class SettingsEditor

final class SettingsEditor {
    
    /**
     * This class should not be instantiated.
     *
     * Use a static ::rewrite() method call instead.
     *
     * @see \Drupal\Core\Site\SettingsEditor::rewrite()
     */
    private function __construct() {
    }
    
    /**
     * Replaces values in settings.php with values in the submitted array.
     *
     * This method rewrites values in place if possible, even for
     * multidimensional arrays. This helps ensure that the documentation remains
     * attached to the correct settings and that old, overridden values do not
     * clutter up the file.
     *
     * @code
     *   $settings['settings']['config_sync_directory'] = (object) [
     *     'value' => 'config_hash/sync',
     *     'required' => TRUE,
     *   ];
     * @endcode
     *   gets dumped as:
     * @code
     *   $settings['config_sync_directory'] = 'config_hash/sync'
     * @endcode
     *
     * @param string $settings_file
     *   Path to the settings file relative to the DRUPAL_ROOT directory.
     * @param array $settings
     *   An array of settings that need to be updated. Multidimensional arrays
     *   are dumped up to a stdClass object. The object can have value, required
     *   and comment properties.
     *
     * @throws \Exception
     */
    public static function rewrite(string $settings_file, array $settings = []) : void {
        // Build list of setting names and insert the values into the global
        // namespace.
        $variable_names = [];
        $settings_settings = [];
        foreach ($settings as $setting => $data) {
            if ($setting !== 'settings') {
                self::setGlobal($GLOBALS[$setting], $data);
            }
            else {
                self::setGlobal($settings_settings, $data);
            }
            $variable_names['$' . $setting] = $setting;
        }
        $contents = file_get_contents($settings_file);
        if ($contents !== FALSE) {
            // Initialize the contents for the settings.php file if it is empty.
            if (trim($contents) === '') {
                $contents = "<?php\n";
            }
            // Step through each token in settings.php and replace any variables that
            // are in the passed-in array.
            $buffer = '';
            $state = 'default';
            foreach (token_get_all($contents) as $token) {
                if (is_array($token)) {
                    [
                        $type,
                        $value,
                    ] = $token;
                }
                else {
                    $type = -1;
                    $value = $token;
                }
                // Do not operate on whitespace.
                if (!in_array($type, [
                    T_WHITESPACE,
                    T_COMMENT,
                    T_DOC_COMMENT,
                ], TRUE)) {
                    switch ($state) {
                        case 'default':
                            if ($type === T_VARIABLE && isset($variable_names[$value])) {
                                // This will be necessary to unset the dumped variable.
                                $parent =& $settings;
                                // This is the current index in parent.
                                $index = $variable_names[$value];
                                // This will be necessary for descending into the array.
                                $current =& $parent[$index];
                                $state = 'candidate_left';
                            }
                            break;
                        case 'candidate_left':
                            if ($value === '[') {
                                $state = 'array_index';
                            }
                            if ($value === '=') {
                                $state = 'candidate_right';
                            }
                            break;
                        case 'array_index':
                            if (self::isArrayIndex($type)) {
                                $index = trim($value, '\'"');
                                $state = 'right_bracket';
                            }
                            else {
                                // $a[foo()] or $a[$bar] or something like that.
                                throw new \Exception('invalid array index');
                            }
                            break;
                        case 'right_bracket':
                            if ($value === ']') {
                                if (isset($current[$index])) {
                                    // If the new settings has this index, descend into it.
                                    $parent =& $current;
                                    $current =& $parent[$index];
                                    $state = 'candidate_left';
                                }
                                else {
                                    // Otherwise, jump back to the default state.
                                    $state = 'wait_for_semicolon';
                                }
                            }
                            else {
                                // $a[1 + 2].
                                throw new \Exception('] expected');
                            }
                            break;
                        case 'candidate_right':
                            if (self::isSimple($type, $value)) {
                                $value = self::exportSingleSettingToPhp($current);
                                // Unsetting $current would not affect $settings at all.
                                unset($parent[$index]);
                                // Skip the semicolon because self::dumpOne() added one.
                                $state = 'semicolon_skip';
                            }
                            else {
                                $state = 'wait_for_semicolon';
                            }
                            break;
                        case 'wait_for_semicolon':
                            if ($value === ';') {
                                $state = 'default';
                            }
                            break;
                        case 'semicolon_skip':
                            if ($value === ';') {
                                $value = '';
                                $state = 'default';
                            }
                            else {
                                // If the expression was $a = 1 + 2; then we replaced 1 and
                                // the + is unexpected.
                                throw new \Exception('Unexpected token after replacing value.');
                            }
                            break;
                    }
                }
                $buffer .= $value;
            }
            foreach ($settings as $name => $setting) {
                $buffer .= self::exportSettingsToPhp($setting, '$' . $name);
            }
            // Write the new settings file.
            if (file_put_contents($settings_file, $buffer) === FALSE) {
                throw new \Exception("Failed to modify '{$settings_file}'. Verify the file permissions.");
            }
            // In case any $settings variables were written, import them into the
            // Settings singleton.
            if (!empty($settings_settings)) {
                $old_settings = Settings::getAll();
                new Settings($settings_settings + $old_settings);
            }
            // The existing settings.php file might have been included already. In
            // case an opcode cache is enabled, the rewritten contents of the file
            // will not be reflected in this process. Ensure to invalidate the file
            // in case an opcode cache is enabled.
            OpCodeCache::invalidate(DRUPAL_ROOT . '/' . $settings_file);
        }
        else {
            throw new \Exception("Failed to open '{$settings_file}'. Verify the file permissions.");
        }
    }
    
    /**
     * Checks whether the given token represents a scalar or NULL.
     *
     * @param int $type
     *   The token type.
     * @param string $value
     *   The value of the token.
     *
     * @return bool
     *   TRUE if this token represents a scalar or NULL.
     *
     * @see token_name()
     */
    private static function isSimple(int $type, string $value) : bool {
        $is_integer = $type === T_LNUMBER;
        $is_float = $type === T_DNUMBER;
        $is_string = $type === T_CONSTANT_ENCAPSED_STRING;
        $is_boolean_or_null = $type === T_STRING && in_array(strtoupper($value), [
            'TRUE',
            'FALSE',
            'NULL',
        ]);
        return $is_integer || $is_float || $is_string || $is_boolean_or_null;
    }
    
    /**
     * Checks whether the token is a valid array index (a number or string).
     *
     * @param int $type
     *   The token type.
     *
     * @return bool
     *   TRUE if this token represents a number or a string.
     *
     * @see token_name()
     */
    private static function isArrayIndex(int $type) : bool {
        $is_integer = $type === T_LNUMBER;
        $is_float = $type === T_DNUMBER;
        $is_string = $type === T_CONSTANT_ENCAPSED_STRING;
        return $is_integer || $is_float || $is_string;
    }
    
    /**
     * Makes the given setting global.
     *
     * @param mixed $ref
     *   A reference to a nested index in $GLOBALS.
     * @param array|object $variable
     *   The nested value of the setting being copied.
     */
    private static function setGlobal(mixed &$ref, array|object $variable) : void {
        if (is_object($variable)) {
            $ref = $variable->value;
        }
        else {
            foreach ($variable as $k => $v) {
                self::setGlobal($ref[$k], $v);
            }
        }
    }
    
    /**
     * Recursively exports one or more settings to a valid PHP string.
     *
     * @param array|object $variable
     *   The container for variable values.
     * @param string $variable_name
     *   Name of variable.
     *
     * @return string
     *   A string containing valid PHP code of the variable suitable for placing
     *   into settings.php.
     */
    private static function exportSettingsToPhp(array|object $variable, string $variable_name) : string {
        $return = '';
        if (is_object($variable)) {
            if (!empty($variable->required)) {
                $return .= self::exportSingleSettingToPhp($variable, "{$variable_name} = ", "\n");
            }
        }
        else {
            foreach ($variable as $k => $v) {
                $return .= self::exportSettingsToPhp($v, $variable_name . "['" . $k . "']");
            }
        }
        return $return;
    }
    
    /**
     * Exports the value of a value property and adds the comment if it exists.
     *
     * @param object $variable
     *   A stdClass object with at least a value property.
     * @param string $prefix
     *   A string to prepend to the variable's value.
     * @param string $suffix
     *   A string to append to the variable's value.
     *
     * @return string
     *   A string containing valid PHP code of the variable suitable for placing
     *   into settings.php.
     */
    private static function exportSingleSettingToPhp(object $variable, string $prefix = '', string $suffix = '') : string {
        $return = $prefix . var_export($variable->value, TRUE) . ';';
        if (!empty($variable->comment)) {
            $return .= ' // ' . $variable->comment;
        }
        $return .= $suffix;
        return $return;
    }

}