Add first test for a generic ConfigurationSetter

We are blocked if a setter has to update several values.
ConfigurationSetter will be updated.

See https://github.com/FreshRSS/FreshRSS/issues/730

app/FreshRSS.php

@@ -17,10 +17,15 @@ class FreshRSS extends Minz_FrontController {
 	}
 
 	private function initConfiguration() {
+		$configuration_setter = new FreshRSS_ConfigurationSetter();
 		$current_user = Minz_Session::param('currentUser', '_');
+
 		Minz_Configuration::register('user',
 		                             join_path(USERS_PATH, $current_user, 'config.php'),
-		                             join_path(USERS_PATH, '_', 'config.default.php'));
+		                             join_path(USERS_PATH, '_', 'config.default.php'),
+		                             $configuration_setter);
+		$system_conf = Minz_Configuration::get('system');
+		$system_conf->_configurationSetter($configuration_setter);
 	}
 
 	private function initAuth() {

app/Models/ConfigurationSetter.php

@@ -0,0 +1,37 @@
+<?php
+
+class FreshRSS_ConfigurationSetter {
+	private $setters = array(
+		'language' => '_language',
+		'posts_per_page' => '_posts_per_page',
+		'view_mode' => '_view_mode',
+	);
+
+	public function handle($key, $value) {
+		if (isset($this->setters[$key])) {
+			$value = call_user_func(array($this, $this->setters[$key]), $value);
+		}
+		return $value;
+	}
+
+	private function _language($value) {
+		$languages = Minz_Translate::availableLanguages();
+		if (!isset($languages[$value])) {
+			$value = 'en';
+		}
+
+		return $value;
+	}
+
+	private function _posts_per_page($value) {
+		$value = intval($value);
+		return $value > 0 ? $value : 10;
+	}
+
+	private function _view_mode($value) {
+		if (!in_array($value, array('global', 'normal', 'reader'))) {
+			$value = 'normal';
+		}
+		return $value;
+	}
+}