toSnakeCase and EventContent::SingleKeyValue

This is a rework of EventContent::SimpleContent previously defined in
simplestateevents.h. Quite a few events (and not only state events) have
just a single key-value pair in their content - this structure (which
is really just a template wrapper around the value) and the accompanying
JsonConverter<> specialisation encapsulate the concept to streamline
definition of such events. This commit only has simplestateevents.h
using it; further commits will use SingleKeyValue in other places.

toSnakeCase is a facility function that converts camelCase used for
C++ variables into snake_case used in JSON payloads. Combined with
the preprocessor trick that makes a string literal from an identifier,
this allows to reduce boilerplate code that repeats the same name for
fields in C++ event classes and fields in JSON. SingleKeyValue uses it,
and there are other cases for it coming.

1 files changed, 16 insertions, 0 deletions

diff --git a/lib/converters.h b/lib/converters.h
index 515c96fd..6515310a 100644
--- a/lib/converters.h
+++ b/lib/converters.h
@@ -414,4 +414,20 @@ inline void addParam(ContT& container, const QString& key, ValT&& value)
     _impl::AddNode<std::decay_t<ValT>, Force>::impl(container, key,
                                                     std::forward<ValT>(value));
 }
+
+// This is a facility function to convert camelCase method/variable names
+// used throughout Quotient to snake_case JSON keys - see usage in
+// single_key_value.h and event.h (DEFINE_CONTENT_GETTER macro).
+inline auto toSnakeCase(QLatin1String s)
+{
+    QString result { s };
+    for (auto it = result.begin(); it != result.end(); ++it)
+        if (it->isUpper()) {
+            const auto offset = static_cast<int>(it - result.begin());
+            result.insert(offset, '_'); // NB: invalidates iterators
+            it = result.begin() + offset + 1;
+            *it = it->toLower();
+        }
+    return result;
+}
 } // namespace Quotient