Register a # hash tag parser

The example will use the SMW::Parser::AfterLinksProcessingComplete to process hash tags (e.g. #foo #foo_bar etc.) to add value annotations for the identified tag and the assigned property.

use SMW\Parser\AnnotationProcessor;

class HashTagParser {

    private $subject;
    private $property;
    private $annotationProcessor;
    private $showErrors = false;

    public function __construct( AnnotationProcessor $annotationProcessor ) {
        $this->annotationProcessor = $annotationProcessor;
    }

    public function setShowErrors( $showErrors ) {
        $this->showErrors = $showErrors;
    }

    public function parse( $text, $property ) {

        $semanticData = $this->annotationProcessor->getSemanticData();

        $this->property = $property;
        $this->subject = $semanticData->getSubject();

        // Twitter regex (include underscore and not start with a number):
        // (?<=^|\P{L})(#\b\p{L}[\p{L}\d_]+)

        // Allow to start with a number
        // (?<!&|\S)#(\w+)

        return preg_replace_callback( '/(?<!&|\S)#(\w+)/u', [ $this, 'process' ], $text );
    }

    public function process( array $matches ) {

        $dataValue = $this->annotationProcessor->newDataValueByText(
            $this->property,
            $matches[1],
            $matches[0],
            $this->subject
        );

        if ( $this->annotationProcessor->canAnnotate() ) {
            $this->annotationProcessor->getSemanticData()->addDataValue( $dataValue );
        }

        // If necessary add an error text
        if ( ( $this->showErrors && !$dataValue->isValid() ) ) {
            // Encode `:` to avoid a comment block and instead of the nowiki tag
            // use &#58; as placeholder
            $result = str_replace( ':', '&#58;', $result ) . $dataValue->getErrorText();
        } else {
            $result = $dataValue->getShortWikitext( true );
        }

        return $result;
    }

}

use SMW\Parser\AnnotationProcessor;

\Hooks::register( 'SMW::Parser::AfterLinksProcessingComplete', function( &$text, AnnotationProcessor $annotationProcessor ) {

    $hashTagParser = new HashTagParser(
        $annotationProcessor
    );

    // Could be set on a context or via a configuration setting
    $property = 'Has keyword';

    $text = $hashTagParser->parse( $text, $property );

    return true;
} );