<?php
session_start();

if (!isset($_SESSION['user_id'])) {
    header('Location: index.php');
    exit;
}

require_once 'db/config.php';

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $id = $_POST['id'] ?? null;
    $grade_name = $_POST['grade_name'] ?? '';
    $min_score = $_POST['min_score'] ?? '';
    $max_score = $_POST['max_score'] ?? '';

    // Basic validation
    if (empty($id) || empty($grade_name) || !is_numeric($min_score) || !is_numeric($max_score)) {
        $_SESSION['error_message'] = 'All fields are required and scores must be numbers.';
        header('Location: school_settings.php');
        exit;
    }

    if ($min_score >= $max_score) {
        $_SESSION['error_message'] = 'Min score must be less than max score.';
        header('Location: school_settings.php');
        exit;
    }

    try {
        $pdo = db();
        $sql = "UPDATE grading_scales SET grade_name = ?, min_score = ?, max_score = ? WHERE id = ?";
        $stmt = $pdo->prepare($sql);
        $stmt->execute([$grade_name, $min_score, $max_score, $id]);

        $_SESSION['success_message'] = 'Grade updated successfully.';

    } catch (PDOException $e) {
        if ($e->errorInfo[1] == 1062) { // Duplicate entry
            $_SESSION['error_message'] = "A grade with that name already exists in this section.";
        } else {
            $_SESSION['error_message'] = 'Database error: ' . $e->getMessage();
        }
    }
}

header('Location: school_settings.php');
exit;