Caching & Performance - 2/2

// Database query analyzer and optimizer
class QueryOptimizer {
  private database: Database;
  private queryStats: Map<string, QueryMetrics> = new Map();
  private slowQueryThreshold: number = 500; // ms

  async analyzeQuery(query: string, params: any[]): Promise<QueryAnalysis> {
    const queryId = this.hashQuery(query);
    const startTime = performance.now();

    // Get query execution plan
    const executionPlan = await this.database.query(
      `EXPLAIN (ANALYZE, BUFFERS, FORMAT JSON) ${query}`,
      params
    );

    const actualRunTime = performance.now() - startTime;

    // Parse execution plan for bottlenecks
    const analysis = this.parseExecutionPlan(executionPlan[0]["QUERY PLAN"][0]);

    // Track query performance
    this.trackQueryPerformance(queryId, actualRunTime, analysis);

    return {
      queryId,
      executionTime: actualRunTime,
      estimatedCost: analysis.totalCost,
      indexUsage: analysis.indexScans,
      sequentialScans: analysis.seqScans,
      recommendations: this.generateRecommendations(analysis),
    };
  }

  // Automatic index recommendation based on query patterns
  async generateIndexRecommendations(): Promise<IndexRecommendation[]> {
    const recommendations: IndexRecommendation[] = [];

    // Find queries with high sequential scan costs
    for (const [queryId, metrics] of this.queryStats.entries()) {
      if (metrics.avgSeqScanCost > 1000 && metrics.executionCount > 100) {
        const query = metrics.sampleQuery;
        const tables = this.extractTablesFromQuery(query);
        const whereConditions = this.extractWhereConditions(query);

        recommendations.push({
          type: "composite_index",
          table: tables[0], // Primary table
          columns: whereConditions.map((c) => c.column),
          reason: `High sequential scan cost (${metrics.avgSeqScanCost}) with ${metrics.executionCount} executions`,
          estimatedImprovement: this.calculateIndexBenefit(metrics),
          priority: this.calculateIndexPriority(metrics),
        });
      }
    }

    return recommendations.sort((a, b) => b.priority - a.priority);
  }

  // Smart query rewriting for common anti-patterns
  async optimizeQuery(originalQuery: string): Promise<OptimizedQuery> {
    let optimizedQuery = originalQuery;
    const optimizations: string[] = [];

    // Replace SELECT * with specific columns where possible
    if (optimizedQuery.includes("SELECT *")) {
      const suggestedColumns = await this.suggestRequiredColumns(originalQuery);
      optimizations.push(
        "Consider selecting only required columns instead of SELECT *"
      );
    }

    // Optimize IN clauses with many values
    const inMatches = optimizedQuery.match(/IN\s*\([^)]+\)/gi);
    if (inMatches) {
      for (const inClause of inMatches) {
        const valueCount = (inClause.match(/,/g) || []).length + 1;
        if (valueCount > 100) {
          optimizations.push(
            `Consider using a temporary table or VALUES clause instead of IN with ${valueCount} values`
          );
        }
      }
    }

    // Detect N+1 query patterns
    if (this.isLikelyNPlusOneQuery(originalQuery)) {
      optimizations.push(
        "Potential N+1 query detected - consider using JOINs or batch loading"
      );
    }

    // Suggest LIMIT for potentially large result sets
    if (
      !optimizedQuery.toUpperCase().includes("LIMIT") &&
      optimizedQuery.toUpperCase().includes("ORDER BY")
    ) {
      optimizations.push(
        "Consider adding LIMIT to ORDER BY queries to prevent large sorts"
      );
    }

    return {
      originalQuery,
      optimizedQuery,
      optimizations,
      estimatedImprovement: optimizations.length * 15, // Rough percentage
    };
  }

  // Advanced query caching with intelligent invalidation
  async executeCachedQuery<T>(
    query: string,
    params: any[],
    options: CacheQueryOptions = {}
  ): Promise<T> {
    const queryKey = this.generateQueryCacheKey(query, params);
    const cacheKey = `query:${queryKey}`;

    // Check if result is cached
    const cached = await this.queryCache.get(cacheKey);
    if (cached && !this.shouldInvalidateCache(cached, options)) {
      this.metrics.increment("db.query.cache_hit");
      return cached.result;
    }

    // Execute query with performance tracking
    const startTime = performance.now();
    const result = await this.database.query(query, params);
    const executionTime = performance.now() - startTime;

    // Cache result with metadata
    const cacheEntry = {
      result,
      executionTime,
      timestamp: Date.now(),
      tables: this.extractTablesFromQuery(query),
      invalidationTags: options.invalidationTags || [],
    };

    const ttl = this.calculateCacheTTL(executionTime, options.ttl);
    await this.queryCache.set(cacheKey, cacheEntry, ttl);

    this.metrics.increment("db.query.cache_miss");
    this.metrics.histogram("db.query.execution_time", executionTime);

    return result;
  }

  // Batch query optimization
  async executeBatchQueries(queries: BatchQuery[]): Promise<BatchResult[]> {
    // Group similar queries for batch execution
    const batchGroups = this.groupSimilarQueries(queries);
    const results: BatchResult[] = [];

    for (const group of batchGroups) {
      if (group.type === "SELECT_BY_ID" && group.queries.length > 1) {
        // Convert multiple SELECT queries into single IN query
        const optimized = this.optimizeSelectBatch(group);
        const batchResult = await this.database.query(
          optimized.query,
          optimized.params
        );

        // Map results back to individual queries
        for (let i = 0; i < group.queries.length; i++) {
          results.push({
            queryIndex: group.queries[i].index,
            result:
              batchResult.filter(
                (row) => row.id === group.queries[i].params[0]
              )[0] || null,
          });
        }
      } else {
        // Execute queries individually if no optimization possible
        for (const query of group.queries) {
          const result = await this.database.query(query.sql, query.params);
          results.push({
            queryIndex: query.index,
            result,
          });
        }
      }
    }

    return results.sort((a, b) => a.queryIndex - b.queryIndex);
  }
}

interface QueryAnalysis {
  queryId: string;
  executionTime: number;
  estimatedCost: number;
  indexUsage: number;
  sequentialScans: number;
  recommendations: string[];
}

interface OptimizedQuery {
  originalQuery: string;
  optimizedQuery: string;
  optimizations: string[];
  estimatedImprovement: number;
}

interface CacheQueryOptions {
  ttl?: number;
  invalidationTags?: string[];
  forceRefresh?: boolean;
}

// Intelligent database connection pool management
class DatabaseConnectionManager {
  private primaryPool: Pool;
  private replicaPools: Pool[];
  private connectionStats: ConnectionStats = {
    activeConnections: 0,
    idleConnections: 0,
    waitingClients: 0,
    totalConnections: 0,
    errors: 0,
  };

  constructor(config: DatabaseConfig) {
    // Primary database pool (writes and critical reads)
    this.primaryPool = new Pool({
      host: config.primary.host,
      database: config.primary.database,
      user: config.primary.user,
      password: config.primary.password,

      // Connection pool configuration
      min: 5, // Minimum connections
      max: 20, // Maximum connections

      // Connection lifecycle
      idleTimeoutMillis: 30000, // Close idle connections after 30s
      connectionTimeoutMillis: 2000, // Wait max 2s for connection
      acquireTimeoutMillis: 60000, // Wait max 60s to acquire connection

      // Health monitoring
      allowExitOnIdle: false,

      // Advanced settings
      statement_timeout: 30000, // Kill queries after 30s
      query_timeout: 10000, // Default query timeout 10s

      // Connection validation
      application_name: "myapp_primary",
    });

    // Read replica pools for load distribution
    this.replicaPools = config.replicas.map(
      (replica, index) =>
        new Pool({
          ...replica,
          min: 2,
          max: 10,
          application_name: `myapp_replica_${index}`,
        })
    );

    this.setupPoolMonitoring();
    this.startConnectionHealthChecks();
  }

  // Intelligent query routing
  async executeQuery<T>(
    query: string,
    params: any[] = [],
    options: QueryOptions = {}
  ): Promise<T> {
    const queryType = this.analyzeQueryType(query);
    const pool = this.selectOptimalPool(queryType, options);

    const client = await this.acquireConnection(pool, options.timeout);

    try {
      const startTime = performance.now();
      const result = await client.query(query, params);
      const executionTime = performance.now() - startTime;

      // Track query performance per pool
      this.trackQueryPerformance(pool.name, executionTime, queryType);

      return result.rows;
    } catch (error) {
      this.handleQueryError(error, pool, query);
      throw error;
    } finally {
      client.release();
    }
  }

  private selectOptimalPool(queryType: QueryType, options: QueryOptions): Pool {
    // Force primary for writes and transactions
    if (queryType === "WRITE" || options.requiresConsistency) {
      return this.primaryPool;
    }

    // Select best replica for reads
    if (queryType === "READ" && this.replicaPools.length > 0) {
      return this.selectBestReplica();
    }

    // Fallback to primary
    return this.primaryPool;
  }

  private selectBestReplica(): Pool {
    // Find replica with lowest current load
    let bestPool = this.replicaPools[0];
    let lowestLoad = this.getPoolLoad(bestPool);

    for (const pool of this.replicaPools.slice(1)) {
      const load = this.getPoolLoad(pool);
      if (load < lowestLoad) {
        lowestLoad = load;
        bestPool = pool;
      }
    }

    return bestPool;
  }

  private getPoolLoad(pool: Pool): number {
    // Calculate load based on active connections and wait queue
    const active = pool.totalCount - pool.idleCount;
    const waiting = pool.waitingCount;
    const capacity = pool.options.max;

    return (active + waiting * 2) / capacity; // Weight waiting clients higher
  }

  // Advanced connection pooling with circuit breaker
  async executeWithCircuitBreaker<T>(
    query: string,
    params: any[],
    options: QueryOptions = {}
  ): Promise<T> {
    const poolName = this.selectOptimalPool(
      this.analyzeQueryType(query),
      options
    ).name;

    const circuitBreaker = this.getCircuitBreaker(poolName);

    return await circuitBreaker.execute(async () => {
      return await this.executeQuery(query, params, options);
    });
  }

  // Dynamic pool scaling based on load
  async scaleConnectionPools(): Promise<void> {
    const stats = await this.getPoolStatistics();

    for (const [poolName, poolStats] of Object.entries(stats)) {
      const utilizationRate =
        poolStats.activeConnections / poolStats.maxConnections;
      const waitingRate = poolStats.waitingClients / poolStats.maxConnections;

      // Scale up if high utilization and clients waiting
      if (utilizationRate > 0.8 && waitingRate > 0.1) {
        await this.scalePoolUp(poolName, poolStats);
      }

      // Scale down if consistently low utilization
      if (utilizationRate < 0.3 && poolStats.averageUtilization < 0.3) {
        await this.scalePoolDown(poolName, poolStats);
      }
    }
  }

  private async scalePoolUp(poolName: string, stats: PoolStats): Promise<void> {
    const pool = this.getPoolByName(poolName);
    const currentMax = pool.options.max;
    const newMax = Math.min(currentMax + 5, 50); // Cap at 50 connections

    if (newMax > currentMax) {
      await this.reconfigurePool(poolName, { max: newMax });

      console.log(
        `Scaled up ${poolName} from ${currentMax} to ${newMax} connections`
      );

      this.metrics.increment(`db.pool.${poolName}.scaled_up`);
    }
  }

  private async scalePoolDown(
    poolName: string,
    stats: PoolStats
  ): Promise<void> {
    const pool = this.getPoolByName(poolName);
    const currentMax = pool.options.max;
    const newMax = Math.max(currentMax - 2, 5); // Minimum 5 connections

    if (newMax < currentMax) {
      await this.reconfigurePool(poolName, { max: newMax });

      console.log(
        `Scaled down ${poolName} from ${currentMax} to ${newMax} connections`
      );

      this.metrics.increment(`db.pool.${poolName}.scaled_down`);
    }
  }

  // Connection leak detection
  startConnectionLeakDetection(): void {
    setInterval(async () => {
      const stats = await this.getDetailedPoolStats();

      for (const [poolName, poolStats] of Object.entries(stats)) {
        // Check for connections held too long
        const longRunningConnections = poolStats.connections.filter(
          (conn) => Date.now() - conn.acquiredAt > 60000 // 1 minute
        );

        if (longRunningConnections.length > 0) {
          console.warn(
            `Detected ${longRunningConnections.length} long-running connections in ${poolName}`
          );

          // Log details for debugging
          longRunningConnections.forEach((conn) => {
            console.warn(
              `Connection ${conn.id} held for ${
                Date.now() - conn.acquiredAt
              }ms by ${conn.lastQuery}`
            );
          });

          this.metrics.increment(`db.pool.${poolName}.connection_leaks`);
        }
      }
    }, 30000); // Check every 30 seconds
  }

  // Database health monitoring
  async performHealthCheck(): Promise<HealthReport> {
    const healthResults: HealthCheckResult[] = [];

    // Check primary database
    healthResults.push(
      await this.checkDatabaseHealth(this.primaryPool, "primary")
    );

    // Check replicas
    for (let i = 0; i < this.replicaPools.length; i++) {
      healthResults.push(
        await this.checkDatabaseHealth(this.replicaPools[i], `replica_${i}`)
      );
    }

    const overallHealth = healthResults.every((result) => result.healthy)
      ? "healthy"
      : "degraded";

    return {
      overall: overallHealth,
      checks: healthResults,
      timestamp: new Date(),
      connectionStats: this.connectionStats,
    };
  }

  private async checkDatabaseHealth(
    pool: Pool,
    name: string
  ): Promise<HealthCheckResult> {
    try {
      const startTime = performance.now();
      await pool.query("SELECT 1");
      const responseTime = performance.now() - startTime;

      return {
        name,
        healthy: responseTime < 1000, // Healthy if response < 1s
        responseTime,
        activeConnections: pool.totalCount - pool.idleCount,
        idleConnections: pool.idleCount,
        waitingClients: pool.waitingCount,
      };
    } catch (error) {
      return {
        name,
        healthy: false,
        error: error.message,
        activeConnections: 0,
        idleConnections: 0,
        waitingClients: pool.waitingCount,
      };
    }
  }
}

interface QueryOptions {
  timeout?: number;
  requiresConsistency?: boolean;
  priority?: "high" | "medium" | "low";
}

type QueryType = "READ" | "WRITE" | "DDL" | "TRANSACTION";

interface ConnectionStats {
  activeConnections: number;
  idleConnections: number;
  waitingClients: number;
  totalConnections: number;
  errors: number;
}

// Advanced memory management and leak detection
class MemoryManager {
  private memorySnapshots: MemorySnapshot[] = [];
  private heapDumpPath: string;
  private gcStats: GCStats[] = [];

  constructor() {
    this.heapDumpPath = path.join(process.cwd(), "heap-dumps");
    this.setupGCMonitoring();
    this.startMemoryMonitoring();
  }

  // Memory usage tracking and analysis
  startMemoryMonitoring(): void {
    setInterval(() => {
      const usage = process.memoryUsage();
      const snapshot: MemorySnapshot = {
        timestamp: Date.now(),
        heapUsed: usage.heapUsed,
        heapTotal: usage.heapTotal,
        external: usage.external,
        rss: usage.rss,
        arrayBuffers: usage.arrayBuffers || 0,
      };

      this.memorySnapshots.push(snapshot);

      // Keep only last 100 snapshots
      if (this.memorySnapshots.length > 100) {
        this.memorySnapshots.shift();
      }

      // Analyze memory trends
      this.analyzeMemoryTrends(snapshot);

      // Record metrics
      this.metrics.gauge("memory.heap_used", usage.heapUsed);
      this.metrics.gauge("memory.heap_total", usage.heapTotal);
      this.metrics.gauge("memory.external", usage.external);
      this.metrics.gauge("memory.rss", usage.rss);
    }, 30000); // Every 30 seconds
  }

  private analyzeMemoryTrends(currentSnapshot: MemorySnapshot): void {
    if (this.memorySnapshots.length < 10) return;

    const recent = this.memorySnapshots.slice(-10);
    const growthRate = this.calculateGrowthRate(recent);

    // Memory leak detection
    if (growthRate.heapUsed > 0.02) {
      // Growing > 2% per interval
      console.warn(
        `Potential memory leak detected: heap growing at ${(
          growthRate.heapUsed * 100
        ).toFixed(2)}% per 30s`
      );

      this.metrics.increment("memory.potential_leak_detected");

      // Create heap dump for analysis
      this.createHeapDump("potential-leak");
    }

    // High memory usage warnings
    const heapUsedMB = currentSnapshot.heapUsed / (1024 * 1024);
    if (heapUsedMB > 512) {
      // > 512MB
      console.warn(`High memory usage: ${heapUsedMB.toFixed(2)}MB heap used`);

      if (heapUsedMB > 1024) {
        // > 1GB
        console.error(
          `Critical memory usage: ${heapUsedMB.toFixed(2)}MB heap used`
        );
        this.metrics.increment("memory.critical_usage");
      }
    }
  }

  // GC monitoring and optimization
  private setupGCMonitoring(): void {
    if (typeof (global as any).gc === "function") {
      const performanceObserver = new PerformanceObserver((list) => {
        const entries = list.getEntries();
        for (const entry of entries) {
          if (entry.name.startsWith("gc")) {
            const gcStats: GCStats = {
              timestamp: Date.now(),
              type: entry.name,
              duration: entry.duration,
              kind: (entry as any).detail?.kind || "unknown",
            };

            this.gcStats.push(gcStats);

            // Keep only last 50 GC events
            if (this.gcStats.length > 50) {
              this.gcStats.shift();
            }

            // Track GC performance
            this.metrics.histogram(
              `gc.${entry.name.replace("gc:", "")}.duration`,
              entry.duration
            );

            // Alert on long GC pauses
            if (entry.duration > 100) {
              // > 100ms
              console.warn(
                `Long GC pause detected: ${
                  entry.name
                } took ${entry.duration.toFixed(2)}ms`
              );
              this.metrics.increment("gc.long_pause");
            }
          }
        }
      });

      performanceObserver.observe({ entryTypes: ["gc"] });
    }
  }

  // Memory optimization strategies
  async optimizeMemoryUsage(): Promise<MemoryOptimizationResult> {
    const beforeUsage = process.memoryUsage();
    const optimizations: string[] = [];

    // Force garbage collection if available
    if (typeof (global as any).gc === "function") {
      (global as any).gc();
      optimizations.push("Forced garbage collection");
    }

    // Clear internal caches
    await this.clearInternalCaches();
    optimizations.push("Cleared internal caches");

    // Analyze and cleanup large objects
    const largeObjects = await this.findLargeObjects();
    if (largeObjects.length > 0) {
      optimizations.push(
        `Found ${largeObjects.length} large objects for cleanup`
      );
    }

    const afterUsage = process.memoryUsage();
    const savedMemory = beforeUsage.heapUsed - afterUsage.heapUsed;

    return {
      beforeMemory: beforeUsage,
      afterMemory: afterUsage,
      savedMemory,
      optimizations,
    };
  }

  // Create heap dump for debugging
  async createHeapDump(reason: string): Promise<string> {
    const timestamp = new Date().toISOString().replace(/[:.]/g, "-");
    const filename = `heap-dump-${reason}-${timestamp}.heapsnapshot`;
    const filepath = path.join(this.heapDumpPath, filename);

    // Ensure directory exists
    await fs.promises.mkdir(this.heapDumpPath, { recursive: true });

    if (typeof (process as any).getHeapSnapshot === "function") {
      const heapSnapshot = (process as any).getHeapSnapshot();
      const writeStream = fs.createWriteStream(filepath);

      await new Promise((resolve, reject) => {
        heapSnapshot.pipe(writeStream);
        writeStream.on("finish", resolve);
        writeStream.on("error", reject);
      });

      console.log(`Heap dump created: ${filepath}`);
      return filepath;
    } else {
      throw new Error(
        "Heap dump creation not supported in this Node.js version"
      );
    }
  }

  // Object pool for frequently created/destroyed objects
  createObjectPool<T>(
    factory: () => T,
    reset: (obj: T) => void,
    maxSize: number = 100
  ): ObjectPool<T> {
    return new ObjectPool(factory, reset, maxSize);
  }

  // Memory usage report
  generateMemoryReport(): MemoryReport {
    const currentUsage = process.memoryUsage();
    const recentGC = this.gcStats.slice(-10);
    const recentSnapshots = this.memorySnapshots.slice(-20);

    return {
      timestamp: new Date(),
      current: {
        heapUsed: currentUsage.heapUsed / (1024 * 1024), // MB
        heapTotal: currentUsage.heapTotal / (1024 * 1024), // MB
        external: currentUsage.external / (1024 * 1024), // MB
        rss: currentUsage.rss / (1024 * 1024), // MB
        arrayBuffers: (currentUsage.arrayBuffers || 0) / (1024 * 1024), // MB
      },
      trends: this.calculateMemoryTrends(recentSnapshots),
      gc: {
        recentEvents: recentGC.length,
        averageDuration:
          recentGC.reduce((sum, gc) => sum + gc.duration, 0) / recentGC.length,
        longestPause: Math.max(...recentGC.map((gc) => gc.duration)),
      },
      recommendations: this.generateMemoryRecommendations(
        currentUsage,
        recentGC
      ),
    };
  }

  private generateMemoryRecommendations(
    usage: NodeJS.MemoryUsage,
    recentGC: GCStats[]
  ): string[] {
    const recommendations: string[] = [];
    const heapUsedMB = usage.heapUsed / (1024 * 1024);

    if (heapUsedMB > 512) {
      recommendations.push(
        "Consider reducing heap usage - currently using more than 512MB"
      );
    }

    const avgGCDuration =
      recentGC.reduce((sum, gc) => sum + gc.duration, 0) / recentGC.length;
    if (avgGCDuration > 50) {
      recommendations.push(
        "GC pauses are high - consider optimizing object creation patterns"
      );
    }

    if (usage.external > usage.heapUsed) {
      recommendations.push(
        "High external memory usage - check for memory leaks in native modules"
      );
    }

    return recommendations;
  }
}

// Object pooling for memory optimization
class ObjectPool<T> {
  private pool: T[] = [];
  private inUse: Set<T> = new Set();

  constructor(
    private factory: () => T,
    private reset: (obj: T) => void,
    private maxSize: number = 100
  ) {}

  acquire(): T {
    let obj: T;

    if (this.pool.length > 0) {
      obj = this.pool.pop()!;
    } else {
      obj = this.factory();
    }

    this.inUse.add(obj);
    return obj;
  }

  release(obj: T): void {
    if (this.inUse.has(obj)) {
      this.inUse.delete(obj);
      this.reset(obj);

      if (this.pool.length < this.maxSize) {
        this.pool.push(obj);
      }
    }
  }

  getStats(): PoolStats {
    return {
      poolSize: this.pool.length,
      inUse: this.inUse.size,
      totalCreated: this.pool.length + this.inUse.size,
    };
  }
}

interface MemorySnapshot {
  timestamp: number;
  heapUsed: number;
  heapTotal: number;
  external: number;
  rss: number;
  arrayBuffers: number;
}

interface GCStats {
  timestamp: number;
  type: string;
  duration: number;
  kind: string;
}

interface MemoryOptimizationResult {
  beforeMemory: NodeJS.MemoryUsage;
  afterMemory: NodeJS.MemoryUsage;
  savedMemory: number;
  optimizations: string[];
}

// Comprehensive auto-scaling management
class AutoScalingManager {
  private currentInstances: Map<string, ServiceInstance[]> = new Map();
  private scalingPolicies: Map<string, ScalingPolicy> = new Map();
  private metrics: MetricsCollector;
  private cloudProvider: CloudProvider;

  constructor(cloudProvider: CloudProvider) {
    this.cloudProvider = cloudProvider;
    this.setupDefaultPolicies();
    this.startScalingMonitor();
  }

  // Define scaling policies for different services
  defineScalingPolicy(serviceName: string, policy: ScalingPolicy): void {
    this.scalingPolicies.set(serviceName, policy);
    console.log(`Scaling policy configured for ${serviceName}:`, policy);
  }

  // Horizontal scaling decision engine
  async evaluateScalingNeeds(): Promise<ScalingDecision[]> {
    const decisions: ScalingDecision[] = [];

    for (const [serviceName, policy] of this.scalingPolicies.entries()) {
      const currentMetrics = await this.getServiceMetrics(serviceName);
      const instances = this.currentInstances.get(serviceName) || [];

      const decision = this.makeScalingDecision(
        serviceName,
        policy,
        currentMetrics,
        instances
      );

      if (decision.action !== "none") {
        decisions.push(decision);
      }
    }

    return decisions;
  }

  private makeScalingDecision(
    serviceName: string,
    policy: ScalingPolicy,
    metrics: ServiceMetrics,
    instances: ServiceInstance[]
  ): ScalingDecision {
    const currentCount = instances.length;
    const avgCpuUsage = metrics.avgCpuUsage;
    const avgMemoryUsage = metrics.avgMemoryUsage;
    const requestRate = metrics.requestRate;
    const errorRate = metrics.errorRate;
    const responseTime = metrics.avgResponseTime;

    // Scale up conditions
    if (this.shouldScaleUp(metrics, policy, currentCount)) {
      const targetCount = Math.min(
        currentCount + policy.scaleUpIncrement,
        policy.maxInstances
      );

      return {
        serviceName,
        action: "scale_up",
        currentCount,
        targetCount,
        reason: this.getScaleUpReason(metrics, policy),
        priority: this.calculatePriority(metrics, policy),
      };
    }

    // Scale down conditions
    if (this.shouldScaleDown(metrics, policy, currentCount)) {
      const targetCount = Math.max(
        currentCount - policy.scaleDownIncrement,
        policy.minInstances
      );

      return {
        serviceName,
        action: "scale_down",
        currentCount,
        targetCount,
        reason: this.getScaleDownReason(metrics, policy),
        priority: 1, // Lower priority than scale up
      };
    }

    // Vertical scaling consideration
    if (this.shouldVerticalScale(metrics, policy)) {
      return {
        serviceName,
        action: "vertical_scale",
        currentCount,
        targetCount: currentCount,
        reason: "High resource utilization suggests vertical scaling",
        verticalScaleType:
          metrics.avgMemoryUsage > metrics.avgCpuUsage ? "memory" : "cpu",
      };
    }

    return {
      serviceName,
      action: "none",
      currentCount,
      targetCount: currentCount,
      reason: "Metrics within acceptable thresholds",
    };
  }

  private shouldScaleUp(
    metrics: ServiceMetrics,
    policy: ScalingPolicy,
    currentCount: number
  ): boolean {
    if (currentCount >= policy.maxInstances) return false;

    return (
      metrics.avgCpuUsage > policy.scaleUpThresholds.cpu ||
      metrics.avgMemoryUsage > policy.scaleUpThresholds.memory ||
      metrics.avgResponseTime > policy.scaleUpThresholds.responseTime ||
      metrics.requestRate > policy.scaleUpThresholds.requestRate ||
      metrics.errorRate > policy.scaleUpThresholds.errorRate
    );
  }

  private shouldScaleDown(
    metrics: ServiceMetrics,
    policy: ScalingPolicy,
    currentCount: number
  ): boolean {
    if (currentCount <= policy.minInstances) return false;

    // All conditions must be met for scale down (more conservative)
    return (
      metrics.avgCpuUsage < policy.scaleDownThresholds.cpu &&
      metrics.avgMemoryUsage < policy.scaleDownThresholds.memory &&
      metrics.avgResponseTime < policy.scaleDownThresholds.responseTime &&
      metrics.requestRate < policy.scaleDownThresholds.requestRate &&
      metrics.errorRate < policy.scaleDownThresholds.errorRate &&
      this.hasBeenStableFor(metrics, policy.cooldownPeriod)
    );
  }

  // Execute scaling decisions
  async executeScalingDecision(decision: ScalingDecision): Promise<void> {
    console.log(
      `Executing scaling decision for ${decision.serviceName}:`,
      decision
    );

    try {
      switch (decision.action) {
        case "scale_up":
          await this.scaleUp(decision);
          break;
        case "scale_down":
          await this.scaleDown(decision);
          break;
        case "vertical_scale":
          await this.verticalScale(decision);
          break;
      }

      this.metrics.increment(`scaling.${decision.action}.success`);
      this.recordScalingEvent(decision, "success");
    } catch (error) {
      console.error(`Scaling failed for ${decision.serviceName}:`, error);
      this.metrics.increment(`scaling.${decision.action}.failed`);
      this.recordScalingEvent(decision, "failed", error.message);
    }
  }

  private async scaleUp(decision: ScalingDecision): Promise<void> {
    const serviceName = decision.serviceName;
    const instancesToAdd = decision.targetCount - decision.currentCount;

    console.log(
      `Scaling up ${serviceName}: adding ${instancesToAdd} instances`
    );

    // Launch new instances
    const newInstances = await this.cloudProvider.launchInstances({
      serviceName,
      count: instancesToAdd,
      instanceConfig: this.getInstanceConfig(serviceName),
    });

    // Wait for instances to be healthy
    await this.waitForInstancesHealthy(newInstances);

    // Register instances with load balancer
    await this.cloudProvider.registerInstancesWithLB(serviceName, newInstances);

    // Update internal tracking
    const currentInstances = this.currentInstances.get(serviceName) || [];
    this.currentInstances.set(serviceName, [
      ...currentInstances,
      ...newInstances,
    ]);

    console.log(
      `Successfully scaled up ${serviceName} to ${decision.targetCount} instances`
    );
  }

  private async scaleDown(decision: ScalingDecision): Promise<void> {
    const serviceName = decision.serviceName;
    const instancesToRemove = decision.currentCount - decision.targetCount;

    console.log(
      `Scaling down ${serviceName}: removing ${instancesToRemove} instances`
    );

    const instances = this.currentInstances.get(serviceName) || [];

    // Select instances to terminate (oldest first, but avoid disrupting active sessions)
    const instancesToTerminate = await this.selectInstancesForTermination(
      instances,
      instancesToRemove
    );

    // Graceful shutdown process
    for (const instance of instancesToTerminate) {
      await this.gracefulShutdown(instance);
    }

    // Remove from load balancer
    await this.cloudProvider.deregisterInstancesFromLB(
      serviceName,
      instancesToTerminate
    );

    // Terminate instances
    await this.cloudProvider.terminateInstances(
      instancesToTerminate.map((i) => i.id)
    );

    // Update internal tracking
    const remainingInstances = instances.filter(
      (instance) => !instancesToTerminate.includes(instance)
    );
    this.currentInstances.set(serviceName, remainingInstances);

    console.log(
      `Successfully scaled down ${serviceName} to ${decision.targetCount} instances`
    );
  }

  // Cost optimization analysis
  async optimizeForCost(): Promise<CostOptimizationReport> {
    const optimizations: CostOptimization[] = [];
    let estimatedMonthlySavings = 0;

    for (const [serviceName, instances] of this.currentInstances.entries()) {
      const utilization = await this.getServiceUtilization(serviceName);

      // Identify under-utilized instances
      const underUtilized = instances.filter((instance) => {
        return utilization[instance.id] < 0.3; // Less than 30% utilized
      });

      if (underUtilized.length > 0) {
        const monthlyCost =
          underUtilized.length * this.getInstanceMonthlyCost(instances[0].type);

        optimizations.push({
          type: "right_sizing",
          serviceName,
          description: `${underUtilized.length} under-utilized instances can be downsized`,
          potentialSavings: monthlyCost * 0.5, // Assume 50% savings from smaller instances
          recommendedAction: "Replace with smaller instance types",
        });

        estimatedMonthlySavings += monthlyCost * 0.5;
      }

      // Identify opportunities for spot instances
      const policy = this.scalingPolicies.get(serviceName);
      if (policy && policy.spotInstancesAllowed) {
        const spotSavings =
          instances.length *
          this.getInstanceMonthlyCost(instances[0].type) *
          0.7; // 70% savings

        optimizations.push({
          type: "spot_instances",
          serviceName,
          description: `Convert ${instances.length} instances to spot instances`,
          potentialSavings: spotSavings,
          recommendedAction: "Implement mixed on-demand/spot instance strategy",
        });

        estimatedMonthlySavings += spotSavings;
      }
    }

    return {
      timestamp: new Date(),
      totalPotentialSavings: estimatedMonthlySavings,
      optimizations: optimizations.sort(
        (a, b) => b.potentialSavings - a.potentialSavings
      ),
    };
  }

  // Predictive scaling based on historical patterns
  async predictScalingNeeds(
    hoursAhead: number = 2
  ): Promise<ScalingPrediction[]> {
    const predictions: ScalingPrediction[] = [];

    for (const serviceName of this.scalingPolicies.keys()) {
      const historicalData = await this.getHistoricalMetrics(serviceName, 30); // Last 30 days
      const prediction = await this.predictDemand(historicalData, hoursAhead);

      const currentInstances = (this.currentInstances.get(serviceName) || [])
        .length;
      const predictedNeed = this.calculateRequiredInstances(prediction);

      if (Math.abs(predictedNeed - currentInstances) > 0) {
        predictions.push({
          serviceName,
          currentInstances,
          predictedInstances: predictedNeed,
          confidence: prediction.confidence,
          timeframe: `${hoursAhead} hours`,
          reasoning: prediction.reasoning,
        });
      }
    }

    return predictions;
  }
}

interface ScalingPolicy {
  minInstances: number;
  maxInstances: number;
  scaleUpThresholds: {
    cpu: number;
    memory: number;
    responseTime: number;
    requestRate: number;
    errorRate: number;
  };
  scaleDownThresholds: {
    cpu: number;
    memory: number;
    responseTime: number;
    requestRate: number;
    errorRate: number;
  };
  scaleUpIncrement: number;
  scaleDownIncrement: number;
  cooldownPeriod: number;
  spotInstancesAllowed: boolean;
}

interface ScalingDecision {
  serviceName: string;
  action: "scale_up" | "scale_down" | "vertical_scale" | "none";
  currentCount: number;
  targetCount: number;
  reason: string;
  priority?: number;
  verticalScaleType?: "cpu" | "memory";
}

interface ServiceMetrics {
  avgCpuUsage: number;
  avgMemoryUsage: number;
  requestRate: number;
  errorRate: number;
  avgResponseTime: number;
}

// Advanced APM system for production applications
class ApplicationPerformanceMonitor {
  private metrics: MetricsCollector;
  private traces: Map<string, TraceSpan[]> = new Map();
  private alerts: AlertManager;
  private dashboards: DashboardManager;

  constructor() {
    this.setupMetricsCollection();
    this.setupDistributedTracing();
    this.startPerformanceAnalysis();
  }

  // Request-level performance tracking
  async trackRequest<T>(
    requestId: string,
    operation: string,
    handler: () => Promise<T>
  ): Promise<T> {
    const span = this.startSpan(requestId, operation);

    try {
      const result = await handler();
      this.endSpan(span, { status: "success" });
      return result;
    } catch (error) {
      this.endSpan(span, {
        status: "error",
        error: error.message,
        stackTrace: error.stack,
      });
      throw error;
    }
  }

  // Database operation monitoring
  async trackDatabaseOperation<T>(
    query: string,
    params: any[],
    executor: () => Promise<T>
  ): Promise<T> {
    const operationId = uuidv4();
    const startTime = Date.now();

    this.metrics.increment("db.operations.total");

    try {
      const result = await executor();
      const duration = Date.now() - startTime;

      this.metrics.histogram("db.operations.duration", duration);
      this.metrics.increment("db.operations.success");

      // Track slow queries
      if (duration > 1000) {
        this.recordSlowQuery(query, params, duration);
      }

      return result;
    } catch (error) {
      this.metrics.increment("db.operations.error");
      this.recordDatabaseError(query, error);
      throw error;
    }
  }

  // Custom business metrics tracking
  trackBusinessMetric(
    name: string,
    value: number,
    tags: Record<string, string> = {}
  ): void {
    this.metrics.gauge(`business.${name}`, value, tags);

    // Real-time alerting for critical business metrics
    if (this.isCriticalBusinessMetric(name)) {
      this.evaluateBusinessMetricThresholds(name, value, tags);
    }
  }

  // Performance anomaly detection
  async detectAnomalies(): Promise<PerformanceAnomaly[]> {
    const anomalies: PerformanceAnomaly[] = [];
    const currentMetrics = await this.getCurrentMetrics();
    const historicalBaseline = await this.getHistoricalBaseline();

    // CPU usage anomalies
    if (currentMetrics.cpuUsage > historicalBaseline.cpuUsage * 1.5) {
      anomalies.push({
        type: "cpu_spike",
        severity: "high",
        description: `CPU usage ${currentMetrics.cpuUsage}% is ${(
          (currentMetrics.cpuUsage / historicalBaseline.cpuUsage - 1) *
          100
        ).toFixed(1)}% above baseline`,
        currentValue: currentMetrics.cpuUsage,
        baselineValue: historicalBaseline.cpuUsage,
        timestamp: new Date(),
      });
    }

    // Memory usage anomalies
    if (currentMetrics.memoryUsage > historicalBaseline.memoryUsage * 1.3) {
      anomalies.push({
        type: "memory_spike",
        severity: "medium",
        description: `Memory usage is ${(
          (currentMetrics.memoryUsage / historicalBaseline.memoryUsage - 1) *
          100
        ).toFixed(1)}% above baseline`,
        currentValue: currentMetrics.memoryUsage,
        baselineValue: historicalBaseline.memoryUsage,
        timestamp: new Date(),
      });
    }

    // Response time anomalies
    if (
      currentMetrics.avgResponseTime >
      historicalBaseline.avgResponseTime * 2
    ) {
      anomalies.push({
        type: "response_time_spike",
        severity: "high",
        description: `Response time ${currentMetrics.avgResponseTime}ms is significantly above baseline ${historicalBaseline.avgResponseTime}ms`,
        currentValue: currentMetrics.avgResponseTime,
        baselineValue: historicalBaseline.avgResponseTime,
        timestamp: new Date(),
      });
    }

    // Error rate anomalies
    if (currentMetrics.errorRate > historicalBaseline.errorRate * 3) {
      anomalies.push({
        type: "error_rate_spike",
        severity: "critical",
        description: `Error rate ${(currentMetrics.errorRate * 100).toFixed(
          2
        )}% is critically high`,
        currentValue: currentMetrics.errorRate,
        baselineValue: historicalBaseline.errorRate,
        timestamp: new Date(),
      });
    }

    return anomalies;
  }

  // Real-time performance dashboard
  async generatePerformanceDashboard(): Promise<PerformanceDashboard> {
    const now = new Date();
    const last24h = new Date(now.getTime() - 24 * 60 * 60 * 1000);

    return {
      timestamp: now,
      overview: {
        requestsPerSecond: await this.metrics.getRate("requests.total"),
        averageResponseTime: await this.metrics.getAverage("requests.duration"),
        errorRate:
          (await this.metrics.getRate("requests.errors")) /
          (await this.metrics.getRate("requests.total")),
        activeUsers: await this.metrics.getGauge("users.active"),
        systemLoad: await this.getSystemLoad(),
      },
      trends: {
        responseTimeTrend: await this.getMetricTrend(
          "requests.duration",
          last24h,
          now
        ),
        errorRateTrend: await this.getMetricTrend(
          "requests.errors",
          last24h,
          now
        ),
        throughputTrend: await this.getMetricTrend(
          "requests.total",
          last24h,
          now
        ),
      },
      topEndpoints: await this.getTopEndpointsByUsage(),
      slowestEndpoints: await this.getSlowestEndpoints(),
      databasePerformance: await this.getDatabasePerformanceMetrics(),
      cachePerformance: await this.getCachePerformanceMetrics(),
      alerts: await this.getActiveAlerts(),
    };
  }

  // Distributed tracing correlation
  private startSpan(traceId: string, operation: string): TraceSpan {
    const span: TraceSpan = {
      traceId,
      spanId: uuidv4(),
      operation,
      startTime: Date.now(),
      tags: {},
      logs: [],
    };

    const spans = this.traces.get(traceId) || [];
    spans.push(span);
    this.traces.set(traceId, spans);

    return span;
  }

  private endSpan(span: TraceSpan, metadata: any): void {
    span.endTime = Date.now();
    span.duration = span.endTime - span.startTime;
    span.metadata = metadata;

    // Record span metrics
    this.metrics.histogram(`spans.${span.operation}.duration`, span.duration);

    if (metadata.status === "error") {
      this.metrics.increment(`spans.${span.operation}.errors`);
    } else {
      this.metrics.increment(`spans.${span.operation}.success`);
    }
  }

  // Performance regression detection
  async detectRegressions(): Promise<PerformanceRegression[]> {
    const regressions: PerformanceRegression[] = [];
    const current = await this.getRecentPerformanceData(1); // Last 1 hour
    const baseline = await this.getRecentPerformanceData(24); // Last 24 hours

    // Check for response time regressions
    for (const [endpoint, currentMetrics] of Object.entries(
      current.endpoints
    )) {
      const baselineMetrics = baseline.endpoints[endpoint];

      if (
        baselineMetrics &&
        currentMetrics.avgResponseTime > baselineMetrics.avgResponseTime * 1.5
      ) {
        regressions.push({
          type: "response_time",
          endpoint,
          currentValue: currentMetrics.avgResponseTime,
          baselineValue: baselineMetrics.avgResponseTime,
          regressionPercentage:
            (currentMetrics.avgResponseTime / baselineMetrics.avgResponseTime -
              1) *
            100,
          confidence: this.calculateRegressionConfidence(
            currentMetrics,
            baselineMetrics
          ),
          detectedAt: new Date(),
        });
      }
    }

    return regressions.filter((r) => r.confidence > 0.8); // Only high-confidence regressions
  }

  // Capacity planning recommendations
  async generateCapacityRecommendations(): Promise<CapacityRecommendation[]> {
    const recommendations: CapacityRecommendation[] = [];
    const projectedGrowth = await this.calculateGrowthProjection();
    const currentCapacity = await this.getCurrentCapacityMetrics();

    // CPU capacity analysis
    const projectedCpuUsage =
      currentCapacity.cpuUsage * projectedGrowth.trafficGrowth;
    if (projectedCpuUsage > 70) {
      recommendations.push({
        resource: "cpu",
        currentUsage: currentCapacity.cpuUsage,
        projectedUsage: projectedCpuUsage,
        recommendation:
          projectedCpuUsage > 90 ? "scale_urgently" : "plan_scaling",
        timeframe: "30 days",
        description: `CPU usage projected to reach ${projectedCpuUsage.toFixed(
          1
        )}% based on current growth trends`,
      });
    }

    // Memory capacity analysis
    const projectedMemoryUsage =
      currentCapacity.memoryUsage * projectedGrowth.dataGrowth;
    if (projectedMemoryUsage > 80) {
      recommendations.push({
        resource: "memory",
        currentUsage: currentCapacity.memoryUsage,
        projectedUsage: projectedMemoryUsage,
        recommendation: "plan_scaling",
        timeframe: "30 days",
        description: `Memory usage projected to reach ${projectedMemoryUsage.toFixed(
          1
        )}% based on data growth`,
      });
    }

    // Database capacity analysis
    const dbGrowthRate = await this.calculateDatabaseGrowthRate();
    if (dbGrowthRate > 0.1) {
      // Growing more than 10% per month
      recommendations.push({
        resource: "database",
        currentUsage: currentCapacity.databaseUsage,
        projectedUsage: currentCapacity.databaseUsage * (1 + dbGrowthRate),
        recommendation: "optimize_queries",
        timeframe: "60 days",
        description: `Database load growing at ${(dbGrowthRate * 100).toFixed(
          1
        )}% per month`,
      });
    }

    return recommendations;
  }
}

interface TraceSpan {
  traceId: string;
  spanId: string;
  operation: string;
  startTime: number;
  endTime?: number;
  duration?: number;
  tags: Record<string, string>;
  logs: any[];
  metadata?: any;
}

interface PerformanceAnomaly {
  type: string;
  severity: "low" | "medium" | "high" | "critical";
  description: string;
  currentValue: number;
  baselineValue: number;
  timestamp: Date;
}

interface PerformanceDashboard {
  timestamp: Date;
  overview: {
    requestsPerSecond: number;
    averageResponseTime: number;
    errorRate: number;
    activeUsers: number;
    systemLoad: number;
  };
  trends: Record<string, number[]>;
  topEndpoints: Array<{ endpoint: string; requestCount: number }>;
  slowestEndpoints: Array<{ endpoint: string; avgResponseTime: number }>;
  databasePerformance: any;
  cachePerformance: any;
  alerts: any[];
}