party-mix-app/apps/backend/internal/handlers/overlay.go

package handlers

import (
	"encoding/json"
	"fmt"
	"net/http"
	"sync"
	"time"

	"github.com/gin-gonic/gin"
)

type OverlayState struct {
	Title       string  `json:"title"`
	Artist      string  `json:"artist"`
	Cover       string  `json:"cover"`
	IsPlaying   bool    `json:"is_playing"`
	Progress    float64 `json:"progress"`
	Duration    float64 `json:"duration"`
	Enabled     bool    `json:"enabled"`
	Design      string  `json:"design"`
	Style       string  `json:"style"`
	AccentColor string  `json:"accent_color"`
	Position    string  `json:"position"`
	Font        string  `json:"font"`
	TextColor   string  `json:"text_color"`
	ShowCover   bool    `json:"show_cover"`
	ShowEq      bool    `json:"show_eq"`
	Palette       string `json:"palette"`
	CustomBg      string `json:"custom_bg"`
	CustomText    string `json:"custom_text"`
	CustomText2   string `json:"custom_text2"`
	CustomChroma  string `json:"custom_chroma"`
	CustomTitleBg string `json:"custom_title_bg"`
	CustomBodyBg  string `json:"custom_body_bg"`
	Margin    float64 `json:"margin"`
	Scale     float64 `json:"scale"`
	Opacity   float64 `json:"opacity"`
	UpdatedAt int64   `json:"updated_at"`
}

type overlayEntry struct {
	mu    sync.RWMutex
	state OverlayState
}

var overlayMap sync.Map // userID -> *overlayEntry

// ── SSE hub ───────────────────────────────────────────────────────────────────

type sseHub struct {
	mu      sync.RWMutex
	clients map[chan OverlayState]struct{}
}

var sseHubs sync.Map // userID -> *sseHub

func getOrCreateOverlayEntry(userID string) *overlayEntry {
	v, _ := overlayMap.LoadOrStore(userID, &overlayEntry{
		state: OverlayState{Design: "minimal", Enabled: true, Scale: 1, Opacity: 1, Margin: 24},
	})
	return v.(*overlayEntry)
}

func getOrCreateHub(userID string) *sseHub {
	v, _ := sseHubs.LoadOrStore(userID, &sseHub{
		clients: make(map[chan OverlayState]struct{}),
	})
	return v.(*sseHub)
}

func broadcastOverlay(userID string, state OverlayState) {
	hub, ok := sseHubs.Load(userID)
	if !ok {
		return
	}
	h := hub.(*sseHub)
	h.mu.RLock()
	defer h.mu.RUnlock()
	for ch := range h.clients {
		select {
		case ch <- state:
		default:
		}
	}
}

// PUT /api/overlay/state  (requires auth)
func PushOverlayState(c *gin.Context) {
	userID := currentUserID(c)
	var state OverlayState
	if err := c.ShouldBindJSON(&state); err != nil {
		c.JSON(http.StatusBadRequest, gin.H{"error": err.Error()})
		return
	}
	state.UpdatedAt = time.Now().UnixMilli()
	entry := getOrCreateOverlayEntry(userID)
	entry.mu.Lock()
	entry.state = state
	entry.mu.Unlock()
	broadcastOverlay(userID, state)
	c.JSON(http.StatusOK, gin.H{"ok": true})
}

// GET /api/overlay/:token/state  (public, fallback polling)
func GetOverlayState(c *gin.Context) {
	token := c.Param("token")
	v, ok := overlayMap.Load(token)
	if !ok {
		c.JSON(http.StatusNotFound, gin.H{"error": "not found"})
		return
	}
	entry := v.(*overlayEntry)
	entry.mu.RLock()
	state := entry.state
	entry.mu.RUnlock()
	c.JSON(http.StatusOK, state)
}

// GET /api/overlay/:token/stream  (SSE, public)
func StreamOverlayState(c *gin.Context) {
	token := c.Param("token")

	c.Header("Content-Type", "text/event-stream")
	c.Header("Cache-Control", "no-cache")
	c.Header("Connection", "keep-alive")
	c.Header("X-Accel-Buffering", "no")

	// Send current state immediately
	if v, ok := overlayMap.Load(token); ok {
		entry := v.(*overlayEntry)
		entry.mu.RLock()
		state := entry.state
		entry.mu.RUnlock()
		data, _ := json.Marshal(state)
		fmt.Fprintf(c.Writer, "data: %s\n\n", data)
	} else {
		fmt.Fprintf(c.Writer, "event: notfound\ndata: {}\n\n")
	}
	c.Writer.Flush()

	ch := make(chan OverlayState, 8)
	hub := getOrCreateHub(token)
	hub.mu.Lock()
	hub.clients[ch] = struct{}{}
	hub.mu.Unlock()

	defer func() {
		hub.mu.Lock()
		delete(hub.clients, ch)
		hub.mu.Unlock()
		close(ch)
	}()

	ctx := c.Request.Context()
	ticker := time.NewTicker(25 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case state, ok := <-ch:
			if !ok {
				return
			}
			data, _ := json.Marshal(state)
			fmt.Fprintf(c.Writer, "data: %s\n\n", data)
			c.Writer.Flush()
		case <-ticker.C:
			fmt.Fprintf(c.Writer, ": keepalive\n\n")
			c.Writer.Flush()
		case <-ctx.Done():
			return
		}
	}
}