package borderless_win

import "core:os"
import win32 "core:sys/windows"

// foreign import win32ex "system:User32.lib" 
// @(default_calling_convention="stdcall")
// foreign win32ex {
//     IsZoomed :: proc (hwnd: win32.HWND) -> win32.BOOL ---
// }
// IsMaximized :: IsZoomed

WM_NCUAHDRAWCAPTION :: (0x00AE)
WM_NCUAHDRAWFRAME :: (0x00AF)

UserData := struct {
	dwm_enabled: win32.BOOL,
	width:       i32,
	height:      i32,
} {
	dwm_enabled = false,
	width       = 0,
	height      = 0,
}

handle_nchittest :: proc "stdcall" (hwnd: win32.HWND, lparam: win32.LPARAM) -> win32.LRESULT {
	// if IsMaximized(hwnd) do	return win32.HTCLIENT
	mouse := win32.POINT{win32.GET_X_LPARAM(lparam), win32.GET_Y_LPARAM(lparam)}
	win32.ScreenToClient(hwnd, &mouse)
	frame_size :=
		win32.GetSystemMetrics(win32.SM_CXFRAME) + win32.GetSystemMetrics(win32.SM_CXPADDEDBORDER)
	diagonal_width := frame_size * 2 + win32.GetSystemMetrics(win32.SM_CXBORDER)

	if mouse.y < frame_size {
		if mouse.x < diagonal_width do return win32.HTTOPLEFT
		if mouse.x >= UserData.width - diagonal_width do return win32.HTTOPRIGHT
		return win32.HTTOP
	}

	if mouse.y >= UserData.height - frame_size {
		if mouse.x < diagonal_width do return win32.HTBOTTOMLEFT
		if mouse.x >= UserData.width - diagonal_width do return win32.HTBOTTOMRIGHT
		return win32.HTBOTTOM
	}

	if mouse.x < frame_size do return win32.HTLEFT
	if mouse.x >= UserData.width - frame_size do return win32.HTRIGHT
	return win32.HTCLIENT
}

handle_windowposchanged :: proc "stdcall" (
	hwnd: win32.HWND,
	pos: ^win32.WINDOWPOS,
) -> win32.LRESULT {
	client: win32.RECT
	win32.GetClientRect(hwnd, &client)
	last_width, last_height := UserData.width, UserData.height
	UserData.width, UserData.height = client.right, client.bottom
	client_changed := UserData.width != last_width || UserData.height != last_height

	if client_changed {
		if UserData.width > last_width do win32.InvalidateRect(hwnd, &(win32.RECT){last_width - 1, 0, last_width, last_height}, true)
		else do win32.InvalidateRect(hwnd,&(win32.RECT){UserData.width - 1, 0, UserData.width, UserData.height}, true)
		if UserData.height > last_height do win32.InvalidateRect(hwnd, &(win32.RECT){0, last_height - 1, last_width, last_height}, true)
		else do win32.InvalidateRect(hwnd, &(win32.RECT){0, UserData.height - 1, UserData.width, UserData.height}, true)
	}
	return 0
}

handle_dwmcompositionchanged :: proc "stdcall" (hwnd: win32.HWND) {
	enabled: win32.BOOL = false
	win32.DwmIsCompositionEnabled(&enabled)
	UserData.dwm_enabled = enabled
	if enabled {
		win32.DwmSetWindowAttribute(
			hwnd,
			u32(win32.DWMWINDOWATTRIBUTE.DWMWA_NCRENDERING_POLICY),
			rawptr(uintptr(win32.DWORD(win32.DWMNCRENDERINGPOLICY.DWMNCRP_ENABLED))),
			size_of(win32.DWORD),
		)
	}
}

handle_win32_events :: proc "stdcall" (
	hwnd: win32.HWND,
	msg: win32.UINT,
	wparam: win32.WPARAM,
	lparam: win32.LPARAM,
) -> win32.LRESULT {
	switch msg {
	case win32.WM_CLOSE:
		win32.DestroyWindow(hwnd)
		return 0
	case win32.WM_DESTROY:
		win32.PostQuitMessage(0)
		return 0
	case win32.WM_PAINT:
		ps: win32.PAINTSTRUCT
		hdc := win32.BeginPaint(hwnd, &ps)
		win32.FillRect(hdc, &ps.rcPaint, win32.HBRUSH(win32.COLOR_BACKGROUND + uintptr(1)))
		win32.EndPaint(hwnd, &ps)
		return 0
	case win32.WM_NCACTIVATE:
		return win32.DefWindowProcW(hwnd, msg, wparam, -1)
	case win32.WM_NCHITTEST:
		return handle_nchittest(hwnd, lparam)
	case win32.WM_WINDOWPOSCHANGED:
		return handle_windowposchanged(hwnd, transmute(^win32.WINDOWPOS)(lparam))
	case win32.WM_NCCALCSIZE:
		return 0
	case win32.WM_NCPAINT:
    	if !UserData.dwm_enabled do return 0
	case win32.WM_LBUTTONDOWN:
		win32.ReleaseCapture()
		win32.SendMessageW(hwnd, win32.WM_NCLBUTTONDOWN, win32.HTCAPTION, 0)
	case win32.WM_DWMCOMPOSITIONCHANGED:
		handle_dwmcompositionchanged(hwnd)
		return 0
	case WM_NCUAHDRAWCAPTION:
		return 0
	case WM_NCUAHDRAWFRAME:
		return 0
	}
	return win32.DefWindowProcW(hwnd, msg, wparam, lparam)
}

main :: proc() {
	hinstance := win32.HINSTANCE(win32.GetModuleHandleW(nil))

	cid := win32.RegisterClassExW(
		&(win32.WNDCLASSEXW) {
			cbSize = size_of(win32.WNDCLASSEXW),
			hInstance = hinstance,
			hbrBackground = win32.HBRUSH(win32.COLOR_WINDOW + uintptr(1)),
			lpszClassName = win32.utf8_to_wstring("OdinBorderlessWindow"),
			hCursor = win32.LoadCursorA(nil, win32.IDC_ARROW),
			lpfnWndProc = handle_win32_events,
		},
	)

	hwnd := win32.CreateWindowExW(
		0,
		win32.LPCWSTR(uintptr(cid)),
		win32.utf8_to_wstring("Borderless Window"),
		win32.WS_OVERLAPPEDWINDOW | win32.WS_SIZEBOX,
		win32.CW_USEDEFAULT,
		win32.CW_USEDEFAULT,
		win32.CW_USEDEFAULT,
		win32.CW_USEDEFAULT,
		nil,
		nil,
		hinstance,
		nil,
	)
	handle_dwmcompositionchanged(hwnd)
	win32.ShowWindow(hwnd, win32.SW_SHOWNORMAL)
	win32.UpdateWindow(hwnd)

	message: win32.MSG
	for win32.GetMessageW(&message, nil, 0, 0) != 0 {
		win32.TranslateMessage(&message)
		win32.DispatchMessageW(&message)
	}

	win32.UnregisterClassW(win32.LPCWSTR(uintptr(cid)), hinstance)
	os.exit(int(message.wParam))
}