Adding notifications support for windows

Invoking PowerShell is slow (around 5 second delay) but I can't find a better way.
Contributions welcome\!

app/app_windows.go

@@ -5,15 +5,34 @@
 package app
 
 import (
+	"fmt"
+	"io/ioutil"
 	"log"
 	"net/url"
 	"os"
+	"os/exec"
 	"path/filepath"
+	"strings"
+	"syscall"
 
 	"fyne.io/fyne"
 	"fyne.io/fyne/theme"
 )
 
+const notificationTemplate = `$title = "%s"
+$content = "%s"
+
+[Windows.UI.Notifications.ToastNotificationManager, Windows.UI.Notifications, ContentType = WindowsRuntime] > $null
+$template = [Windows.UI.Notifications.ToastNotificationManager]::GetTemplateContent([Windows.UI.Notifications.ToastTemplateType]::ToastText02)
+$toastXml = [xml] $template.GetXml()
+$toastXml.GetElementsByTagName("text")[0].AppendChild($toastXml.CreateTextNode($title)) > $null
+$toastXml.GetElementsByTagName("text")[1].AppendChild($toastXml.CreateTextNode($content)) > $null
+
+$xml = New-Object Windows.Data.Xml.Dom.XmlDocument
+$xml.LoadXml($toastXml.OuterXml)
+$toast = [Windows.UI.Notifications.ToastNotification]::new($xml)
+[Windows.UI.Notifications.ToastNotificationManager]::CreateToastNotifier("appID").Show($toast);`
+
 func defaultTheme() fyne.Theme {
 	return theme.DarkTheme()
 }
@@ -31,6 +50,37 @@ func (app *fyneApp) OpenURL(url *url.URL) error {
 	return cmd.Run()
 }
 
+var scriptNum = 0
+
 func (app *fyneApp) SendNotification(notify *fyne.Notification) {
-	log.Println("NOT YET IMPLEMENTED") // TODO
+	title := escapeNotifyString(notify.Title)
+	content := escapeNotifyString(notify.Content)
+
+	script := fmt.Sprintf(notificationTemplate, title, content)
+	go runScript("notify", script)
+}
+
+func escapeNotifyString(in string) string {
+	noSlash := strings.ReplaceAll(in, "`", "``")
+	return strings.ReplaceAll(noSlash, "\"", "`\"")
+}
+
+func runScript(name, script string) {
+	scriptNum++
+	appID := fyne.CurrentApp().UniqueID()
+	fileName := fmt.Sprintf("fyne-%s-%s-%d.ps1", appID, name, scriptNum)
+	log.Println(fileName)
+
+	tmpFilePath := filepath.Join(os.TempDir(), fileName)
+	err := ioutil.WriteFile(tmpFilePath, []byte(script), 0600)
+	if err != nil {
+		fyne.LogError("Could not write script to show notification", err)
+		return
+	}
+	log.Println("PATH", tmpFilePath)
+	defer os.Remove(tmpFilePath)
+
+	cmd := exec.Command("PowerShell", "-ExecutionPolicy", "Bypass", "-File", tmpFilePath)
+	cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+	err = cmd.Run()
 }

app/app_windows_test.go

@@ -0,0 +1,16 @@
+package app
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestEscapeNotifyString(t *testing.T) {
+	assert.Equal(t, "normal", escapeNotifyString("normal"))
+	assert.Equal(t, "isn't", escapeNotifyString("isn't"))
+	assert.Equal(t, "`\"mine`\"", escapeNotifyString(`"mine"`))
+	assert.Equal(t, "sla\\sh", escapeNotifyString(`sla\sh`))
+	assert.Equal(t, "qu``ote", escapeNotifyString("qu`ote"))
+	assert.Equal(t, "escaped ```\" string", escapeNotifyString("escaped `\" string"))
+}