feat: integrate CircuitBreakerService and adjust request timeout and queue management for improved API stability

src/lib/services/circuit-breaker.service.ts

@@ -0,0 +1,78 @@
+/**
+ * Circuit Breaker pour éviter de surcharger Komga quand il est défaillant
+ * Évite l'effet avalanche en coupant les requêtes vers un service défaillant
+ */
+interface CircuitBreakerState {
+  state: 'CLOSED' | 'OPEN' | 'HALF_OPEN';
+  failureCount: number;
+  lastFailureTime: number;
+  nextAttemptTime: number;
+}
+
+class CircuitBreaker {
+  private state: CircuitBreakerState = {
+    state: 'CLOSED',
+    failureCount: 0,
+    lastFailureTime: 0,
+    nextAttemptTime: 0,
+  };
+
+  private readonly config = {
+    failureThreshold: 5, // Nombre d'échecs avant ouverture
+    recoveryTimeout: 30000, // 30s avant tentative de récupération
+    successThreshold: 3, // Nombre de succès pour fermer le circuit
+  };
+
+  async execute<T>(operation: () => Promise<T>): Promise<T> {
+    if (this.state.state === 'OPEN') {
+      if (Date.now() < this.state.nextAttemptTime) {
+        throw new Error('Circuit breaker is OPEN - Komga service unavailable');
+      }
+      this.state.state = 'HALF_OPEN';
+    }
+
+    try {
+      const result = await operation();
+      this.onSuccess();
+      return result;
+    } catch (error) {
+      this.onFailure();
+      throw error;
+    }
+  }
+
+  private onSuccess(): void {
+    if (this.state.state === 'HALF_OPEN') {
+      this.state.failureCount = 0;
+      this.state.state = 'CLOSED';
+      console.log('[CIRCUIT-BREAKER] ✅ Circuit closed - Komga recovered');
+    }
+  }
+
+  private onFailure(): void {
+    this.state.failureCount++;
+    this.state.lastFailureTime = Date.now();
+
+    if (this.state.failureCount >= this.config.failureThreshold) {
+      this.state.state = 'OPEN';
+      this.state.nextAttemptTime = Date.now() + this.config.recoveryTimeout;
+      console.warn(`[CIRCUIT-BREAKER] 🔴 Circuit OPEN - Komga failing (${this.state.failureCount} failures)`);
+    }
+  }
+
+  getState(): CircuitBreakerState {
+    return { ...this.state };
+  }
+
+  reset(): void {
+    this.state = {
+      state: 'CLOSED',
+      failureCount: 0,
+      lastFailureTime: 0,
+      nextAttemptTime: 0,
+    };
+    console.log('[CIRCUIT-BREAKER] 🔄 Circuit reset');
+  }
+}
+
+export const CircuitBreakerService = new CircuitBreaker();