class Utilities {

    func withQuickFolder( action : Action, folder : File ) = action.split().apply {
        onDemand( ::buildFolderMenu.curry( folder ) )
    }

    // A split menu. Click to open the folder, Pull down to choose from the files/subfolders.
    func quickFolder( label : String, folder : File ) = SplitMenu( label, ::openFolder.curry(folder) )
        .onDemand( ::buildFolderMenu.curry( folder ) )

    // Creates Features for each of the folder's files/subfolders. The features open the file/subfolder in a new tab.
    func buildFolderMenu( folder : File ) = mapFilesToOpenFeatures( folder.filesAndFolders() )
    func buildFolderMenuFromContext( context : Context ) = mapFilesToOpenFeatures( (context.value as File).filesAndFolders() )

    func openFolder( folder : File ) {
        openContext( Context( Context.FOLDER, folder ) )
    }

    func mapFilesToOpenFeatures( files : List<File> ) : List<Feature> {
        val result = listOf<Feature>()
        for ( file in files ) {
            result.add(
                Action( file.nameOrSlash(), HelperFunctions::openFile.curry( file ) )
            )
        }
        return result
    }

    /**
     * Creates a StringProperty asking for file extensions.
     * Convert the value to a list using `extensionsStringToList`.
     */
    func extensionsProperty( defaultValue : String ) = stringProperty( "File Extensions", defaultValue )
        .rows( 1 ).columns( 0 )
        .description( """File extensions separated by whitespace.
The word NONE will match files without an extensions.

Leave blank to search all files.""" )

    /**
     * Takes the value from `str` and converts it to a List<String>.
     * An empty list implies search all files.
     * The special value "NONE" is converted to "".
     */
    func extensionsStringToList( str : String ) : List<String> {
        if ( str.isEmpty() ) {
            return listOf<String>()
        } else {
            val result = str.split( "\\s+" ).toList<String>()
            
            if (result.contains("NONE")) {
                result.remove( "NONE" )
                result.add("")
            }
            return result
        }
    }
}