SkyArtShop/backend/config/database.js

const { Pool } = require("pg");
const crypto = require("crypto");
const logger = require("./logger");
require("dotenv").config();

const pool = new Pool({
  host: process.env.DB_HOST || "localhost",
  port: process.env.DB_PORT || 5432,
  database: process.env.DB_NAME || "skyartshop",
  user: process.env.DB_USER || "skyartapp",
  password: process.env.DB_PASSWORD,
  max: 30, // Increased to 30 for higher concurrency
  min: 10, // Keep 10 connections warm for instant response
  idleTimeoutMillis: 60000,
  connectionTimeoutMillis: 3000,
  application_name: "skyartshop-api",
  keepAlive: true, // TCP keepalive
  keepAliveInitialDelayMillis: 10000,
  statement_timeout: 30000, // 30s query timeout
});

pool.on("connect", () => logger.info("✓ PostgreSQL connected"));
pool.on("error", (err) => logger.error("PostgreSQL error:", err));

// Query cache for SELECT statements with crypto-based keys
const queryCache = new Map();
const queryCacheOrder = []; // LRU tracking
const QUERY_CACHE_TTL = 15000; // 15 seconds (increased)
const QUERY_CACHE_MAX_SIZE = 500; // 500 cached queries (increased)
const SLOW_QUERY_THRESHOLD = 50; // 50ms threshold (stricter)

// Generate fast cache key using crypto hash
const getCacheKey = (text, params) => {
  const hash = crypto.createHash("md5");
  hash.update(text);
  if (params) hash.update(JSON.stringify(params));
  return hash.digest("hex");
};

const query = async (text, params) => {
  const start = Date.now();
  const isSelect = text.trim().toUpperCase().startsWith("SELECT");

  // Check cache for SELECT queries
  if (isSelect) {
    const cacheKey = getCacheKey(text, params);
    const cached = queryCache.get(cacheKey);

    if (cached && Date.now() - cached.timestamp < QUERY_CACHE_TTL) {
      logger.debug("Query cache hit", { duration: Date.now() - start });
      return cached.data;
    }
  }

  try {
    const res = await pool.query(text, params);
    const duration = Date.now() - start;

    // Cache SELECT queries with LRU eviction
    if (isSelect) {
      const cacheKey = getCacheKey(text, params);

      // LRU eviction
      if (queryCache.size >= QUERY_CACHE_MAX_SIZE) {
        const oldestKey = queryCacheOrder.shift();
        if (oldestKey) queryCache.delete(oldestKey);
      }

      queryCache.set(cacheKey, { data: res, timestamp: Date.now() });
      queryCacheOrder.push(cacheKey);
    }

    // Log slow queries
    if (duration > SLOW_QUERY_THRESHOLD) {
      logger.warn("Slow query", {
        duration,
        text: text.substring(0, 100),
        rows: res.rowCount,
        params: params?.length || 0,
      });
    }

    return res;
  } catch (error) {
    const duration = Date.now() - start;
    logger.error("Query error", {
      text: text.substring(0, 100),
      error: error.message,
      duration,
      code: error.code,
    });
    throw error;
  }
};

// Transaction helper
const transaction = async (callback) => {
  const client = await pool.connect();
  try {
    await client.query("BEGIN");
    const result = await callback(client);
    await client.query("COMMIT");
    return result;
  } catch (error) {
    await client.query("ROLLBACK");
    logger.error("Transaction rolled back:", error);
    throw error;
  } finally {
    client.release();
  }
};

// Batch query execution for parallel operations
const batchQuery = async (queries) => {
  try {
    const results = await Promise.all(
      queries.map(({ text, params }) => query(text, params))
    );
    return results;
  } catch (error) {
    logger.error("Batch query error:", error);
    throw error;
  }
};

// Clear query cache (useful for cache invalidation)
const clearQueryCache = (pattern) => {
  if (pattern) {
    // Clear specific pattern
    for (const key of queryCache.keys()) {
      if (key.includes(pattern)) {
        queryCache.delete(key);
      }
    }
  } else {
    // Clear all
    queryCache.clear();
    queryCacheOrder.length = 0;
  }
  logger.info("Query cache cleared", { pattern: pattern || "all" });
};

// Health check with pool metrics
const healthCheck = async () => {
  try {
    const result = await query(
      "SELECT NOW() as time, current_database() as database"
    );
    return {
      healthy: true,
      database: result.rows[0].database,
      timestamp: result.rows[0].time,
      pool: {
        total: pool.totalCount,
        idle: pool.idleCount,
        waiting: pool.waitingCount,
      },
      cache: {
        size: queryCache.size,
        maxSize: QUERY_CACHE_MAX_SIZE,
      },
    };
  } catch (error) {
    logger.error("Database health check failed:", error);
    return {
      healthy: false,
      error: error.message,
    };
  }
};

module.exports = {
  pool,
  query,
  transaction,
  batchQuery,
  clearQueryCache,
  healthCheck,
};