Make codebase consistent with design.md

src/main.cpp

@@ -87,10 +87,28 @@ int main(int argc, char *argv[]) {
   })";
   auto copy = sample_json;
 
-  if (parser.parse(request, copy.data(), copy.size())) {
+  auto parse_result = parser.parse(request, copy.data(), copy.size());
+  if (parse_result == CommitRequestParser::ParseResult::Success) {
     print_stats(request);
   } else {
-    std::cout << "✗ Failed to parse commit request" << std::endl;
+    std::cout << "✗ Failed to parse commit request: ";
+    switch (parse_result) {
+    case CommitRequestParser::ParseResult::InvalidJson:
+      std::cout << "Invalid JSON format" << std::endl;
+      break;
+    case CommitRequestParser::ParseResult::MissingField:
+      std::cout << "Missing required field" << std::endl;
+      break;
+    case CommitRequestParser::ParseResult::InvalidField:
+      std::cout << "Invalid field value" << std::endl;
+      break;
+    case CommitRequestParser::ParseResult::OutOfMemory:
+      std::cout << "Out of memory" << std::endl;
+      break;
+    default:
+      std::cout << "Unknown error" << std::endl;
+      break;
+    }
   }
 
   // Demonstrate streaming parsing