big-bitfield/index.js

library for storing a bitfield with a large number of options stored as an array/buffer, suitable for e.g. permissions systems

'use strict';

const DEFAULT_SIZE = 8;

class BitField {

	#array;

	// data number for number of bits or base64 representation of array
	constructor(data = DEFAULT_SIZE) {
		const arrayFrom = typeof data === 'number'
			? data
			: Buffer.from(data, 'base64');
		this.#array = new Uint8Array(arrayFrom);
	}

	// return boolean for state of a bit, always false if larger than the length
	get(bit) {
		const i = bit >> 3;
		if (i >= this.#array.length) {
			console.warn('big-bitfield attempted to get bit', bit, 'which is more than the array size', this.#array.length, 'can store. This always returns false.');
			return false;
		}
		return (this.#array[i] & 128 >> bit % 8) === 128 >> bit % 8;
	}

	// set a bit, default true if not specified, noop if larger than size
	set(bit, value = true) {
		const i = bit >> 3;
		if (i < this.#array.length) {
			if (value === true) {
				this.#array[i] |= (128 >> bit % 8);
			} else {
				this.#array[i] &= ~(128 >> bit % 8);
			}
		} else {
			console.warn('big-bitfield attempted to set bit', bit, 'which is more than the array size', this.#array.length, 'can store. This is a noop.');
		}
	}

	// set all bits from an array
	setAll(bits = [], value = true) {
		bits.forEach(bit => this.set(bit, value));
	}

	// return boolean for if ALL bits given in arguments spread are true
	hasAll(...bits) {
		return !bits
			.some(b => this.get(b) !== true);
	}

	// return boolean for if ANY bits given in arguments spread are true
	hasAny(...bits) {
		return bits
			.some(b => this.get(b) === true);
	}

	// return the internal array
	get array() {
		return this.#array;
	}

	// return base64 representation
	get base64() {
		return Buffer
			.from(this.#array)
			.toString('base64');
	}

}

module.exports = BitField;