[v3 plugins] Support single-instance on Windows

v3/plugins/single_instance/plugin_windows.go

@@ -0,0 +1,35 @@
+//go:build windows
+
+package single_instance
+
+import (
+	"github.com/wailsapp/wails/v3/pkg/w32"
+	"syscall"
+)
+
+type enumWindowsCallback func(hwnd syscall.Handle, lParam uintptr) uintptr
+
+func enumWindowsProc(hwnd syscall.Handle, lParam uintptr) uintptr {
+	_, processID := w32.GetWindowThreadProcessId(uintptr(hwnd))
+	targetProcessID := uint32(lParam)
+	if uint32(processID) == targetProcessID {
+		// Bring the window forward
+		w32.SetForegroundWindow(w32.HWND(hwnd))
+		println("Found window: ", hwnd)
+	}
+
+	// Continue enumeration
+	return 1
+}
+
+func (p *Plugin) activeInstance(pid int) error {
+
+	// Get the window associated with the process ID.
+	targetProcessID := uint32(pid) // Replace with the desired process ID
+
+	w32.EnumWindows(
+		syscall.NewCallback(enumWindowsCallback(enumWindowsProc)),
+		uintptr(targetProcessID),
+	)
+	return nil
+}