<?php
// Database connection
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "popularcomputer";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);

// Check connection
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

echo "<h2>Adding missing columns to student_exams table</h2>";

// Add time_taken column
$addTimeTaken = "ALTER TABLE student_exams 
                 ADD COLUMN time_taken INT NULL COMMENT 'in minutes' AFTER end_time";

if ($conn->query($addTimeTaken) === TRUE) {
    echo "<p>Successfully added time_taken column.</p>";
    
    // Update existing records to calculate time_taken based on start_time and end_time
    $updateTimeTaken = "UPDATE student_exams 
                       SET time_taken = TIMESTAMPDIFF(MINUTE, start_time, end_time) 
                       WHERE start_time IS NOT NULL AND end_time IS NOT NULL";
    
    if ($conn->query($updateTimeTaken) === TRUE) {
        echo "<p>Updated existing records with time_taken values.</p>";
    } else {
        echo "<p>Error updating time_taken: " . $conn->error . "</p>";
    }
} else {
    echo "<p>Error adding time_taken column: " . $conn->error . "</p>";
}

// Add total_questions column
$addTotalQuestions = "ALTER TABLE student_exams 
                      ADD COLUMN total_questions INT NOT NULL DEFAULT 0 AFTER time_taken";

if ($conn->query($addTotalQuestions) === TRUE) {
    echo "<p>Successfully added total_questions column.</p>";
} else {
    echo "<p>Error adding total_questions column: " . $conn->error . "</p>";
}

// Add correct_answers column
$addCorrectAnswers = "ALTER TABLE student_exams 
                      ADD COLUMN correct_answers INT NOT NULL DEFAULT 0 AFTER total_questions";

if ($conn->query($addCorrectAnswers) === TRUE) {
    echo "<p>Successfully added correct_answers column.</p>";
    
    // Update existing records to calculate correct answers from student_exam_answers table
    $updateCorrectAnswers = "UPDATE student_exams se 
                            SET correct_answers = (
                                SELECT COUNT(*) 
                                FROM student_exam_answers sea 
                                JOIN exam_questions eq ON sea.question_id = eq.id
                                WHERE sea.student_exam_id = se.id 
                                AND (
                                    (eq.question_type = 'mcq' AND sea.selected_option = eq.correct_option)
                                    OR
                                    (eq.question_type = 'descriptive' AND sea.marks_awarded = eq.mark)
                                )
                            )";
    
    if ($conn->query($updateCorrectAnswers) === TRUE) {
        echo "<p>Updated existing records with correct_answers values.</p>";
    } else {
        echo "<p>Error updating correct_answers: " . $conn->error . "</p>";
    }
    
    // Update total_questions based on exam_questions table
    $updateTotalQuestions = "UPDATE student_exams se
                            SET total_questions = (
                                SELECT COUNT(*)
                                FROM exam_questions eq
                                WHERE eq.exam_id = se.exam_id
                            )";
    
    if ($conn->query($updateTotalQuestions) === TRUE) {
        echo "<p>Updated existing records with total_questions values.</p>";
    } else {
        echo "<p>Error updating total_questions: " . $conn->error . "</p>";
    }
} else {
    echo "<p>Error adding correct_answers column: " . $conn->error . "</p>";
}

// Close connection
$conn->close();

echo "<p><a href='student/exam-results.php'>Go to Exam Results</a></p>";
?>