from bs4.dammit import EntitySubstitution

class Formatter(EntitySubstitution):
    """Describes a strategy to use when outputting a parse tree to a string.

    Some parts of this strategy come from the distinction between
    HTML4, HTML5, and XML. Others are configurable by the user.

    Formatters are passed in as the `formatter` argument to methods
    like `PageElement.encode`. Most people won't need to think about
    formatters, and most people who need to think about them can pass
    in one of these predefined strings as `formatter` rather than
    making a new Formatter object:

    For HTML documents:
     * 'html' - HTML entity substitution for generic HTML documents. (default)
     * 'html5' - HTML entity substitution for HTML5 documents, as
                 well as some optimizations in the way tags are rendered.
     * 'minimal' - Only make the substitutions necessary to guarantee
                   valid HTML.
     * None - Do not perform any substitution. This will be faster
              but may result in invalid markup.

    For XML documents:
     * 'html' - Entity substitution for XHTML documents.
     * 'minimal' - Only make the substitutions necessary to guarantee
                   valid XML. (default)
     * None - Do not perform any substitution. This will be faster
              but may result in invalid markup.
    """
    # Registries of XML and HTML formatters.
    XML_FORMATTERS = {}
    HTML_FORMATTERS = {}

    HTML = 'html'
    XML = 'xml'

    HTML_DEFAULTS = dict(
        cdata_containing_tags=set(["script", "style"]),
    )

    def _default(self, language, value, kwarg):
        if value is not None:
            return value
        if language == self.XML:
            return set()
        return self.HTML_DEFAULTS[kwarg]

    def __init__(
            self, language=None, entity_substitution=None,
            void_element_close_prefix='/', cdata_containing_tags=None,
            empty_attributes_are_booleans=False, indent=1,
    ):
        r"""Constructor.

        :param language: This should be Formatter.XML if you are formatting
           XML markup and Formatter.HTML if you are formatting HTML markup.

        :param entity_substitution: A function to call to replace special
           characters with XML/HTML entities. For examples, see 
           bs4.dammit.EntitySubstitution.substitute_html and substitute_xml.
        :param void_element_close_prefix: By default, void elements
           are represented as  (XML rules) rather than 
           (HTML rules). To get , pass in the empty string.
        :param cdata_containing_tags: The list of tags that are defined
           as containing CDATA in this dialect. For example, in HTML,