npm package: @serum-enterprises/cache
Description: Simple In-Memory Cache Library written in NodeJS
Author: Philipp Steckenbauer
Latest version: 3.0.0

# Cache
This Node.js module, `Cache`, is a simple yet efficient in-memory Cache implementation using Node's Buffers for Data. This Library offers a Base Class called MLC (Manual LifeCycle) that does no Cache Invalidation by itself, as well as the 2 very popular Cache policies LFU (Least Frequently Used) and LRU (Least Recently Used).

## Features
- MLC Strategy: Manual Lifecycle, no Cache Invalidation by itself. If an Item is too big for the Cache, `set` will silently fail.
- LFU Strategy: Least Frequently Used Items get removed first when the Cache reaches its size limit.
- LRU Strategy: Least Recently Used Items get removed first when the Cache reaches its size limit.
- Maximum Cache Size given in Bytes. A value of `0` effectively disables the Cache.
- Stores NodeJS Buffers as Values.
- Methods to `get`, `set`, `rename`, `delete` and check existence (`has`) of Items in the Cache.
- A convenient Method to `clear` the Cache.

## Installation
You can install this Library in your Project using `npm`:

```bash
npm install --save @serum-enterprises/cache
```

## Usage

Import the relevant Classes into your file:

```javascript
const { MLC, LFU, LRU } = require('@serum-enterprises/cache');
```

Note: All Classes have the same Interface and can be used interchangeably. For the rest of this Documentation, we will use `Cache` to refer to any Implementation.

Note: Both LFU and LRU are derived from MLC, which only handles Cache Size, while LFU and LRU handle Cache Invalidation as well.

### Create a new Cache

```javascript
// Create a new Cache with a maximum size of 1MB (1024 * 1024 Bytes)
const cache = new Cache(1024 * 1024);
```
You can specify the maximum Cache size in Bytes while creating the `Cache` object. A Value of `0` effectively disables the Cache.

### Get and Set values

```javascript
let bufferValue = Buffer.from('Hello, World!');
cache.set('greeting', bufferValue);

let retrievedBuffer = cache.get('greeting');
console.log(retrievedBuffer.toString()); // Prints: 'Hello, World!'
```
The `set` Method is used to store a Buffer in the Cache, while the `get` Method retrieves the stored Buffer. 
On the LFU and LRU Strategies, the `set` Method also ensures that the new Value fits into the Cache by removing the least frequently or least recently used Items respectively if necessary. On the MLC Strategy, if there is not enough Space, the `set` Method will silently fail.
If the Buffer Value is larger than the maximum Cache size, it won't be added to the Cache and the `set` Method will silently fail.
The `get` Method returns `undefined` if the Key is not found in the Cache.
If the Key already exists in the Cache, the `set` Method will overwrite the existing Value.

### Other operations

```javascript
// Check if an Item exists based on its Key
cache.has('greeting');
// Rename an Item (change its Key)
cache.rename('greeting', 'hello'); 
// Get all Keys as an Array
cache.keys();
// Delete an Item based on its Key
cache.delete('hello');
// Clear the Cache
cache.clear();
```

The Cache provides Methods for checking if an Item exists (`has`), renaming an Item (`rename`), getting all Keys (`keys`), deleting an Item (`delete`), and clearing the entire Cache (`clear`).

### Error Handling

Methods will throw a `TypeError` if an Argument has a wrong Data Type.

## Tests

Tests for this Library are written using Jest and have 100% Code Coverage.

To run the Tests, use the following Command:
```bash
npm run test
```

## License

MIT License

Copyright (c) 2023 Serum Enterprises

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.