/*
	PianoLibrary
	Copyright (C) 2025  OmniaX-Dev

	This file is part of PianoLibrary.

	PianoLibrary is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	PianoLibrary is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with PianoLibrary.  If not, see <https://www.gnu.org/licenses/>.
*/

#pragma once

#include <ostd/string/String.hpp>

namespace utc
{
	// Portable timegm: temporarily override TZ to UTC, call mktime, restore.
	// Works on POSIX, MSVC, MinGW, MSYS2 — everywhere mktime exists.
	static std::time_t portable_timegm(std::tm* tm)
	{
	#if defined(_WIN32) || defined(__MINGW32__)
		// _mkgmtime is MSVC/UCRT's timegm equivalent, also available in MSYS2 UCRT64.
		return _mkgmtime(tm);
	#else
		return timegm(tm);
	#endif
	}

	static String toLocal(const String& iso)
	{
		std::tm tm = {};

		// Manual parse — avoids strptime, which MSVC lacks entirely.
		// Expected format: "2026-06-20T14:00:00Z"
		if (std::sscanf(iso.c_str(), "%d-%d-%dT%d:%d:%dZ",
			&tm.tm_year, &tm.tm_mon, &tm.tm_mday,
			&tm.tm_hour, &tm.tm_min, &tm.tm_sec) != 6)
			return iso; // Unparseable -> return as-is.

		tm.tm_year -= 1900;
		tm.tm_mon  -= 1;
		tm.tm_isdst = -1;

		std::time_t utc = portable_timegm(&tm);
		std::tm* local  = std::localtime(&utc);

		char buf[64];
		std::strftime(buf, sizeof(buf), "%d %b %Y, %H:%M %Z", local);
		return buf;
	}
}