auth_check.php

<?php
/**
 * Authentication Check
 * 
 * This file checks if a user is logged in and redirects if necessary.
 * It also provides functions for authentication-related operations.
 */

// Start session if not already started
if (session_status() === PHP_SESSION_NONE) {
    session_start();
}

/**
 * Check if user is logged in
 * 
 * @return boolean True if user is logged in, false otherwise
 */
function isLoggedIn() {
    return isset($_SESSION['user_id']) && !empty($_SESSION['user_id']);
}

/**
 * Check if current user is a faculty member
 * 
 * @return boolean True if user is faculty, false otherwise
 */
function isFaculty() {
    return isLoggedIn() && $_SESSION['user_type'] === 'faculty';
}

/**
 * Check if current user is a student
 * 
 * @return boolean True if user is a student, false otherwise
 */
function isStudent() {
    return isLoggedIn() && $_SESSION['user_type'] === 'student';
}

/**
 * Redirect non-logged in users to login page
 * 
 * @param string $message Optional message to display after redirect
 * @return void
 */
function requireLogin($message = 'Please login to access this page.') {
    if (!isLoggedIn()) {
        $_SESSION['auth_message'] = $message;
        header('Location: login.php');
        exit;
    }
}

/**
 * Redirect non-faculty users
 * 
 * @param string $message Optional message to display after redirect
 * @return void
 */
function requireFaculty($message = 'Faculty access required.') {
    requireLogin();
    
    if (!isFaculty()) {
        $_SESSION['auth_message'] = $message;
        header('Location: index.php');
        exit;
    }
}

/**
 * Require user to be student to access page
 * Redirects to index page if not student
 */
function requireStudent() {
    requireLogin();
    if (!isStudent()) {
        header("Location: index.php");
        exit;
    }
}

/**
 * Get user ID from session
 * 
 * @return mixed User ID if logged in, null otherwise
 */
function getCurrentUserId() {
    return isLoggedIn() ? $_SESSION['user_id'] : null;
}

/**
 * Get username from session
 * 
 * @return mixed Username if logged in, null otherwise
 */
function getCurrentUsername() {
    return isLoggedIn() ? $_SESSION['username'] : null;
}

/**
 * Get user type from session
 * 
 * @return mixed User type if logged in, null otherwise
 */
function getCurrentUserType() {
    return isLoggedIn() ? $_SESSION['user_type'] : null;
}

/**
 * Update the last login time for a user
 */
function updateLastLogin($conn, $user_id) {
    $query = "UPDATE users SET last_login = NOW() WHERE id = ?";
    $stmt = $conn->prepare($query);
    $stmt->bind_param("i", $user_id);
    $stmt->execute();
}

// Define variables to use in header
$is_logged_in = isLoggedIn();
$is_faculty = isFaculty();
$is_student = isStudent();
?>