<?php
declare(strict_types=1);

/**
 * Tracks the MQTT client keepalive independently from inbound broker traffic.
 *
 * MQTT keepalive is a client-to-broker obligation. Receiving a continuous
 * stream of PUBLISH packets must therefore never postpone the next PINGREQ.
 */
final class NiroMqttKeepalive
{
    private int $lastPingAt;

    public function __construct(int $connectedAt, private readonly int $intervalSeconds = 15)
    {
        if ($intervalSeconds < 1) {
            throw new InvalidArgumentException('MQTT keepalive interval must be positive');
        }
        $this->lastPingAt = $connectedAt;
    }

    public function isDue(int $now): bool
    {
        return $now - $this->lastPingAt >= $this->intervalSeconds;
    }

    public function markSent(int $now): void
    {
        $this->lastPingAt = $now;
    }
}