From 595dfe169eb0ad0dbddf24cf3f94b954718b3cb5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?John=20Ankarstr=C3=B6m?= <john@ankarstrom.se>
Date: Thu, 21 Jul 2022 22:10:22 +0200
Subject: Simplify OnTerminate.

No, not "awful", AWFUN!

Speaking of AWFUN, here is an alternative implementation of it:

#define AWFUN(t, f) cond_fun<t, f##A, f##W>

template <typename T, auto F, auto G>
std::enable_if_t<std::is_same_v<T, char>, decltype(F)> cond_fun = F;

template <auto F, auto G>
auto cond_fun<wchar_t, F, G> = G;

This implementation uses a variable template instead of a function
template, but I decided against it, as (at least I think) it would
instantiate useless variables that merely point to pre-existing API
functions. Like,

auto cond_fun__wchar_t__blablabla = MessageBoxW;
auto cond_fun__char__blablabla = MessageBoxA;

which is quite useless. Better to just have a constexpr function,
which the compiler may inline, return the real function pointer.
---
 c/common.h | 13 +++++++++++++
 c/main.cpp | 36 +++++++++++++++++++++---------------
 2 files changed, 34 insertions(+), 15 deletions(-)

diff --git a/c/common.h b/c/common.h
index 0343914..4b42f45 100644
--- a/c/common.h
+++ b/c/common.h
@@ -74,6 +74,19 @@ inline T prefer(const T x)
 	return x;
 }
 
+/* Conditionally select between ANSI and wide string literal. */
+#define AWTEXT(t, s) cond_text<t>(s, L"" s)
+template <typename T> constexpr const T* cond_text(const char*, const wchar_t*);
+template <> constexpr const char* cond_text<char>(const char* sz, const wchar_t*) { return sz; }
+template <> constexpr const wchar_t* cond_text<wchar_t>(const char*, const wchar_t* wsz) { return wsz; }
+
+/* Conditionally select between ANSI and wide Windows API function. */
+#define AWFUN(t, f) cond_fun<t, f##A, f##W>()
+template <typename T, auto F, auto G>
+constexpr std::enable_if_t<std::is_same_v<T, char>, decltype(F)> cond_fun() { return F; }
+template <typename T, auto F, auto G>
+constexpr std::enable_if_t<std::is_same_v<T, wchar_t>, decltype(G)> cond_fun() { return G; }
+
 /* Return integer scaled for current DPI. */
 inline int Dpi(const int i)
 {
diff --git a/c/main.cpp b/c/main.cpp
index c426c65..4f31e7b 100644
--- a/c/main.cpp
+++ b/c/main.cpp
@@ -1,4 +1,5 @@
 #include <exception>
+#include <sstream>
 #include <windows.h>
 #include <commctrl.h>
 #include <uxtheme.h>
@@ -46,30 +47,35 @@ static LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);
 static INT_PTR CALLBACK AboutDlgProc(HWND, UINT, WPARAM, LPARAM);
 static void UpdateTheme();
 
+template <typename T>
+void TerminateMsg(const T* sz1, const T* sz2) noexcept
+{
+	std::basic_ostringstream<T> ss;
+	ss << AWTEXT(T, "Episode Browser was terminated due to ");
+	ss << sz1;
+	if (sz2)
+		ss << ": " << sz2;
+	else
+		ss << ".";
+	AWFUN(T, MessageBox)((HWND)NULL, ss.str().c_str(), AWTEXT(T, "Fatal Error"), MB_ICONERROR);
+}
+
 void OnTerminate() noexcept
 {
 	try {
 		std::rethrow_exception(std::current_exception());
         } catch (const term_t& t) {
-		std::basic_string<TCHAR> tstr = TEXT("Episode Browser was terminated due to a Prolog exception: ");
 		TCHAR* tsz;
-		if (PL_get_tchars(t, &tsz, CVT_WRITE)) {
-			tstr += tsz;
-			MessageBox(NULL, tstr.c_str(), TEXT("Fatal Error"), MB_ICONERROR);
-		} else
-			MessageBoxA(NULL, "Episode Browser was terminated due to a Prolog exception.",
-			    "Fatal Error", MB_ICONERROR);
+		if (PL_get_tchars(t, &tsz, CVT_WRITE))
+			TerminateMsg<TCHAR>(TEXT("a Prolog exception"), tsz);
+		else
+			TerminateMsg<char>("a Prolog exception", NULL);
 	} catch (Win32Error& e) {
-		std::basic_string<TCHAR> tstr = TEXT("Episode Browser was terminated due to a Windows error: ");
-		tstr += e.what<TCHAR>();
-		MessageBox(NULL, tstr.c_str(), TEXT("Fatal Error"), MB_ICONERROR);
+		TerminateMsg<TCHAR>(TEXT("a Windows error"), e.what<TCHAR>());
 	} catch (std::exception& e) {
-		std::string str = "Episode Browser was terminated due to an exception: ";
-		str += e.what();
-		MessageBoxA(NULL, str.c_str(), "Fatal Error", MB_ICONERROR);
+		TerminateMsg<char>("an exception", e.what());
 	} catch (...) {
-		MessageBoxA(NULL, "Episode Browser was terminated due to an exception.",
-		    "Fatal Error", MB_ICONERROR);
+		TerminateMsg<char>("an exception", NULL);
 	}
 	_Exit(1);
 }
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