resolve_partial(partial: "EditablePartial[T]") -> T:
    """
    Recursively resolves a collection of Partials into whatever type they are
    """
    if isinstance(partial, EditablePartial):
        partial.args = resolve_partial(partial.args)
        partial.kwargs = resolve_partial(partial.kwargs)
        return partial()
    elif isinstance(partial, list):
        return [resolve_partial(x) for x in partial]
    elif isinstance(partial, dict):
        return {key: resolve_partial(x) for key, x in partial.items()}
    else:
        return partial


def to_railroad(
    element: pyparsing.ParserElement,
    diagram_kwargs: typing.Optional[dict] = None,
    vertical: int = 3,
    show_results_names: bool = False,
    show_groups: bool = False,
) -> List[NamedDiagram]:
    """
    Convert a pyparsing element tree into a list of diagrams. This is the recommended entrypoint to diagram
    creation if you want to access the Railroad tree before it is converted to HTML
    :param element: base element of the parser being diagrammed
    :param diagram_kwargs: kwargs to pass to the Diagram() constructor
    :param vertical: (optional) - int - limit at which number of alternatives should be
       shown vertically instead of horizontally
    :param show_results_names - bool to indicate whether results name annotations should be
       included in the diagram
    :param show_groups - bool to indicate whether groups should be highlighted with an unlabeled
       surrounding box
    """
    # Convert the whole tree underneath the root
    lookup = ConverterState(diagram_kwargs=diagram_kwargs or {})
    _to_diagram_element(
        element,
        lookup=lookup,
        parent=None,
        vertical=vertical,
        show_results_names=show_results_names,
        show_groups=show_groups,
    )

    root_id = id(element)
    # Convert the root if it hasn't been already
    if root_id in lookup:
        if not element.customName:
            lookup[root_id].name = ""
        lookup[root_id].mark_for_extraction(root_id, lookup, force=True)

    # Now that we're finished, we can convert from intermediate structures into Railroad elements
    diags = list(lookup.diagrams.values())
    if len(diags) > 1:
        # collapse out duplicate diags with the same name
        seen = set()
        deduped_diags = []
        for d in diags:
            # don't extract SkipTo elements, they are uninformative as subdiagrams
            if d.name == "...":
                continue
            if d.name is not None and d.name not in seen:
                seen.add(d.name)
                deduped_diags.append(d)
        resolved = [resolve_partial(partial) for partial in deduped_diags]
    else:
        # special case - if just one diagram, always display it, even if
        # it has no name
        resolved = [resolve_partial(partial) for partial in diags]
    return sorted(resolved, key=lambda diag: diag.index)


def _should_vertical(
    specification: int, exprs: Iterable[pyparsing.ParserElement]
) -> bool:
    """
    Returns true if we should return a vertical list of elements
    """
    if specification is None:
        return False
    else:
        return len(_visible_exprs(exprs)) >= specification


class ElementState:
    """
    State recorded for an individual pyparsing Element
    """

    # Note: this should be a dataclass, but we have to support Python 3.5
    def __init__(
        self,
        element: pyparsing.ParserElement,
        converted: EditablePartial,
        parent: EditablePartial,
        number: int,
        name: str = None,
        parent_index: typing.Optional[int] = None,
    ):
        #: The pyparsing element that this represents
        self.element: pyparsing.ParserElement = element
        #: The name of the element
        self.name: typing.Optional[str] = name
        #: The output Railroad element in an unconverted state
        self.converted: EditablePartial = converted
        #: The parent Railroad element, which we store so that we can extract this if it's duplicated
        self.parent: EditablePartial = parent
        #: The order in which we found this element, used for sorting diagrams if this is extracted into a diagram
        self.number: int = number
        #: The index of this inside its parent
        self.parent_index: typing.Optional[int] = parent_index
        #: If true, we should extract this out into a subdiagram
        self.extract: bool = False
        #: If true, all of this element's children have been filled out
        self.complete: bool = False

    def mark_for_extraction(
        self, el_id: int, state: "ConverterState", name: str = None, force: bool = False
    ):
        """
        Called when this instance has been seen twice, and thus should eventually be extracted into a sub-diagram
        :param el_id: id of the element
        :param state: element/diagram state tracker
        :param name: name to use for this element's text
        :param force: If true, force extraction now, regardless of the state of this. Only useful for extracting the
        root element when we know we're finished
        """
        self.extract = True

        # Set the name
        if not self.name:
            if name:
                # Allow forcing a custom name
                self.name = name
            elif self.element.customName:
                self.name = self.element.customName
            else:
                self.name = ""

        # Just because this is marked for extraction doesn't mean we can do it yet. We may have to wait for children
        # to be added
        # Also, if this is just a string literal etc, don't bother extracting it
        if force or (self.complete and _worth_extracting(self.element)):
            state.extract_into_diagram(el_id)


class ConverterState:
    """
    Stores some state that persists between recursions into the element tree
    """

    def __init__(self, diagram_kwargs: typing.Optional[dict] = None):
        #: A dictionary mapping ParserElements to state relating to them
        self._element_diagram_states: Dict[int, ElementState] = {}
        #: A dictionary mapping ParserElement IDs to subdiagrams generated from them
        self.diagrams: Dict[int, EditablePartial[NamedDiagram]] = {}
        #: The index of the next unnamed element
        self.unnamed_index: int = 1
        #: The index of the next element. This is used for sorting
        self.index: int = 0
        #: Shared kwargs that are used to customize the construction of diagrams
        self.diagram_kwargs: dict = diagram_kwargs or {}
        self.extracted_diagram_names: Set[str] = set()

    def __setitem__(self, key: int, value: ElementState):
        self._element_diagram_states[key] = value

    def __getitem__(self, key: int) -> ElementState:
        return self._element_diagram_states[key]

    def __delitem__(self, key: int):
        del self._element_diagram_states[key]

    def __contains__(self, key: int):
        return key in self._element_diagram_states

    def generate_unnamed(self) -> int:
        """
        Generate a number used in the name of an otherwise unnamed diagram
        """
        self.unnamed_index += 1
        return self.unnamed_index

    def generate_index(self) -> int:
        """
        Generate a number used to index a diagram
        """
        self.index += 1
        return self.index

    def extract_into_diagram(self, el_id: int):
        """
        Used when we encounter the same token twice in the same tree. When this
        happens, we replace all instances of that token with a terminal, and
        create a new subdiagram for the token
        """
        position = self[el_id]

        # Replace the original definition of this element with a regular block
        if position.parent:
            ret = EditablePartial.from_call(railroad.NonTerminal, text=position.name)
            if "item" in position.parent.kwargs:
                position.parent.kwargs["item"] = ret
            elif "items" in position.parent.kwargs:
                position.parent.kwargs["items"][position.parent_index] = ret

        # If the element we're extracting is a group, skip to its content but keep the title
        if position.converted.func == railroad.Group:
            content = position.converted.kwargs["item"]
        else:
            content = position.converted

        self.diagrams[el_id] = EditablePartial.from_call(
            NamedDiagram,
            name=position.name,
            diagram=EditablePartial.from_call(
                railroad.Diagram, content, **self.diagram_kwargs
            ),
            index=position.number,
        )

        del self[el_id]


def _worth_extracting(element: pyparsing.ParserElement) -> bool:
    """
    Returns true if this element is worth having its own sub-diagram. Simply, if any of its children
    themselves have children, then its complex enough to extract
    """
    children = element.recurse()
    return any(child.recurse() for child in children)


def _apply_diagram_item_enhancements(fn):
    """
    decorator to ensure enhancements to a diagram item (such as results name annotations)
    get applied on return from _to_diagram_element (we do this since there are several
    returns in _to_diagram_element)
    """

    def _inner(
        element: pyparsing.ParserElement,
        parent: typing.Optional[EditablePartial],
        lookup: ConverterState = None,
        vertical: int = None,
        index: int = 0,
        name_hint: str = None,
        show_results_names: bool = False,
        show_groups: bool = False,
    ) -> typing.Optional[EditablePartial]:

        ret = fn(
            element,
            parent,
            lookup,
            vertical,
            index,
            name_hint,
            show_results_names,
            show_groups,
        )

        # apply annotation for results name, if present
        if show_results_names and ret is not None:
            element_results_name = element.resultsName
            if element_results_name:
                # add "*" to indicate if this is a "list all results" name
                element_results_name += "" if element.modalResults else "*"
                ret = EditablePartial.from_call(
                    railroad.Group, item=ret, label=element_results_name
                )

        return ret

    return _inner


def _visible_exprs(exprs: Iterable[pyparsing.ParserElement]):
    non_diagramming_exprs = (
        pyparsing.ParseElementEnhance,
        pyparsing.PositionToken,
        pyparsing.And._ErrorStop,
    )
    return [
        e
        for e in exprs
        if not (e.customName or e.resultsName or isinstance(e, non_diagramming_exprs))
    ]


@_apply_diagram_item_enhancements
def _to_diagram_element(
    element: pyparsing.ParserElement,
    parent: typing.Optional[EditablePartial],
    lookup: ConverterState = None,
    vertical: int = None,
    index: int = 0,
    name_hint: str = None,
    show_results_names: bool = False,
    show_groups: bool = False,
) -> typing.Optional[EditablePartial]:
    """
    Recursively converts a PyParsing Element to a railroad Element
    :param lookup: The shared converter state that keeps track of useful things
    :param index: The index of this element within the parent
    :param parent: The parent of this element in the output tree
    :param vertical: Controls at what point we make a list of elements vertical. If this is an integer (the default),
    it sets the threshold of the number of items before we go vertical. If True, always go vertical, if False, never
    do so
    :param name_hint: If provided, this will override the generated name
    :param show_results_names: bool flag indicating whether to add annotations for results names
    :returns: The converted version of the input element, but as a Partial that hasn't yet been constructed
    :param show_groups: bool flag indicating whether to show groups using bounding box
    """
    exprs = element.recurse()
    name = name_hint or element.customName or element.__class__.__name__

    # Python's id() is used to provide a unique identifier for elements
    el_id = id(element)

    element_results_name = element.resultsName

    # Here we basically bypass processing certain wrapper elements if they contribute nothing to the diagram
    if not element.customName:
        if isinstance(
            element,
            (
                # pyparsing.TokenConverter,
                # pyparsing.Forward,
                pyparsing.Located,
            ),
        ):
            # However, if this element has a useful custom name, and its child does not, we can pass it on to the child
            if exprs:
                if not exprs[0].customName:
                    propagated_name = name
                else:
                    propagated_name = None

                return _to_diagram_element(
                    element.expr,
                    parent=parent,
                    lookup=lookup,
                    vertical=vertical,
                    index=index,
                    name_hint=propagated_name,
                    show_results_names=show_results_names,
                    show_groups=show_groups,
                )

    # If the element isn't worth extracting, we always treat it as the first time we say it
    if _worth_extracting(element):
        if el_id in lookup:
            # If we've seen this element exactly once before, we are only just now finding out that it's a duplicate,
            # so we have to extract it into a new diagram.
            looked_up = lookup[el_id]
            looked_up.mark_for_extraction(el_id, lookup, name=name_hint)
            ret = EditablePartial.from_call(railroad.NonTerminal, text=looked_up.name)
            return ret

        elif el_id in lookup.diagrams:
            # If we have seen the element at least twice before, and have already extracted it into a subdiagram, we
            # just put in a marker element that refers to the sub-diagram
            ret = EditablePartial.from_call(
                railroad.NonTerminal, text=lookup.diagrams[el_id].kwargs["name"]
            )
            return ret

    # Recursively convert child elements
    # Here we find the most relevant Railroad element for matching pyparsing Element
    # We use ``items=[]`` here to hold the place for where the child elements will go once created
    if isinstance(element, pyparsing.And):
        # detect And's created with ``expr*N`` notation - for these use a OneOrMore with a repeat
        # (all will have the same name, and resultsName)
        if not exprs:
            return None
        if len(set((e.name, e.resultsName) for e in exprs)) == 1:
            ret = EditablePartial.from_call(
                railroad.OneOrMore, item="", repeat=str(len(exprs))
            )
        elif _should_vertical(vertical, exprs):
            ret = EditablePartial.from_call(railroad.Stack, items=[])
        else:
            ret = EditablePartial.from_call(railroad.Sequence, items=[])
    elif isinstance(element, (pyparsing.Or, pyparsing.MatchFirst)):
        if not exprs:
            return None
        if _should_vertical(vertical, exprs):
            ret = EditablePartial.from_call(railroad.Choice, 0, items=[])
        else:
            ret = EditablePartial.from_call(railroad.HorizontalChoice, items=[])
    elif isinstance(element, pyparsing.Each):
        if not exprs:
            return None
        ret = EditablePartial.from_call(EachItem, items=[])
    elif isinstance(element, pyparsing.NotAny):
        ret = EditablePartial.from_call(AnnotatedItem, label="NOT", item="")
    elif isinstance(element, pyparsing.FollowedBy):
        ret = EditablePartial.from_call(AnnotatedItem, label="LOOKAHEAD", item="")
    elif isinstance(element, pyparsing.PrecededBy):
        ret = EditablePartial.from_call(AnnotatedItem, label="LOOKBEHIND", item="")
    elif isinstance(element, pyparsing.Group):
        if show_groups:
            ret = EditablePartial.from_call(AnnotatedItem, label="", item="")
        else:
            ret = EditablePartial.from_call(railroad.Group, label="", item="")
    elif isinstance(element, pyparsing.TokenConverter):
        ret = EditablePartial.from_call(
            AnnotatedItem, label=type(element).__name__.lower(), item=""
        )
    elif isinstance(element, pyparsing.Opt):
        ret = EditablePartial.from_call(railroad.Optional, item="")
    elif isinstance(element, pyparsing.OneOrMore):
        ret = EditablePartial.from_call(railroad.OneOrMore, item="")
    elif isinstance(element, pyparsing.ZeroOrMore):
        ret = EditablePartial.from_call(railroad.ZeroOrMore, item="")
    elif isinstance(element, pyparsing.Group):
        ret = EditablePartial.from_call(
            railroad.Group, item=None, label=element_results_name
        )
    elif isinstance(element, pyparsing.Empty) and not element.customName:
        # Skip unnamed "Empty" elements
        ret = None
    elif len(exprs) > 1:
        ret = EditablePartial.from_call(railroad.Sequence, items=[])
    elif len(exprs) > 0 and not element_results_name:
        ret = EditablePartial.from_call(railroad.Group, item="", label=name)
    else:
        terminal = EditablePartial.from_call(railroad.Terminal, element.defaultName)
        ret = terminal

    if ret is None:
        return

    # Indicate this element's position in the tree so we can extract it if necessary
    lookup[el_id] = ElementState(
        element=element,
        converted=ret,
        parent=parent,
        parent_index=index,
        number=lookup.generate_index(),
    )
    if element.customName:
        lookup[el_id].mark_for_extraction(el_id, lookup, element.customName)

    i = 0
    for expr in exprs:
        # Add a placeholder index in case we have to extract the child before we even add it to the parent
        if "items" in ret.kwargs:
            ret.kwargs["items"].insert(i, None)

        item = _to_diagram_element(
            expr,
            parent=ret,
            lookup=lookup,
            vertical=vertical,
            index=i,
            show_results_names=show_results_names,
            show_groups=show_groups,
        )

        # Some elements don't need to be shown in the diagram
        if item is not None:
            if "item" in ret.kwargs:
                ret.kwargs["item"] = item
            elif "items" in ret.kwargs:
                # If we've already extracted the child, don't touch this index, since it's occupied by a nonterminal
                ret.kwargs["items"][i] = item
                i += 1
        elif "items" in ret.kwargs:
            # If we're supposed to skip this element, remove it from the parent
            del ret.kwargs["items"][i]

    # If all this items children are none, skip this item
    if ret and (
        ("items" in ret.kwargs and len(ret.kwargs["items"]) == 0)
        or ("item" in ret.kwargs and ret.kwargs["item"] is None)
    ):
        ret = EditablePartial.from_call(railroad.Terminal, name)

    # Mark this element as "complete", ie it has all of its children
    if el_id in lookup:
        lookup[el_id].complete = True

    if el_id in lookup and lookup[el_id].extract and lookup[el_id].complete:
        lookup.extract_into_diagram(el_id)
        if ret is not None:
            ret = EditablePartial.from_call(
                railroad.NonTerminal, text=lookup.diagrams[el_id].kwargs["name"]
            )

    return ret
