Add electrsApiService cachedRequest function, switch outspends

frontend/src/app/components/transactions-list/transactions-list.component.ts

@@ -75,7 +75,7 @@ export class TransactionsListComponent implements OnInit, OnChanges {
               for (let i = 0; i < txIds.length; i += 50) {
                 batches.push(txIds.slice(i, i + 50));
               }
-              return forkJoin(batches.map(batch => this.electrsApiService.getOutspendsBatched$(batch)));
+              return forkJoin(batches.map(batch => { return this.electrsApiService.cachedRequest(this.electrsApiService.getOutspendsBatched$, 250, batch); }));
             } else {
               return of([]);
             }

frontend/src/app/components/tx-bowtie-graph/tx-bowtie-graph.component.ts

@@ -124,7 +124,7 @@ export class TxBowtieGraphComponent implements OnInit, OnChanges {
         .pipe(
           switchMap((txid) => {
             if (!this.cached) {
-              return this.electrsApiService.getOutspendsBatched$([txid]);
+              return this.electrsApiService.cachedRequest(this.electrsApiService.getOutspendsBatched$, 250, [txid]);
             } else {
               return of(null);
             }

frontend/src/app/services/electrs-api.service.ts

@@ -1,6 +1,6 @@
 import { Injectable } from '@angular/core';
 import { HttpClient, HttpParams } from '@angular/common/http';
-import { Observable, from, of, switchMap } from 'rxjs';
+import { BehaviorSubject, Observable, catchError, filter, from, of, shareReplay, switchMap, take, tap } from 'rxjs';
 import { Transaction, Address, Outspend, Recent, Asset, ScriptHash } from '../interfaces/electrs.interface';
 import { StateService } from './state.service';
 import { BlockExtended } from '../interfaces/node-api.interface';
@@ -13,6 +13,8 @@ export class ElectrsApiService {
   private apiBaseUrl: string; // base URL is protocol, hostname, and port
   private apiBasePath: string; // network path is /testnet, etc. or '' for mainnet
 
+  private requestCache = new Map<string, { subject: BehaviorSubject<any>, expiry: number }>;
+
   constructor(
     private httpClient: HttpClient,
     private stateService: StateService,
@@ -30,6 +32,46 @@ export class ElectrsApiService {
     });
   }
 
+  private generateCacheKey(functionName: string, params: any[]): string {
+    return functionName + JSON.stringify(params);
+  }
+
+  // delete expired cache entries
+  private cleanExpiredCache(): void {
+    this.requestCache.forEach((value, key) => {
+      if (value.expiry < Date.now()) {
+        this.requestCache.delete(key);
+      }
+    });
+  }
+
+  cachedRequest<T, F extends (...args: any[]) => Observable<T>>(
+    apiFunction: F,
+    expireAfter: number, // in ms
+    ...params: Parameters<F>
+  ): Observable<T> {
+    this.cleanExpiredCache();
+
+    const cacheKey = this.generateCacheKey(apiFunction.name, params);
+    if (!this.requestCache.has(cacheKey)) {
+      const subject = new BehaviorSubject<T | null>(null);
+      this.requestCache.set(cacheKey, { subject, expiry: Date.now() + expireAfter });
+
+      apiFunction.bind(this)(...params).pipe(
+        tap(data => {
+          subject.next(data as T);
+        }),
+        catchError((error) => {
+          subject.error(error);
+          return of(null);
+        }),
+        shareReplay(1),
+      ).subscribe();
+    }
+
+    return this.requestCache.get(cacheKey).subject.asObservable().pipe(filter(val => val !== null), take(1));
+  }
+
   getBlock$(hash: string): Observable<BlockExtended> {
     return this.httpClient.get<BlockExtended>(this.apiBaseUrl + this.apiBasePath + '/api/block/' + hash);
   }