<?php

if (session_status() === PHP_SESSION_NONE) {
    session_start();
}

require_once __DIR__ . '/default.php';

function getBrowserIdentifier() {
    $agent = $_SERVER['HTTP_USER_AGENT'] ?? 'unknown';
    if (preg_match('/(Edg|Chrome|Chromium|Firefox|Safari|Opera|MSIE|Trident)/i', $agent, $matches)) {
        return trim($matches[1]);
    }
    return 'unknown';
}

function isGuestModeEnabled() {
    return defined('GUEST_USER_ENABLED') && GUEST_USER_ENABLED === true;
}

function getGuestUsername() {
    return defined('GUEST_USERNAME') ? (string) GUEST_USERNAME : 'guest';
}

function isGuestUsername($username) {
    return isGuestModeEnabled() && strtolower(trim((string) $username)) === strtolower(getGuestUsername());
}

function isGuestSession() {
    return isGuestModeEnabled() && !empty($_SESSION['auth_user']['username']) && isGuestUsername($_SESSION['auth_user']['username']);
}

function createGuestUser() {
    return [
        'username' => getGuestUsername(),
        'role' => 'guest',
        'guest' => true,
        'email' => '',
        'passwordHash' => ''
    ];
}

function loginAsGuest() {
    if (!isGuestModeEnabled()) {
        return false;
    }

    $_SESSION['auth_user'] = [
        'username' => getGuestUsername(),
        'role' => 'guest'
    ];
    return true;
}

function getRememberMeCookieName($username) {
    return 'kai_remember_' . sanitizeUsername($username);
}

function createRememberMeToken($username) {
    $browser = getBrowserIdentifier();
    $randomValue = bin2hex(random_bytes(16));
    $token = hash_hmac('sha256', $username . '|' . $browser . '|' . $randomValue, APP_SECRET);

    return [
        'token' => $token,
        'browser' => $browser,
        'createdAt' => time(),
        'lastUsedAt' => time()
    ];
}

function setRememberMeCookie($username) {
    $username = trim((string) $username);
    if ($username === '') {
        return false;
    }

    $tokenData = createRememberMeToken($username);
    $config = getUserConfig($username);
    $tokens = is_array($config['rememberMeTokens'] ?? null) ? $config['rememberMeTokens'] : [];
    $tokens[] = $tokenData;

    if (count($tokens) > 10) {
        usort($tokens, function ($a, $b) {
            return ($a['lastUsedAt'] ?? 0) <=> ($b['lastUsedAt'] ?? 0);
        });
        $tokens = array_slice($tokens, -10);
    }

    $config['rememberMeTokens'] = $tokens;
    if (!saveUserConfigData($username, $config)) {
        return false;
    }

    $cookieName = getRememberMeCookieName($username);
    return setcookie($cookieName, $tokenData['token'], time() + 60 * 60 * 24 * 30, '/', '', false, true);
}

function clearRememberMeCookie($username) {
    $username = trim((string) $username);
    if ($username === '') {
        return;
    }

    $cookieName = getRememberMeCookieName($username);
    setcookie($cookieName, '', time() - 3600, '/', '', false, true);
}

function tryRememberMeLogin() {
    if (!empty($_SESSION['auth_user']['username'])) {
        return true;
    }

    foreach ($_COOKIE as $cookieName => $cookieValue) {
        if (strpos($cookieName, 'kai_remember_') !== 0) {
            continue;
        }

        $username = sanitizeUsername(substr($cookieName, strlen('kai_remember_')));
        if ($username === '') {
            continue;
        }

        $user = findUserByUsername($username);
        if ($user === null) {
            continue;
        }

        $config = getUserConfig($username);
        $tokens = is_array($config['rememberMeTokens'] ?? null) ? $config['rememberMeTokens'] : [];
        $browser = getBrowserIdentifier();
        foreach ($tokens as &$entry) {
            if (($entry['token'] ?? '') !== $cookieValue) {
                continue;
            }
            if (!empty($entry['browser']) && $entry['browser'] !== $browser) {
                continue;
            }

            $entry['lastUsedAt'] = time();
            $config['rememberMeTokens'] = $tokens;
            saveUserConfigData($username, $config);

            $_SESSION['auth_user'] = [
                'username' => $user['username'],
                'role' => $user['role'] ?? 'user'
            ];
            return true;
        }
    }

    return false;
}

function ensureConfigDirectory() {
    if (!is_dir(USER_CONFIG_DIR)) {
        if (!mkdir(USER_CONFIG_DIR, 0755, true) && !is_dir(USER_CONFIG_DIR)) {
            throw new RuntimeException('Unable to create config directory.');
        }
    }
}

function sanitizeUsername($username) {
    $username = trim((string) $username);
    $username = preg_replace('/[^A-Za-z0-9._-]/', '', $username);
    return $username !== '' ? $username : 'user';
}

function getUserConfigPath($username) {
    return USER_CONFIG_DIR . '/' . sanitizeUsername($username) . '-config.json';
}

function getUserChatPath($username) {
    return USER_CONFIG_DIR . '/' . sanitizeUsername($username) . '-chat.json';
}

function getConfiguredDefaultModel() {
    $defaultModel = defined('DEFAULT_MODEL') ? trim((string) DEFAULT_MODEL) : '';
    return $defaultModel !== '' ? $defaultModel : 'llama3';
}

function getDefaultModelForUser($username) {
    $config = getUserConfig($username);
    $storedModel = trim((string) ($config['defaultModel'] ?? ''));
    return $storedModel !== '' ? $storedModel : getConfiguredDefaultModel();
}

function readUserConfig($username) {
    $path = getUserConfigPath($username);
    if (!file_exists($path)) {
        // Try migrating from legacy PHP file if present
        $legacy = USER_CONFIG_DIR . '/' . sanitizeUsername($username) . '-config.php';
        if (file_exists($legacy)) {
            $raw = @file_get_contents($legacy);
            if ($raw !== false) {
                // attempt to include safely
                $data = @include $legacy;
                if (is_array($data)) {
                    // write JSON migration
                    writeUserConfig($username, $data);
                    return $data;
                }
            }
        }
        return [];
    }

    $raw = @file_get_contents($path);
    if ($raw === false) {
        return [];
    }

    $decoded = json_decode($raw, true);
    return is_array($decoded) ? $decoded : [];
}

function writeUserConfig($username, $config) {
    ensureConfigDirectory();

    $username = trim((string) $username);
    if ($username === '') {
        return false;
    }
    $data = is_array($config) ? $config : [];
    $data['username'] = $username;
    $data['role'] = (string) ($data['role'] ?? 'user');
    $data['email'] = (string) ($data['email'] ?? '');
    $data['passwordHash'] = (string) ($data['passwordHash'] ?? '');
    $storedDefaultModel = trim((string) ($data['defaultModel'] ?? ''));
    $data['defaultModel'] = $storedDefaultModel !== '' ? $storedDefaultModel : getConfiguredDefaultModel();

    $json = json_encode($data, JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    if ($json === false) {
        return false;
    }

    $path = getUserConfigPath($username);
    $tmp = $path . '.tmp';
    if (@file_put_contents($tmp, $json . "\n") === false) {
        return false;
    }
    return @rename($tmp, $path);
}

function readUserChat($username) {
    $path = getUserChatPath($username);
    if (!file_exists($path)) {
        // Try migrating legacy PHP chat file
        $legacy = USER_CONFIG_DIR . '/' . sanitizeUsername($username) . '-chat.php';
        if (file_exists($legacy)) {
            $data = @include $legacy;
            if (is_array($data)) {
                writeUserChat($username, $data);
                return $data;
            }
        }
        return [];
    }

    $raw = @file_get_contents($path);
    if ($raw === false) {
        return [];
    }

    $decoded = json_decode($raw, true);
    return is_array($decoded) ? $decoded : [];
}

function writeUserChat($username, $chats) {
    ensureConfigDirectory();

    $username = trim((string) $username);
    if ($username === '') {
        return false;
    }
    $json = json_encode(is_array($chats) ? $chats : [], JSON_PRETTY_PRINT | JSON_UNESCAPED_SLASHES | JSON_UNESCAPED_UNICODE);
    if ($json === false) {
        return false;
    }

    $path = getUserChatPath($username);
    $tmp = $path . '.tmp';
    if (@file_put_contents($tmp, $json . "\n") === false) {
        return false;
    }
    return @rename($tmp, $path);
}

function renameUserFiles($oldUsername, $newUsername) {
    $oldUsername = trim((string) $oldUsername);
    $newUsername = trim((string) $newUsername);

    if ($oldUsername === '' || $newUsername === '' || $oldUsername === $newUsername) {
        return;
    }

    $oldConfigPath = getUserConfigPath($oldUsername);
    $newConfigPath = getUserConfigPath($newUsername);
    if (file_exists($oldConfigPath) && !file_exists($newConfigPath)) {
        @rename($oldConfigPath, $newConfigPath);
    }

    $oldChatPath = getUserChatPath($oldUsername);
    $newChatPath = getUserChatPath($newUsername);
    if (file_exists($oldChatPath) && !file_exists($newChatPath)) {
        @rename($oldChatPath, $newChatPath);
    }
}

function hashPassword($password) {
    return password_hash($password, PASSWORD_DEFAULT);
}

function verifyPassword($password, $hash) {
    return password_verify($password, $hash);
}

function getUserConfig($username) {
    $username = trim((string) $username);
    if ($username === '') {
        return [];
    }

    return readUserConfig($username);
}

function saveUserConfigData($username, $config) {
    return writeUserConfig($username, $config);
}

function loadUsers() {
    ensureConfigDirectory();
    $files = glob(USER_CONFIG_DIR . '/*-config.json');
    if ($files === false) {
        $files = [];
    }

    $users = [];
    // load json config files
    foreach ($files as $file) {
        $username = basename($file, '-config.json');
        $user = readUserConfig($username);
        if (!empty($user) && !empty($user['username'])) {
            $users[] = $user;
        }
    }

    // detect legacy php config files and migrate
    $legacyFiles = glob(USER_CONFIG_DIR . '/*-config.php');
    if ($legacyFiles !== false) {
        foreach ($legacyFiles as $legacy) {
            $username = basename($legacy, '-config.php');
            // if already loaded from json, skip
            $exists = false;
            foreach ($users as $u) {
                if (($u['username'] ?? '') === $username) {
                    $exists = true;
                    break;
                }
            }
            if ($exists) continue;

            $data = @include $legacy;
            if (is_array($data) && !empty($data['username'])) {
                // migrate to json
                writeUserConfig($username, $data);
                // remove legacy files
                @unlink($legacy);
                $users[] = $data;
            }
        }
    }

    usort($users, function ($a, $b) {
        return strcmp(($a['username'] ?? ''), ($b['username'] ?? ''));
    });

    return $users;
}

function saveUsers($users, $previousUsers = null) {
    ensureConfigDirectory();

    $normalizedUsers = [];
    foreach ($users as $index => $user) {
        $entry = is_array($user) ? $user : [];
        $username = trim((string) ($entry['username'] ?? ''));
        if ($username === '') {
            continue;
        }

        $entry['username'] = $username;
        $entry['role'] = (string) ($entry['role'] ?? 'user');
        $entry['email'] = (string) ($entry['email'] ?? '');
        $entry['passwordHash'] = (string) ($entry['passwordHash'] ?? '');
        $entry['defaultModel'] = trim((string) ($entry['defaultModel'] ?? '')) !== '' ? trim((string) $entry['defaultModel']) : getConfiguredDefaultModel();
        $normalizedUsers[] = $entry;
    }

    $previousUsers = is_array($previousUsers) ? $previousUsers : loadUsers();
    foreach ($normalizedUsers as $index => $entry) {
        $oldUsername = isset($previousUsers[$index]) ? trim((string) ($previousUsers[$index]['username'] ?? '')) : '';
        $newUsername = trim((string) ($entry['username'] ?? ''));
        if ($oldUsername !== '' && $oldUsername !== $newUsername) {
            renameUserFiles($oldUsername, $newUsername);
        }

        if (!writeUserConfig($newUsername, $entry)) {
            return false;
        }
    }

    $currentUsernames = [];
    foreach ($normalizedUsers as $entry) {
        $currentUsernames[] = sanitizeUsername($entry['username']);
    }

    $files = glob(USER_CONFIG_DIR . '/*-config.json');
    if ($files !== false) {
        foreach ($files as $file) {
            $name = basename($file, '-config.json');
            if (!in_array($name, $currentUsernames, true)) {
                @unlink(USER_CONFIG_DIR . '/' . $name . '-config.json');
                @unlink(USER_CONFIG_DIR . '/' . $name . '-chat.json');
                @unlink(USER_CONFIG_DIR . '/' . $name . '-config.php');
                @unlink(USER_CONFIG_DIR . '/' . $name . '-chat.php');
            }
        }
    }

    return true;
}

function findUserByUsername($username) {
    $username = trim((string) $username);
    if ($username === '') {
        return null;
    }

    foreach (loadUsers() as $user) {
        if (($user['username'] ?? '') === $username) {
            return $user;
        }
    }

    return null;
}

function findUserByEmail($email) {
    $email = trim((string) $email);
    if ($email === '') {
        return null;
    }

    foreach (loadUsers() as $user) {
        if (strtolower((string) ($user['email'] ?? '')) === strtolower($email)) {
            return $user;
        }
    }

    return null;
}

function generateRegistrationCode() {
    return str_pad((string) random_int(0, 999999), 6, '0', STR_PAD_LEFT);
}

function sendRegistrationVerificationEmail($email, $code) {
    $email = trim((string) $email);
    if ($email === '') {
        return false;
    }

    $subject = 'Your KaI registration verification code';
    $message = "Hello,\n\n"
        . "You requested to create a KaI account.\n"
        . "Your verification code is: {$code}\n\n"
        . "Please enter this code on the registration page to complete your account setup.";
    $headers = "From: " . MAIL_FROM_NAME . " <" . MAIL_FROM . ">\r\n"
        . "Reply-To: " . MAIL_FROM . "\r\n"
        . "X-Mailer: PHP/" . phpversion();

    return mail($email, $subject, $message, $headers);
}

function savePendingRegistration($username, $email, $password, $code) {
    if (session_status() === PHP_SESSION_NONE) {
        session_start();
    }

    $_SESSION['pending_registration'] = [
        'username' => trim((string) $username),
        'email' => trim((string) $email),
        'password' => (string) $password,
        'code' => (string) $code,
        'createdAt' => time(),
    ];

    return true;
}

function getPendingRegistration() {
    if (session_status() === PHP_SESSION_NONE) {
        session_start();
    }

    return $_SESSION['pending_registration'] ?? null;
}

function clearPendingRegistration() {
    if (session_status() === PHP_SESSION_NONE) {
        session_start();
    }

    unset($_SESSION['pending_registration']);
}

function createUser($username, $password, $role = 'user', $email = '') {
    $username = trim((string) $username);
    $email = trim((string) $email);
    if ($username === '' || $password === '') {
        return false;
    }

    $users = loadUsers();
    if (findUserByUsername($username) !== null) {
        return false;
    }

    if ($email !== '' && findUserByEmail($email) !== null) {
        return false;
    }

    $users[] = [
        'username' => $username,
        'email' => $email,
        'passwordHash' => hashPassword($password),
        'role' => $role,
        'defaultModel' => getConfiguredDefaultModel()
    ];

    if (!writeUserChat($username, [])) {
        return false;
    }

    return saveUsers($users);
}

function requestPasswordReset($email) {
    $email = trim((string) $email);
    if ($email === '') {
        return false;
    }

    $user = findUserByEmail($email);
    if ($user === null) {
        return false;
    }

    $token = bin2hex(random_bytes(32));
    $users = loadUsers();
    foreach ($users as &$entry) {
        if (($entry['username'] ?? '') === ($user['username'] ?? '')) {
            $entry['resetTokenHash'] = password_hash($token, PASSWORD_DEFAULT);
            $entry['resetTokenExpires'] = time() + 3600;
            break;
        }
    }

    if (!saveUsers($users)) {
        return false;
    }

    $link = APP_BASE_URL . '/reset.php?token=' . urlencode($token);
    $subject = 'Password reset for KaI';
    $message = "Hello {$user['username']},\n\n"
        . "You requested a password reset for your KaI account.\n"
        . "Please use the following link to set a new password:\n\n"
        . $link . "\n\n"
        . "If you did not request this, you can ignore this email.";
    $headers = "From: " . MAIL_FROM_NAME . " <" . MAIL_FROM . ">\r\n"
        . "Reply-To: " . MAIL_FROM . "\r\n"
        . "X-Mailer: PHP/" . phpversion();

    return mail($email, $subject, $message, $headers);
}

function validatePasswordResetToken($token) {
    $token = (string) $token;
    if ($token === '') {
        return null;
    }

    foreach (loadUsers() as $user) {
        $expiresAt = (int) ($user['resetTokenExpires'] ?? 0);
        if ($expiresAt > time() && !empty($user['resetTokenHash']) && password_verify($token, (string) $user['resetTokenHash'])) {
            return $user;
        }
    }

    return null;
}

function completePasswordReset($token, $newPassword) {
    $token = (string) $token;
    $newPassword = (string) $newPassword;
    if ($token === '' || $newPassword === '') {
        return false;
    }

    $users = loadUsers();
    foreach ($users as &$entry) {
        $expiresAt = (int) ($entry['resetTokenExpires'] ?? 0);
        if ($expiresAt > time() && !empty($entry['resetTokenHash']) && password_verify($token, (string) $entry['resetTokenHash'])) {
            $entry['passwordHash'] = hashPassword($newPassword);
            unset($entry['resetTokenHash'], $entry['resetTokenExpires']);
            return saveUsers($users);
        }
    }

    return false;
}

function isLoggedIn() {
    return !empty($_SESSION['auth_user']['username']);
}

function getAuthenticatedUser() {
    if (!isLoggedIn()) {
        return null;
    }

    if (isGuestSession()) {
        return createGuestUser();
    }

    return findUserByUsername($_SESSION['auth_user']['username'] ?? '');
}

function getAuthenticatedUsername() {
    $user = getAuthenticatedUser();
    if ($user !== null) {
        return (string) ($user['username'] ?? '');
    }

    return (string) ($_SESSION['auth_user']['username'] ?? '');
}

function requireAuthentication() {
    if (!isLoggedIn()) {
        http_response_code(403);
        echo json_encode(['error' => 'Authentication required.']);
        exit;
    }
}

function requireAdmin() {
    $user = getAuthenticatedUser();
    if (!$user || (($user['role'] ?? 'user') !== 'admin')) {
        http_response_code(403);
        echo json_encode(['error' => 'Admin access required.']);
        exit;
    }
}

function logoutUser() {
    $username = trim((string) ($_SESSION['auth_user']['username'] ?? ''));
    unset($_SESSION['auth_user']);

    if ($username !== '') {
        clearRememberMeCookie($username);
    }
}