Lazy translation during error response generation

Now when parameterized messages are added to an error response, they are
not immediately instantiated (translated). Instead the message id and
the parameters of the message are recorded. The instantiation of the
messages happens right before generating the final content of the
response.

src/server/i18n.h

@@ -107,6 +107,9 @@ public: // functions
 
   std::string getText(const std::string& lang) const;
 
+  const std::string& getMsgId()  const { return msgId; }
+  const Parameters&  getParams() const { return params; }
+
 private: // data
   const std::string msgId;
   const Parameters  params;

src/server/response.cpp

@@ -183,6 +183,18 @@ public:
     return s.empty() ? Data(false) : Data(s);
   }
 
+  static Data from(const ParameterizedMessage& pmsg)
+  {
+    Object obj;
+    for(const auto& kv : pmsg.getParams()) {
+      obj[kv.first] = kv.second;
+    }
+    return Object{
+              { "msgid", pmsg.getMsgId() },
+              { "params", Data(obj) }
+    };
+  }
+
 private:
   bool isString() const { return std::holds_alternative<std::string>(data); }
   bool isList()   const { return std::holds_alternative<List>(data); }
@@ -192,6 +204,16 @@ private:
   bool               boolValue()   const { return std::get<bool>(data); }
   const List&        listValue()   const { return std::get<List>(data); }
   const Object&      objectValue() const { return std::get<Object>(data); }
+
+  const Data* get(const std::string& key) const
+  {
+    if ( !isObject() )
+      return nullptr;
+
+    const auto& obj = objectValue();
+    const auto it = obj.find(key);
+    return it != obj.end() ? &it->second : nullptr;
+  }
 };
 
 MustacheData ContentResponseBlueprint::Data::toMustache(const std::string& lang) const
@@ -203,11 +225,22 @@ MustacheData ContentResponseBlueprint::Data::toMustache(const std::string& lang)
     }
     return l;
   } else if ( this->isObject() ) {
+    const Data* msgId = this->get("msgid");
+    const Data* msgParams = this->get("params");
+    if ( msgId && msgId->isString() && msgParams && msgParams->isObject() ) {
+      std::map<std::string, std::string> params;
+      for(const auto& kv : msgParams->objectValue()) {
+        params[kv.first] = kv.second.stringValue();
+      }
+      const ParameterizedMessage msg(msgId->stringValue(), ParameterizedMessage::Parameters(params));
+      return msg.getText(lang);
+    } else {
       kainjow::mustache::object o;
       for ( const auto& kv : this->objectValue() ) {
         o[kv.first] = kv.second.toMustache(lang);
       }
       return o;
+    }
   } else if ( this->isString() ) {
     return this->stringValue();
   } else {
@@ -229,11 +262,6 @@ ContentResponseBlueprint::ContentResponseBlueprint(const RequestContext* request
 
 ContentResponseBlueprint::~ContentResponseBlueprint() = default;
 
-std::string ContentResponseBlueprint::getMessage(const std::string& msgId) const
-{
-  return getTranslatedString(m_request.get_user_language(), msgId);
-}
-
 std::unique_ptr<ContentResponse> ContentResponseBlueprint::generateResponseObject() const
 {
   kainjow::mustache::data d = m_data->toMustache(m_request.get_user_language());
@@ -255,8 +283,8 @@ HTTPErrorResponse::HTTPErrorResponse(const RequestContext& request,
   Data::List emptyList;
   *this->m_data = Data(Data::Object{
                     {"CSS_URL", Data::onlyAsNonEmptyValue(cssUrl) },
-                    {"PAGE_TITLE",   getMessage(pageTitleMsgId)},
-                    {"PAGE_HEADING", getMessage(headingMsgId)},
+                    {"PAGE_TITLE",   Data::from(nonParameterizedMessage(pageTitleMsgId))},
+                    {"PAGE_HEADING", Data::from(nonParameterizedMessage(headingMsgId))},
                     {"details", emptyList}
   });
 }
@@ -278,8 +306,7 @@ UrlNotFoundResponse::UrlNotFoundResponse(const RequestContext& request)
 
 HTTPErrorResponse& HTTPErrorResponse::operator+(const ParameterizedMessage& details)
 {
-  const std::string msg = details.getText(m_request.get_user_language());
-  (*m_data)["details"].push_back(Data::Object{{"p", msg}});
+  (*m_data)["details"].push_back(Data::Object{{"p", Data::from(details)}});
   return *this;
 }
 

src/server/response.h

@@ -135,9 +135,6 @@ public: // functions
 protected: // types
   class Data;
 
-protected: // functions
-  std::string getMessage(const std::string& msgId) const;
-
 protected: //data
   const RequestContext& m_request;
   const int m_httpStatusCode;