<?php
/**
 * Header list parsing.
 *
 * @package FormPilot
 * @since   1.0.0
 */

declare( strict_types = 1 );

namespace FormPilot\Webhooks;

if ( ! defined( 'ABSPATH' ) ) {
	exit;
}

/**
 * Turns the header box in the editor into a header map, and back.
 *
 * Written as `Name: value`, one per line, because that is what an API's own
 * documentation shows and what somebody will paste in.
 *
 * Both halves are stripped of carriage returns and newlines. A header value
 * carrying one would end that header and start another, which is how an
 * innocuous looking authorisation token turns into a second header the site
 * never intended to send.
 *
 * @since 1.0.0
 */
final class WebhookHeaders {

	/**
	 * Largest number of headers accepted.
	 */
	private const LIMIT = 20;

	/**
	 * Parses a block of `Name: value` lines.
	 *
	 * @param string $raw Text as typed.
	 *
	 * @return array<string, string> Values keyed by header name.
	 */
	public static function parse( string $raw ): array {
		$headers = array();

		foreach ( preg_split( '/[\r\n]+/', $raw ) ?: array() as $line ) {
			$line = trim( (string) $line );

			if ( '' === $line || ! str_contains( $line, ':' ) ) {
				continue;
			}

			list( $name, $value ) = explode( ':', $line, 2 );

			$name  = self::clean_name( $name );
			$value = self::clean_value( $value );

			if ( '' === $name || '' === $value ) {
				continue;
			}

			$headers[ $name ] = $value;

			if ( count( $headers ) >= self::LIMIT ) {
				break;
			}
		}

		return $headers;
	}

	/**
	 * Renders a header map back into the text the editor shows.
	 *
	 * @param array<string, string> $headers Values keyed by header name.
	 */
	public static function format( array $headers ): string {
		$lines = array();

		foreach ( $headers as $name => $value ) {
			$lines[] = $name . ': ' . $value;
		}

		return implode( "\n", $lines );
	}

	/**
	 * Cleans a header name.
	 *
	 * @param string $name Raw name.
	 *
	 * @return string The name, or an empty string when it is not usable.
	 */
	private static function clean_name( string $name ): string {
		$name = trim( $name );

		// RFC 9110 token characters. Anything else is not a header name.
		return 1 === preg_match( '/^[A-Za-z0-9!#$%&\'*+.^_`|~-]+$/', $name ) ? $name : '';
	}

	/**
	 * Cleans a header value.
	 *
	 * @param string $value Raw value.
	 */
	private static function clean_value( string $value ): string {
		return trim( str_replace( array( "\r", "\n", "\0" ), '', $value ) );
	}
}