api: implement redis/memory store for cache

api/src/store/memory-store.js

@@ -0,0 +1,72 @@
+import { MinPriorityQueue } from '@datastructures-js/priority-queue'
+import { Store } from './base-store.js';
+
+// minimum delay between sweeps to avoid repeatedly
+// sweeping entries close in proximity one by one.
+const MIN_THRESHOLD_MS = 2500;
+
+export default class MemoryStore extends Store {
+    #store = new Map();
+    #timeouts = new MinPriorityQueue/*<{ t: number, k: unknown }>*/((obj) => obj.t);
+    #nextSweep = { id: null, t: null };
+
+    constructor(name) {
+        super(name);
+    }
+
+    async _get(key) {
+        const val = this.#store.get(key);
+
+        return val === undefined ? null : val;
+    }
+
+    async _set(key, val, exp_sec = -1) {
+        if (this.#store.has(key)) {
+            this.#timeouts.remove(o => o.k === key);
+        }
+
+        if (exp_sec > 0) {
+            const exp = 1000 * exp_sec;
+            const timeout_at = +new Date() + exp;
+
+            this.#timeouts.enqueue({ k: key, t: timeout_at });
+        }
+
+        this.#store.set(key, val);
+        this.#reschedule();
+    }
+
+    #reschedule() {
+        const current_time = new Date().getTime();
+        const time = this.#timeouts.front()?.t;
+        if (!time) {
+            return;
+        } else if (time < current_time) {
+            return this.#sweepNow();
+        }
+
+        const sweep = this.#nextSweep;
+        if (sweep.id === null || sweep.t > time) {
+            if (sweep.id) {
+                clearTimeout(sweep.id);
+            }
+
+            sweep.t = time;
+            sweep.id = setTimeout(
+                () => this.#sweepNow(),
+                Math.max(MIN_THRESHOLD_MS, time - current_time)
+            );
+        }
+    }
+
+    #sweepNow() {
+        while (this.#timeouts.front()?.t < new Date().getTime()) {
+            const item = this.#timeouts.dequeue();
+            this.#store.delete(item.k);
+        }
+
+        this.#nextSweep.id = null;
+        this.#nextSweep.t = null;
+        this.#reschedule();
+    }
+}