[BE] Add a queue to Sunat API calls

src/controller/person/SunatQueue.ts

@@ -0,0 +1,56 @@
+
+type ResolveFn = (v: null) => void;
+const waitTime = 500;
+
+const queue: Array<Promise<null>> = [];
+
+function schedule(resolve: ResolveFn) {
+    if (queue.length === 0) {
+        // Call resolve after 500ms
+        const newPromise = new Promise<null>((newResolve) => {
+            setTimeout(() => {
+                // Remove this promise from the queue
+                queue.shift();
+
+                // Resolve the original promise
+                resolve(null);
+
+                // Resolve this promise,
+                // to allow chaining
+                newResolve(null);
+            }, waitTime);
+        });
+
+        queue.push(newPromise);
+    } else {
+        // Create a new promise, and make it wait
+        // for the last promise in the queue
+        const lastPromise = queue[queue.length - 1];
+
+        const newPromise = new Promise<null>((newResolve) => {
+            // Chain to last promise
+            lastPromise.then(() => {
+                setTimeout(() => {
+                    // Remove this promise from the queue
+                    queue.shift();
+
+                    // Resolve the original promise
+                    resolve(null);
+
+                    // Resolve this promise,
+                    // to allow chaining
+                    newResolve(null);
+                }, waitTime);
+            });
+        });
+
+        queue.push(newPromise);
+    }
+}
+
+export function waitForSunatApi(): Promise<null> {
+    return new Promise((resolve) => {
+        schedule(resolve);
+    });
+}
+

src/controller/person/person.service.ts

@@ -4,6 +4,7 @@ import { DataSource, Repository } from "typeorm";
 import { Persona } from "../../model/Persona/persona.entity";
 import { Person } from "../../types/Person";
 import axios from "axios";
+import { waitForSunatApi } from "./SunatQueue";
 
 interface SunatPerson {
     apellidoPaterno: string,
@@ -34,6 +35,15 @@ export class PersonService {
         }
     }
 
+    /**
+     * ALL CALLS TO THIS METHOD ARE INSERTED TO A QUEUE,
+     * EACH REQUEST TO SUNAT WAITS AT LEAST 500ms,
+     * to avoid hitting rate limits.
+     *
+     * @param dni Dni of the person
+     * @returns A person, if found, or throws if not found
+     * @throws A 404 exception if not found
+     */
     async getByDni(dni: string): Promise<Person> {
         // Search person in new tables
         const person = await this.personaRepository.findOneBy({
@@ -57,6 +67,10 @@ export class PersonService {
         // Search person in SUNAT API
         let personSunat: SunatPerson | null = null;
         try {
+            // Enter Sunat API queue
+            await waitForSunatApi();
+
+            // Then perform the actual request
             const personSunatR = await axios.get<SunatPerson>(`https://api.apis.net.pe/v1/dni?numero=${dni}`, {
                 headers: {
                     "Authorization": `Bearer ${token}`,