<?php
session_start();

// Check if student is logged in
if (!isset($_SESSION['user_id']) || $_SESSION['role'] !== 'student') {
    echo json_encode([
        'success' => false,
        'message' => 'Unauthorized access'
    ]);
    exit();
}

// Include database connection
require_once('../includes/db_config.php');

$userId = $_SESSION['user_id'];

// Check if course ID is provided
if (!isset($_GET['course_id']) || empty($_GET['course_id'])) {
    echo json_encode([
        'success' => false,
        'message' => 'Course ID is required'
    ]);
    exit();
}

$courseId = intval($_GET['course_id']);

try {
    // Check if the user is enrolled in this course
    $stmt = $conn->prepare("
        SELECT e.* 
        FROM enrollments e
        WHERE e.user_id = ? AND e.course_id = ?
    ");
    $stmt->bind_param('ii', $userId, $courseId);
    $stmt->execute();
    $result = $stmt->get_result();
    
    if ($result->num_rows === 0) {
        echo json_encode([
            'success' => false,
            'message' => 'You are not enrolled in this course'
        ]);
        exit();
    }
    
    $enrollment = $result->fetch_assoc();
    
    // Get course details with instructor information
    $stmt = $conn->prepare("
        SELECT c.*, 
               CONCAT(u.first_name, ' ', u.last_name) as instructor_name
        FROM courses c
        LEFT JOIN users u ON c.instructor_id = u.id
        WHERE c.id = ?
    ");
    $stmt->bind_param('i', $courseId);
    $stmt->execute();
    $result = $stmt->get_result();
    
    if ($result->num_rows === 0) {
        echo json_encode([
            'success' => false,
            'message' => 'Course not found'
        ]);
        exit();
    }
    
    $course = $result->fetch_assoc();
    
    // Format course data
    $courseData = [
        'id' => $course['id'],
        'title' => $course['title'],
        'description' => $course['description'] ?? '',
        'duration' => $course['duration'] ?? '',
        'price' => $course['price'] ?? 0,
        'discount_price' => $course['discount_price'] ?? 0,
        'image' => $course['image'] ?? '',
        'status' => $course['status'] ?? 'active',
        'instructor_id' => $course['instructor_id'] ?? '',
        'enrollment_date' => date('M d, Y', strtotime($enrollment['enrollment_date'])),
        'enrollment_status' => $enrollment['status'],
        'completion_date' => $enrollment['completion_date'] ? date('M d, Y', strtotime($enrollment['completion_date'])) : null,
        'certificate_number' => $enrollment['certificate_number'] ?? null,
        'certificate_path' => $enrollment['certificate_path'] ?? null
    ];
    
    // Get payment information if exists
    $stmt = $conn->prepare("
        SELECT 
            SUM(amount) as total_paid,
            MAX(payment_date) as last_payment_date,
            COUNT(*) as payment_count
        FROM payments
        WHERE user_id = ? AND course_id = ? AND status IN ('completed', 'verified')
    ");
    $stmt->bind_param('ii', $userId, $courseId);
    $stmt->execute();
    $result = $stmt->get_result();
    
    $paymentInfo = [
        'total_paid' => 0,
        'payment_count' => 0,
        'last_payment_date' => null
    ];
    
    if ($result->num_rows > 0) {
        $payment = $result->fetch_assoc();
        $paymentInfo['total_paid'] = floatval($payment['total_paid'] ?? 0);
        $paymentInfo['payment_count'] = intval($payment['payment_count'] ?? 0);
        $paymentInfo['last_payment_date'] = $payment['last_payment_date'] 
            ? date('M d, Y', strtotime($payment['last_payment_date'])) 
            : null;
    }
    
    // Get course fee based on payment plan
    $course_fee = $courseData['discount_price'] > 0 && $courseData['discount_price'] < $courseData['price'] 
        ? $courseData['discount_price'] 
        : $courseData['price'];
    
    if ($enrollment['payment_plan'] === 'monthly') {
        $paymentInfo['fee_amount'] = round($course_fee / 12, 2);
        $paymentInfo['total_fee'] = $course_fee;
        $paymentInfo['payments_count'] = 12;
        $paymentInfo['payment_type'] = 'Monthly';
    } else if ($enrollment['payment_plan'] === 'six_month') {
        $paymentInfo['fee_amount'] = round($course_fee / 6, 2);
        $paymentInfo['total_fee'] = $course_fee;
        $paymentInfo['payments_count'] = 6;
        $paymentInfo['payment_type'] = 'Six-Month';
    } else {
        $paymentInfo['fee_amount'] = $course_fee;
        $paymentInfo['total_fee'] = $course_fee;
        $paymentInfo['payments_count'] = 1;
        $paymentInfo['payment_type'] = 'Full Payment';
    }
    
    // Calculate remaining amount
    $paymentInfo['remaining_amount'] = max(0, $paymentInfo['total_fee'] - $paymentInfo['total_paid']);
    
    // Ensure payment progress is properly calculated and capped at 100%
    if ($paymentInfo['total_fee'] > 0) {
        $paymentInfo['payment_progress'] = min(100, round(($paymentInfo['total_paid'] / $paymentInfo['total_fee']) * 100));
    } else {
        $paymentInfo['payment_progress'] = 0;
    }
    
    // If total paid is greater than or equal to total fee, set progress to 100%
    if ($paymentInfo['total_paid'] >= $paymentInfo['total_fee']) {
        $paymentInfo['payment_progress'] = 100;
        $paymentInfo['remaining_amount'] = 0;
    }
    
    // Get next payment amount
    $paymentInfo['next_payment'] = min($paymentInfo['remaining_amount'], $paymentInfo['fee_amount']);
    
    // Add additional payment status information
    $paymentInfo['is_paid_in_full'] = $paymentInfo['total_paid'] >= $paymentInfo['total_fee'];
    $paymentInfo['payment_status'] = $paymentInfo['is_paid_in_full'] ? 'Completed' : 'In Progress';
    
    echo json_encode([
        'success' => true,
        'course' => $courseData,
        'payment' => $paymentInfo
    ]);
    
} catch (Exception $e) {
    echo json_encode([
        'success' => false,
        'message' => 'Error retrieving course details: ' . $e->getMessage()
    ]);
}

$conn->close();