<?php

namespace Framework\Middleware;

/**
 * Middleware to ensure every request has a correlation ID.
 *
 * The correlation ID is used to trace all log entries for a single request.
 * It can be passed in via X-Correlation-ID header or generated automatically.
 */
final class CorrelationMiddleware
{
    /**
     * Handle the request and set correlation ID.
     *
     * @param callable $next The next handler in the chain
     */
    public function handle(callable $next): void
    {
        $correlationId = $this->getOrCreateCorrelationId();

        // Make globally available
        $_SERVER['CORRELATION_ID'] = $correlationId;

        // Set response header for tracing
        if (!headers_sent()) {
            header("X-Correlation-ID: {$correlationId}");
        }

        $next();
    }

    /**
     * Get existing correlation ID from header or generate new one.
     */
    private function getOrCreateCorrelationId(): string
    {
        // Check for existing correlation ID in headers
        if (isset($_SERVER['HTTP_X_CORRELATION_ID']) && $_SERVER['HTTP_X_CORRELATION_ID'] !== '') {
            return $_SERVER['HTTP_X_CORRELATION_ID'];
        }

        // Generate new correlation ID
        return bin2hex(random_bytes(8));
    }

    /**
     * Get the current correlation ID.
     */
    public static function getCorrelationId(): string
    {
        return $_SERVER['CORRELATION_ID'] ?? bin2hex(random_bytes(8));
    }
}