WIP plugins: add theme support

server/lib/plugins/theme-utils.ts

@@ -0,0 +1,24 @@
+import { DEFAULT_THEME } from '../../initializers/constants'
+import { PluginManager } from './plugin-manager'
+import { CONFIG } from '../../initializers/config'
+
+function getThemeOrDefault (name: string) {
+  if (isThemeRegistered(name)) return name
+
+  // Fallback to admin default theme
+  if (name !== CONFIG.THEME.DEFAULT) return getThemeOrDefault(CONFIG.THEME.DEFAULT)
+
+  return DEFAULT_THEME
+}
+
+function isThemeRegistered (name: string) {
+  if (name === DEFAULT_THEME) return true
+
+  return !!PluginManager.Instance.getRegisteredThemes()
+                        .find(r => r.name === name)
+}
+
+export {
+  getThemeOrDefault,
+  isThemeRegistered
+}