function validateRequired(value, fieldName) {
    if (!value || value.trim() === '') {
        return `${fieldName} is required`;
    }
    return null;
}

function validateUsername(username) {
    if (!username || username.trim() === '') {
        return 'Username is required';
    }
    if (username.length < 3) {
        return 'Username must be at least 3 characters';
    }
    if (username.length > 50) {
        return 'Username must be less than 50 characters';
    }
    if (!/^[a-zA-Z0-9_]+$/.test(username)) {
        return 'Username can only contain letters, numbers, and underscores';
    }
    return null;
}

function validatePassword(password) {
    if (!password || password.trim() === '') {
        return 'Password is required';
    }
    if (password.length < 6) {
        return 'Password must be at least 6 characters';
    }
    return null;
}

function showFieldError(field, error) {
    field.classList.add('error');
    let errorDiv = field.nextElementSibling;
    if (!errorDiv || !errorDiv.classList.contains('field-error')) {
        errorDiv = document.createElement('div');
        errorDiv.className = 'field-error';
        field.parentNode.insertBefore(errorDiv, field.nextSibling);
    }
    errorDiv.textContent = error;
}

function clearFieldError(field) {
    field.classList.remove('error');
    const errorDiv = field.nextElementSibling;
    if (errorDiv && errorDiv.classList.contains('field-error')) {
        errorDiv.remove();
    }
}