```javascript
const mongoose = require('mongoose');
const bcrypt = require('bcryptjs');

const UserSchema = new mongoose.Schema({
    name: {
        type: String,
        required: true
    },
    email: {
        type: String,
        required: true,
        unique: true
    },
    password: {
        type: String,
        required: true
    },
    role: {
        type: String,
        enum: ['admin', 'manager', 'employee'],
        default: 'employee'
    },
    department: {
        type: mongoose.Schema.Types.ObjectId,
        ref: 'Department'
    },
    date: {
        type: Date,
        default: Date.now
    }
});

UserSchema.pre('save', async function(next) {
    if (!this.isModified('password')) return next();
    
    const salt = await bcrypt.genSalt(10);
    this.password = await bcrypt.hash(this.password, salt);
    next();
});

module.exports = mongoose.model('User', UserSchema);
```