SearchExactMatchRescorer.php

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<?php
class SearchExactMatchRescorer {
    public function rescore( $search, $namespaces, $srchres, $limit ) {
        // Pick namespace (based on PrefixSearch::defaultSearchBackend)
        $ns = in_array( NS_MAIN, $namespaces ) ? NS_MAIN : reset( $namespaces );
        $t = Title::newFromText( $search, $ns );
        if ( !$t || !$t->exists() ) {
            // No exact match so just return the search results
            return $srchres;
        }
        $string = $t->getPrefixedText();
        $key = array_search( $string, $srchres );
        if ( $key !== false ) {
            // Exact match was in the results so just move it to the front
            return $this->pullFront( $key, $srchres );
        }
        // Exact match not in the search results so check for some redirect handling cases
        if ( $t->isRedirect() ) {
            $target = $this->getRedirectTarget( $t );
            $key = array_search( $target, $srchres );
            if ( $key !== false ) {
                // Exact match is a redirect to one of the returned matches so pull the
                // returned match to the front.  This might look odd but the alternative
                // is to put the redirect in front and drop the match.  The name of the
                // found match is often more descriptive/better formed than the name of
                // the redirect AND by definition they share a prefix.  Hopefully this
                // choice is less confusing and more helpful.  But it might not be.  But
                // it is the choice we're going with for now.
                return $this->pullFront( $key, $srchres );
            }
            $redirectTargetsToRedirect = $this->redirectTargetsToRedirect( $srchres );
            if ( isset( $redirectTargetsToRedirect[$target] ) ) {
                // The exact match and something in the results list are both redirects
                // to the same thing!  In this case we'll pull the returned match to the
                // top following the same logic above.  Again, it might not be a perfect
                // choice but it'll do.
                return $this->pullFront( $redirectTargetsToRedirect[$target], $srchres );
            }
        } else {
            $redirectTargetsToRedirect = $this->redirectTargetsToRedirect( $srchres );
            if ( isset( $redirectTargetsToRedirect[$string] ) ) {
                // The exact match is the target of a redirect already in the results list so remove
                // the redirect from the results list and push the exact match to the front
                array_splice( $srchres, $redirectTargetsToRedirect[$string], 1 );
                array_unshift( $srchres, $string );
                return $srchres;
            }
        }

        // Exact match is totally unique from the other results so just add it to the front
        array_unshift( $srchres, $string );
        // And roll one off the end if the results are too long
        if ( count( $srchres ) > $limit ) {
            array_pop( $srchres );
        }
        return $srchres;
    }

    private function redirectTargetsToRedirect( array $titles ) {
        $result = [];
        foreach ( $titles as $key => $titleText ) {
            $title = Title::newFromText( $titleText );
            if ( !$title || !$title->isRedirect() ) {
                continue;
            }
            $target = $this->getRedirectTarget( $title );
            if ( !$target ) {
                continue;
            }
            $result[$target] = $key;
        }
        return $result;
    }

    private function pullFront( $key, array $array ) {
        $cut = array_splice( $array, $key, 1 );
        array_unshift( $array, $cut[0] );
        return $array;
    }

    private function getRedirectTarget( $title ) {
        $page = WikiPage::factory( $title );
        if ( !$page->exists() ) {
            return null;
        }
        $redir = $page->getRedirectTarget();
        return $redir ? $redir->getPrefixedText() : null;
    }
}