<?php
/**
 * Fixed-window counter for things that leave no database row, such as photo uploads.
 *
 * @package Fitzaro
 */

namespace Fitzaro\Limits;

defined( 'ABSPATH' ) || exit;

/**
 * Storage is injected (transients in WordPress). Two simultaneous hits may both pass: fine for an
 * abuse brake, which is all this is. Money is guarded by Limits, which counts database rows.
 */
final class Throttle {

	/**
	 * Receives a key, returns the stored value or false.
	 *
	 * @var callable
	 */
	private $get;

	/**
	 * Receives ( key, value, lifetime in seconds ).
	 *
	 * @var callable
	 */
	private $set;

	/**
	 * Returns the current Unix time.
	 *
	 * @var callable
	 */
	private $clock;

	/**
	 * Creates the throttle.
	 *
	 * @param callable $get   Receives a key, returns the stored value or false.
	 * @param callable $set   Receives ( key, value, lifetime ).
	 * @param callable $clock Returns the current Unix time.
	 */
	public function __construct( callable $get, callable $set, callable $clock ) {
		$this->get   = $get;
		$this->set   = $set;
		$this->clock = $clock;
	}

	/**
	 * Counts one hit; false when the limit for the current window is already reached.
	 *
	 * @param string $key    Counter key.
	 * @param int    $limit  Hits per window; 0 for unlimited.
	 * @param int    $window Window length in seconds.
	 */
	public function hit( string $key, int $limit, int $window ): bool {
		if ( $limit <= 0 ) {
			return true;
		}

		$now    = (int) ( $this->clock )();
		$stored = ( $this->get )( $key );
		$start  = is_array( $stored ) && isset( $stored[0], $stored[1] ) ? (int) $stored[1] : $now;
		$count  = is_array( $stored ) && isset( $stored[0], $stored[1] ) ? (int) $stored[0] : 0;

		if ( $now - $start >= $window ) {
			$start = $now;
			$count = 0;
		}

		if ( $count >= $limit ) {
			return false;
		}

		( $this->set )( $key, array( $count + 1, $start ), max( 1, $window - ( $now - $start ) ) );

		return true;
	}
}