<?php
// SPDX-License-Identifier: GPL-3.0-or-later
declare(strict_types=1);

namespace Aiwend\Chat;

/**
 * Reads the cancel flag that the cancel endpoint writes, from inside the request that is streaming the answer.
 *
 * Two properties matter: the read is rate-limited (the transport asks "cancelled?" on every progress tick and every chunk, which
 * must not become a database query each time), and once the flag has been seen the answer stays "cancelled" (latch). The read itself
 * is injected, so the WordPress-specific cache bypass lives in the controller and this class stays unit-testable.
 */
final class CancelFlagReader
{
    private bool $seen = false;
    private ?float $lastRead = null;

    /**
     * @param \Closure(): bool $read true when the flag exists right now, read past any per-request "missing" cache
     * @param \Closure(): float $now seconds (microtime(true))
     */
    public function __construct(private \Closure $read, private \Closure $now, private float $minInterval = 0.4)
    {
    }

    public function __invoke(): bool
    {
        if ($this->seen) {
            return true;
        }
        $t = ($this->now)();
        if ($this->lastRead !== null && $t - $this->lastRead < $this->minInterval) {
            return false;
        }
        $this->lastRead = $t;
        $this->seen = ($this->read)();
        return $this->seen;
    }
}