feat(api): proper caching/in-flight handling of urls

src/lib/api/database.ts

@@ -8,11 +8,20 @@ import { HttpResponse } from '@capacitor-community/http';
 import { Team } from '../model/team';
 import { Player } from '../model/player';
 
+const DEFAULT_CACHE_KEEP = 10 * 60 * 1000; // 10 minutes
+
+interface CacheEntry {
+  url: string,
+  response: Promise<HttpResponse>,
+  time: number,
+}
+
 @Injectable({
   providedIn: 'root'
 })
 export class APIDatabase {
-  private cache = {} as { [key: string]: any };
+  private cache = {} as { [url: string]: CacheEntry };
+  private inFlight = {} as { [url: string]: Promise<HttpResponse> };
   private root = 'https://cors-proxy.blaseball-reference.com/database';
 
   constructor() {
@@ -23,18 +32,39 @@ export class APIDatabase {
     });
   }
 
-  private async get(url: string, force?: boolean) {
-    if (!force && this.cache[url]) {
-      return this.cache[url];
+  private async get(url: string, force?: boolean): Promise<HttpResponse> {
+    const now = Date.now();
+    const cacheEntry = this.cache[url];
+    const inFlight = this.inFlight[url];
+
+    if (!force) {
+      // if we're not forcing a new get, then check if there is an existing cached or in-flight request
+      if (inFlight) {
+        // if there's an in-flight one, just return it
+        console.debug(`APIDatabase.get(): already in-flight: ${url}`);
+        return inFlight;
+      } else if (cacheEntry) {
+        // if there's a cache entry...
+        if ((cacheEntry.time + DEFAULT_CACHE_KEEP) < now) {
+          // check if it's old; if it is, fall through to a new request
+          console.debug(`APIDatabase.get(): stale: ${url}`);
+        } else {
+          // otherwise, return the cached response
+          console.debug(`APIDatabase.get(): cached: ${url} (${new Date(cacheEntry.time).toISOString()})`);
+          return this.cache[url].response;
+        }
+      }
     }
 
+
     const { Http } = Plugins;
 
-    const ret = await Http.request({
+    console.debug(`APIDatabase.get(): uncached: ${url}`);
+    this.inFlight[url] = Http.request({
       method: 'GET',
       url: url,
     }).catch((err:any) => {
-      console.error('request failed, trying again in 1s:', err);
+      console.error('APIDatabase.get(): request failed, trying again in 1s:', err);
       return new Promise((resolve, reject) => {
         setTimeout(async () => {
           try {
@@ -49,18 +79,31 @@ export class APIDatabase {
         }, 1000);
       });
     });
-    this.cache[url] = (ret as any).data;
-    // console.debug('data=', ret.data);
-    return (ret as any).data;
+
+    // delete from the in-flight list as soon as it finishes
+    this.inFlight[url].finally(() => {
+      delete this.inFlight[url];
+    });
+
+    return this.inFlight[url].then((ret: HttpResponse) => {
+      // if it succeeds, cache it
+      console.debug(`APIDatabase.get(): caching: ${url}`);
+      this.cache[url] = {
+        url: url,
+        response: Promise.resolve(ret),
+        time: now,
+      };
+      return ret;
+    });
   }
 
   public async teams(force?: boolean): Promise<Team[]> {
     const url = `${this.root}/allTeams`;
-    console.debug(`APIDatabase.teams(): GET ${url}`);
+    // console.debug(`APIDatabase.teams(): GET ${url}`);
     try {
       const ret = await this.get(url, force);
       if (ret) {
-        return ret.map((team:any) => new Team(team));
+        return ret.data.map((team:any) => new Team(team));
       }
     } catch (err) {
       console.error('APIDatabase.teams(): failed to get list of teams', err);
@@ -77,11 +120,11 @@ export class APIDatabase {
       return [] as Player[];
     }
     const url = `${this.root}/players?ids=${args.join(',')}`;
-    console.debug(`APIDatabase.players(): GET ${url}`);
+    // console.debug(`APIDatabase.players(): GET ${url}`);
     try {
       const ret = await this.get(url, force);
       if (ret) {
-        return ret.map((player:any) => new Player(player));
+        return ret.data.map((player:any) => new Player(player));
       }
     } catch (err) {
       console.error('APIDatabase.players(): failed to get players', err);