Release Management

// Feature Flag Implementation
interface FeatureFlag {
  key: string;
  name: string;
  description: string;
  type: 'release' | 'experiment' | 'ops' | 'permission';
  status: 'enabled' | 'disabled' | 'percentage' | 'user-segment';
  rolloutPercentage?: number;
  targetUsers?: string[];
  targetSegments?: string[];
  createdDate: Date;
  owner: string;
  expiryDate?: Date; // Feature flags should not live forever
}

// Simple feature flag service
class FeatureFlagService {
  private flags: Map = new Map();

  isEnabled(flagKey: string, userId?: string): boolean {
    const flag = this.flags.get(flagKey);
    if (!flag) return false;

    switch (flag.status) {
      case 'enabled':
        return true;
      case 'disabled':
        return false;
      case 'percentage':
        if (!userId || !flag.rolloutPercentage) return false;
        // Deterministic hash for consistent user experience
        const hash = this.hashUserId(userId, flagKey);
        return hash < flag.rolloutPercentage;
      case 'user-segment':
        if (!userId) return false;
        return flag.targetUsers?.includes(userId) ?? false;
      default:
        return false;
    }
  }

  private hashUserId(userId: string, flagKey: string): number {
    let hash = 0;
    const str = `${userId}:${flagKey}`;
    for (let i = 0; i < str.length; i++) {
      const char = str.charCodeAt(i);
      hash = ((hash << 5) - hash) + char;
      hash = hash & hash; // Convert to 32-bit integer
    }
    return Math.abs(hash) % 100;
  }
}

// Usage in application code
const featureFlags = new FeatureFlagService();

function renderCheckout(userId: string) {
  if (featureFlags.isEnabled('new-checkout-flow', userId)) {
    return renderNewCheckout();
  }
  return renderLegacyCheckout();
}

// Deployment Strategies
type DeploymentStrategy = {
  name: string;
  description: string;
  riskLevel: 'low' | 'medium' | 'high';
  rollbackTime: string;
  resourceCost: string;
};

const deploymentStrategies: DeploymentStrategy[] = [
  {
    name: 'Blue-Green',
    description: 'Maintain two identical environments. Deploy to inactive (green), switch traffic from active (blue) to green.',
    riskLevel: 'low',
    rollbackTime: 'Seconds (switch back to blue)',
    resourceCost: 'High (2x infrastructure)'
  },
  {
    name: 'Canary',
    description: 'Route a small percentage (1-5%) of traffic to the new version. Gradually increase if metrics look good.',
    riskLevel: 'low',
    rollbackTime: 'Seconds (route all traffic to old version)',
    resourceCost: 'Medium (small additional capacity)'
  },
  {
    name: 'Rolling',
    description: 'Gradually replace old instances with new ones, one at a time or in batches.',
    riskLevel: 'medium',
    rollbackTime: 'Minutes (redeploy old version)',
    resourceCost: 'Low (no extra infrastructure)'
  },
  {
    name: 'Big Bang',
    description: 'Replace everything at once during a maintenance window.',
    riskLevel: 'high',
    rollbackTime: 'Minutes to hours',
    resourceCost: 'Low'
  }
];