class Page:
    """
    Misago page utility

    Allows for adding custom views to "sectioned" pages like
    User Control Panel, Users List or Threads Lists
    """

    def __init__(self, name):
        self._finalized = False
        self.name = name
        self._unsorted_list = []
        self._sorted_list = []

    def assert_is_finalized(self):
        if not self._finalized:
            self._finalized = True
            self._finalize()

    def _finalize(self):
        iterations = 0
        while self._unsorted_list:
            iterations += 1
            if iterations > 512:
                message = "%s page hierarchy is invalid or too complex  to resolve. Sections left: %s"
                raise ValueError(message % self._unsorted_list)

            for index, section in enumerate(self._unsorted_list):
                if section["after"]:
                    section_added = self._insert_section(
                        section, after=section["after"]
                    )
                elif section["before"]:
                    section_added = self._insert_section(
                        section, before=section["before"]
                    )
                else:
                    section_added = self._insert_section(section)

                if section_added:
                    del self._unsorted_list[index]
                    break

    def _insert_section(self, inserted_section, after=None, before=None):
        if after:
            new_sorted_list = []
            for section in self._sorted_list:
                new_sorted_list.append(section)
                if section["link"] == after:
                    new_sorted_list.append(inserted_section)
                    self._sorted_list = new_sorted_list
                    return True
            else:
                return False
        elif before:
            new_sorted_list = []
            for section in self._sorted_list:
                if section["link"] == before:
                    new_sorted_list.append(inserted_section)
                    new_sorted_list.append(section)
                    self._sorted_list = new_sorted_list
                    return True
                else:
                    new_sorted_list.append(section)
            else:
                return False
        else:
            self._sorted_list.append(inserted_section)
            return True

    def add_section(
        self,
        link,
        after=None,
        before=None,
        visible_if=None,
        get_metadata=None,
        **kwargs
    ):
        if self._finalized:
            message = (
                "%s page was initialized already and no longer accepts new sections"
            )
            raise RuntimeError(message % self.name)

        if after and before:
            raise ValueError("after and before arguments are exclusive")

        kwargs.update(
            {
                "link": link,
                "after": after,
                "before": before,
                "visible_if": visible_if,
                "get_metadata": get_metadata,
            }
        )

        self._unsorted_list.append(kwargs)

    def _active_link_name(self, request):
        namespace = request.resolver_match.namespace
        url_name = request.resolver_match.url_name

        if namespace:
            active_link = "%s:%s" % (namespace, url_name)
        else:
            active_link = url_name
        return active_link

    def get_sections(self, request, *args):
        self.assert_is_finalized()
        active_link = self._active_link_name(request)
        visible_sections = []

        for section_definition in self._sorted_list:
            section = section_definition.copy()

            is_visible = True
            if section["visible_if"]:
                is_visible = section["visible_if"](request, *args)

            if is_visible:
                if section["get_metadata"]:
                    section["metadata"] = section["get_metadata"](request, *args)
                section["is_active"] = active_link.startswith(section["link"])
                visible_sections.append(section)
        return visible_sections

    def get_default_link(self):
        self.assert_is_finalized()
        return self._sorted_list[0]["link"]