server/server -> server/core

server/core/helpers/promise-cache.ts

@@ -0,0 +1,39 @@
+export class CachePromiseFactory <A, R> {
+  private readonly running = new Map<string, Promise<R>>()
+
+  constructor (
+    private readonly fn: (arg: A) => Promise<R>,
+    private readonly keyBuilder: (arg: A) => string
+  ) {
+  }
+
+  run (arg: A) {
+    return this.runWithContext(null, arg)
+  }
+
+  runWithContext (ctx: any, arg: A) {
+    const key = this.keyBuilder(arg)
+
+    if (this.running.has(key)) return this.running.get(key)
+
+    const p = this.fn.apply(ctx || this, [ arg ])
+
+    this.running.set(key, p)
+
+    return p.finally(() => this.running.delete(key))
+  }
+}
+
+export function CachePromise (options: {
+  keyBuilder: (...args: any[]) => string
+}) {
+  return function (_target, _key, descriptor: PropertyDescriptor) {
+    const promiseCache = new CachePromiseFactory(descriptor.value, options.keyBuilder)
+
+    descriptor.value = function () {
+      if (arguments.length !== 1) throw new Error('Cache promise only support methods with 1 argument')
+
+      return promiseCache.runWithContext(this, arguments[0])
+    }
+  }
+}