try to fix this spaghetti of a code

lib/core.js

@@ -0,0 +1,19 @@
+const crypto = require('node:crypto');
+class AppError extends Error {
+    constructor(code, message, status = 400) { super(message); this.code = code; this.status = status; }
+}
+class KeyedQueue {
+    constructor() { this.tails = new Map(); }
+    run(keys, task) {
+        keys = [...new Set(keys)].sort();
+        const previous = keys.map(key => this.tails.get(key) || Promise.resolve());
+        const result = Promise.all(previous).then(task);
+        const tail = result.catch(() => {});
+        for (const key of keys) this.tails.set(key, tail);
+        tail.then(() => { for (const key of keys) if (this.tails.get(key) === tail) this.tails.delete(key); });
+        return result;
+    }
+    async drain() { await Promise.all([...this.tails.values()]); }
+}
+const hash = value => crypto.createHash('sha256').update(value).digest('hex');
+module.exports = {AppError, KeyedQueue, hash};