refactor: change meta class structure to include types.

Introduce requiredness of translations via implemented interface.

src/core/Thing.ts

@@ -14,7 +14,7 @@
  */
 import {SCOrganization} from './things/Organization';
 import {SCPerson} from './things/Person';
-import {SCTranslations} from './types/i18n';
+import {SCMetaTranslations, SCTranslations} from './types/i18n';
 import {SCISO8601Date} from './types/Time';
 import {SCUuid} from './types/UUID';
 
@@ -187,41 +187,6 @@ export interface SCThingUserOrigin extends SCThingOrigin {
   updated?: SCISO8601Date;
 }
 
-/**
- * Meta information about things
- */
-export class SCThingMeta {
-  /**
-   * Translations of fields
-   */
-  static fieldTranslations: any = {
-    de: {
-      alternateNames: 'alternative Namen',
-      description: 'Beschreibung',
-      image: 'Bild',
-      name: 'Name',
-      translations: 'Übersetzungen',
-      type: 'Typ',
-      uid: 'Identifikation',
-      url: 'URL',
-    },
-    en: {
-      alternateNames: 'alternate names',
-      description: 'description',
-      uid: 'identification',
-    },
-  };
-
-  /**
-   * Translations of values of fields
-   */
-  static fieldValueTranslations: any = {
-    de: {
-      type: 'Ding',
-    },
-  };
-}
-
 /**
  * Translatable properties of things
  */
@@ -249,3 +214,63 @@ export interface SCThingTranslatablePropertyOrigin {
    */
   name: string;
 }
+
+/**
+ * Meta information about things
+ */
+export class SCThingMeta implements SCMetaTranslations<SCThing> {
+  /**
+   * Set type definiton for singleton instance
+   */
+  protected static _instance: SCThingMeta;
+
+  /**
+   * Translations of fields
+   */
+  fieldTranslations = {
+    de: {
+      alternateNames: 'alternative Namen',
+      description: 'Beschreibung',
+      image: 'Bild',
+      name: 'Name',
+      origin: 'Ursprung',
+      translations: 'Übersetzungen',
+      type: 'Typ',
+      uid: 'Identifikation',
+      url: 'URL',
+    },
+    en: {
+      alternateNames: 'alternate names',
+      description: 'description',
+      image: 'image',
+      name: 'name',
+      origin: 'origin',
+      translations: 'translations',
+      type: 'type',
+      uid: 'identification',
+      url: 'URL',
+    },
+  };
+
+  /**
+   * Translations of values of fields
+   */
+  fieldValueTranslations  = {
+    de: {
+      type: 'Ding',
+    },
+    en: {
+      type: 'Thing',
+    },
+  };
+
+  /**
+   * Function to retrieve typed singleton instance
+   */
+  public static getInstance<T extends SCThingMeta>(): T {
+    const typedThis = this as any as typeof SCThingMeta;
+    return (typedThis._instance || (typedThis._instance = new this())) as T;
+  }
+
+  protected constructor() {}
+}