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

struct Symbol(char[] SymName, Ret, Params...)
{
    alias Params        Parameters;
    alias Ret           ReturnValue;
    const char[] Name = SymName;
    extern(Windows) alias ReturnValue function(Params) FunctionType;
}

// FP_Function
private template MixinMember(S) //S = Symbol template
{
    mixin("public alias S.FunctionType FP_" ~ S.Name ~ ";");
    mixin("public S.FunctionType " ~ S.Name ~ ";");
}


private template MixinAllMembers(S, V...)
{
    mixin MixinMember!(S);
    static if(V.length > 0)
    {
        mixin MixinAllMembers!(V);
    }
}


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

    public mixin MixinAllMembers!(Symbols);

    public this()
    {
        load(Path);
        initMembers();
    }

    public ~this()
    {
        free();
    }

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

    void load(char[] path)
    {
        
//       m_handle = LoadLibraryW(toUtf16z(path));
        m_handle = LoadLibraryA(toStringz(path));
        assert(m_handle);
    }

    void free()
    {
        if(m_handle != null)
        {
            FreeLibrary(m_handle);
            m_handle = null;
        }
    }

    public T getSymbol(T)(char[] sym)
    {
        return cast(T)getSymbol1(sym);
    }

    public void* getSymbol1(char[] sym)
    {
        return GetProcAddress(m_handle, toStringz(sym));
    }

}


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

    dll.MessageBoxW(null, "Hello! DLL! W", "Title W", MB_OK);
    dll.MessageBoxA(null, "Hello! DLL! A", "Title A", MB_OK);

}