Lru cache

Javascript/cache algorithm/lru.js

@@ -0,0 +1,106 @@
+class Node {
+    constructor(key, value, expiry) {
+        this.key = key;
+        this.value = value;
+        this.expiry = expiry;
+        this.prev = null;
+        this.next = null;
+    }
+}
+
+export class LRUCache {
+    constructor({ max = 100, ttl = 0 } = {}) {
+        this.max = max;
+        this.ttl = ttl;
+        this.map = new Map();
+
+        // Dummy head and tail (avoid edge checks)
+        this.head = new Node(null, null, null);
+        this.tail = new Node(null, null, null);
+
+        this.head.next = this.tail;
+        this.tail.prev = this.head;
+    }
+
+    _addNode(node) {
+        node.prev = this.head;
+        node.next = this.head.next;
+
+        this.head.next.prev = node;
+        this.head.next = node;
+    }
+
+    _removeNode(node) {
+        node.prev.next = node.next;
+        node.next.prev = node.prev;
+    }
+
+    _moveToFront(node) {
+        this._removeNode(node);
+        this._addNode(node);
+    }
+
+    _removeLRU() {
+        const lru = this.tail.prev;
+        if (lru === this.head) return;
+
+        this._removeNode(lru);
+        this.map.delete(lru.key);
+    }
+
+    _isExpired(node) {
+        return this.ttl > 0 && Date.now() > node.expiry;
+    }
+
+    get(key) {
+        const node = this.map.get(key);
+        if (!node) return null;
+
+        if (this._isExpired(node)) {
+            this._removeNode(node);
+            this.map.delete(key);
+            return null;
+        }
+
+        this._moveToFront(node);
+        return node.value;
+    }
+
+    set(key, value) {
+        let node = this.map.get(key);
+        const expiry = this.ttl > 0 ? Date.now() + this.ttl : Infinity;
+
+        if (node) {
+            node.value = value;
+            node.expiry = expiry;
+            this._moveToFront(node);
+            return;
+        }
+
+        node = new Node(key, value, expiry);
+        this.map.set(key, node);
+        this._addNode(node);
+
+        if (this.map.size > this.max) {
+            this._removeLRU();
+        }
+    }
+
+    delete(key) {
+        const node = this.map.get(key);
+        if (!node) return false;
+
+        this._removeNode(node);
+        return this.map.delete(key);
+    }
+
+    clear() {
+        this.map.clear();
+        this.head.next = this.tail;
+        this.tail.prev = this.head;
+    }
+
+    size() {
+        return this.map.size;
+    }
+}