#ifndef COMMON_H
#define COMMON_H

#include <memory>
#include <optional>
#include <windows.h>

#ifdef UNICODE
#define WA "W"
#else
#define WA "A"
#endif

template <typename T> std::basic_string<T> BstrFromSz(const char* sz, int iCp = CP_UTF8);
int EBMessageBox(const TCHAR* tszText, const TCHAR* tszCaption, unsigned uType);

/* Conditionally choose between two values. */
template <bool B, typename X, typename Y>
constexpr std::enable_if_t<B == true, X> choose(X x, Y) { return x; }
template <bool B, typename X, typename Y>
constexpr std::enable_if_t<B == false, Y> choose(X, Y y) { return y; }

/* Conditionally choose between ANSI and wide string literal. */
#define AWTEXT(t, s) choose<std::is_same_v<t, wchar_t>>(L"" s, s)

/* Conditionally choose between ANSI and wide Windows API function. */
#define AWFUN(t, f) choose<std::is_same_v<t, wchar_t>>(f##W, f##A)

struct Win32Error : public std::exception
{
	Win32Error();
	Win32Error(DWORD dwErr);
	~Win32Error();
	template <typename T = char> const T* what() const noexcept;
	DWORD dwErr;
private:
	char* m_szMsg = NULL;
	wchar_t* m_wszMsg = NULL;
};

template <typename T>
const T* Win32Error::what() const noexcept
{
	TCHAR* tszMsg = choose<std::is_same_v<T, wchar_t>>(m_wszMsg, m_szMsg);
	if (!tszMsg)
		AWFUN(T, FormatMessage)(
		    FORMAT_MESSAGE_ALLOCATE_BUFFER|FORMAT_MESSAGE_FROM_SYSTEM|FORMAT_MESSAGE_IGNORE_INSERTS,
		    NULL,
		    dwErr,
		    MAKELANGID(LANG_ENGLISH, SUBLANG_ENGLISH_US),
		    (TCHAR*)&tszMsg,
		    0, NULL);
	return tszMsg;
}

struct Library
{
	Library(const TCHAR* tszLibrary);
	~Library();
	template <class T> T* GetProcAddress(const char* szProc);
private:
	HMODULE m_hModule;
};

template <typename T>
T* Library::GetProcAddress(const char* const szProc)
{
	return (T*)(void*)::GetProcAddress(m_hModule, szProc);
}

/* Create and return an object of type C. If construction fails,
 * return nothing. The returned value must be checked before being
 * used, as dereferencing is undefined if the value is empty. */
template <typename T, typename... U>
std::optional<T> maybe_make(U... xs)
{
	try {
		return T(xs...);
	} catch (...) {
		return {};
	}
}

/* Variable template for caching values from GetSystemMetrics. */
template <int I>
const auto Metric = GetSystemMetrics(I);

/* Check result of Windows API call, throwing error on NULL. */
template <typename T>
inline T require(const T x)
{
	if (!x) throw Win32Error();
	return x;
}

/* Check result of Windows API call, showing a warning on NULL. */
template <typename T>
inline T prefer(const T x)
{
	if (!x) {
		EBMessageBox(Win32Error().what<TCHAR>(),
		    TEXT("System Error"), MB_ICONWARNING);
		return (T)NULL;
	}
	return x;
}

/* Return integer scaled for current DPI. */
inline int Dpi(const int i)
{
	extern int g_iDPI;
	return MulDiv(i, g_iDPI, 96);
}

inline int Cmp(const int a, const int b)
{
	if (a == b) return 0;
	if (a > b) return 1;
	return -1;
}

/* Get window rectangle relative to parent. */
inline BOOL GetRelativeRect(const HWND hWnd, RECT* const pRr)
{
	if (!GetClientRect(hWnd, pRr)) return 0;
	return MapWindowPoints(hWnd, GetParent(hWnd), (POINT*)pRr, 2);
}

inline BOOL SetWindowRect(const HWND hWnd,
    const long left, const long top, const long right, const long bottom)
{
	return MoveWindow(hWnd,
	    left, top,
	    right-left, bottom-top,
	    TRUE);
}

inline BOOL SetWindowRect(const HWND hWnd, const RECT r)
{
	return SetWindowRect(hWnd, r.left, r.top, r.right, r.bottom);
}

#endif