<?php
/**
 * Per-host request spacing.
 *
 * @package Unbreak
 */

namespace Unbreak\Check;

defined( 'ABSPATH' ) || exit;

/**
 * At most one request per host every 2 seconds. Each lane owns a fixed set of hosts, so the
 * per-lane state (last request time per host) is never written by two jobs at once.
 */
class HostThrottle {

	public const MIN_GAP = 2.0;

	/**
	 * Lane index.
	 *
	 * @var int
	 */
	private $lane;

	/**
	 * Last request time per host (microtime floats).
	 *
	 * @var array<string,float>
	 */
	private $last = array();

	/**
	 * Constructor: loads the lane's state from the previous batch.
	 *
	 * @param int $lane Lane index.
	 */
	public function __construct( int $lane ) {
		$this->lane = $lane;
		$stored     = get_option( $this->option(), array() );
		if ( is_array( $stored ) ) {
			foreach ( $stored as $host => $time ) {
				$this->last[ (string) $host ] = (float) $time;
			}
		}
	}

	/**
	 * Seconds to wait before the host may be requested again.
	 *
	 * @param string $host Host.
	 */
	public function wait_time( string $host ): float {
		if ( ! isset( $this->last[ $host ] ) ) {
			return 0.0;
		}
		return max( 0.0, $this->last[ $host ] + self::MIN_GAP - $this->now() );
	}

	/**
	 * Record a request to a host.
	 *
	 * @param string $host Host.
	 */
	public function record( string $host ): void {
		$this->last[ $host ] = $this->now();
	}

	/**
	 * Sleep until the host may be requested.
	 *
	 * @param string $host Host.
	 */
	public function wait( string $host ): void {
		$wait = $this->wait_time( $host );
		if ( $wait > 0 ) {
			$this->sleep( $wait );
		}
	}

	/**
	 * Persist entries that still matter for the next batch.
	 */
	public function save(): void {
		$now  = $this->now();
		$keep = array();
		foreach ( $this->last as $host => $time ) {
			if ( $now - $time < self::MIN_GAP + 1 ) {
				$keep[ $host ] = $time;
			}
		}
		update_option( $this->option(), $keep, false );
	}

	/**
	 * Current time (overridable in subclasses).
	 */
	protected function now(): float {
		return microtime( true );
	}

	/**
	 * Sleep (overridable in subclasses).
	 *
	 * @param float $seconds Seconds.
	 */
	protected function sleep( float $seconds ): void {
		usleep( (int) ( $seconds * 1000000 ) );
	}

	/**
	 * Option name for this lane's state.
	 */
	private function option(): string {
		return 'unbreak_throttle_lane_' . $this->lane;
	}
}