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import { FetchDecoratorResponse } from '@/helpers/fetch';
import { cstorage } from '@/utils/storage';
/**
* Represents a single node in the doubly-linked list used by {@link HttpLru}.
* Each node holds a cached HTTP response keyed by its request hash, along with
* pointers to the previous and next nodes for O(1) reordering.
*
* @interface LruNode
* @source
*/
interface LruNode {
/** The request hash used as the cache lookup key */
key: string;
/** The cached HTTP response data */
value: FetchDecoratorResponse;
/** Pointer to the previous (more recently used) node, or `null` if this is the head */
prev: LruNode | null;
/** Pointer to the next (less recently used) node, or `null` if this is the tail */
next: LruNode | null;
}
/** Default maximum number of entries the LRU cache will hold before evicting */
const DEFAULT_CAPACITY = 100;
/**
* A singleton LRU (Least Recently Used) cache for HTTP responses, backed by
* `cstorage.local` for persistence across browser sessions.
*
* The cache uses a doubly-linked list combined with a `Map` for O(1) lookups,
* insertions, and evictions. When the cache exceeds its configured capacity,
* the least recently accessed entry is automatically evicted.
*
* State is persisted to `cstorage.local` on every mutation so that
* cached responses survive extension restarts and browser closures.
*
* @category Utils
* @example
* ```typescript
* const cache = await HttpLru.getInstance(50);
* const cached = await cache.getByHash(requestHash);
* if (!cached) {
* const response = await fetchDecorator(url, options);
* await cache.putByHash(requestHash, response);
* }
* ```
*
* @class HttpLru
* @source
*/
export class HttpLru {
/** The singleton instance, lazily initialized via {@link HttpLru.getInstance} */
static #instance: HttpLru | null = null;
/** Maximum number of entries before the least recently used entry is evicted */
private capacity: number;
/** Hash map providing O(1) access to linked-list nodes by request hash */
private cache: Map<string, LruNode>;
/** Pointer to the most recently used node (front of the list) */
private head: LruNode | null;
/** Pointer to the least recently used node (back of the list) */
private tail: LruNode | null;
/**
* Creates a new HttpLru instance. Private to enforce the singleton pattern —
* use {@link HttpLru.getInstance} instead.
*
* @param capacity - Maximum number of entries to store before evicting (default: `DEFAULT_CAPACITY`)
* @source
*/
private constructor(capacity: number = DEFAULT_CAPACITY) {
this.capacity = capacity;
this.cache = new Map();
this.head = null;
this.tail = null;
}
/**
* Returns the singleton HttpLru instance, restoring persisted state from
* `cstorage.local` on first access. Subsequent calls return the
* same in-memory instance without hitting storage.
*
* @param capacity - Maximum number of entries (only applied when creating a new instance)
* @returns The singleton HttpLru instance
*
* @example
* ```typescript
* const cache = await HttpLru.getInstance();
* ```
* @source
*/
public static async getInstance(capacity: number = DEFAULT_CAPACITY): Promise<HttpLru> {
if (HttpLru.#instance) {
return HttpLru.#instance;
}
const data = await cstorage.local.get([CACHE.HTTP_LRU]);
if (!data[CACHE.HTTP_LRU]) {
HttpLru.#instance = new HttpLru(capacity);
return HttpLru.#instance;
}
const httplru = new HttpLru(capacity);
httplru.cache = new Map(Object.entries(data[CACHE.HTTP_LRU].cache));
httplru.head = data[CACHE.HTTP_LRU].head;
httplru.tail = data[CACHE.HTTP_LRU].tail;
HttpLru.#instance = httplru;
return httplru;
}
/**
* Retrieves a cached response by its request hash. This is a convenience
* wrapper around {@link HttpLru.get} that makes the hash-based lookup
* intent explicit.
*
* @param hash - The request hash generated by `generateRequestHash`
* @returns The cached response, or `null` if no entry exists for the hash
* @source
*/
async getByHash(hash: string): Promise<FetchDecoratorResponse | null> {
return await this.get(hash);
}
/**
* Stores a response in the cache keyed by its request hash. This is a
* convenience wrapper around {@link HttpLru.put} that makes the hash-based
* storage intent explicit.
*
* @param hash - The request hash generated by `generateRequestHash`
* @param value - The HTTP response to cache
* @source
*/
async putByHash(hash: string, value: FetchDecoratorResponse): Promise<void> {
return await this.put(hash, value);
}
/**
* Retrieves a cached response by key and promotes it to the head of the
* linked list (marking it as most recently used).
*
* @param key - The cache key to look up
* @returns The cached response if found, or `null` if the key is not in the cache
* @source
*/
async get(key: string): Promise<FetchDecoratorResponse | null> {
if (this.cache.has(key)) {
const node = this.cache.get(key)!;
this.moveToHead(node);
return node.value;
}
return null;
}
/**
* Inserts or updates a cached response. If the key already exists, its value
* is updated and the node is promoted to the head. If the key is new, a new
* node is created at the head. When the cache exceeds its capacity, the
* least recently used entry (tail) is evicted.
*
* Persists the updated cache state to `cstorage.local` after mutation.
*
* @param key - The cache key (typically a request hash)
* @param value - The HTTP response to store
* @source
*/
async put(key: string, value: FetchDecoratorResponse): Promise<void> {
if (this.cache.has(key)) {
const node = this.cache.get(key)!;
node.value = value;
this.moveToHead(node);
} else {
const newNode: LruNode = { key, value, prev: null, next: this.head };
if (this.head) {
this.head.prev = newNode;
}
this.head = newNode;
if (!this.tail) {
this.tail = newNode;
}
this.cache.set(key, newNode);
if (this.cache.size > this.capacity) {
this.cache.delete(this.tail.key);
this.tail = this.tail.prev;
if (this.tail) {
this.tail.next = null;
} else {
this.head = null;
}
}
}
// Save to cstorage.local
await this.saveToStorage();
}
/**
* Detaches a node from its current position in the doubly-linked list and
* reinserts it at the head, marking it as the most recently used entry.
* Persists the reordered state to `cstorage.local`.
*
* @param node - The node to promote to the head of the list
* @source
*/
private async moveToHead(node: LruNode): Promise<void> {
if (node === this.head) {
return;
}
if (node === this.tail) {
this.tail = node.prev;
} else if (node.prev) {
node.prev.next = node.next;
}
if (node.next) {
node.next.prev = node.prev;
}
node.prev = null;
node.next = this.head;
if (this.head) {
this.head.prev = node;
}
this.head = node;
// Save to cstorage.local after moving node
await this.saveToStorage();
}
/**
* Serializes the current cache state (map entries, head, and tail pointers)
* and writes it to `cstorage.local` under the `httplru` key.
* Called internally after every mutation to ensure persistence.
*
* @source
*/
private async saveToStorage(): Promise<void> {
const cacheData = Object.fromEntries(this.cache);
await cstorage.local.set({
[CACHE.HTTP_LRU]: {
cache: cacheData,
head: this.head,
tail: this.tail,
},
});
}
}
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