[accelerator] on-demand polling support

backend/src/api/services/acceleration.ts

@@ -1,8 +1,10 @@
 import config from '../../config';
 import logger from '../../logger';
-import { BlockExtended, PoolTag } from '../../mempool.interfaces';
+import { BlockExtended } from '../../mempool.interfaces';
 import axios from 'axios';
 
+type MyAccelerationStatus = 'requested' | 'accelerating' | 'done';
+
 export interface Acceleration {
   txid: string,
   added: number,
@@ -35,18 +37,88 @@ export interface AccelerationHistory {
 };
 
 class AccelerationApi {
-  public async $fetchAccelerations(): Promise<Acceleration[] | null> {
+  private apiPath = config.MEMPOOL.OFFICIAL ? (config.MEMPOOL_SERVICES.API + '/accelerator/accelerations') : (config.EXTERNAL_DATA_SERVER.MEMPOOL_API + '/accelerations');
+  private _accelerations: Acceleration[] | null = null;
+  private lastPoll = 0;
+  private forcePoll = false;
+  private myAccelerations: Record<string, { status: MyAccelerationStatus, added: number, acceleration?: Acceleration }> = {};
+
+  public get accelerations(): Acceleration[] | null {
+    return this._accelerations;
+  }
+
+  public countMyAccelerationsWithStatus(filter: MyAccelerationStatus): number {
+    return Object.values(this.myAccelerations).reduce((count, {status}) => { return count + (status === filter ? 1 : 0); }, 0);
+  }
+
+  public accelerationRequested(txid: string): void {
+    this.myAccelerations[txid] = { status: 'requested', added: Date.now() };
+  }
+
+  public accelerationConfirmed(): void {
+    this.forcePoll = true;
+  }
+
+  private async $fetchAccelerations(): Promise<Acceleration[] | null> {
+    try {
+      const response = await axios.get(this.apiPath, { responseType: 'json', timeout: 10000 });
+      return response?.data || [];
+    } catch (e) {
+      logger.warn('Failed to fetch current accelerations from the mempool services backend: ' + (e instanceof Error ? e.message : e));
+      return null;
+    }
+  }
+
+  public async $updateAccelerations(): Promise<Acceleration[] | null> {
     if (config.MEMPOOL_SERVICES.ACCELERATIONS) {
-      try {
-        const response = await axios.get(`${config.MEMPOOL_SERVICES.API}/accelerator/accelerations`, { responseType: 'json', timeout: 10000 });
-        return response.data as Acceleration[];
-      } catch (e) {
-        logger.warn('Failed to fetch current accelerations from the mempool services backend: ' + (e instanceof Error ? e.message : e));
-        return null;
+      const accelerations = await this.$fetchAccelerations();
+      if (accelerations) {
+        this._accelerations = accelerations;
+        return this._accelerations;
       }
     } else {
-      return [];
+      return this.$updateAccelerationsOnDemand();
     }
+    return null;
+  }
+
+  private async $updateAccelerationsOnDemand(): Promise<Acceleration[] | null> {
+    const shouldUpdate = this.forcePoll
+      || this.countMyAccelerationsWithStatus('requested') > 0
+      || (this.countMyAccelerationsWithStatus('accelerating') > 0 && this.lastPoll < (Date.now() - (10 * 60 * 1000)));
+
+    // update accelerations if necessary
+    if (shouldUpdate) {
+      const accelerations = await this.$fetchAccelerations();
+      this.lastPoll = Date.now();
+      this.forcePoll = false;
+      if (accelerations) {
+        const latestAccelerations: Record<string, Acceleration> = {};
+        // set relevant accelerations to 'accelerating'
+        for (const acc of accelerations) {
+          if (this.myAccelerations[acc.txid]) {
+            latestAccelerations[acc.txid] = acc;
+            this.myAccelerations[acc.txid] = { status: 'accelerating', added: Date.now(), acceleration: acc };
+          }
+        }
+        // txs that are no longer accelerating are either confirmed or canceled, so mark for expiry
+        for (const [txid, { status, acceleration }] of Object.entries(this.myAccelerations)) {
+          if (status === 'accelerating' && !latestAccelerations[txid]) {
+            this.myAccelerations[txid] = { status: 'done', added: Date.now(), acceleration };
+          }
+        }
+      }
+    }
+
+    // clear expired accelerations (confirmed / failed / not accepted) after 10 minutes
+    for (const [txid, { status, added }] of Object.entries(this.myAccelerations)) {
+      if (['requested', 'done'].includes(status) && added < (Date.now() - (1000 * 60 * 10))) {
+        delete this.myAccelerations[txid];
+      }
+    }
+
+    this._accelerations = Object.values(this.myAccelerations).map(({ acceleration }) => acceleration).filter(acc => acc) as Acceleration[];
+    return this._accelerations;
   }
 
   public async $fetchAccelerationHistory(page?: number, status?: string): Promise<AccelerationHistory[] | null> {