refactor: README

packages/idb-cache/README.md

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+# idb-cache
+
+IndexedDB-based caching library with encryption and chunked storage, designed for performance and security. Implements AsyncStorage interface.
+
+```typescript
+interface AsyncStorage {
+  getItem: (key: string) => Promise<string | null>;
+  setItem: (key: string, value: string) => Promise<unknown>;
+  removeItem: (key: string) => Promise<void>;
+  clear: () => Promise<void>;
+}
+```
+
+## Why encrypt data in IndexedDB?
+
+Encryption keeps data in IndexedDB private, even when a browser profile is shared on the same device. Only one with access to the `cacheKey` can decrypt the data.
+
+## Installation
+
+```bash
+npm install @instructure/idb-cache
+```
+
+## Usage
+
+```typescript
+import { IDBCache } from '@instructure/idb-cache';
+
+// Initialize the cache
+const cache = new IDBCache({
+  cacheKey: 'your-secure-key',
+  cacheBuster: 'unique-cache-buster',
+  // chunkSize?: number;
+  // cleanupInterval?: number;
+  // dbName?: string;
+  // debug?: boolean,
+  // gcTime?: number;
+  // maxTotalChunks?: number
+  // pbkdf2Iterations?: number;
+  // priority?: "normal" | "low"
+});
+
+// Store an item
+await cache.setItem('key', 'value');
+
+// Retrieve an item
+const token = await cache.getItem('key');
+console.log(token); // Outputs: 'value'
+
+// Remove an item
+await cache.removeItem('key');
+
+// Count stored chunks
+const totalChunks = await cache.count();
+
+// Removes expired items, busted items, and limits chunks
+// Runs at interval
+await cache.cleanup();
+
+// Clears all items from cache
+await cache.clear();
+
+// Destroy the cache instance
+await cache.destroy();
+```
+
+## Features
+
+- **Web Worker**: Offloads encryption and decryption tasks to prevent blocking the main thread.
+- **Chunking**: Efficiently handles large data by splitting it into chunks.
+- **Encryption**: Secures data using AES-GCM with PBKDF2 key derivation.
+- **Garbage collection**: Expires and cleans up outdated cache entries.
+- **Task processing**: Uses parallelism and queue to mitigate crypto/CPU overload.
+
+## Usage with TanStack Query
+
+Integrate idb-cache as an AsyncStorage persister for TanStack Query.
+
+```typescript
+import { QueryClient } from '@tanstack/query-core';
+import { experimental_createPersister } from '@tanstack/query-persist-client-core';
+import { IDBCache } from 'idb-cache';
+
+const cacheBuster = 'my_salt'; // Doubles as salt for encryption
+
+const idbCache = new IDBCache({
+  cacheKey: 'user_cache_key',
+  cacheBuster,
+});
+
+// Create the persister
+const persister = experimental_createPersister({
+  storage: idbCache,
+  maxAge: 1000 * 60 * 60 * 24 * 7, // 7 days
+  buster: cacheBuster,
+});
+
+// Initialize the QueryClient with the persister
+export const queryClient = new QueryClient({
+  defaultOptions: {
+    queries: {
+      staleTime: 1000 * 60 * 60, // 1 hour
+      gcTime: 1000 * 60 * 60 * 24 * 7, // 7 days
+      persister,
+    },
+  },
+});
+```
+
+## Data flow
+
+### setItem
+
+```mermaid
+flowchart TD
+    Application([Client app]) --> |".setItem()"| IDBCache[[IDBCache]]
+    IDBCache -.-> |"Unencrypted chunks"| WebWorker{{Web Worker}}
+    WebWorker -.-> |"Encrypted chunks"| IDBCache
+    IDBCache -.-> |"Encrypted chunks"| IndexedDB[(IndexedDB)]
+```
+
+### getItem
+
+```mermaid
+flowchart TD
+    Application([Client app]) --> |".getItem()"| IDBCache[[IDBCache]]
+    IDBCache --> |Get chunks| IndexedDB[(IndexedDB)]
+    IndexedDB -.-> |Encrypted chunks| IDBCache
+    IDBCache -.-> |Encrypted chunks| WebWorker{{Web Worker}}
+    WebWorker -.-> |Decrypted chunks| IDBCache
+    IDBCache --> |"Item"| Application
+```
+
+## Technologies used
+
+- [IndexedDB](https://developer.mozilla.org/en-US/docs/Web/API/IndexedDB_API)
+- [Web Workers](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API)
+  - [SharedWorker](https://developer.mozilla.org/en-US/docs/Web/API/SharedWorker)
+  - [MessageChannel](https://developer.mozilla.org/en-US/docs/Web/API/MessageChannel)
+  - [MessagePort](https://developer.mozilla.org/en-US/docs/Web/API/MessagePort)
+  - [Transferable objects](https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Transferable_objects)
+- [Web Crypto API](https://developer.mozilla.org/en-US/docs/Web/API/Web_Crypto_API)
+  - [SubtleCrypto](https://developer.mozilla.org/en-US/docs/Web/API/SubtleCrypto)
+  - [AES-GCM](https://developer.mozilla.org/en-US/docs/Web/API/AesGcmParams)
+  - [PBKDF2](https://developer.mozilla.org/en-US/docs/Web/API/Pbkdf2Params)
+- [ArrayBuffer](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/ArrayBuffer)
+
+## Related reading
+
+- [Is postMessage slow?](https://surma.dev/things/is-postmessage-slow/)
+- [Measure performance with the RAIL model](https://web.dev/articles/rail)
+- [LocalStorage vs. IndexedDB vs. Cookies vs. OPFS vs. WASM-SQLite](https://rxdb.info/articles/localstorage-indexeddb-cookies-opfs-sqlite-wasm.html)