<?php

declare(strict_types=1);

namespace LinkCheckup\Features\Checking;

use function ltrim;
use function preg_match;
use function preg_replace;
use function str_starts_with;
use function strrpos;
use function strstr;
use function substr;

final class LocationResolver {

	private const ABSOLUTE_PATTERN  = '#^https?://#i';
	private const ORIGIN_PATTERN    = '#^([^:/?\#]+://[^/?\#]*).*$#s';
	private const PROTOCOL_RELATIVE = '//';
	private const PATH_SEPARATOR    = '/';
	private const SCHEME_SEPARATOR  = ':';

	public function resolve( string $base_url, string $location ): string {
		if ( 1 === preg_match( self::ABSOLUTE_PATTERN, $location ) ) {
			return $location;
		}

		if ( str_starts_with( $location, self::PROTOCOL_RELATIVE ) ) {
			$scheme = (string) strstr(
				$base_url,
				self::SCHEME_SEPARATOR,
				true
			);

			return $scheme . self::SCHEME_SEPARATOR . $location;
		}

		if ( str_starts_with( $location, self::PATH_SEPARATOR ) ) {
			return $this->origin_of( $base_url ) . $location;
		}

		return $this->origin_of( $base_url )
			. $this->directory_of( $base_url )
			. $location;
	}

	private function origin_of( string $base_url ): string {
		return (string) preg_replace( self::ORIGIN_PATTERN, '$1', $base_url );
	}

	private function directory_of( string $base_url ): string {
		$path           = (string) wp_parse_url( $base_url, PHP_URL_PATH );
		$last_separator = (int) strrpos( $path, self::PATH_SEPARATOR );
		$directory      = substr( $path, 0, $last_separator + 1 );

		return self::PATH_SEPARATOR
			. ltrim( $directory, self::PATH_SEPARATOR );
	}
}