#ifndef WIN_H
#define WIN_H

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

/* Run given procedure at creation of next window. */
void WithNextWindow(void (*proc)(HWND));
/* Display message box centered in main window. */
int EBMessageBox(std::wstring_view text, std::wstring_view data, UINT uType);
/* Retrieve mouse position relative to given window's client area. */
int GetRelativeCursorPos(HWND hWnd, POINT* pt) noexcept;
/* Cached values from GetSystemMetrics. */
template <int I> auto Metric = GetSystemMetrics(I);

/* Exception for Windows API errors. */
struct Win32Error : public std::exception
{
	Win32Error() noexcept;
	Win32Error(DWORD code) noexcept;
	~Win32Error() noexcept;
	const char* what() const noexcept override;
	const wchar_t* What() const noexcept;
	DWORD code;
private:
	char* m_szMsg = nullptr;
	wchar_t* m_wszMsg = nullptr;
};

/* Wrapper for loading and freeing dynamically linked libraries. */
struct Library
{
	/* Non-throwing named constructor. */
	static std::optional<Library> Maybe(const wchar_t* lib) noexcept;

	Library(const wchar_t* lib);
	~Library() noexcept;

	template <class T> T* GetProcAddress(const char* szProc) noexcept;
private:
	/* Non-throwing constructor used by Maybe. */
	Library(HMODULE hModule) noexcept;
	HMODULE m_hModule;
};

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

/* 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(), L"System Error", MB_ICONWARNING);
		return (T)0;
	}
	return x;
}

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

/* Retrieve given window's rectangle relative to parent's client area. */
inline BOOL GetRelativeRect(const HWND hWnd, RECT* const rr)
{
	if (!GetClientRect(hWnd, rr)) return 0;
	return MapWindowPoints(hWnd, GetParent(hWnd), reinterpret_cast<POINT*>(rr), 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);
}

/* The following functions call uxtheme.dll functions, if uxtheme.dll
 * exists, and otherwise do nothing. */

inline BOOL EBIsThemeActive()
{
	extern BOOL (*IsThemeActive)();
	return IsThemeActive? IsThemeActive(): 0;
}

inline BOOL EBSetWindowTheme(const HWND hWnd, const wchar_t* const pszSubAppName,
    const wchar_t* const pszSubIdList)
{
	extern BOOL (*SetWindowTheme)(HWND, const wchar_t*, const wchar_t*);
	return SetWindowTheme? SetWindowTheme(hWnd, pszSubAppName, pszSubIdList): 0;
}

#endif