04_GraphQLAPI_Melvyn/pages/api/graphql.js

const { ApolloServer } = require('@apollo/server');
const { startServerAndCreateNextHandler } = require('@as-integrations/next');
const { Pool } = require('pg');

// 1. Inisialisasi Pool PostgreSQL untuk Serverless
const pool = new Pool({
  connectionString: process.env.DATABASE_URL,
  ssl: {
    rejectUnauthorized: false,
  },
  max: 1,
});

// 2. Definisi Schema GraphQL
const typeDefs = `#graphql
  type Category {
    id: ID!
    name: String!
    description: String
    products: [Product!]!
  }

  type Product {
    id: ID!
    title: String!
    price: Float!
    category_id: Int
    created_by: ID
    category: Category
  }

  type Query {
    categories: [Category!]!
    category(id: ID!): Category
    products: [Product!]!
    product(id: ID!): Product
  }
`;

// 3. Plugin Apollo untuk menyuntikkan log counter ke response extensions
const metricsPlugin = {
  async requestDidStart() {
    return {
      async willSendResponse({ response, contextValue }) {
        if (response.body.kind === 'single') {
          response.body.singleResult.extensions = {
            ...response.body.singleResult.extensions,
            nPlusOneMetrics: {
              totalCalls: contextValue.metrics.categoryProductsCalls,
              resolverLogs: contextValue.metrics.callLogs,
            },
          };
        }
      },
    };
  },
};

// 4. Definisi Resolver
const resolvers = {
  Query: {
    categories: async () => {
      const result = await pool.query('SELECT * FROM categories ORDER BY id ASC');
      return result.rows;
    },
    category: async (_, { id }) => {
      const result = await pool.query('SELECT * FROM categories WHERE id = $1', [id]);
      return result.rows[0] || null;
    },
    products: async () => {
      const result = await pool.query(
        'SELECT id, title, price::float, category_id, created_by FROM products ORDER BY id ASC'
      );
      return result.rows;
    },
    product: async (_, { id }) => {
      const result = await pool.query(
        'SELECT id, title, price::float, category_id, created_by FROM products WHERE id = $1',
        [id]
      );
      return result.rows[0] || null;
    },
  },

  // Resolver Relasi Category -> Products (One-to-Many)
  Category: {
    products: async (parent, _, contextValue) => {
      // Increment counter di context request saat ini
      contextValue.metrics.categoryProductsCalls += 1;
      const currentCall = contextValue.metrics.categoryProductsCalls;

      // Simpan log urutan pemanggilan ke array context
      contextValue.metrics.callLogs.push(
        `[resolver counter] Category.products dipanggil ${currentCall} kali (category_id=${parent.id})`
      );

      const result = await pool.query(
        'SELECT id, title, price::float, category_id, created_by FROM products WHERE category_id = $1 ORDER BY id ASC',
        [parent.id]
      );
      return result.rows;
    },
  },

  // Resolver Relasi Product -> Category (Many-to-One)
  Product: {
    category: async (parent) => {
      if (!parent.category_id) return null;
      const result = await pool.query('SELECT * FROM categories WHERE id = $1', [parent.category_id]);
      return result.rows[0] || null;
    },
  },
};

// 5. Inisialisasi Apollo Server dengan Plugin
const server = new ApolloServer({
  typeDefs,
  resolvers,
  introspection: true,
  csrfPrevention: false,
  plugins: [metricsPlugin],
});

// 6. Inisialisasi Handler dengan Context Per-Request
const apolloHandler = startServerAndCreateNextHandler(server, {
  context: async () => ({
    metrics: {
      categoryProductsCalls: 0,
      callLogs: [],
    },
  }),
});

// 7. Handler CORS dan Serverless Entrypoint
module.exports = async function handler(req, res) {
  const allowedOrigins = new Set([
    'https://studio.apollographql.com',
    'https://embeddable-sandbox.cdn.apollographql.com',
  ]);
  const origin = req.headers.origin;

  if (allowedOrigins.has(origin)) {
    res.setHeader('Access-Control-Allow-Origin', origin);
    res.setHeader('Vary', 'Origin');
  }

  res.setHeader('Access-Control-Allow-Methods', 'GET,POST,OPTIONS');
  res.setHeader(
    'Access-Control-Allow-Headers',
    'Content-Type, Authorization, apollo-require-preflight, x-apollo-operation-name'
  );

  if (req.method === 'OPTIONS') {
    res.status(200).end();
    return;
  }

  return apolloHandler(req, res);
};