Refactoring: Move data loading code under the datasource directory

src/datasource/data_source.ts

@@ -0,0 +1,30 @@
+import {IndiInfo} from 'topola';
+import {TopolaData} from '../util/gedcom_util';
+
+/** Supported data sources. */
+export enum DataSourceEnum {
+  UPLOADED,
+  GEDCOM_URL,
+  WIKITREE,
+}
+
+/** Source specification together with individual selection. */
+export interface SourceSelection<SourceSpecT> {
+  spec: SourceSpecT;
+  selection?: IndiInfo;
+}
+
+/** Interface encapsulating functions specific for a data source. */
+export interface DataSource<SourceSpecT> {
+  /**
+   * Returns true if the application is now loading a completely new data set
+   * and the existing one should be wiped.
+   */
+  isNewData(
+    newSource: SourceSelection<SourceSpecT>,
+    oldSource: SourceSelection<SourceSpecT>,
+    data?: TopolaData,
+  ): boolean;
+  /** Loads data from the data source. */
+  loadData(spec: SourceSelection<SourceSpecT>): Promise<TopolaData>;
+}