server.js

require('dotenv').config();
const express = require('express');
const multer = require('multer');
const cors = require('cors');
const mysql = require('mysql2/promise');
const { S3Client, PutObjectCommand } = require('@aws-sdk/client-s3');
const path = require('path');

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

// Config
app.use(cors());
app.use(express.json());
app.use(express.static(__dirname));

// Multer memory storage (buffer files in memory before S3 upload)
const storage = multer.memoryStorage();
const upload = multer({ storage: storage });

// AWS S3 Configuration
const s3Client = new S3Client({
    region: process.env.AWS_REGION,
    credentials: {
        accessKeyId: process.env.AWS_ACCESS_KEY_ID,
        secretAccessKey: process.env.AWS_SECRET_ACCESS_KEY
    }
});
const BUCKET_NAME = process.env.S3_BUCKET_NAME;

// Database Connection Pool
const pool = mysql.createPool({
    host: process.env.DB_HOST,
    user: process.env.DB_USER,
    password: process.env.DB_PASS,
    database: process.env.DB_NAME,
    waitForConnections: true,
    connectionLimit: 10,
    queueLimit: 0
});

// --- API ROUTES ---

// GET all notes from MySQL
app.get('/api/notes', async (req, res) => {
    try {
        const [rows] = await pool.query('SELECT * FROM notes ORDER BY upload_date DESC');
        res.json(rows);
    } catch (error) {
        console.error('Database connection or query error:', error);
        res.status(500).json({ error: 'Failed to fetch notes from database' });
    }
});

// POST a new note (Upload to S3, save to MySQL)
app.post('/api/upload', upload.single('file'), async (req, res) => {
    try {
        const { title, subject } = req.body;
        const file = req.file;

        if (!title || !subject || !file) {
            return res.status(400).json({ error: 'Title, subject, and file are required.' });
        }

        // 1. Upload to AWS S3
        const objectKey = `uploads/${Date.now()}-${file.originalname.replace(/\s+/g, '_')}`;
        
        const putObjectParams = {
            Bucket: BUCKET_NAME,
            Key: objectKey,
            Body: file.buffer,
            ContentType: file.mimetype
        };

        const command = new PutObjectCommand(putObjectParams);
        await s3Client.send(command);

        // 2. Construct public S3 URL
        const fileUrl = `https://${BUCKET_NAME}.s3.${process.env.AWS_REGION}.amazonaws.com/${objectKey}`;

        // 3. Save to MySQL (AWS RDS)
        const query = 'INSERT INTO notes (title, subject, file_url) VALUES (?, ?, ?)';
        const [result] = await pool.execute(query, [title, subject, fileUrl]);

        res.status(201).json({
            id: result.insertId,
            title,
            subject,
            file_url: fileUrl
        });

    } catch (error) {
        console.error('Failed to upload file or save to database:', error);
        res.status(500).json({ error: 'Internal Server Error' });
    }
});

// Start the server
app.listen(PORT, () => {
    console.log(`Server is running on http://localhost:${PORT}`);
});