Support the conversion of date & datetime format to GraphQL type

[tian-sheng-low]

Just wondering if OtG has any plan to support the conversion of date/datetime format schema into graphql-scalar date types etc.

I read this issue and it seems like date/datetime type is out of the support scope, I just want to make sure that if I understand it correctly.
#244 (comment)

The way I see is that for the complex use cases can be handled by people saving schema and making some manual tweaks like:
Adding scalars ( like Date or https://github.com/Urigo/graphql-scalars)
Adding directives
Adding interfaces etc.
For some of those people might need to drop some extra code in the form of custom resolver but this will be much simple rather than trying to cover all those in the generic engine cases.

If that is not the case(support for date/datetime type is fine with the scope), then I am happy to send a PR for that.

[abhinavsrv]

#include
#include
#include
#include
#include
#include

std::string to_iso8601(const std::chrono::system_clock::time_point& tp) {
auto in_time_t = std::chrono::system_clock::to_time_t(tp);
std::stringstream ss;
ss << std::put_time(std::gmtime(&in_time_t), "%Y-%m-%dT%H:%M:%SZ");
return ss.str();
}

std::chrono::system_clock::time_point from_iso8601(const std::string& iso_str) {
std::tm t{};
std::istringstream ss(iso_str);
if (!(ss >> std::get_time(&t, "%Y-%m-%dT%H:%M:%SZ"))) {
throw std::runtime_error("Invalid ISO 8601 DateTime format.");
}
return std::chrono::system_clock::from_time_t(std::mktime(&t));
}

class GraphQLDateTimeScalar {
public:
static std::string serialize(const std::chrono::system_clock::time_point& tp) {
return to_iso8601(tp);
}

static std::chrono::system_clock::time_point parseValue(const std::string& value) {
    return from_iso8601(value);
}

static std::chrono::system_clock::time_point parseLiteral(const std::string& literal) {
    return from_iso8601(literal);
}

};

std::string getEventDateTime() {
std::chrono::system_clock::time_point now = std::chrono::system_clock::now();
return GraphQLDateTimeScalar::serialize(now);
}

void createEvent(const std::string& eventName, const std::string& dateTimeStr) {
try {
std::chrono::system_clock::time_point parsedDateTime = GraphQLDateTimeScalar::parseValue(dateTimeStr);
std::cout << "Creating event '" << eventName << "' at " << GraphQLDateTimeScalar::serialize(parsedDateTime) << std::endl;
} catch (const std::runtime_error& e) {
std::cerr << "Error parsing DateTime: " << e.what() << std::endl;
}
}

int main() {
std::string serializedDateTime = getEventDateTime();
std::cout << "Current DateTime for GraphQL response: " << serializedDateTime << std::endl;
createEvent("Team Meeting", "2025-07-29T14:30:00Z");
createEvent("Invalid Event", "not-a-date");
return 0;
}