const express = require('express');
const cors = require('cors');
const morgan = require('morgan');
const { Pool } = require('pg');
const { createClient } = require('redis');
const dotenv = require('dotenv');

dotenv.config();

const app = express();
const port = process.env.PORT || 3000;

// Middleware
app.use(cors());
app.use(express.json());
app.use(morgan('combined'));

// Database
const pool = new Pool({
  connectionString: process.env.DATABASE_URL
});

// Redis
const redisClient = createClient({
  url: process.env.REDIS_URL
});
redisClient.on('error', (err) => console.log('Redis Client Error', err));

(async () => {
  await redisClient.connect();
  console.log('Connected to Redis');
})();

// Health Check
app.get('/health', (req, res) => {
  res.json({ status: 'ok', timestamp: new Date() });
});

const srp = require('secure-remote-password/server');
const jwt = require('jsonwebtoken');

// Route: Registration
app.post('/auth/register', async (req, res) => {
  try {
    const { email, salt, verifier } = req.body;
    if (!email || !salt || !verifier) {
      return res.status(400).json({ error: 'Missing fields' });
    }

    // Check if user exists
    const userCheck = await pool.query('SELECT id FROM api.users WHERE email = $1', [email]);
    if (userCheck.rows.length > 0) {
      return res.status(409).json({ error: 'User already exists' });
    }

    await pool.query(
      'INSERT INTO api.users (email, salt, verifier) VALUES ($1, $2, $3)',
      [email, salt, verifier]
    );
    res.status(201).json({ message: 'User registered' });
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Registration failed' });
  }
});

// Route: Login Step 1
app.post('/auth/login/step1', async (req, res) => {
  try {
    const { email, clientPublic } = req.body; // clientPublic is 'A'
    if (!email || !clientPublic) return res.status(400).json({ error: 'Missing email or clientPublic' });

    const result = await pool.query('SELECT id, salt, verifier FROM api.users WHERE email = $1', [email]);
    if (result.rows.length === 0) {
      return res.status(404).json({ error: 'User not found' });
    }
    const user = result.rows[0];

    // Generate server ephemeral (B)
    const serverEphemeral = srp.generateEphemeral(user.verifier);
    // serverEphemeral contains { secret, public } (b, B)

    // Store session in Redis
    const sessionKey = `srp:${email}`;
    await redisClient.set(sessionKey, JSON.stringify({
      salt: user.salt,
      verifier: user.verifier,
      serverSecret: serverEphemeral.secret,
      serverPublic: serverEphemeral.public,
      clientPublic: clientPublic,
      userId: user.id
    }), {
      EX: 300 // 5 minutes expiration
    });

    res.json({
      salt: user.salt,
      serverPublic: serverEphemeral.public
    });
  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Login step 1 failed' });
  }
});

// Route: Login Step 2
app.post('/auth/login/step2', async (req, res) => {
  try {
    const { email, clientProof } = req.body; // clientProof is 'M1'
    if (!email || !clientProof) return res.status(400).json({ error: 'Missing email or clientProof' });

    const sessionKey = `srp:${email}`;
    const sessionDataString = await redisClient.get(sessionKey);

    if (!sessionDataString) {
      return res.status(401).json({ error: 'Session expired or invalid' });
    }

    const session = JSON.parse(sessionDataString);

    // Calculate server session
    const serverSession = srp.deriveSession(
      session.serverSecret,
      session.clientPublic,
      session.salt,
      email,
      session.verifier,
      clientProof
    );

    if (!serverSession) {
      return res.status(401).json({ error: 'Authentication failed' });
    }

    // Generate JWT
    const token = jwt.sign(
      {
        sub: session.userId,
        role: 'authenticated', // For PostgREST
        email: email
      },
      process.env.JWT_SECRET,
      { expiresIn: '1h' }
    );

    // Clear session (optional, prevents replay of step 2 within window, though M1 is unique per session usually)
    await redisClient.del(sessionKey);

    res.json({
      serverProof: serverSession.proof, // M2
      token: token
    });

  } catch (err) {
    console.error(err);
    res.status(500).json({ error: 'Login step 2 failed' });
  }
});


app.listen(port, () => {
  console.log(`API listening on port ${port}`);
});