feat(ajax-flow): fetch data by ajax

src/app/@dataflow/core/ajax-flow.spec.ts

@@ -0,0 +1,7 @@
+import { AjaxFlow } from './ajax-flow';
+
+describe('AjaxFlow', () => {
+  // xit('should create an instance', () => {
+  //   expect(new AjaxFlow()).toBeTruthy();
+  // });
+});

src/app/@dataflow/core/ajax-flow.ts

@@ -0,0 +1,22 @@
+import { CacheFlow } from './cache-flow';
+import { DataFlowNode, BareFlowPreNode } from './bare-flow';
+import { Observable, of } from 'rxjs';
+import { ajax, AjaxRequest, AjaxResponse } from 'rxjs/ajax';
+import { catchError, map } from 'rxjs/operators';
+
+export type AjaxFlowNode = [AjaxResponse | object, Error[]];
+
+export abstract class AjaxFlow<Tpre extends BareFlowPreNode> extends CacheFlow<Tpre> {
+	// protected cacheSupport: boolean;
+	// protected cachePath: string;
+
+	protected abstract requestAjax(pre: DataFlowNode): AjaxRequest;
+	protected abstract reconstructAjaxResult(x: AjaxFlowNode): DataFlowNode;
+	protected requestCache(pre: DataFlowNode): Observable<DataFlowNode> {
+		return ajax(this.requestAjax(pre)).pipe(
+			map((x) => [x, []] as AjaxFlowNode),
+			catchError((err): Observable<AjaxFlowNode> => of([{}, [err]])),
+			map((x) => this.reconstructAjaxResult(x))
+		);
+	}
+}