#include <Windows.h>
#include <oleidl.h>
#include <stdio.h>

#include "vector.h"
#include "_cgo_export.h"

#define STDULONGMETHODIMP STDMETHODIMP_(ULONG)
#define DRAGDROP_MAXFILEPATHSIZE 32767

typedef struct
{
    IDropTargetVtbl *_vtbl;
    long _refCount;

    uint32_t _handle;
    HWND _windowHandle;
} DragDropHandler;

static void screenToClient(HWND windowHandle, POINTL *point)
{
    ScreenToClient(windowHandle, (LPPOINT)point);
}

static STDMETHODIMP QueryInterface(IDropTarget *this, REFIID riid, LPVOID *ppvObj)
{
    // Always set out parameter to NULL, validating it first.
    if (!ppvObj)
        return E_INVALIDARG;
    *ppvObj = NULL;
    if (IsEqualIID(riid, &IID_IUnknown) || IsEqualIID(riid, &IID_IDropTarget))
    {
        // Increment the reference count and return the pointer.
        *ppvObj = (LPVOID)this;
        ((DragDropHandler *)this)->_vtbl->AddRef(this);
        return NOERROR;
    }
    return E_NOINTERFACE;
}

static STDULONGMETHODIMP AddRef(IDropTarget *this)
{
    InterlockedIncrement(&((DragDropHandler *)this)->_refCount);
    return ((DragDropHandler *)this)->_refCount;
}

static STDULONGMETHODIMP Release(IDropTarget *this)
{
    // Decrement the object's internal counter.
    ULONG ulRefCount = InterlockedDecrement(&((DragDropHandler *)this)->_refCount);
    if (0 == ((DragDropHandler *)this)->_refCount)
    {
        GlobalFree(this);
    }
    return ulRefCount;
}

static STDMETHODIMP DragEnter(IDropTarget *this, __RPC__in_opt IDataObject *pDataObj, DWORD grfKeyState, POINTL pt, __RPC__inout DWORD *pdwEffect)
{
    *pdwEffect = DROPEFFECT_COPY;

    wchar_t filePath[DRAGDROP_MAXFILEPATHSIZE];

    FORMATETC format;
    format.cfFormat = CF_HDROP;
    format.ptd = NULL;
    format.dwAspect = DVASPECT_CONTENT;
    format.lindex = -1;
    format.tymed = TYMED_HGLOBAL;

    STGMEDIUM medium;

    HRESULT result = pDataObj->lpVtbl->GetData(pDataObj, &format, &medium);
    if (result != S_OK)
        return E_UNEXPECTED;
    HDROP drop = (HDROP)GlobalLock(medium.hGlobal);

    clearFiles(((DragDropHandler *)this)->_handle);
    UINT numberOfFiles = DragQueryFile(drop, 0xFFFFFFFF, NULL, 0);
    for (UINT fileIndex = 0; fileIndex < numberOfFiles; fileIndex++)
    {
        UINT length = DragQueryFileW(drop, fileIndex, filePath, DRAGDROP_MAXFILEPATHSIZE);
        addFile(((DragDropHandler *)this)->_handle, &filePath[0], length);
    }

    GlobalUnlock(medium.hGlobal);
    if (medium.pUnkForRelease != NULL)
        medium.pUnkForRelease->lpVtbl->Release(medium.pUnkForRelease);

    screenToClient(((DragDropHandler *)this)->_windowHandle, &pt);
    onDragEnter(((DragDropHandler *)this)->_handle, pt.x, pt.y);

    return S_OK;
}

static STDMETHODIMP DragOver(IDropTarget *this, DWORD grfKeyState, POINTL pt, __RPC__inout DWORD *pdwEffect)
{
    *pdwEffect = DROPEFFECT_COPY;
    screenToClient(((DragDropHandler *)this)->_windowHandle, &pt);
    onDragOver(((DragDropHandler *)this)->_handle, pt.x, pt.y);
    return S_OK;
}

static STDMETHODIMP DragLeave(IDropTarget *this)
{
    onDragLeave(((DragDropHandler *)this)->_handle);
    return S_OK;
}

static STDMETHODIMP Drop(IDropTarget *this, __RPC__in_opt IDataObject *pDataObj, DWORD grfKeyState, POINTL pt, __RPC__inout DWORD *pdwEffect)
{
    *pdwEffect = DROPEFFECT_COPY;
    screenToClient(((DragDropHandler *)this)->_windowHandle, &pt);
    onDrop(((DragDropHandler *)this)->_handle, pt.x, pt.y);
    return S_OK;
}

static const IDropTargetVtbl DragDropHandlerVtbl = {
    QueryInterface,
    AddRef,
    Release,
    DragEnter,
    DragOver,
    DragLeave,
    Drop,
};

static DragDropHandler *newDragDropHandler(HWND windowHandle, uint32_t handle)
{
    DragDropHandler *handler = malloc(sizeof(DragDropHandler));
    handler->_vtbl = (IDropTargetVtbl *)&DragDropHandlerVtbl;
    handler->_refCount = 0;
    handler->_windowHandle = windowHandle;
    handler->_handle = handle;
    return handler;
}

BOOL dragDropInitialized = FALSE;
typedef vector(DragDropHandler *) DragDropHandlers;
DragDropHandlers handlers;

static void VerifyResult(CHAR *component, HRESULT result)
{
    if (result == S_OK)
        return;
    printf("%s failed (error code: %d)\n", component, result);
}

static void initDragDrop(void)
{
    if (dragDropInitialized == TRUE)
        return;

    HRESULT result = OleInitialize(NULL);
    VerifyResult("OleInitialize", result);

    vector_init(handlers);

    dragDropInitialized = TRUE;
}

uint32_t RegisterHandler(void *window)
{
    initDragDrop();

    size_t handle = handlers.count + 1;
    HWND windowHandle = (HWND)window;
    DragDropHandler *handler = newDragDropHandler(windowHandle, handle);
    vector_append(DragDropHandler *, handlers, handler);

    DragAcceptFiles(windowHandle, TRUE);
    HRESULT result = RegisterDragDrop(windowHandle, (IDropTarget *)handler);
    VerifyResult("RegisterDragDrop", result);

    return (uint32_t)handle;
}