wm_char and sending unicode codepoint event

wm_char.cpp

// window.event.character_input -- // note(matias): not always triggered by keydown
case WM_CHAR: {
	State& state = *(State*)GetWindowLongPtrW(hwnd, GWLP_USERDATA);
	uint32_t ch = (uint32_t)wParam;

	// note(matias): searching for utf-16 in wikipedia helps a lot here

	// ch.is_printable?
	if ((ch >= 32 && ch != 127) || ch == '\t' || ch == '\n' || ch == '\r') {

		// ch.in_basic_multilingual_plane? -> single 16-bit code unit
		if (ch < 0xd800) {

			// note(matias): [enter] comes as either '\r' or '\n' so we normalize to '\n'
			if (ch == (uint32_t)'\r') {
				ch = (uint32_t)'\n';
			}
			// todo(matias): reset state.high_surrogate = 0?

		// ch.in_high_surrogate_plane? -> save first code unit
		} else if (ch >= 0xd800 && ch <= 0xdbff) {
			state.high_surrogate = ch;
			return 0;

		// ch.in_low_surrogate_plane? -> combine both code units
		} else if (ch >= 0xdc00 && ch <= 0xdfff) {

			// todo(matias): what happens if state.high_surrogate is 0?
			uint32_t low_surrogate = ch;
			ch = 0x10000;
			ch += (state.high_surrogate & 0x03ff) << 10;
			ch += low_surrogate & 0x03ff;
			// todo(matias): reset state.high_surrogate = 0?

		} else [[unlikely]] {
			// note(matias): probably an error, so let's just ignore it
			return 0;
		}

		// event.push(character_input)
		Event& event = state.events[state.events_count];
		event.kind = EventKind_CharacterInput;
		event.codepoint = ch;
		state.events_count++;
	}

	return 0;
}