<?php
session_start();

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

require_once 'db/config.php';

if ($_SERVER['REQUEST_METHOD'] === 'POST') {
    $name = $_POST['name'] ?? '';
    $email = $_POST['email'] ?? '';
    $password = $_POST['password'] ?? '';
    $role = $_POST['role'] ?? '';

    $errors = [];

    if (empty($name)) {
        $errors['name'] = 'Name is required.';
    }

    if (empty($email)) {
        $errors['email'] = 'Email is required.';
    } elseif (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $errors['email'] = 'Invalid email format.';
    } else {
        try {
            $pdo = db();
            $stmt = $pdo->prepare("SELECT id FROM users WHERE email = ?");
            $stmt->execute([$email]);
            if ($stmt->fetch()) {
                $errors['email'] = 'Email already exists.';
            }
        } catch (PDOException $e) {
            $errors['db'] = "Database error: " . $e->getMessage();
        }
    }

    if (empty($password)) {
        $errors['password'] = 'Password is required.';
    } elseif (strlen($password) < 8) {
        $errors['password'] = 'Password must be at least 8 characters long.';
    }

    // Check for role uniqueness: Bursar and Assistant Bursar
    if ($role === 'Bursar' || $role === 'Assistant Bursar') {
        try {
            $pdo = db();
            $stmt = $pdo->prepare("SELECT id FROM users WHERE role = ?");
            $stmt->execute([$role]);
            if ($stmt->fetch()) {
                // Using 'db' to show a general form error, as there's no specific field for this.
                $errors['db'] = "A user with the role '{$role}' already exists. Only one is allowed.";
            }
        } catch (PDOException $e) {
            $errors['db'] = "Database error while checking role uniqueness: " . $e->getMessage();
        }
    }

    if (empty($errors)) {
        try {
            $pdo = db();
            $hashed_password = password_hash($password, PASSWORD_DEFAULT);
            $sql = "INSERT INTO users (name, email, password, role) VALUES (?, ?, ?, ?)";
            $stmt = $pdo->prepare($sql);
            $stmt->execute([$name, $email, $hashed_password, $role]);
            
            $_SESSION['success_message'] = 'User created successfully.';
            header("Location: users.php");
            exit;
        } catch (PDOException $e) {
            $errors['db'] = "Database error: " . $e->getMessage();
        }
    }

    $_SESSION['errors'] = $errors;
    $_SESSION['old_input'] = $_POST;
    header("Location: add_user.php");
    exit;
}

header("Location: add_user.php");
exit;