<?php
session_start();
require_once 'database/db_config.php';

// Check if user has admin privileges
require_admin_privileges('login.php');

if ($_SERVER['REQUEST_METHOD'] === 'POST' && isset($_POST['user_id'])) {
    $user_id = (int)$_POST['user_id'];
    
    // Prevent self-deletion
    if ($user_id === $_SESSION['user_id']) {
        $_SESSION['error_messages'] = ["You cannot delete your own account"];
        header('Location: users.php');
        exit();
    }
    
    // Check if user exists
    $stmt = $conn->prepare("SELECT id, role, profile_image FROM users WHERE id = ?");
    $stmt->bind_param("i", $user_id);
    $stmt->execute();
    $result = $stmt->get_result();
    
    if ($result->num_rows === 0) {
        $_SESSION['error_messages'] = ["User not found"];
        header('Location: users.php');
        exit();
    }
    
    $user = $result->fetch_assoc();
    
    // Prevent deletion of the last admin
    if ($user['role'] === 'admin') {
        $stmt = $conn->prepare("SELECT COUNT(*) as admin_count FROM users WHERE role = 'admin'");
        $stmt->execute();
        $admin_count = $stmt->get_result()->fetch_assoc()['admin_count'];
        
        if ($admin_count <= 1) {
            $_SESSION['error_messages'] = ["Cannot delete the last admin user"];
            header('Location: users.php');
            exit();
        }
    }
    
    // Begin transaction to handle related data
    $conn->begin_transaction();
    
    try {
        // Delete user's enrollments
        $stmt = $conn->prepare("DELETE FROM enrollments WHERE user_id = ?");
        $stmt->bind_param("i", $user_id);
        $stmt->execute();
        
        // Delete user's submissions
        $stmt = $conn->prepare("DELETE FROM submissions WHERE user_id = ?");
        $stmt->bind_param("i", $user_id);
        $stmt->execute();
        
        // Delete user's payments
        $stmt = $conn->prepare("DELETE FROM payments WHERE user_id = ?");
        $stmt->bind_param("i", $user_id);
        $stmt->execute();
        
        // If user is an instructor, handle their courses
        if ($user['role'] === 'instructor') {
            // Get all courses by this instructor
            $stmt = $conn->prepare("SELECT id FROM courses WHERE instructor_id = ?");
            $stmt->bind_param("i", $user_id);
            $stmt->execute();
            $courses = $stmt->get_result()->fetch_all(MYSQLI_ASSOC);
            
            foreach ($courses as $course) {
                // Delete course lessons
                $stmt = $conn->prepare("DELETE FROM lessons WHERE course_id = ?");
                $stmt->bind_param("i", $course['id']);
                $stmt->execute();
                
                // Delete course assignments
                $stmt = $conn->prepare("DELETE FROM assignments WHERE course_id = ?");
                $stmt->bind_param("i", $course['id']);
                $stmt->execute();
                
                // Delete course enrollments
                $stmt = $conn->prepare("DELETE FROM enrollments WHERE course_id = ?");
                $stmt->bind_param("i", $course['id']);
                $stmt->execute();
                
                // Delete course categories
                $stmt = $conn->prepare("DELETE FROM course_categories WHERE course_id = ?");
                $stmt->bind_param("i", $course['id']);
                $stmt->execute();
                
                // Delete the course
                $stmt = $conn->prepare("DELETE FROM courses WHERE id = ?");
                $stmt->bind_param("i", $course['id']);
                $stmt->execute();
            }
        }
        
        // Delete the user's profile image if exists
        if (!empty($user['profile_image'])) {
            $profile_image_path = '../' . $user['profile_image'];
            if (file_exists($profile_image_path)) {
                unlink($profile_image_path);
            }
        }
        
        // Finally, delete the user
        $stmt = $conn->prepare("DELETE FROM users WHERE id = ?");
        $stmt->bind_param("i", $user_id);
        $stmt->execute();
        
        // Commit the transaction
        $conn->commit();
        
        $_SESSION['success_message'] = "User and all related data deleted successfully";
        
        // Redirect based on role
        if ($user['role'] === 'instructor') {
            header('Location: instructors.php');
        } else {
            header('Location: users.php');
        }
        
    } catch (Exception $e) {
        // Rollback the transaction on error
        $conn->rollback();
        $_SESSION['error_messages'] = ["Error deleting user: " . $e->getMessage()];
        header('Location: users.php');
    }
    
    exit();
}

// If not POST request or no user_id provided, redirect to users page
header('Location: users.php');
exit();