const mongoose = require('mongoose');

mongoose.connect(process.env.MONGODB_URI, {
  useNewUrlParser: true,
  useUnifiedTopology: true
});

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

const userSchema = new mongoose.Schema({
  name: {
    type: String,
    required: [true, 'Name is required'],
    trim: true,
    minlength: 3,
    maxlength: 50
  },
  email: {
    type: String,
    required: true,
    unique: true,
    lowercase: true
  },
  age: {
    type: Number,
    min: 18,
    max: 120
  },
  role: {
    type: String,
    enum: ['user', 'admin'],
    default: 'user'
  }
}, {
  timestamps: true  // createdAt, updatedAt
});

const User = mongoose.model('User', userSchema);

// Create
const user = await User.create({
  name: 'John Doe',
  email: 'john@example.com'
});

// Read
const users = await User.find({ age: { $gte: 18 } });
const user = await User.findById(id);
const user = await User.findOne({ email: 'john@example.com' });

// Update
const updated = await User.findByIdAndUpdate(
  id,
  { name: 'Jane Doe' },
  { new: true, runValidators: true }
);

// Delete
await User.findByIdAndDelete(id);
await User.deleteMany({ age: { $lt: 18 } });

const postSchema = new mongoose.Schema({
  title: String,
  content: String,
  author: {
    type: mongoose.Schema.Types.ObjectId,
    ref: 'User'
  }
});

// Populate relationship
const post = await Post.findById(id).populate('author');
// post.author is now full user object

userSchema.index({ email: 1 }, { unique: true });
userSchema.index({ name: 1, age: -1 });

userSchema.pre('save', async function(next) {
  if (this.isModified('password')) {
    this.password = await bcrypt.hash(this.password, 10);
  }
  next();
});

userSchema.virtual('fullName').get(function() {
  return `${this.firstName} ${this.lastName}`;
});

const stats = await User.aggregate([
  { $match: { age: { $gte: 18 } } },
  { $group: {
    _id: '$role',
    count: { $sum: 1 },
    avgAge: { $avg: '$age' }
  }},
  { $sort: { count: -1 } }
]);

// Comparison
User.find({ age: { $gt: 18 } })     // Greater than
User.find({ age: { $gte: 18 } })    // Greater or equal
User.find({ age: { $lt: 65 } })     // Less than
User.find({ age: { $lte: 65 } })    // Less or equal
User.find({ age: { $ne: 30 } })     // Not equal

// Logical
User.find({ $and: [{ age: { $gte: 18 } }, { age: { $lte: 65 } }] })
User.find({ $or: [{ role: 'admin' }, { role: 'moderator' }] })

// Array
User.find({ tags: { $in: ['node', 'mongodb'] } })
User.find({ tags: { $nin: ['deprecated'] } })

// Regex
User.find({ email: /gmail\.com$/ })