// SeededRandom provides a very simple random number generator
// that can be seeded (since NodeJS built-ins can't).
//
// See also:
// - https://arxiv.org/pdf/1704.00358
// - https://en.wikipedia.org/wiki/Middle-square_method

// Some large odd number, see https://en.wikipedia.org/wiki/Weyl_sequence
const step = BigInt('0x12345678ABCDE123'); // uint64
const maxSize = BigInt(1) << BigInt(64);

const extractMiddle = (value: bigint, halfSize: bigint) => {
	// Remove the lower quarter
	const quarterSize = halfSize / BigInt(2);
	value >>= quarterSize;

	// Remove the upper quarter
	const halfMaximumValue = BigInt(1) << halfSize;
	value %= halfMaximumValue;

	return value;
};

export default class SeededRandom {
	private value_: bigint;
	private nextStep_: bigint = step;
	private halfSize_ = BigInt(32);

	public constructor(seed: number) {
		this.value_ = BigInt(seed);
	}

	public next() {
		this.value_ = this.value_ * this.value_ + this.nextStep_;

		// Move to the next item in the sequence. Mod to prevent from getting
		// too large. See https://en.wikipedia.org/wiki/Weyl_sequence.
		this.nextStep_ = (step + this.nextStep_) % maxSize;

		this.value_ = extractMiddle(this.value_, this.halfSize_);
		return this.value_;
	}

	// The resultant range includes `a` but excludes `b`.
	public nextInRange(a: number, b: number) {
		if (b <= a + 1) return a;

		const range = b - a;
		return Number(this.next() % BigInt(range)) + a;
	}
}