@prismicio/mock/src/lib/PRNG.ts

Generate mock Prismic documents, fields, Slices, and models for development and testing environments

/**
 * The following code is a modified version of Prando from `zeh/prando` on GitHub.
 *
 * Source: https://github.com/zeh/prando/blob/acc2a3c09df12a41b5c82fbf44e49e070e6f60ac/src/Prando.ts
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2016 Zeh Fernando
 *
 * 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.
 */

const MIN = -2147483648 // Int32 min
const MAX = 2147483647 // Int32 max

const xorshift = (value: number): number => {
	// Xorshift*32
	// Based on George Marsaglia's work: http://www.jstatsoft.org/v08/i14/paper
	value ^= value << 13
	value ^= value >> 17
	value ^= value << 5

	return value
}

/** Pseudorandom number generator. */
export class PRNG {
	private _value: number

	/**
	 * Generate a new pseudo-random number generator.
	 *
	 * @param seed - A number or string seed that determines which pseudo-random number sequence will
	 *   be created.
	 */
	constructor(seed: number | string) {
		if (typeof seed === "string") {
			let hash = 0
			if (seed) {
				const l = seed.length
				for (let i = 0; i < l; i++) {
					hash = (hash << 5) - hash + seed.charCodeAt(i)
					hash |= 0
					hash = xorshift(hash)
				}
			}

			this._value = hash
		} else {
			this._value = seed
		}

		if (this._value === 0) {
			this._value = 1
		}
	}

	/**
	 * Generates a pseudo-random number.
	 *
	 * @returns The generated pseudo-random number.
	 */
	public next(): number {
		this._value = xorshift(this._value)

		return (this._value - MIN) / (MAX - MIN)
	}
}