# Copyright 2004-2023 Tom Rothamel <pytom@bishoujo.us>
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

# This file contains code that handles the execution of python code
# contained within the script file. It also handles rolling back the
# game state to some time in the past.

from __future__ import division, absolute_import, with_statement, print_function, unicode_literals
from renpy.compat import PY2, basestring, bchr, bord, chr, open, pystr, range, round, str, tobytes, unicode # *

from typing import Optional

import marshal
import random
import weakref
import re
import sys
import time
import io
import types
import copyreg
import functools

import renpy

# Deleted is a singleton object that's used to represent an object that has
# been deleted from the store.

class StoreDeleted(object):

    def __reduce__(self):
        if PY2:
            return b"deleted"
        else:
            return "deleted"


deleted = StoreDeleted()


# Code that computes reachable objects, which is used to filter
# the rollback list before rollback or serialization.


class SlottedNoRollback(object):
    """
    :doc: norollback class

    Instances of classes inheriting from this class do not participate
    in rollback. The difference between this and :class:`NoRollback` is that
    this class does not have an associated dictionary, hence can be used
    with ``__slots__`` to reduce memory usage.

    Objects reachable through an instance of a NoRollback class only participate
    in rollback if they are reachable through other paths.
    """
    __slots__ = ()


class NoRollback(SlottedNoRollback):
    """
    :doc: norollback class

    Instances of this class, and classes inheriting from this class,
    do not participate in rollback. Objects reachable through an instance
    of a NoRollback class only participate in rollback if they are
    reachable through other paths.
    """

# parents = [ ]

class AlwaysRollback(renpy.revertable.RevertableObject):
    """
    This is a revertable object that always participates in rollback.
    It's used when a revertable object is created by an object that
    doesn't participate in the rollback system.
    """

    def __new__(cls, *args, **kwargs):
        self = super(AlwaysRollback, cls).__new__(cls)

        log = renpy.game.log
        if log is not None:
            del log.mutated[id(self)]

        return self


NOROLLBACK_TYPES = tuple() # type: tuple[type, type, type, type, type]


def reached(obj, reachable, wait):
    """
    @param obj: The object that was reached.

    `reachable`
        A map from id(obj) to int. The int is 1 if the object was reached
        normally, and 0 if it was reached, but inherits from NoRollback.
    """

    if wait:
        wait()

    idobj = id(obj)

    if idobj in reachable:
        return

    reachable[idobj] = obj

    if isinstance(obj, NOROLLBACK_TYPES):
        return

    try:
        nosave = getattr(obj, "nosave", None)

        if nosave is not None:

            nosave = getattr(obj, "noreach", nosave)

            for k, v in vars(obj).items():
                if k not in nosave:
                    reached(v, reachable, wait)

        else:

            # Fields have to be indexed by strings, so no need to check if
            # the filed is reached.
            for v in vars(obj).values():
                reached(v, reachable, wait)

    except Exception:
        pass

    # Below this, we only consider containers with a defined size.
    try:
        if (not len(obj)) or isinstance(obj, basestring):
            return
    except Exception:
        return

    try:
        # Treat as iterable.
        for v in obj.__iter__():
            reached(v, reachable, wait)
    except Exception:
        pass

    try:
        # Treat as dict.
        for v in obj.values():
            reached(v, reachable, wait)
    except Exception:
        pass


def reached_vars(store, reachable, wait):
    """
    Marks everything reachable from the variables in the store
    or from the context info objects as reachable.

    `store`
        A map from variable name to variable value.

    `reachable`
        A dictionary that will be filled in with a map from id(obj) to obj.
    """

    for v in store.values():
        reached(v, reachable, wait)

    for c in renpy.game.contexts:
        reached(c.info, reachable, wait)
        reached(c.music, reachable, wait)
        for d in c.dynamic_stack:
            for v in d.values():
                reached(v, reachable, wait)

# This is the code that actually handles the logging and managing
# of the rollbacks.

generation = time.time()
serial = 0


rng = renpy.revertable.DetRandom()

class Rollback(renpy.object.Object):
    """
    Allows the state of the game to be rolled back to the point just
    before a node began executing.

    @ivar context: A shallow copy of the context we were in before
    we started executing the node. (Shallow copy also includes
    a copy of the associated SceneList.)

    @ivar objects: A list of tuples, each containing an object and a
    token of information that, when passed to the rollback method on
    that object, causes that object to rollback.

    @ivar store: A list of updates to store that will cause the state
    of the store to be rolled back to the start of node
    execution. This is a list of tuples, either (key, value) tuples
    representing a value that needs to be assigned to a key, or (key,)
    tuples that mean the key should be deleted.

    @ivar checkpoint: True if this is a user-visible checkpoint,
    false otherwise.

    @ivar purged: True if purge_unreachable has already been called on
    this Rollback, False otherwise.

    @ivar random: A list of random numbers that were generated during the
    execution of this element.
    """

    __version__ = 5

    identifier = None
    not_greedy = False

    def __init__(self):

        super(Rollback, self).__init__()

        self.context = renpy.game.context().rollback_copy()

        self.objects = [ ]
        self.purged = False
        self.random = [ ]
        self.forward = None

        # A map of maps name -> (variable -> value)
        self.stores = { }

        # A map from store name to the changes to ever_been_changed that
        # need to be reverted.
        self.delta_ebc = { }

        # If true, we retain the data in this rollback when a load occurs.
        self.retain_after_load = False

        # True if this is a checkpoint we can roll back to.
        self.checkpoint = False

        # True if this is a hard checkpoint, where the rollback counter
        # decreases.
        self.hard_checkpoint = False

        # True if this is a not-greedy checkpoint, which should end
        # rollbacks that occur in greedy mode.
        self.not_greedy = False

        # A unique identifier for this rollback object.

        global serial
        self.identifier = (generation, serial)
        serial += 1

    def after_upgrade(self, version):

        if version < 2:
            self.stores = { "store" : { } }

            for i in self.store: # type: ignore
                if len(i) == 2:
                    k, v = i
                    self.stores["store"][k] = v
                else:
                    k, = i
                    self.stores["store"][k] = deleted

        if version < 3:
            self.retain_after_load = False

        if version < 4:
            self.hard_checkpoint = self.checkpoint

        if version < 5:
            self.delta_ebc = { }

    def purge_unreachable(self, reachable, wait):
        """
        Adds objects that are reachable from the store of this
        rollback to the set of reachable objects, and purges
        information that is stored about totally unreachable objects.

        Returns True if this is the first time this method has been
        called, or False if it has already been called once before.
        """

        if self.purged:
            return False

        self.purged = True

        # Add objects reachable from the stores. (Objects that might be
        # unreachable at the moment.)
        for changes in self.stores.values():
            for _k, v in changes.items():
                if v is not deleted:
                    reached(v, reachable, wait)

        # Add in objects reachable through the context.
        reached(self.context.info, reachable, wait)
        for d in self.context.dynamic_stack:
            for v in d.values():
                reached(v, reachable, wait)

        # Add in objects reachable through displayables.
        reached(self.context.scene_lists.get_all_displayables(), reachable, wait)

        # Purge object update information for unreachable objects.
        new_objects = [ ]

        objects_changed = True
        seen = set()

        while objects_changed:

            objects_changed = False

            for o, rb in self.objects:

                id_o = id(o)

                if id_o in seen or id_o not in reachable:
                    continue

                seen.add(id_o)

                if isinstance(o, NOROLLBACK_TYPES):
                    continue

                objects_changed = True

                new_objects.append((o, rb))
                reached(rb, reachable, wait)

        del self.objects[:]
        self.objects.extend(new_objects)

        return True

    def rollback(self):
        """
        Reverts the state of the game to what it was at the start of the
        previous checkpoint.
        """

        store_dicts = renpy.python.store_dicts

        for obj, roll in reversed(self.objects):

            if roll is not None:
                obj._rollback(roll)

        for name, changes in self.stores.items():
            store = store_dicts.get(name, None)
            if store is None:
                continue

            for name, value in changes.items():
                if value is deleted:
                    if name in store:
                        del store[name]
                else:
                    store[name] = value

        for name, changes in self.delta_ebc.items():

            store = store_dicts.get(name, None)
            if store is None:
                continue

            store.ever_been_changed -= changes

        rng.pushback(self.random)

        self.rollback_control()


    def rollback_control(self):
        """
        This rolls back only the control information, while leaving
        the data information intact.
        """

        renpy.game.contexts = renpy.game.contexts[:-1] + [ self.context ]


class RollbackLog(renpy.object.Object):
    """
    This class manages the list of Rollback objects.

    @ivar log: The log of rollback objects.

    @ivar current: The current rollback object. (Equivalent to
    log[-1])

    @ivar rollback_limit: The number of steps left that we can
    interactively rollback.

    Not serialized:

    @ivar mutated: A dictionary that maps object ids to a tuple of
    (weakref to object, information needed to rollback that object)
    """

    __version__ = 5

    nosave = [ 'old_store', 'mutated', 'identifier_cache' ]
    identifier_cache = None
    force_checkpoint = False

    def __init__(self):

        super(RollbackLog, self).__init__()

        self.log = [ ]
        self.current = None
        self.mutated = { }
        self.rollback_limit = 0
        self.rollback_is_fixed = False
        self.checkpointing_suspended = False
        self.fixed_rollback_boundary = None
        self.forward = [ ]
        self.old_store = { }

        # Did we just do a roll forward?
        self.rolled_forward = False

        # Reset the RNG on the creation of a new game.
        rng.reset()

        # True if we should retain data from here to the next checkpoint
        # on load.
        self.retain_after_load_flag = False

        # Has there been an interaction since the last time this log was
        # reset?
        self.did_interaction = True

        # Should we force a checkpoint before completing the current
        # statement.
        self.force_checkpoint = False

    def after_setstate(self):
        self.mutated = { }
        self.rolled_forward = False

    def after_upgrade(self, version):
        if version < 2:
            self.ever_been_changed = { "store" : set(self.ever_been_changed) }
        if version < 3:
            self.rollback_is_fixed = False
            self.fixed_rollback_boundary = None
        if version < 4:
            self.retain_after_load_flag = False

        if version < 5:

            # We changed what the rollback limit represents, so recompute it
            # here.
            if self.rollback_limit:
                nrbl = 0

                for rb in self.log[-self.rollback_limit:]:
                    if rb.hard_checkpoint:
                        nrbl += 1

                self.rollback_limit = nrbl

    def begin(self, force=False):
        """
        Called before a node begins executing, to indicate that the
        state needs to be saved for rollbacking.
        """

        self.identifier_cache = None

        context = renpy.game.context()

        if not context.rollback:
            return

        # We only begin a checkpoint if the previous statement reached a checkpoint,
        # or an interaction took place. (Or we're forced.)
        ignore = True

        if force:
            ignore = False
        elif self.did_interaction:
            ignore = False
        elif self.current is not None:
            if self.current.checkpoint:
                ignore = False
            elif self.current.retain_after_load:
                ignore = False

        if ignore:
            return

        self.did_interaction = False

        if self.current is not None:
            self.complete(True)
        else:
            renpy.python.begin_stores()

        # If the log is too long, prune it.
        while len(self.log) > renpy.config.rollback_length:
            self.log.pop(0)

        # check for the end of fixed rollback
        if len(self.log) >= 2:
            if self.log[-2].context.current == self.fixed_rollback_boundary:
                self.rollback_is_fixed = False

        # A lack of rollback data in fixed rollback mode ends rollback.
        if self.rollback_is_fixed and not self.forward:
            self.fixed_rollback_boundary = self.current.context.current
            self.rollback_is_fixed = False

        self.current = Rollback()
        self.current.retain_after_load = self.retain_after_load_flag

        self.log.append(self.current)

        self.mutated.clear()

        # Flag a mutation as having happened. This is used by the
        # save code.
        renpy.revertable.mutate_flag = True

        self.rolled_forward = False

    def replace_node(self, old, new):
        """
        Replaces references to the `old` ast node with a reference to the
        `new` ast node.
        """

        for i in self.log:
            i.context.replace_node(old, new)

    def complete(self, begin=False):
        """
        Called after a node is finished executing, before a save
        begins, or right before a rollback is attempted. This may be
        called more than once between calls to begin, and should always
        be called after an update to the store but before a rollback
        occurs.

        `begin`
            Should be true if called from begin().
        """

        if self.force_checkpoint:
            self.checkpoint(hard=False)
            self.force_checkpoint = False

        # Update self.current.stores with the changes from each store.
        # Also updates .ever_been_changed.
        for name, sd in renpy.python.store_dicts.items():
            delta = sd.get_changes(begin)
            if delta:
                self.current.stores[name], self.current.delta_ebc[name] = delta

        # Update the list of mutated objects and what we need to do to
        # restore them.

        for _i in range(4):

            del self.current.objects[:]

            try:
                for _k, v in self.mutated.items():

                    if v is None:
                        continue

                    (ref, clean) = v

                    obj = ref()
                    if obj is None:
                        continue

                    compressed = obj._compress(clean)
                    self.current.objects.append((obj, compressed))

                break

            except RuntimeError:
                # This can occur when self.mutated is changed as we're
                # iterating over it.
                pass

    def get_roots(self):
        """
        Return a map giving the current roots of the store. This is a
        map from a variable name in the store to the value of that
        variable. A variable is only in this map if it has ever been
        changed since the init phase finished.
        """

        rv = { }

        for store_name, sd in renpy.python.store_dicts.items():
            for name in sd.ever_been_changed:
                if name in sd:
                    rv[store_name + "." + name] = sd[name]
                else:
                    rv[store_name + "." + name] = deleted

        for i in reversed(renpy.game.contexts[1:]):
            i.pop_dynamic_roots(rv)

        return rv

    def purge_unreachable(self, roots, wait=None):
        """
        This is called to purge objects that are unreachable from the
        roots from the object rollback lists inside the Rollback entries.

        This should be called immediately after complete(), so that there
        are no changes queued up.
        """

        # This needs to be set late, so that StoreModule is available.

        global NOROLLBACK_TYPES
        NOROLLBACK_TYPES = (types.ModuleType, renpy.python.StoreModule, SlottedNoRollback, io.IOBase, type)

        reachable = { }

        reached_vars(roots, reachable, wait)

        revlog = self.log[:]
        revlog.reverse()

        for i in revlog:
            if not i.purge_unreachable(reachable, wait):
                break

        # Break any cycles.
        reachable.clear()

    def in_rollback(self):
        if self.forward:
            return True
        else:
            return False

    def in_fixed_rollback(self):
        return self.rollback_is_fixed

    def forward_info(self):
        """
        Returns the current forward info, if any.
        """

        if self.forward:

            name, data = self.forward[0]

            if self.current.context.current == name:
                return data

        return None

    def checkpoint(self, data=None, keep_rollback=False, hard=True):
        """
        Called to indicate that this is a checkpoint, which means
        that the user may want to rollback to just before this
        node.
        """

        if self.checkpointing_suspended:
            hard = False

        if hard:
            self.retain_after_load_flag = False

        if self.current.checkpoint:
            return

        if not renpy.game.context().rollback:
            return

        self.current.checkpoint = True

        if hard and (not self.current.hard_checkpoint):
            if self.rollback_limit < renpy.config.hard_rollback_limit:
                self.rollback_limit += 1

            if hard == "not_greedy":
                self.current.not_greedy = True
            else:
                self.current.hard_checkpoint = hard

        if self.in_fixed_rollback() and self.forward:
            # use data from the forward stack
            fwd_name, fwd_data = self.forward[0]
            if self.current.context.current == fwd_name:
                self.current.forward = fwd_data
                self.forward.pop(0)
            else:
                self.current.forward = data
                del self.forward[:]

        elif data is not None:
            if self.forward:
                # If the data is the same, pop it from the forward stack.
                # Otherwise, clear the forward stack.
                fwd_name, fwd_data = self.forward[0]

                if (self.current.context.current == fwd_name
                    and data == fwd_data
                    and (keep_rollback or self.rolled_forward)
                    ):
                    self.forward.pop(0)
                else:
                    del self.forward[:]

            # Log the data in case we roll back again.
            self.current.forward = data

    def suspend_checkpointing(self, flag):
        """
        Called to temporarily suspend checkpointing, so any rollback
        will jump to prior to this statement
        """

        self.checkpointing_suspended = flag
        self.current.not_greedy = True
        renpy.game.contexts[0].force_checkpoint = True

    def block(self, purge=False):
        """
        Called to indicate that the user should not be able to rollback
        through this checkpoint.
        """

        self.rollback_limit = 0
        if self.current is not None:
            self.current.not_greedy = True
        renpy.game.context().force_checkpoint = True

        if purge:
            del self.log[:]

    def retain_after_load(self):
        """
        Called to return data from this statement until the next checkpoint
        when the game is loaded.
        """

        if renpy.display.predict.predicting:
            return

        self.retain_after_load_flag = True
        self.current.retain_after_load = True

        for rb in reversed(self.log):
            if rb.hard_checkpoint:
                break

            rb.retain_after_load = True

        renpy.game.context().force_checkpoint = True

    def fix_rollback(self):
        if not self.rollback_is_fixed and len(self.log) > 1:
            self.fixed_rollback_boundary = self.log[-2].context.current
        renpy.game.context().force_checkpoint = True

    def can_rollback(self):
        """
        Returns True if we can rollback.
        """

        return self.rollback_limit > 0

    def load_failed(self):
        """
        This is called to try to recover when rollback fails.
        """

        lfl = renpy.config.load_failed_label
        if callable(lfl):
            lfl = lfl()

        if not lfl:
            raise Exception("Couldn't find a place to stop rolling back. Perhaps the script changed in an incompatible way?")

        rb = self.log.pop()
        rb.rollback()

        while renpy.exports.call_stack_depth():
            renpy.exports.pop_call()

        renpy.game.contexts[0].force_checkpoint = True
        renpy.game.contexts[0].goto_label(lfl)

        raise renpy.game.RestartTopContext()

    def rollback(self, checkpoints, force=False, label=None, greedy=True, on_load=False, abnormal=True, current_label=None):
        """
        This rolls the system back to the first valid rollback point
        after having rolled back past the specified number of checkpoints.

        If we're currently executing code, it's expected that complete()
        will be called before a rollback is attempted.

        force makes us throw an exception if we can't find a place to stop
        rolling back, otherwise if we run out of log this call has no
        effect.

        `label`
            A label that is called after rollback has finished, if the
            label exists.

        `greedy`
            If true, rollback will keep going until just after the last
            checkpoint. If False, it will stop immediately before the
            current statement.

        `on_load`
            Should be true if this rollback is being called in response to a
            load. Used to implement .retain_after_load()

        `abnormal`
            If true, treats this as an abnormal event, suppressing transitions
            and so on.

        `current_label`
            A label that is called when control returns to the current statement,
            after rollback. (At most one of `current_label` and `label` can be
            provided.)
        """

        # If we have exceeded the rollback limit, and don't have force,
        # give up.
        if checkpoints and (self.rollback_limit <= 0) and (not force):
            return

        self.suspend_checkpointing(False)
        # will always rollback to before suspension

        self.purge_unreachable(self.get_roots())

        revlog = [ ]

        # Find the place to roll back to.
        while self.log:
            rb = self.log.pop()
            revlog.append(rb)

            if rb.hard_checkpoint:
                self.rollback_limit -= 1

            if rb.hard_checkpoint or (on_load and rb.checkpoint):
                checkpoints -= 1

            if checkpoints <= 0:
                if renpy.game.script.has_label(rb.context.current):
                    break

        else:
            # Otherwise, just give up.

            revlog.reverse()
            self.log.extend(revlog)

            if force:
                self.load_failed()
            else:
                print("Can't find a place to rollback to. Not rolling back.")

            return

        force_checkpoint = False

        # Try to rollback to just after the previous checkpoint.
        while greedy and self.log:

            rb = self.log[-1]

            if not renpy.game.script.has_label(rb.context.current):
                break

            if rb.hard_checkpoint:
                break

            if rb.not_greedy:
                break

            revlog.append(self.log.pop())

        # Decide if we're replacing the current context (rollback command),
        # or creating a new set of contexts (loading).
        if renpy.game.context().rollback:
            replace_context = False
            other_contexts = [ ]

        else:
            replace_context = True
            other_contexts = renpy.game.contexts[1:]
            renpy.game.contexts = renpy.game.contexts[0:1]

        if on_load and revlog[-1].retain_after_load:
            retained = revlog.pop()
            self.retain_after_load_flag = True
        else:
            retained = None

        come_from = None

        if current_label is not None:
            come_from = renpy.game.context().current
            label = current_label

        # Actually roll things back.
        for rb in revlog:
            rb.rollback()

            if (rb.context.current == self.fixed_rollback_boundary) and (rb.context.current):
                self.rollback_is_fixed = True

            if rb.forward is not None:
                self.forward.insert(0, (rb.context.current, rb.forward))

        if retained is not None:
            retained.rollback_control()
            self.log.append(retained)

        if (label is not None) and (come_from is None):
            come_from = renpy.game.context().current

        if come_from is not None:
            renpy.game.context().come_from(come_from, label)

        # Disable the next transition, as it's pointless. (Only when not used with a label.)
        renpy.game.interface.suppress_transition = abnormal

        # If necessary, reset the RNG.
        if force:
            rng.reset()
            del self.forward[:]

        # Flag that we're in the transition immediately after a rollback.
        renpy.game.after_rollback = abnormal

        # Stop the sounds.
        renpy.audio.audio.rollback()

        # Stop any hiding in progress.
        for i in renpy.game.contexts:
            i.scene_lists.remove_all_hidden()

        renpy.game.contexts.extend(other_contexts)

        renpy.exports.execute_default_statement(False)

        self.mutated.clear()
        renpy.python.begin_stores()

        # Restart the context or the top context.
        if replace_context:

            if force_checkpoint:
                renpy.game.contexts[0].force_checkpoint = True

            self.current = Rollback()
            self.current.context = renpy.game.contexts[0].rollback_copy()

            if self.log is not None:
                self.log.append(self.current)

            raise renpy.game.RestartTopContext()

        else:

            self.current = Rollback()
            self.current.context = renpy.game.context().rollback_copy()

            if self.log is not None:
                self.log.append(self.current)

            if force_checkpoint:
                renpy.game.context().force_checkpoint = True

            raise renpy.game.RestartContext()

    def freeze(self, wait=None):
        """
        This is called to freeze the store and the log, in preparation
        for serialization. The next call on log should either be
        unfreeze (called after a serialization reload) or discard_freeze()
        (called after the save is complete).
        """

        # Purge unreachable objects, so we don't save them.
        self.complete(False)
        roots = self.get_roots()

        self.purge_unreachable(roots, wait=wait)

        # The current is not purged.
        self.current.purged = False

        return roots

    def discard_freeze(self):
        """
        Called to indicate that we will not be restoring from the
        frozen state.
        """

    def unfreeze(self, roots, label=None):
        """
        Used to unfreeze the game state after a load of this log
        object. This call will always throw an exception. If we're
        lucky, it's the one that indicates load was successful.

        @param roots: The roots returned from freeze.

        @param label: The label that is jumped to in the game script
        after rollback has finished, if it exists.
        """

        # Fix up old screens.
        renpy.display.screen.before_restart() # @UndefinedVariable

        # Set us up as the game log.
        renpy.game.log = self

        renpy.python.clean_stores()
        renpy.translation.init_translation()

        store_dicts = renpy.python.store_dicts

        for name, value in roots.items():

            if "." in name:
                store_name, name = name.rsplit(".", 1)
            else:
                store_name = "store"

            if store_name not in store_dicts:
                continue

            store = store_dicts[store_name]
            store.ever_been_changed.add(name)

            if value is deleted:
                if name in store:
                    del store[name]
            else:
                store[name] = value

        # Now, rollback to an acceptable point.

        greedy = renpy.session.pop("_greedy_rollback", False)
        self.rollback(0, force=True, label=label, greedy=greedy, on_load=True)

        # Because of the rollback, we never make it this far.

    def build_identifier_cache(self):

        if self.identifier_cache is not None:
            return

        rollback_limit = self.rollback_limit
        checkpoints = 1

        self.identifier_cache = { }

        for i in reversed(self.log):

            if i.identifier is not None:
                if renpy.game.script.has_label(i.context.current):
                    self.identifier_cache[i.identifier] = checkpoints

            if i.hard_checkpoint:
                checkpoints += 1

            if i.checkpoint:
                rollback_limit -= 1

            if not rollback_limit:
                break

    def get_identifier_checkpoints(self, identifier):
        self.build_identifier_cache()
        return self.identifier_cache.get(identifier, None)
