// 24 march 2014

package ui

import (
	"fmt"
	"syscall"
	"unsafe"
	"sync"
	"image"
)

const (
	areastyle = _WS_HSCROLL | _WS_VSCROLL | controlstyle
	areaxstyle = 0 | controlxstyle
)

const (
	areaWndClassFormat = "gouiarea%X"
)

var (
	areaWndClassNum uintptr
	areaWndClassNumLock sync.Mutex
)

var (
	_getUpdateRect = user32.NewProc("GetUpdateRect")
	_beginPaint = user32.NewProc("BeginPaint")
	_endPaint = user32.NewProc("EndPaint")
	_gdipCreateBitmapFromScan0 = gdiplus.NewProc("GdipCreateBitmapFromScan0")
	_gdipCreateFromHDC = gdiplus.NewProc("GdipCreateFromHDC")
	_gdipDrawImageI = gdiplus.NewProc("GdipDrawImageI")
	_gdipDeleteGraphics = gdiplus.NewProc("GdipDeleteGraphics")
	_gdipDisposeImage = gdiplus.NewProc("GdipDisposeImage")
)

const (
	// from winuser.h
	_WM_PAINT = 0x000F
)

func paintArea(s *sysData) {
	const (
		// from gdipluspixelformats.h
		_PixelFormatGDI = 0x00020000
		_PixelFormatAlpha = 0x00040000
		_PixelFormatCanonical = 0x00200000
		_PixelFormat32bppARGB = (10 | (32 << 8) | _PixelFormatAlpha | _PixelFormatGDI | _PixelFormatCanonical)
	)

	var xrect _RECT
	var ps _PAINTSTRUCT

	// TODO send _TRUE if we want to erase the clip area
	r1, _, _ := _getUpdateRect.Call(
		uintptr(s.hwnd),
		uintptr(unsafe.Pointer(&xrect)),
		uintptr(_FALSE))
	if r1 == 0 {			// no update rect; do nothing
		return
	}

	cliprect := image.Rect(int(xrect.Left), int(xrect.Top), int(xrect.Right), int(xrect.Bottom))
	// TODO offset cliprect by scroll position
	// make sure the cliprect doesn't fall outside the size of the Area
	cliprect = cliprect.Intersect(image.Rect(0, 0, 320, 240))	// TODO change when adding resizing
	if cliprect.Empty() {		// still no update rect
		return
	}

	r1, _, err := _beginPaint.Call(
		uintptr(s.hwnd),
		uintptr(unsafe.Pointer(&ps)))
	if r1 == 0 {		// failure
		panic(fmt.Errorf("error beginning Area repaint: %v", err))
	}
	hdc := _HANDLE(r1)

	i := s.handler.Paint(cliprect)
	// the pixels are arranged in RGBA order, but GDI+ requires BGRA
	// we don't have a choice but to convert it ourselves
	// TODO make realbits a part of sysData to conserve memory
	realbits := make([]byte, 4 * i.Rect.Dx() * i.Rect.Dy())
	p := 0
	q := 0
	for y := i.Rect.Min.Y; y < i.Rect.Max.Y; y++ {
		nextp := p + i.Stride
		for x := i.Rect.Min.X; x < i.Rect.Max.X; x++ {
			realbits[q + 0] = byte(i.Pix[p + 2])		// B
			realbits[q + 1] = byte(i.Pix[p + 1])		// G
			realbits[q + 2] = byte(i.Pix[p + 0])		// R
			realbits[q + 3] = byte(i.Pix[p + 3])		// A
			p += 4
			q += 4
		}
		p = nextp
	}

	var bitmap, graphics uintptr

	r1, _, err = _gdipCreateBitmapFromScan0.Call(
		uintptr(i.Rect.Dx()),
		uintptr(i.Rect.Dy()),
		uintptr(i.Rect.Dx() * 4),			// got rid of extra stride
		uintptr(_PixelFormat32bppARGB),
		uintptr(unsafe.Pointer(&realbits[0])),
		uintptr(unsafe.Pointer(&bitmap)))
	if r1 != 0 {			// failure
		panic(fmt.Errorf("error creating GDI+ bitmap to blit (GDI+ error code %d; Windows last error %v)", r1, err))
	}
	r1, _, err = _gdipCreateFromHDC.Call(
		uintptr(hdc),
		uintptr(unsafe.Pointer(&graphics)))
	if r1 != 0 {			// failure
		panic(fmt.Errorf("error creating GDI+ graphics context to blit to (GDI+ error code %d; Windows last error %v)", r1, err))
	}
	r1, _, err = _gdipDrawImageI.Call(
		graphics,
		bitmap,
		uintptr(xrect.Left),			// cliprect is adjusted; use original
		uintptr(xrect.Top))
	if r1 != 0 {			// failure
		panic(fmt.Errorf("error blitting GDI+ bitmap (GDI+ error code %d; Windows last error %v)", r1, err))
	}
	r1, _, err = _gdipDeleteGraphics.Call(graphics)
	if r1 != 0 {			// failure
		panic(fmt.Errorf("error freeing GDI+ graphics context to blit to (GDI+ error code %d; Windows last error %v)", r1, err))
	}
	// TODO this is the destructor of Image (Bitmap's base class); I don't see a specific destructor for Bitmap itself so
	r1, _, err = _gdipDisposeImage.Call(bitmap)
	if r1 != 0 {			// failure
		panic(fmt.Errorf("error freeing GDI+ bitmap to blit (GDI+ error code %d; Windows last error %v)", r1, err))
	}

	// return value always nonzero according to MSDN
	_endPaint.Call(
		uintptr(s.hwnd),
		uintptr(unsafe.Pointer(&ps)))
}

var (
	_getWindowRect = user32.NewProc("GetWindowRect")
)

func getAreaControlSize(hwnd _HWND) (width int, height int) {
	var rect _RECT

	r1, _, err := _getWindowRect.Call(
		uintptr(hwnd),
		uintptr(unsafe.Pointer(&rect)))
	if r1 == 0 {		// failure
		panic(fmt.Errorf("error getting size of actual Area control: %v", err))
	}
	return int(rect.Right - rect.Left),
		int(rect.Bottom - rect.Top)
}

func adjustAreaScrollbars(hwnd _HWND) {
	var si _SCROLLINFO

	cwid, cht := getAreaControlSize(hwnd)

	// the trick is we want a page to be the width/height of the visible area
	// so the scroll range would go from [0..image_dimension - control_dimension]
	// but judging from the sample code on MSDN, we don't need to do this; the scrollbar will do it for us

	// have to do horizontal and vertical separately
	si.cbSize = uint32(unsafe.Sizeof(si))
	si.fMask = _SIF_RANGE | _SIF_PAGE
	si.nMin = 0
	si.nMax = int32(320)
	si.nPage = uint32(cwid)
	_setScrollInfo.Call(
		uintptr(hwnd),
		uintptr(_SB_HORZ),
		uintptr(unsafe.Pointer(&si)),
		uintptr(_TRUE))			// redraw the scroll bar

	si.cbSize = uint32(unsafe.Sizeof(si))			// MSDN sample code does this a second time; let's do it too to be safe
	si.fMask = _SIF_RANGE | _SIF_PAGE
	si.nMin = 0
	si.nMax = int32(240)
	si.nPage = uint32(cht)
	_setScrollInfo.Call(
		uintptr(hwnd),
		uintptr(_SB_VERT),
		uintptr(unsafe.Pointer(&si)),
		uintptr(_TRUE))			// redraw the scroll bar
}

func areaWndProc(s *sysData) func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
	return func(hwnd _HWND, uMsg uint32, wParam _WPARAM, lParam _LPARAM) _LRESULT {
		switch uMsg {
		case _WM_PAINT:
			paintArea(s)
			return _LRESULT(0)
		case _WM_HSCROLL:
			fallthrough	// TODO
		case _WM_VSCROLL:
			fallthrough	// TODO
		case _WM_SIZE:
			adjustAreaScrollbars(hwnd)		// don't use s.hwnd; this message can be sent before that's loaded
			return 0
		default:
			r1, _, _ := defWindowProc.Call(
				uintptr(hwnd),
				uintptr(uMsg),
				uintptr(wParam),
				uintptr(lParam))
			return _LRESULT(r1)
		}
		panic(fmt.Sprintf("areaWndProc message %d did not return: internal bug in ui library", uMsg))
	}
}

func registerAreaWndClass(s *sysData) (newClassName string, err error) {
	const (
		// from winuser.h
		_CS_DBLCLKS = 0x0008
	)

	areaWndClassNumLock.Lock()
	newClassName = fmt.Sprintf(areaWndClassFormat, areaWndClassNum)
	areaWndClassNum++
	areaWndClassNumLock.Unlock()

	wc := &_WNDCLASS{
		style:			_CS_DBLCLKS,		// needed to be able to register double-clicks
		lpszClassName:	uintptr(unsafe.Pointer(syscall.StringToUTF16Ptr(newClassName))),
		lpfnWndProc:		syscall.NewCallback(areaWndProc(s)),
		hInstance:		hInstance,
		hIcon:			icon,
		hCursor:			cursor,
		hbrBackground:	_HBRUSH(_COLOR_BTNFACE + 1),
	}

	ret := make(chan uiret)
	defer close(ret)
	uitask <- &uimsg{
		call:		_registerClass,
		p:		[]uintptr{uintptr(unsafe.Pointer(wc))},
		ret:		ret,
	}
	r := <-ret
	if r.ret == 0 {		// failure
		return "", r.err
	}
	return newClassName, nil
}

type _PAINTSTRUCT struct {
	hdc			_HANDLE
	fErase		int32		// originally BOOL
	rcPaint		_RECT
	fRestore		int32		// originally BOOL
	fIncUpdate	int32		// originally BOOL
	rgbReserved	[32]byte
}