<?php

declare(strict_types=1);

namespace PhpQml\Bridge;

/**
 * Per-request correlation key holder.
 *
 * The HTTP request's `Idempotency-Key` (PLAN.md §4 *Idempotency*) is
 * stashed here on RequestEvent and read back by ModelPublisher when
 * it builds Mercure envelopes, so QML clients can match Mercure echoes
 * to the optimistic mutation that originated them (§5).
 *
 * Cleared on TerminateEvent. CLI commands and out-of-request mutations
 * see no correlation key, which is the correct behaviour.
 */
final class CorrelationContext
{
    private ?string $key = null;

    public function set(?string $key): void
    {
        $this->key = $key;
    }

    public function get(): ?string
    {
        return $this->key;
    }

    public function clear(): void
    {
        $this->key = null;
    }
}