refactor(eventsub): enforce static error categories (#5903)

lib/twitch-eventsub-ws/src/errors.cpp

@@ -0,0 +1,34 @@
+#include "twitch-eventsub-ws/errors.hpp"
+
+#include <cassert>
+
+namespace chatterino::eventsub::lib::error {
+
+std::string ApplicationErrorCategory::message(int ev) const
+{
+    using namespace std::string_literals;
+
+    static_assert(sizeof(int) == sizeof(Kind));
+    auto kind = static_cast<Kind>(ev);
+
+    switch (kind)
+    {
+        case Kind::FieldMissing:
+            return "Missing required key"s;
+        case Kind::ExpectedObject:
+            return "Expected an object"s;
+        case Kind::ExpectedString:
+            return "Expected a string"s;
+        case Kind::UnknownEnumValue:
+            return "Unknown enum value"s;
+        case Kind::InnerRootMissing:
+            return "Missing inner root"s;
+        case Kind::NoMessageHandler:
+            return "No message handler found"s;
+    }
+
+    assert(false);
+    return "Unknown error"s;
+}
+
+}  // namespace chatterino::eventsub::lib::error