<?php
require_once '../../config/config.php';
header('Content-Type: application/json');

try {
    $examIds = $_POST['exam_ids'] ?? [];
    $courseIds = $_POST['course_ids'] ?? [];
    
    if (empty($examIds) || empty($courseIds)) {
        echo json_encode(['success' => false, 'message' => 'Exam IDs and Course IDs are required']);
        exit;
    }
    
    // Convert arrays to comma-separated strings for SQL IN clause
    $examIdsStr = implode(',', array_map('intval', $examIds));
    $courseIdsStr = implode(',', array_map('intval', $courseIds));
    
    // Get exam details
    $examsSql = "SELECT e.exam_id, e.exam_name, e.academic_year, e.semester
                 FROM exams e
                 WHERE e.exam_id IN ($examIdsStr) AND e.status = 'Active'";
    
    $examsStmt = $pdo->prepare($examsSql);
    $examsStmt->execute();
    $exams = $examsStmt->fetchAll(PDO::FETCH_ASSOC);
    
    if (empty($exams)) {
        echo json_encode(['success' => false, 'message' => 'No active exams found']);
        exit;
    }
    
    $previewData = [];
    
    foreach ($exams as $exam) {
        // Get subjects for the selected courses and this exam's semester
        $subjectsSql = "SELECT s.subject_id, s.subject_name, s.subject_code, c.course_id, c.course_name
                        FROM subjects s
                        LEFT JOIN courses c ON c.course_id = s.course_id
                        WHERE s.course_id IN ($courseIdsStr) AND s.semester = ?
                        ORDER BY c.course_name, s.subject_name";
        
        $subjectsStmt = $pdo->prepare($subjectsSql);
        $subjectsStmt->execute([$exam['semester']]);
        $subjects = $subjectsStmt->fetchAll(PDO::FETCH_ASSOC);
        
        if (empty($subjects)) {
            continue; // Skip if no subjects found
        }
        
        // Check existing exam subjects for this exam
        $existingSql = "SELECT es.subject_id, s.subject_name, s.subject_code
                        FROM exam_subjects es
                        LEFT JOIN subjects s ON s.subject_id = es.subject_id
                        WHERE es.exam_id = ?";
        
        $existingStmt = $pdo->prepare($existingSql);
        $existingStmt->execute([$exam['exam_id']]);
        $existingSubjects = $existingStmt->fetchAll(PDO::FETCH_ASSOC);
        
        $existingSubjectIds = array_column($existingSubjects, 'subject_id');
        
        // Group subjects by course
        $subjectsByCourse = [];
        foreach ($subjects as $subject) {
            $courseId = $subject['course_id'];
            if (!isset($subjectsByCourse[$courseId])) {
                $subjectsByCourse[$courseId] = [
                    'course_id' => $courseId,
                    'course_name' => $subject['course_name'],
                    'subjects' => []
                ];
            }
            $subjectsByCourse[$courseId]['subjects'][] = $subject;
        }
        
        // Process each course
        foreach ($subjectsByCourse as $courseData) {
            $subjectsToSync = [];
            $subjectsExisting = [];
            
            foreach ($courseData['subjects'] as $subject) {
                if (in_array($subject['subject_id'], $existingSubjectIds)) {
                    $subjectsExisting[] = $subject['subject_name'];
                } else {
                    $subjectsToSync[] = $subject['subject_name'];
                }
            }
            
            $previewData[] = [
                'exam_id' => $exam['exam_id'],
                'exam_name' => $exam['exam_name'],
                'course_id' => $courseData['course_id'],
                'course_name' => $courseData['course_name'],
                'semester' => $exam['semester'],
                'subjects_to_sync' => count($subjectsToSync),
                'subjects_existing' => count($subjectsExisting),
                'subjects_to_sync_list' => $subjectsToSync,
                'subjects_existing_list' => $subjectsExisting
            ];
        }
    }
    
    echo json_encode([
        'success' => true,
        'data' => $previewData,
        'summary' => [
            'total_exams' => count($previewData),
            'total_to_sync' => array_sum(array_column($previewData, 'subjects_to_sync')),
            'total_existing' => array_sum(array_column($previewData, 'subjects_existing'))
        ]
    ]);
    
} catch (Exception $e) {
    http_response_code(500);
    echo json_encode(['success' => false, 'message' => 'Database error: ' . $e->getMessage()]);
}
?>