feat: support service completion

Closes coop-cloud/organising#165.

pkg/config/app.go

@@ -190,6 +190,38 @@ func GetApps(appFiles AppFiles) ([]App, error) {
 	return apps, nil
 }
 
+// GetAppServiceNames retrieves a list of app service names.
+func GetAppServiceNames(appName string) ([]string, error) {
+	var serviceNames []string
+
+	appFiles, err := LoadAppFiles("")
+	if err != nil {
+		return serviceNames, err
+	}
+
+	app, err := GetApp(appFiles, appName)
+	if err != nil {
+		return serviceNames, err
+	}
+
+	composeFiles, err := GetAppComposeFiles(app.Type, app.Env)
+	if err != nil {
+		return serviceNames, err
+	}
+
+	opts := stack.Deploy{Composefiles: composeFiles}
+	compose, err := GetAppComposeConfig(app.Type, opts, app.Env)
+	if err != nil {
+		return serviceNames, err
+	}
+
+	for _, service := range compose.Services {
+		serviceNames = append(serviceNames, service.Name)
+	}
+
+	return serviceNames, nil
+}
+
 // GetAppNames retrieves a list of app names.
 func GetAppNames() ([]string, error) {
 	var appNames []string