SEND:
			recordJobsHub.broadcast(jobsSnapshotJSON())
		}
	}()

	// Debounced broadcaster (done changed)
	go func() {
		for range doneNotify {
			time.Sleep(40 * time.Millisecond)
			for {
				select {
				case <-doneNotify:
				default:
					goto SEND
				}
			}
		SEND:
			seq := atomic.AddUint64(&doneSeq, 1)
			b := []byte(fmt.Sprintf(`{"type":"doneChanged","seq":%d,"ts":%d}`, seq, time.Now().UnixMilli()))
			doneHub.broadcast(b)
		}
	}()

	// ✅ Debounced broadcaster (assets task)
	go func() {
		for range assetsNotify {
			time.Sleep(80 * time.Millisecond)
			for {
				select {
				case <-assetsNotify:
				default:
					goto SEND
				}
			}
		SEND:
			b := assetsSnapshotJSON()
			if len(b) > 0 {
				assetsHub.broadcast(b)
			}
		}
	}()
}

// -------------------- SSE: /api/record/stream --------------------

// jobsSnapshotJSON liefert die aktuelle (gefilterte) Job-Liste als JSON.
// Greift auf jobs/jobsMu aus main.go zu (gleiches Package).
func jobsSnapshotJSON() []byte {
	jobsMu.Lock()
	list := make([]*RecordJob, 0, len(jobs))
	for _, j := range jobs {
		// Hidden-Jobs niemals an die UI senden
		if j == nil || j.Hidden {
			continue
		}
		c := *j
		c.cancel = nil // nicht serialisieren
		list = append(list, &c)
	}
	jobsMu.Unlock()

	// neueste zuerst
	sort.Slice(list, func(i, j int) bool {
		return list[i].StartedAt.After(list[j].StartedAt)
	})

	b, _ := json.Marshal(list)
	return b
}

func recordStream(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "Nur GET erlaubt", http.StatusMethodNotAllowed)
		return
	}

	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "Streaming nicht unterstützt", http.StatusInternalServerError)
		return
	}

	// SSE-Header
	h := w.Header()
	h.Set("Content-Type", "text/event-stream; charset=utf-8")
	h.Set("Cache-Control", "no-cache, no-transform")
	h.Set("Connection", "keep-alive")
	h.Set("X-Accel-Buffering", "no") // hilfreich bei Reverse-Proxies

	// sofort starten
	w.WriteHeader(http.StatusOK)

	writeEvent := func(event string, data []byte) bool {
		// returns false => client weg / write error
		if event != "" {
			if _, err := fmt.Fprintf(w, "event: %s\n", event); err != nil {
				return false
			}
		}
		if len(data) > 0 {
			if _, err := fmt.Fprintf(w, "data: %s\n\n", data); err != nil {
				return false
			}
		} else {
			// empty payload ok (nur terminator)
			if _, err := io.WriteString(w, "\n"); err != nil {
				return false
			}
		}
		flusher.Flush()
		return true
	}

	writeComment := func(msg string) bool {
		if _, err := fmt.Fprintf(w, ": %s\n\n", msg); err != nil {
			return false
		}
		flusher.Flush()
		return true
	}

	// Reconnect-Hinweis
	if _, err := fmt.Fprintf(w, "retry: 3000\n\n"); err != nil {
		return
	}
	flusher.Flush()

	// Channel + Hub
	ch := make(chan []byte, 32)
	recordJobsHub.add(ch)
	defer recordJobsHub.remove(ch)

	// Initialer Snapshot sofort
	if b := jobsSnapshotJSON(); len(b) > 0 {
		if !writeEvent("jobs", b) {
			return
		}
	}

	ctx := r.Context()

	// Ping/Keepalive
	ping := time.NewTicker(15 * time.Second)
	defer ping.Stop()

	for {
		select {
		case <-ctx.Done():
			return

		case b, ok := <-ch:
			if !ok {
				return
			}
			if len(b) == 0 {
				continue
			}

			// Burst-Coalescing: wenn viele Updates schnell kommen, nur das neueste senden
			last := b
		drain:
			for i := 0; i < 64; i++ {
				select {
				case nb, ok := <-ch:
					if !ok {
						return
					}
					if len(nb) > 0 {
						last = nb
					}
				default:
					break drain
				}
			}

			if !writeEvent("jobs", last) {
				return
			}

		case <-ping.C:
			// Keepalive als Kommentar (stört nicht, hält Verbindungen offen)
			if !writeComment(fmt.Sprintf("ping %d", time.Now().Unix())) {
				return
			}
		}
	}
}

// -------------------- SSE: /api/tasks/assets/stream --------------------

func assetsSnapshotJSON() []byte {
	assetsTaskMu.Lock()
	st := assetsTaskState
	assetsTaskMu.Unlock()

	b, _ := json.Marshal(st)
	return b
}

func assetsStream(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		http.Error(w, "Nur GET erlaubt", http.StatusMethodNotAllowed)
		return
	}

	flusher, ok := w.(http.Flusher)
	if !ok {
		http.Error(w, "Streaming nicht unterstützt", http.StatusInternalServerError)
		return
	}

	h := w.Header()
	h.Set("Content-Type", "text/event-stream; charset=utf-8")
	h.Set("Cache-Control", "no-cache, no-transform")
	h.Set("Connection", "keep-alive")
	h.Set("X-Accel-Buffering", "no")

	w.WriteHeader(http.StatusOK)

	// Reconnect-Hinweis
	fmt.Fprintf(w, "retry: 3000\n\n")
	flusher.Flush()

	writeEvent := func(event string, data []byte) bool {
		if event != "" {
			if _, err := fmt.Fprintf(w, "event: %s\n", event); err != nil {
				return false
			}
		}
		if _, err := fmt.Fprintf(w, "data: %s\n\n", data); err != nil {
			return false
		}
		flusher.Flush()
		return true
	}

	writeComment := func(msg string) bool {
		if _, err := fmt.Fprintf(w, ": %s\n\n", msg); err != nil {
			return false
		}
		flusher.Flush()
		return true
	}

	ch := make(chan []byte, 32)
	assetsHub.add(ch)
	defer assetsHub.remove(ch)

	// Initial Snapshot
	if b := assetsSnapshotJSON(); len(b) > 0 {
		if !writeEvent("state", b) {
			return
		}
	}

	ctx := r.Context()
	ping := time.NewTicker(15 * time.Second)
	defer ping.Stop()

	for {
		select {
		case <-ctx.Done():
			return

		case b, ok := <-ch:
			if !ok {
				return
			}
			if len(b) == 0 {
				continue
			}
			// coalesce
			last := b
		drain:
			for i := 0; i < 64; i++ {
				select {
				case nb, ok := <-ch:
					if !ok {
						return
					}
					if len(nb) > 0 {
						last = nb
					}
				default:
					break drain
				}
			}

			if !writeEvent("state", last) {
				return
			}

		case <-ping.C:
			if !writeComment(fmt.Sprintf("ping %d", time.Now().Unix())) {
				return
			}
		}
	}
}