Redis & Caching Strategy untuk Developer

const Redis = require('ioredis');
const redis = new Redis();
const db = require('./database'); // Database connection

// ==========================================
// CACHE-ASIDE PATTERN
// ==========================================

async function getProductById(productId) {
  const cacheKey = `product:${productId}`;

  // Langkah 1: Cek cache
  const cached = await redis.get(cacheKey);
  if (cached) {
    console.log('✅ Cache HIT');
    return JSON.parse(cached);
  }

  // Langkah 2: Cache MISS — query database
  console.log('❌ Cache MISS — querying database');
  const product = await db.query(
    'SELECT * FROM products WHERE id = ?', [productId]
  );

  if (!product) return null;

  // Langkah 3: Simpan ke cache dengan TTL 1 jam
  await redis.setex(cacheKey, 3600, JSON.stringify(product));

  return product;
}

// ==========================================
// CACHE INVALIDATION
// ==========================================

async function updateProduct(productId, newData) {
  // Update database dulu
  await db.query(
    'UPDATE products SET name = ?, price = ? WHERE id = ?',
    [newData.name, newData.price, productId]
  );

  // Hapus cache (bukan update!) — biar lazy reload
  await redis.del(`product:${productId}`);

  // Atau: update cache langsung (write-through ringan)
  const updated = { id: productId, ...newData };
  await redis.setex(`product:${productId}`, 3600, JSON.stringify(updated));
}

// ==========================================
// WRITE-THROUGH PATTERN
// ==========================================

async function createProduct(productData) {
  // Langkah 1: Tulis ke database
  const result = await db.query(
    'INSERT INTO products (name, price, stock) VALUES (?, ?, ?)',
    [productData.name, productData.price, productData.stock]
  );

  const newProduct = {
    id: result.insertId,
    ...productData,
    created_at: new Date().toISOString()
  };

  // Langkah 2: Tulis ke cache SEKALIGUS
  const cacheKey = `product:${newProduct.id}`;
  await redis.setex(cacheKey, 3600, JSON.stringify(newProduct));

  // Langkah 3: Tambahkan ke list produk terbaru
  await redis.lpush('products:latest', JSON.stringify(newProduct));
  await redis.ltrim('products:latest', 0, 49); // Simpan 50 terbaru

  return newProduct;
}

// Kelebihan: Cache selalu up-to-date
// Kekurangan: Write latency lebih tinggi (harus tulis ke 2 tempat)
// Cocok untuk: Data yang sering dibaca dan jarang diubah

// ==========================================
// WRITE-BEHIND PATTERN
// Data ditulis ke cache dulu, database di-update belakangan
// ==========================================

const writeQueue = [];

async function updatePageView(pageId) {
  // Langkah 1: Tulis ke Redis (sangat cepat)
  await redis.incr(`page:${pageId}:views`);

  // Langkah 2: Tambahkan ke queue untuk update database nanti
  writeQueue.push({
    type: 'page_view',
    pageId: pageId,
    timestamp: Date.now()
  });
}

// Background worker — flush ke database setiap 10 detik
setInterval(async () => {
  if (writeQueue.length === 0) return;

  const batch = writeQueue.splice(0, writeQueue.length);
  console.log(`Flushing ${batch.length} writes ke database...`);

  try {
    // Batch update ke database
    for (const item of batch) {
      await db.query(
        'UPDATE pages SET views = views + 1 WHERE id = ?',
        [item.pageId]
      );
    }
  } catch (err) {
    console.error('Flush error:', err);
    // Kembalikan ke queue untuk retry
    writeQueue.unshift(...batch);
  }
}, 10000);

// Cocok untuk: Counter, analytics, logging — data yang toleran kehilangan
// ⚠️ Risiko: Data hilang jika Redis crash sebelum flush