fix: restore existing window on repeated launch

single_instance_activate_windows.go

@@ -16,8 +16,13 @@ const (
 var (
 	user32Activate               = windows.NewLazySystemDLL("user32.dll")
 	procAllowSetForegroundWindow = user32Activate.NewProc("AllowSetForegroundWindow")
+	procAttachThreadInput        = user32Activate.NewProc("AttachThreadInput")
 	procEnumWindows              = user32Activate.NewProc("EnumWindows")
+	procGetForegroundWindow      = user32Activate.NewProc("GetForegroundWindow")
+	procGetWindow                = user32Activate.NewProc("GetWindow")
+	procGetWindowTextLengthW     = user32Activate.NewProc("GetWindowTextLengthW")
 	procGetWindowThreadProcessID = user32Activate.NewProc("GetWindowThreadProcessId")
+	procIsIconic                 = user32Activate.NewProc("IsIconic")
 	procIsWindowVisible          = user32Activate.NewProc("IsWindowVisible")
 	procShowWindow               = user32Activate.NewProc("ShowWindow")
 	procSetForegroundWindow      = user32Activate.NewProc("SetForegroundWindow")
@@ -25,6 +30,7 @@ var (
 )
 
 const (
+	gwOwner       = 4
 	hwndTopmost   = ^uintptr(0)
 	hwndNotopmost = ^uintptr(1)
 	swpNoMove     = 0x0002
@@ -44,8 +50,13 @@ func activateExistingSingleInstanceWindow(pid int) {
 	}
 	grantExistingSingleInstanceForeground(pid)
 	if hwnd := findTopLevelWindowByPID(uint32(pid)); hwnd != 0 {
-		procShowWindow.Call(hwnd, swShow)
 		procShowWindow.Call(hwnd, swRestore)
+		procShowWindow.Call(hwnd, swShow)
+		if ok, _, _ := procSetForegroundWindow.Call(hwnd); ok == 0 {
+			attachForegroundThreadInput(hwnd, func() {
+				procSetForegroundWindow.Call(hwnd)
+			})
+		}
 		if ok, _, _ := procSetForegroundWindow.Call(hwnd); ok == 0 {
 			procSetWindowPos.Call(hwnd, hwndTopmost, 0, 0, 0, 0, swpNoMove|swpNoSize|swpShowWindow)
 			procSetWindowPos.Call(hwnd, hwndNotopmost, 0, 0, 0, 0, swpNoMove|swpNoSize|swpShowWindow)
@@ -54,23 +65,77 @@ func activateExistingSingleInstanceWindow(pid int) {
 	}
 }
 
+func attachForegroundThreadInput(hwnd uintptr, fn func()) {
+	foreground, _, _ := procGetForegroundWindow.Call()
+	if foreground == 0 || hwnd == 0 {
+		fn()
+		return
+	}
+
+	var foregroundPID uint32
+	foregroundThread, _, _ := procGetWindowThreadProcessID.Call(foreground, uintptr(unsafe.Pointer(&foregroundPID)))
+	var targetPID uint32
+	targetThread, _, _ := procGetWindowThreadProcessID.Call(hwnd, uintptr(unsafe.Pointer(&targetPID)))
+	if foregroundThread == 0 || targetThread == 0 || foregroundThread == targetThread {
+		fn()
+		return
+	}
+
+	procAttachThreadInput.Call(foregroundThread, targetThread, 1)
+	defer procAttachThreadInput.Call(foregroundThread, targetThread, 0)
+	fn()
+}
+
 func findTopLevelWindowByPID(pid uint32) uintptr {
-	var matched uintptr
+	type candidateWindow struct {
+		hwnd      uintptr
+		visible   bool
+		titled    bool
+		owned     bool
+		minimized bool
+	}
+	var candidates []candidateWindow
 	callback := windows.NewCallback(func(hwnd uintptr, lparam uintptr) uintptr {
 		var windowPID uint32
 		procGetWindowThreadProcessID.Call(hwnd, uintptr(unsafe.Pointer(&windowPID)))
 		if windowPID == pid {
-			if visible, _, _ := procIsWindowVisible.Call(hwnd); visible == 0 && matched != 0 {
-				return 1
-			}
-			matched = hwnd
-			if visible, _, _ := procIsWindowVisible.Call(hwnd); visible != 0 {
-				return 0
-			}
-			return 1
+			visible, _, _ := procIsWindowVisible.Call(hwnd)
+			titleLength, _, _ := procGetWindowTextLengthW.Call(hwnd)
+			owner, _, _ := procGetWindow.Call(hwnd, gwOwner)
+			minimized, _, _ := procIsIconic.Call(hwnd)
+			candidates = append(candidates, candidateWindow{
+				hwnd:      hwnd,
+				visible:   visible != 0,
+				titled:    titleLength > 0,
+				owned:     owner != 0,
+				minimized: minimized != 0,
+			})
 		}
 		return 1
 	})
 	procEnumWindows.Call(callback, 0)
-	return matched
+	if len(candidates) == 0 {
+		return 0
+	}
+	for _, candidate := range candidates {
+		if candidate.visible && candidate.titled && !candidate.owned {
+			return candidate.hwnd
+		}
+	}
+	for _, candidate := range candidates {
+		if candidate.titled && !candidate.owned {
+			return candidate.hwnd
+		}
+	}
+	for _, candidate := range candidates {
+		if candidate.visible && !candidate.owned {
+			return candidate.hwnd
+		}
+	}
+	for _, candidate := range candidates {
+		if candidate.minimized && !candidate.owned {
+			return candidate.hwnd
+		}
+	}
+	return candidates[0].hwnd
 }