<?php
/**
 * Enrollment related functions
 */

/**
 * Generate a unique enrollment number for a student
 * 
 * Format: YEAR-COURSE_CODE-SEQUENTIAL_NUMBER
 * Example: 2023-CS101-0001
 * 
 * @param mysqli $conn Database connection
 * @param int $course_id Course ID
 * @return string Unique enrollment number
 */
function generate_enrollment_number($conn, $course_id) {
    // Get current year
    $year = date('Y');
    
    // Get course code
    $course_code = 'C';
    $course_query = "SELECT course_code FROM courses WHERE id = ?";
    $stmt = $conn->prepare($course_query);
    if ($stmt) {
        $stmt->bind_param("i", $course_id);
        $stmt->execute();
        $result = $stmt->get_result();
        if ($row = $result->fetch_assoc()) {
            $course_code = !empty($row['course_code']) ? $row['course_code'] : 'C' . sprintf('%03d', $course_id);
        } else {
            $course_code = 'C' . sprintf('%03d', $course_id);
        }
        $stmt->close();
    }
    
    // Get the highest sequential number for this course in the current year
    $sequence = 1;
    $query = "SELECT enrollment_number FROM enrollments 
              WHERE enrollment_number LIKE ? 
              ORDER BY enrollment_number DESC LIMIT 1";
    $pattern = $year . '-' . $course_code . '-%';
    
    $stmt = $conn->prepare($query);
    if ($stmt) {
        $stmt->bind_param("s", $pattern);
        $stmt->execute();
        $result = $stmt->get_result();
        if ($row = $result->fetch_assoc()) {
            // Extract the sequential number from the last enrollment number
            $parts = explode('-', $row['enrollment_number']);
            if (count($parts) == 3) {
                $sequence = intval($parts[2]) + 1;
            }
        }
        $stmt->close();
    }
    
    // Format the enrollment number: YEAR-COURSE_CODE-SEQUENCE
    $enrollment_number = sprintf('%s-%s-%04d', $year, $course_code, $sequence);
    
    return $enrollment_number;
}

/**
 * Log enrollment details for diagnostic purposes
 * 
 * @param object $conn Database connection
 * @param int $enrollment_id Enrollment ID
 * @return void
 */
function log_enrollment_details($conn, $enrollment_id) {
    try {
        $stmt = $conn->prepare("SELECT e.*, c.title as course_title, u.email, u.first_name, u.last_name 
                                FROM enrollments e 
                                JOIN courses c ON e.course_id = c.id 
                                JOIN users u ON e.user_id = u.id 
                                WHERE e.id = ?");
        $stmt->bind_param("i", $enrollment_id);
        $stmt->execute();
        $result = $stmt->get_result();
        
        if ($result->num_rows > 0) {
            $enrollment = $result->fetch_assoc();
            
            // Format the log message
            $log_message = "ENROLLMENT DETAILS - ID: {$enrollment['id']}, " .
                          "User: {$enrollment['first_name']} {$enrollment['last_name']} (ID: {$enrollment['user_id']}), " .
                          "Course: {$enrollment['course_title']} (ID: {$enrollment['course_id']}), " .
                          "Status: {$enrollment['status']}, " .
                          "Payment Plan: " . ($enrollment['payment_plan'] ?? 'NULL') . ", " .
                          "Enrollment Number: {$enrollment['enrollment_number']}, " .
                          "Enrollment Date: {$enrollment['enrollment_date']}";
            
            error_log($log_message);
        } else {
            error_log("ENROLLMENT DETAILS - No enrollment found with ID: $enrollment_id");
        }
    } catch (Exception $e) {
        error_log("Error logging enrollment details: " . $e->getMessage());
    }
}

/**
 * Check if a payment plan is valid
 * 
 * @param string $plan Payment plan to validate
 * @return bool Whether the plan is valid
 */
function is_valid_payment_plan($plan) {
    $valid_plans = ['monthly', 'half_duration', 'quarterly', 'six_month', 'full'];
    return in_array($plan, $valid_plans);
}

/**
 * Create a new enrollment record with proper validation
 * 
 * @param object $conn Database connection
 * @param int $user_id User ID
 * @param int $course_id Course ID
 * @param string $payment_plan Payment plan ('monthly', 'half_duration', 'full', etc.)
 * @param string $verification_token Verification token
 * @return int|bool Enrollment ID if successful, false otherwise
 */
function create_enrollment($conn, $user_id, $course_id, $payment_plan, $verification_token = null) {
    try {
        // Validate payment plan
        if (!is_valid_payment_plan($payment_plan)) {
            error_log("Invalid payment plan: $payment_plan - Defaulting to 'full'");
            $payment_plan = 'full'; // Default to full payment if invalid
        }
        
        // Generate verification token if not provided
        if ($verification_token === null) {
            $verification_token = bin2hex(random_bytes(16));
        }
        
        // Generate a unique enrollment number
        $enrollment_number = generate_enrollment_number($conn, $course_id);
        
        // Check if enrollment already exists
        $check_stmt = $conn->prepare("SELECT id FROM enrollments WHERE user_id = ? AND course_id = ?");
        $check_stmt->bind_param("ii", $user_id, $course_id);
        $check_stmt->execute();
        $check_result = $check_stmt->get_result();
        
        if ($check_result->num_rows > 0) {
            // Enrollment already exists, update it
            $enrollment = $check_result->fetch_assoc();
            $enrollment_id = $enrollment['id'];
            
            $update_stmt = $conn->prepare("UPDATE enrollments SET status = 'active', payment_plan = ? WHERE id = ?");
            $update_stmt->bind_param("si", $payment_plan, $enrollment_id);
            
            if ($update_stmt->execute()) {
                error_log("Updated existing enrollment #$enrollment_id with payment plan: $payment_plan");
                log_enrollment_details($conn, $enrollment_id);
                return $enrollment_id;
            } else {
                error_log("Failed to update enrollment: " . $update_stmt->error);
                return false;
            }
        } else {
            // Create a new enrollment
            $insert_stmt = $conn->prepare("INSERT INTO enrollments (user_id, course_id, status, verification_token, payment_plan, enrollment_number) 
                                         VALUES (?, ?, 'active', ?, ?, ?)");
            $insert_stmt->bind_param("iisss", $user_id, $course_id, $verification_token, $payment_plan, $enrollment_number);
            
            if ($insert_stmt->execute()) {
                $enrollment_id = $conn->insert_id;
                error_log("Created new enrollment #$enrollment_id with payment plan: $payment_plan");
                log_enrollment_details($conn, $enrollment_id);
                return $enrollment_id;
            } else {
                error_log("Failed to create enrollment: " . $insert_stmt->error);
                return false;
            }
        }
    } catch (Exception $e) {
        error_log("Error in create_enrollment function: " . $e->getMessage());
        return false;
    }
}