"""Undo/redo as a stack of reversible commands.

Commands own the DOM mutation in both directions. Nothing here touches Tk: the view is
refreshed through a callback that main registers at startup, which also keeps the
import graph free of cycles (sax_file and wiresheet both push commands here).
"""

import app_state
import palette
import schema
from sax_dom import remove_prop, restore_children, set_prop_value, update_meta_property

_undo_stack = []
_redo_stack = []
_saved_depth = 0        # len(_undo_stack) as of the last save
_refresh_view = None


def set_refresh_callback(callback):
    """Registers how the view should be rebuilt after an undo or redo."""
    global _refresh_view
    _refresh_view = callback


def _refresh():
    if _refresh_view is not None:
        _refresh_view()

    # Undoing back to the last saved state should clear the dirty marker, not keep it lit.
    if len(_undo_stack) == _saved_depth:
        app_state.mark_clean()
    else:
        app_state.mark_dirty()


def push(command):
    """Records an already-applied command. Any redo history becomes unreachable."""
    _undo_stack.append(command)
    _redo_stack.clear()


def can_undo():
    return bool(_undo_stack)


def can_redo():
    return bool(_redo_stack)


def undo():
    if not _undo_stack:
        return None
    command = _undo_stack.pop()
    command.undo()
    _redo_stack.append(command)
    _refresh()
    return command.label


def redo():
    if not _redo_stack:
        return None
    command = _redo_stack.pop()
    command.redo()
    _undo_stack.append(command)
    _refresh()
    return command.label


def mark_saved():
    """Pins the current stack depth as the on-disk state."""
    global _saved_depth
    _saved_depth = len(_undo_stack)


def reset():
    """Drops all history, for when a different file is loaded."""
    global _saved_depth
    _undo_stack.clear()
    _redo_stack.clear()
    _saved_depth = 0


def reload_schema_registry():
    """Recompiles the slot registry after the <schema> block changed.

    A failure is swallowed: undo and redo only ever land on a state that resolved once
    already, so a missing manifest here means Sedona home moved underneath the session,
    which the next action reports in its own words.
    """
    palette.invalidate()
    try:
        schema.load_schema_kits_and_manifests()
    except schema.MissingManifestError:
        pass


class SchemaBlockCommand:
    """A change to the file's <schema> block, held as a before/after snapshot.

    Kit entries decide which manifest describes which type, so the slot registry is
    recompiled in both directions — a repinned kit can change a component's slots.
    """

    def __init__(self, schema_element, before, after, label="update kits"):
        # before/after: snapshots from sax_dom.snapshot_children
        self.schema_element = schema_element
        self.before = before
        self.after = after
        self.label = label

    def undo(self):
        restore_children(self.schema_element, self.before)
        reload_schema_registry()

    def redo(self):
        restore_children(self.schema_element, self.after)
        reload_schema_registry()


class MetaMoveCommand:
    """One or many components changing position, i.e. their packed meta x/y."""

    def __init__(self, changes, label="move"):
        # changes: list of (element, old_meta_val, new_x, new_y)
        self.changes = changes
        self.label = label

    def undo(self):
        for element, old_val, _, _ in self.changes:
            meta_prop = element.find("prop[@name='meta']")
            if meta_prop is not None and old_val is not None:
                meta_prop.set("val", old_val)

    def redo(self):
        for element, old_val, new_x, new_y in self.changes:
            update_meta_property(element, old_val, new_x, new_y)


class SlotValueCommand:
    """One Save from the Properties dialog: every slot it changed, as one undoable step.

    A change is recorded as the <prop>'s value before and after, with None standing for
    "the file had no such prop". Undoing back to None removes the prop again rather than
    writing the default out, so a component that only ever carried the props the file
    shipped with still carries exactly those.
    """

    def __init__(self, changes, label="edit properties"):
        # changes: list of (element, prop_name, old_val_or_None, new_val_or_None)
        self.changes = changes
        self.label = label

    def _apply(self, value_index):
        for change in self.changes:
            element, prop_name = change[0], change[1]
            value = change[value_index]
            if value is None:
                remove_prop(element, prop_name)
            else:
                set_prop_value(element, prop_name, value)

    def undo(self):
        self._apply(2)

    def redo(self):
        self._apply(3)


class AddComponentCommand:
    """Placing a component.

    Nothing here touches <schema>. The kit a placement needs is declared when the file is
    saved, from the component types actually in the DOM, so undoing a placement takes its
    kit out of that reckoning without this command having to unwind anything.
    """

    def __init__(self, parent, index, element, label="add"):
        self.parent = parent
        self.index = index
        self.element = element
        self.label = label

    def undo(self):
        if self.element in list(self.parent):
            self.parent.remove(self.element)

    def redo(self):
        if self.element not in list(self.parent):
            self.parent.insert(self.index, self.element)


class AddLinkCommand:
    """Adding a single link to the <links> section."""

    def __init__(self, links_parent, link_element, label="add link"):
        self.links_parent = links_parent
        self.link_element = link_element
        self.label = label

    def undo(self):
        if self.link_element in list(self.links_parent):
            self.links_parent.remove(self.link_element)

    def redo(self):
        if self.link_element not in list(self.links_parent):
            self.links_parent.append(self.link_element)


class DeleteLinkCommand:
    """Removing a single link from the <links> section."""

    def __init__(self, links_parent, index, link_element, label="delete link"):
        self.links_parent = links_parent
        self.index = index
        self.link_element = link_element
        self.label = label

    def undo(self):
        if self.link_element not in list(self.links_parent):
            self.links_parent.insert(self.index, self.link_element)

    def redo(self):
        if self.link_element in list(self.links_parent):
            self.links_parent.remove(self.link_element)


class DeleteComponentCommand:
    """A cascading delete: the component subtree plus every link that referenced it."""

    def __init__(self, parent, index, element, link_records, label="delete"):
        # link_records: list of (links_parent, index, link_element)
        self.parent = parent
        self.index = index
        self.element = element
        self.link_records = link_records
        self.label = label

    def undo(self):
        self.parent.insert(self.index, self.element)
        # Ascending order so each link lands back on its original index.
        for links_parent, index, link in sorted(self.link_records, key=lambda r: r[1]):
            links_parent.insert(index, link)

    def redo(self):
        for links_parent, _, link in self.link_records:
            if link in list(links_parent):
                links_parent.remove(link)
        if self.element in list(self.parent):
            self.parent.remove(self.element)


class RenameComponentCommand:
    """A rename, plus every link whose path ran through the component's old name."""

    def __init__(self, element, old_name, new_name, link_changes, label="rename"):
        # link_changes: list of (link_element, attr, old_value, new_value)
        self.element = element
        self.old_name = old_name
        self.new_name = new_name
        self.link_changes = link_changes
        self.label = label

    def undo(self):
        self.element.set("name", self.old_name)
        for link, attr, old_value, _ in self.link_changes:
            link.set(attr, old_value)

    def redo(self):
        self.element.set("name", self.new_name)
        for link, attr, _, new_value in self.link_changes:
            link.set(attr, new_value)