feat: slider pre-flash advance (0-3s) dans settings UI

backend/api/leds_api.py

@@ -158,6 +158,36 @@ async def measure_ambient_lux(request: Request):
         return JSONResponse({"ok": False, "error": str(e)}, status_code=500)
 
 
+@router.get("/leds/flash-timing")
+async def get_flash_timing(request: Request):
+    """Retourne les paramètres de timing du flash."""
+    cfg = request.app.state.config.leds
+    return {
+        "pre_flash_advance": cfg.pre_flash_advance,
+        "countdown_duration": cfg.countdown_duration,
+    }
+
+
+@router.put("/leds/flash-timing")
+async def set_flash_timing(
+    request: Request,
+    pre_flash_advance: float = Query(..., ge=0.0, le=3.0, description="Secondes avant fin countdown pour démarrer le flash"),
+    save: bool = Query(default=True),
+):
+    """Règle combien de secondes avant la fin du countdown le flash démarre (0–3s)."""
+    cfg = request.app.state.config.leds
+    cfg.pre_flash_advance = pre_flash_advance
+    if save:
+        config_svc = request.app.state.config_service
+        with open(config_svc.path, encoding="utf-8") as f:
+            import yaml
+            raw = yaml.safe_load(f) or {}
+        raw.setdefault("leds", {})["pre_flash_advance"] = pre_flash_advance
+        with open(config_svc.path, "w", encoding="utf-8") as f:
+            yaml.dump(raw, f, allow_unicode=True, default_flow_style=False)
+    return {"ok": True, "pre_flash_advance": pre_flash_advance}
+
+
 @router.put("/leds/effect/{effect_name}")
 async def update_effect(
     request: Request,

frontend/templates/admin/settings.html

@@ -466,6 +466,19 @@ select.field {
           <button class="btn btn-ghost btn-sm" onclick="setFlashPreset(255,220,120,0.25,2)">Blanc neutre</button>
           <button class="btn btn-ghost btn-sm" onclick="setFlashPreset(255,180,40,0.35,2)">Ambre</button>
         </div>
+
+        <div style="margin-top:1rem; padding-top:.75rem; border-top:1px solid var(--border);">
+          <label style="font-size:.82rem; color:var(--text-muted)">⏱ Déclencher le flash
+            <strong id="pre-flash-val">0.5</strong> s avant la fin du countdown</label>
+          <input type="range" id="pre-flash-advance" min="0" max="3" step="0.1" value="0.5"
+                 oninput="document.getElementById('pre-flash-val').textContent=parseFloat(this.value).toFixed(1)"
+                 style="width:100%; margin-top:.4rem">
+          <div style="display:flex; justify-content:space-between; font-size:.72rem; color:var(--text-muted)">
+            <span>0 s (au moment de la capture)</span><span>3 s (très en avance)</span>
+          </div>
+          <button class="btn btn-primary btn-sm" style="margin-top:.5rem" onclick="savePreFlash()">&#x1F4BE; Sauvegarder</button>
+          <span id="pre-flash-status" style="font-size:.82rem; color:var(--text-muted); margin-left:.5rem"></span>
+        </div>
       </div>
     </div>
 
@@ -883,6 +896,25 @@ async function loadFlashConfig() {
       document.getElementById('flash-count').value = cap.flashes;
     }
   } catch(e) { console.warn('loadFlashConfig:', e); }
+  // Charger le timing pre-flash
+  try {
+    const t = await api('GET', '/api/leds/flash-timing');
+    const v = t.pre_flash_advance ?? 0.5;
+    document.getElementById('pre-flash-advance').value = v;
+    document.getElementById('pre-flash-val').textContent = v.toFixed(1);
+  } catch(e) { console.warn('loadFlashTiming:', e); }
+}
+
+async function savePreFlash() {
+  const v = parseFloat(document.getElementById('pre-flash-advance').value);
+  const status = document.getElementById('pre-flash-status');
+  try {
+    await api('PUT', `/api/leds/flash-timing?pre_flash_advance=${v}`);
+    status.textContent = `✅ Sauvegardé (${v.toFixed(1)} s)`;
+    setTimeout(() => status.textContent = '', 3000);
+  } catch(e) {
+    status.textContent = '❌ Erreur';
+  }
 }
 
 async function measureAmbient() {