type FlagValue = boolean | string | number;

interface FeatureFlag {
  key: string;
  value: FlagValue;
  environment: 'production' | 'staging' | 'development';
}

class FeatureFlagService {
  private static instance: FeatureFlagService | null = null;
  private flags = new Map<string, FlagValue>();
  private lastFetchedAt: Date | null = null;
  private readonly TTL_MS = 60_000; // refresh every minute

  private constructor() {
    // Lazy initialization — flags loaded on first use
  }

  static getInstance(): FeatureFlagService {
    if (!FeatureFlagService.instance) {
      FeatureFlagService.instance = new FeatureFlagService();
    }
    return FeatureFlagService.instance;
  }

  async loadFlags(apiUrl: string): Promise<void> {
    const now = new Date();
    const isStale =
      !this.lastFetchedAt ||
      now.getTime() - this.lastFetchedAt.getTime() > this.TTL_MS;

    if (!isStale) return; // use cached values

    const response = await fetch(apiUrl);
    const data: FeatureFlag[] = await response.json();

    this.flags.clear();
    for (const flag of data) {
      this.flags.set(flag.key, flag.value);
    }
    this.lastFetchedAt = now;
  }

  isEnabled(key: string): boolean {
    return Boolean(this.flags.get(key));
  }

  get<T extends FlagValue>(key: string, defaultValue: T): T {
    return (this.flags.get(key) as T) ?? defaultValue;
  }
}

// בכל מקום באפליקציה — אותו Service
const flags = FeatureFlagService.getInstance();

if (flags.isEnabled('new-checkout-flow')) {
  // הצג checkout חדש
}

const maxRetries = flags.get<number>('payment-max-retries', 3);
Singleton Pattern — מופע יחיד

Singleton Pattern — מופע יחיד

Singleton Pattern — מופע יחיד
