?cxx/ClassSys.*xx: +classSysConsoleHasAnsiColors()

	`SUSUWU_SH_RUNTIME_COLORS` will use this.
?`cxx/ClassSys.cxx`: ?`classSysInit`: if not `SUSUWU_SH_SKIP_COLORS`, warn unless `classSysConsoleHasAnsiColors()` is true.

?`README.md`: howto use `SUSUWU_SH_RUNTIME_COLORS`

Has to do with #17 (runtime detection of Command Sequence Introducer support for color/format codes)

Is followup to c97fa94 (?cxx/Macros.hxx +`SUSUWU_SH_RUNTIME_COLORS`)

TODO: posts/

cxx/ClassSys.cxx

@@ -36,6 +36,11 @@ const bool classSysInit(int argc, const char **args) {
 		assert(SUSUWU_NULLPTR != args[0]); /* `clangtidy` off: NOLINT(cppcoreguidelines-pro-bounds-pointer-arithmetic) */
 		return true;
 	}
+#ifndef SUSUWU_SH_SKIP_COLORS
+	if(!classSysConsoleHasAnsiColors()) {
+		SUSUWU_WARNING("classSysInit() {(!classSysConsoleHasAnsiColors()) /* Command Sequence Introducers disabled */}")
+	}
+#endif /* ndef SUSUWU_SH_SKIP_COLORS */
 	return false;
 }
 
@@ -221,6 +226,37 @@ const unsigned char classSysGetConsoleAttributes() {
 	errno = ENOTTY;
 	return 0;
 }
+const bool classSysConsoleHasAnsiColors() {
+#ifdef __WIN32__
+# include <windows.h> /* CONSOLE_SCREEN_BUFFER_INFO DWORD GetConsoleMode GetStdHandle SetConsoleMode STD_OUTPUT_HANDLE */
+	HANDLE hConsole = GetStdHandle(STD_OUTPUT_HANDLE);
+	if(INVALID_HANDLE_VALUE == hConsole) {
+		SUSUWU_PRINT(WARNING, "classSysConsoleHasAnsiColors() {!GetConsoleScreenBufferInfo()}, GetLastError(): " SUSUWU_SH_PURPLE + std::to_string(GetLastError()));
+		return false;
+	}
+	DWORD mode;
+	if(!GetConsoleMode(hConsole, &mode)) {
+		return false;
+	}
+	SetConsoleMode(hConsole, mode | ENABLE_VIRTUAL_TERMINAL_PROCESSING); /* virtual mode allows CSI colors */
+	return true;
+#elif defined _POSIX_VERSION
+	return true;
+#else
+	const char *term = getenv("TERM");
+	switch(std::string(term)) {
+		case "screen":
+		case "screen-256color":
+		case "vt100":
+		case "xterm":
+		case "xterm-256color":
+			return true;
+		/* case "dumb": */
+		default:
+			return false
+	}
+#endif
+}
 
 static void classSysHexTests(const std::string &value) {
 	const size_t ss = classSysHexStr(value).size();

cxx/ClassSys.hxx

@@ -80,6 +80,7 @@ const FILE *classSysFopenOwnPath() /* TODO: SUSUWU_NOEXCEPT(std::is_nothrow_invo
 static const bool classSysGetConsoleInput() { return std::cin.good() && !std::cin.eof(); }
 const bool classSysSetConsoleInput(bool input); /* Set to `false` for unit tests/background tasks (acts as if user pressed `<ctrl>+d`, thus input prompts will use default choices.) Returns `classSysGetConsoleInput();` */
 const unsigned char classSysGetConsoleAttributes(); /* if(_WIN32 || ) { return (background * 16) + foreground color; } else if(_POSIX_SOURCE) { return "\033[%1;%2m" -> (%1 * 16) + %2 ; } else { return 0; } */
+const bool classSysConsoleHasAnsiColors();
 
 template<class Os, class Str>
 inline Os &classSysHexOs(Os &os, const Str &value) {