show What's New dialog when launching updated version

backend/app.go

@@ -46,6 +46,8 @@ type App struct {
 	appName       string
 	appVersionTag string
 	configFile    string
+
+	isFirstLaunch bool // set by config file reader
 	bgrndCtx      context.Context
 	cancel        context.CancelFunc
 }
@@ -119,14 +121,23 @@ func StartupApp(appName, displayAppName, appVersionTag, configFile, latestReleas
 	return a, nil
 }
 
+func (a *App) IsFirstLaunch() bool {
+	return a.isFirstLaunch
+}
+
 func (a *App) readConfig() {
 	configdir.MakePath(configdir.LocalConfig(a.appName))
 	cfgPath := a.configPath()
+	var cfgExists bool
+	if _, err := os.Stat(cfgPath); err == nil {
+		cfgExists = true
+	}
+	a.isFirstLaunch = !cfgExists
 	cfg, err := ReadConfigFile(cfgPath, a.appVersionTag)
 	if err != nil {
 		log.Printf("Error reading app config file: %v", err)
 		cfg = DefaultConfig(a.appVersionTag)
-		if _, err := os.Stat(cfgPath); err == nil {
+		if cfgExists {
 			backupCfgName := fmt.Sprintf("%s.bak", a.configFile)
 			log.Printf("Config file may be malformed: copying to %s", backupCfgName)
 			_ = util.CopyFile(cfgPath, path.Join(configdir.LocalConfig(a.appName), backupCfgName))

backend/config.go

@@ -25,6 +25,7 @@ type AppConfig struct {
 	WindowWidth         int
 	WindowHeight        int
 	LastCheckedVersion  string
+	LastLaunchedVersion string
 	EnableSystemTray    bool
 	CloseToSystemTray   bool
 	StartupPage         string
@@ -128,6 +129,7 @@ func DefaultConfig(appVersionTag string) *Config {
 			WindowWidth:         1000,
 			WindowHeight:        800,
 			LastCheckedVersion:  appVersionTag,
+			LastLaunchedVersion: "",
 			EnableSystemTray:    true,
 			CloseToSystemTray:   false,
 			StartupPage:         "Albums",