// dll.d
// A simple DLL wrapper
// Author: Wei Li (wstring@gmail.com)


import std.c.windows.windows;
import std.stdio;
import std.traits;
import std.string;

struct Symbol(char[] Sym, Func)
{
    const char[] Name = Sym;
    extern(Windows) alias ReturnType!(Func) 
        function(ParameterTypeTuple!(Func))     FunctionType;

    // extern(Windows) alias FuncType   FunctionType // Why is this Invalid? DMD's bug?
}

private template MixinMembers(S, V...)
{
    mixin("alias S.FunctionType FP_" ~ S.Name ~ ";");
    mixin("S.FunctionType " ~ S.Name ~ ";");
    
    static if(V.length > 0)
        mixin MixinMembers!(V);
}


final class Module(char[] Path, Symbols...)
{
    private HMODULE m_handle = null;

    public mixin MixinMembers!(Symbols);

    public this()
    {
        load();
        initSymbols();
    }

    public ~this()
    {
        free();
    }

    private void initSymbols()
    {
        foreach (i, S; Symbols)
        {
            mixin(S.Name ~ " = getSymbol!(FP_" ~ S.Name ~ ")(S.Name);");
        }
    }


    private void load()
    {
        m_handle = LoadLibraryA(toStringz(Path));
        assert(m_handle);
    }

    private void free()
    {
        FreeLibrary(m_handle);
    }

    public T getSymbol(T)(char[] sym)
    {
        return cast(T)getSymbolAddress(sym);
    }

    public void* getSymbolAddress(char[] sym)
    {
        return GetProcAddress(m_handle, toStringz(sym));
    }
}


void main()
{
    
    scope auto dll = new Module!("User32.dll", 
            Symbol!("MessageBoxW", int function(HWND, LPCWSTR, LPCWSTR, UINT)), 
            Symbol!("MessageBoxA", int function(HWND, LPCSTR, LPCSTR, UINT))
            ); 

    dll.MessageBoxW(null, "Hello! DLL! ", "Hello from MessageBoxW", MB_OK);
    dll.MessageBoxA(null, "Hello! DLL! ", "Hello from MessageBoxA", MB_OK);

}