const mongoose = require('mongoose');
require('./models'); // Load all schemas

/**
 * Connect to MongoDB with reconnection logic
 * @param {string} uri - MongoDB connection URI (from process.env.MONGODB_URI)
 * @param {object} options - Optional Mongoose connection options
 * @returns {Promise<void>}
 */
async function connectMongoDB(uri, options = {}) {
    if (!uri) {
        throw new Error('MONGODB_URI is required. Add it to your .env file.');
    }

    const defaultOptions = {
        serverSelectionTimeoutMS: 5000,
        socketTimeoutMS: 45000,
        ...options
    };

    try {
        await mongoose.connect(uri, defaultOptions);
        console.log('✓ Connected to MongoDB');
        
        mongoose.connection.on('error', (err) => {
            console.error('MongoDB connection error:', err);
        });

        mongoose.connection.on('disconnected', () => {
            console.warn('MongoDB disconnected. Attempting to reconnect...');
        });

        mongoose.connection.on('reconnected', () => {
            console.log('✓ MongoDB reconnected');
        });

    } catch (err) {
        console.error('Failed to connect to MongoDB:', err.message);
        console.error('Stack:', err.stack);
        throw err;
    }
}

/**
 * Gracefully close MongoDB connection
 * @returns {Promise<void>}
 */
async function closeMongoDB() {
    try {
        await mongoose.connection.close();
        console.log('MongoDB connection closed');
    } catch (err) {
        console.error('Error closing MongoDB:', err);
    }
}

/**
 * Retry a function on Mongoose connection errors.
 * @param {Function} fn - async function to execute
 * @param {object} options - { retries: 3, delayMs: 500 }
 * @returns {Promise<*>}
 */
async function withRetry(fn, options = {}) {
    const { retries = 3, delayMs = 500 } = options;
    let lastError;
    for (let attempt = 0; attempt <= retries; attempt++) {
        try {
            return await fn();
        } catch (err) {
            lastError = err;
            const isConnectionError = err.name === 'MongoNetworkError' ||
                mongoose.connection.readyState !== 1;
            if (!isConnectionError || attempt >= retries) throw err;
            await new Promise(r => setTimeout(r, delayMs));
        }
    }
    throw lastError;
}

module.exports = {
    connectMongoDB,
    closeMongoDB,
    withRetry,
    mongoose
};