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<?php

namespace GuzzleHttp\Psr7;

use Psr\Http\Message\UriInterface;

/**

 * Resolves a URI reference in the context of a base URI and the opposite way.

 *

 * @author Tobias Schultze

 *

 * @link https://tools.ietf.org/html/rfc3986#section-5

 */

final class UriResolver

{

    /**

     * Removes dot segments from a path and returns the new path.

     *

     * @param string $path

     *

     * @return string

     * @link http://tools.ietf.org/html/rfc3986#section-5.2.4

     */

    public static function removeDotSegments($path)

    {

        if ($path === '' || $path === '/') {

            return $path;

        }

        $results = [];

        $segments = explode('/', $path);

        foreach ($segments as $segment) {

            if ($segment === '..') {

                array_pop($results);

            } elseif ($segment !== '.') {

                $results[] = $segment;

            }

        }

        $newPath = implode('/', $results);

        if ($path[0] === '/' && (!isset($newPath[0]) || $newPath[0] !== '/')) {

            // Re-add the leading slash if necessary for cases like "/.."

            $newPath = '/' . $newPath;

        } elseif ($newPath !== '' && ($segment === '.' || $segment === '..')) {

            // Add the trailing slash if necessary

            // If newPath is not empty, then $segment must be set and is the last segment from the foreach

            $newPath .= '/';

        }

        return $newPath;

    }

    /**

     * Converts the relative URI into a new URI that is resolved against the base URI.

     *

     * @param UriInterface $base Base URI

     * @param UriInterface $rel  Relative URI

     *

     * @return UriInterface

     * @link http://tools.ietf.org/html/rfc3986#section-5.2

     */

    public static function resolve(UriInterface $base, UriInterface $rel)

    {

        if ((string) $rel === '') {

            // we can simply return the same base URI instance for this same-document reference

            return $base;

        }

        if ($rel->getScheme() != '') {

            return $rel->withPath(self::removeDotSegments($rel->getPath()));

        }

        if ($rel->getAuthority() != '') {

            $targetAuthority = $rel->getAuthority();

            $targetPath = self::removeDotSegments($rel->getPath());

            $targetQuery = $rel->getQuery();

        } else {

            $targetAuthority = $base->getAuthority();

            if ($rel->getPath() === '') {

                $targetPath = $base->getPath();

                $targetQuery = $rel->getQuery() != '' ? $rel->getQuery() : $base->getQuery();

            } else {

                if ($rel->getPath()[0] === '/') {

                    $targetPath = $rel->getPath();

                } else {

                    if ($targetAuthority != '' && $base->getPath() === '') {

                        $targetPath = '/' . $rel->getPath();

                    } else {

                        $lastSlashPos = strrpos($base->getPath(), '/');

                        if ($lastSlashPos === false) {

                            $targetPath = $rel->getPath();

                        } else {

                            $targetPath = substr($base->getPath(), 0, $lastSlashPos + 1) . $rel->getPath();

                        }

                    }

                }

                $targetPath = self::removeDotSegments($targetPath);

                $targetQuery = $rel->getQuery();

            }

        }

        return new Uri(Uri::composeComponents(

            $base->getScheme(),

            $targetAuthority,

            $targetPath,

            $targetQuery,

            $rel->getFragment()

        ));

    }

    /**

     * Returns the target URI as a relative reference from the base URI.

     *

     * This method is the counterpart to resolve():

     *

     *    (string) $target === (string) UriResolver::resolve($base, UriResolver::relativize($base, $target))

     *

     * One use-case is to use the current request URI as base URI and then generate relative links in your documents

     * to reduce the document size or offer self-contained downloadable document archives.

     *

     *    $base = new Uri('http://example.com/a/b/');

     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/b/c'));  // prints 'c'.

     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/x/y'));  // prints '../x/y'.

     *    echo UriResolver::relativize($base, new Uri('http://example.com/a/b/?q')); // prints '?q'.

     *    echo UriResolver::relativize($base, new Uri('http://example.org/a/b/'));   // prints '//example.org/a/b/'.

     *

     * This method also accepts a target that is already relative and will try to relativize it further. Only a

     * relative-path reference will be returned as-is.

     *

     *    echo UriResolver::relativize($base, new Uri('/a/b/c'));  // prints 'c' as well

     *

     * @param UriInterface $base   Base URI

     * @param UriInterface $target Target URI

     *

     * @return UriInterface The relative URI reference

     */

    public static function relativize(UriInterface $base, UriInterface $target)

    {

        if ($target->getScheme() !== '' &&

            ($base->getScheme() !== $target->getScheme() || $target->getAuthority() === '' && $base->getAuthority() !== '')

        ) {

            return $target;

        }

        if (Uri::isRelativePathReference($target)) {

            // As the target is already highly relative we return it as-is. It would be possible to resolve

            // the target with `$target = self::resolve($base, $target);` and then try make it more relative

            // by removing a duplicate query. But let's not do that automatically.

            return $target;

        }

        if ($target->getAuthority() !== '' && $base->getAuthority() !== $target->getAuthority()) {

            return $target->withScheme('');

        }

        // We must remove the path before removing the authority because if the path starts with two slashes, the URI

        // would turn invalid. And we also cannot set a relative path before removing the authority, as that is also

        // invalid.

        $emptyPathUri = $target->withScheme('')->withPath('')->withUserInfo('')->withPort(null)->withHost('');

        if ($base->getPath() !== $target->getPath()) {

            return $emptyPathUri->withPath(self::getRelativePath($base, $target));

        }

        if ($base->getQuery() === $target->getQuery()) {

            // Only the target fragment is left. And it must be returned even if base and target fragment are the same.

            return $emptyPathUri->withQuery('');

        }

        // If the base URI has a query but the target has none, we cannot return an empty path reference as it would

        // inherit the base query component when resolving.

        if ($target->getQuery() === '') {

            $segments = explode('/', $target->getPath());

            $lastSegment = end($segments);

            return $emptyPathUri->withPath($lastSegment === '' ? './' : $lastSegment);

        }

        return $emptyPathUri;

    }

    private static function getRelativePath(UriInterface $base, UriInterface $target)

    {

        $sourceSegments = explode('/', $base->getPath());

        $targetSegments = explode('/', $target->getPath());

        array_pop($sourceSegments);

        $targetLastSegment = array_pop($targetSegments);

        foreach ($sourceSegments as $i => $segment) {

            if (isset($targetSegments[$i]) && $segment === $targetSegments[$i]) {

                unset($sourceSegments[$i], $targetSegments[$i]);

            } else {

                break;

            }

        }

        $targetSegments[] = $targetLastSegment;

        $relativePath = str_repeat('../', count($sourceSegments)) . implode('/', $targetSegments);

        // A reference to am empty last segment or an empty first sub-segment must be prefixed with "./".

        // This also applies to a segment with a colon character (e.g., "file:colon") that cannot be used

        // as the first segment of a relative-path reference, as it would be mistaken for a scheme name.

        if ('' === $relativePath || false !== strpos(explode('/', $relativePath, 2)[0], ':')) {

            $relativePath = "./$relativePath";

        } elseif ('/' === $relativePath[0]) {

            if ($base->getAuthority() != '' && $base->getPath() === '') {

                // In this case an extra slash is added by resolve() automatically. So we must not add one here.

                $relativePath = ".$relativePath";

            } else {

                $relativePath = "./$relativePath";

            }

        }

        return $relativePath;

    }

    private function __construct()

    {

        // cannot be instantiated

    }

}