server.js

require("dotenv").config();
const express = require("express");
const cors = require("cors");
const path = require("path");
const mongoose = require("mongoose");
const {
  connectToMongoDB,
  requireMongoConnection,
} = require("./src/config/database");

let compression;
try {
  compression = require("compression");
} catch (e) {
  console.warn(
    "⚠️  Compression module not found. Run: npm install compression",
  );
}

let rateLimit;
try {
  rateLimit = require("express-rate-limit");
} catch (e) {
  console.warn(
    "⚠️  Rate limiting module not found. Run: npm install express-rate-limit",
  );
}

// ─── OpenAPI Spec ─────────────────────────────────────────────────────────────
let swaggerJsdoc;
try {
  swaggerJsdoc = require("swagger-jsdoc");
} catch (e) {
  console.warn("⚠️  swagger-jsdoc not found. Run: npm install swagger-jsdoc");
}

let __swaggerSpec = null;
if (swaggerJsdoc) {
  __swaggerSpec = swaggerJsdoc({
    definition: {
      openapi: "3.0.0",
      info: {
        title: "PolyCode API",
        version: "1.0.0",
        description: "API reference for PolyCode Backend",
      },
      servers: [
        {
          url: `http://localhost:${process.env.PORT || 5000}`,
          description: "Dev server",
        },
      ],
      components: {
        schemas: {
          Document: {
            type: "object",
            properties: {
              title: { type: "string" },
              path: { type: "string" },
              category: { type: "string" },
              fileType: { type: "string" },
              size: { type: "number" },
              excerpt: { type: "string" },
              lines: { type: "number" },
              wordCount: { type: "number" },
            },
          },
          ErrorResponse: {
            type: "object",
            properties: { error: { type: "string" } },
          },
        },
      },
      // paths: {} routers was define here and now they are on their own files
    },
    apis: [],
  });
  console.log("✅ API spec ready");
}

// ─── App ──────────────────────────────────────────────────────────────────────
const app = express();
app.disable("x-powered-by");

function normalizeOrigin(origin = "") { // normalizeOrigin is a function that normalizes the origin
  return origin.trim().replace(/\/$/, "");
}

const defaultAllowedOrigins = [ // defaultAllowedOrigins is an array of allowed origins
  "https://code.quantumlogicslimited.com",
  "https://www.code.quantumlogicslimited.com",
  "https://digital-logics-studio.vercel.app",
  "https://poly-code-frontend-iota.vercel.app",
  "http://localhost:3000",
  "http://127.0.0.1:3000",
];

const allowedOrigins = new Set( // Set is a collection of unique values
  [
    ...defaultAllowedOrigins,
    process.env.FRONTEND_URL,
    process.env.PROD_FRONTEND_URL,
    ...(process.env.CORS_ORIGINS || "")
      .split(",")
      .map((origin) => origin.trim())
      .filter(Boolean),
  ]
    .map(normalizeOrigin)
    .filter(Boolean),
);

const isAllowedOrigin = (origin) => {
  if (!origin) return true;

  const normalizedOrigin = normalizeOrigin(origin);
  let hostname = "";
  try {
    hostname = new URL(normalizedOrigin).hostname;
  } catch (error) {
    return false;
  }

  return (
    allowedOrigins.has(normalizedOrigin) || /\.vercel\.app$/.test(hostname)
  );
};

const corsOptions = { // corsOptions is an object that contains the options for the cors middleware
  origin(origin, callback) {
    // Server-to-server tools (curl, health checks) omit Origin.
    if (!origin) return callback(null, true);

    if (isAllowedOrigin(origin)) {
      return callback(null, normalizeOrigin(origin));
    }

    console.warn(`🚫 CORS blocked origin: ${origin}`);
    return callback(new Error(`CORS: Origin ${origin} is not allowed`));
  },
  credentials: true,
  methods: ["GET", "POST", "PUT", "DELETE", "PATCH", "OPTIONS"],
  allowedHeaders: ["Content-Type", "Authorization", "X-Requested-With"],
  optionsSuccessStatus: 204,
};

app.use((req, res, next) => {
  res.setHeader("X-Content-Type-Options", "nosniff");
  res.setHeader("X-Frame-Options", "DENY");
  res.setHeader("Referrer-Policy", "no-referrer");
  res.setHeader("Cross-Origin-Opener-Policy", "same-origin");
  next();
});

if (compression) {
  app.use(
    compression({
      level: 6,
      threshold: 1024,
      filter: (req, res) => {
        if (req.headers["x-no-compression"]) return false;
        return compression.filter(req, res);
      },
    }),
  );
  console.log("✅ Compression enabled");
}

app.use(cors(corsOptions));
app.options(/.*/, cors(corsOptions));

app.use(express.json({ limit: "2mb" }));
app.use(express.urlencoded({ extended: true }));

app.use((req, res, next) => {
  const start = Date.now();
  res.on("finish", () => {
    const d = Date.now() - start;
    if (d > 1000) console.warn(`🐌 Slow: ${req.method} ${req.path} - ${d}ms`);
    else console.log(`⚡ ${req.method} ${req.path} - ${d}ms`);
  });
  next();
});

if (rateLimit) {
  app.use(
    "/api/",
    rateLimit({
      windowMs: 15 * 60 * 1000,
      max: 100,
      message: "Too many requests from this IP, please try again later.",
      standardHeaders: true,
      legacyHeaders: false,
    }),
  );
  console.log("✅ Rate limiting enabled");
}

// ─── Docs routes ──────────────────────────────────────────────────────────────
// Serve logo.png from the project root
app.get("/logo.png", (req, res) => {
  res.sendFile(path.join(__dirname, "logo.png"));
});

// Raw OpenAPI JSON spec
app.get("/api-docs.json", (req, res) => {
  if (!__swaggerSpec)
    return res.status(503).json({ error: "Spec not available" });
  res.setHeader("Content-Type", "application/json");
  res.send(__swaggerSpec);
});

// Custom docs HTML page
app.get("/api-docs", (req, res) => {
  res.sendFile(path.join(__dirname, "api-docs.html"));
});

// ─── API Routes ───────────────────────────────────────────────────────────────
// Warm MongoDB on cold start (serverless); auth routes also await connection.
connectToMongoDB().catch((err) => {
  console.error("MongoDB initialization error:", err.message);
});

// Auth Routes (User & Progress) — require DB before register/login
const authRoutes = require("./src/modules/auth/auth.router");
app.use("/api/auth", requireMongoConnection, authRoutes);

const documentRoutes = require("./src/modules/documents/documents.router");
app.use("/api/documents", documentRoutes);

const playgroundRoutes = require("./src/modules/playground/playground.route");
app.use("/api/playground", playgroundRoutes);

const challengeRoutes = require("./src/routes/challenge");
app.use("/api/challenges", challengeRoutes);

// Backward compatibility for older frontend builds requesting /languages directly
app.get("/languages", (req, res) => {
  return res.redirect(307, "/api/documents/languages");
});

app.get("/api/health", async (req, res) => {
  let mongo = "not_configured";
  try {
    if (!process.env.MONGODB_URI?.trim()) {
      mongo = "not_configured";
    } else {
      await connectToMongoDB();
      mongo =
        mongoose.connection.readyState === 1 ? "connected" : "disconnected";
    }
  } catch (error) {
    mongo = "error";
  }

  res.json({
    status: "OK",
    timestamp: new Date().toISOString(),
    message: "Backend is running",
    mongo,
  });
});

// Serve bundled frontend only when API and UI run on the same host (not on Vercel backend-only).
if (process.env.NODE_ENV === "production" && !process.env.VERCEL) {
  app.use(express.static(path.join(__dirname, "../PolyCode-Frontend/build")));
  app.get("*", (req, res) => {
    res.sendFile(path.join(__dirname, "../PolyCode-Frontend/build/index.html"));
  });
}

// ─── Start ────────────────────────────────────────────────────────────────────
const PORT = process.env.PORT || 5000;

// Vercel runs Express as a serverless function — export the app, do not call listen().
if (process.env.VERCEL) {
  module.exports = app;
} else {
  app.listen(PORT, () => {
    console.log(`🚀  Server:    http://localhost:${PORT}`);
    console.log(`📖  API Docs:  http://localhost:${PORT}/api-docs`);
  });
}