<?php
/**
 * A small, local, seedable PRNG for demo mode.
 *
 * @package Tagsmith
 */

declare(strict_types=1);

namespace Tagsmith\Demo;

defined( 'ABSPATH' ) || exit;

/**
 * A xorshift32 PRNG, instantiated per request so FakeReports/
 * FakeSearchConsole can produce deterministic, reproducible output without
 * touching PHP's global `mt_rand()` state (which any other code on the
 * request, including a real Google call elsewhere in the same process,
 * might rely on).
 */
class Prng {

	/**
	 * The 32-bit generator state (never 0; xorshift is stuck at 0 forever).
	 *
	 * @var int
	 */
	private int $state;

	/**
	 * Constructor.
	 *
	 * @param int $seed Any integer seed.
	 */
	public function __construct( int $seed ) {
		$state = $seed % 4294967296;

		if ( $state < 0 ) {
			$state += 4294967296;
		}

		$this->state = 0 === $state ? 1 : $state;
	}

	/**
	 * A pseudo-random integer in [$min, $max], inclusive.
	 *
	 * @param int $min Minimum (inclusive).
	 * @param int $max Maximum (inclusive).
	 */
	public function int( int $min, int $max ): int {
		if ( $min >= $max ) {
			return $min;
		}

		$range = $max - $min + 1;

		return $min + ( $this->next() % $range );
	}

	/**
	 * A pseudo-random float in [0, 1).
	 */
	public function float(): float {
		return $this->next() / 4294967296.0;
	}

	/**
	 * Advances the xorshift32 state and returns it.
	 */
	private function next(): int {
		$x  = $this->state;
		$x ^= ( $x << 13 ) & 0xFFFFFFFF;
		$x ^= $x >> 17;
		$x ^= ( $x << 5 ) & 0xFFFFFFFF;
		$x &= 0xFFFFFFFF;

		$this->state = $x;

		return $x;
	}
}