Fill.py

import collections
import itertools
import logging
import typing
from collections import Counter, deque

from BaseClasses import CollectionState, Item, Location, LocationProgressType, MultiWorld
from Options import Accessibility

from worlds.AutoWorld import call_all
from worlds.generic.Rules import add_item_rule


class FillError(RuntimeError):
    def __init__(self, *args: typing.Union[str, typing.Any], **kwargs) -> None:
        if "multiworld" in kwargs and isinstance(args[0], str):
            placements = (args[0] + f"\nAll Placements:\n" +
                          f"{[(loc, loc.item) for loc in kwargs['multiworld'].get_filled_locations()]}")
            args = (placements, *args[1:])
        super().__init__(*args)


def _log_fill_progress(name: str, placed: int, total_items: int) -> None:
    logging.info(f"Current fill step ({name}) at {placed}/{total_items} items placed.")


def sweep_from_pool(base_state: CollectionState, itempool: typing.Sequence[Item] = tuple(),
                    locations: typing.Optional[typing.List[Location]] = None) -> CollectionState:
    new_state = base_state.copy()
    for item in itempool:
        new_state.collect(item, True)
    new_state.sweep_for_advancements(locations=locations)
    return new_state


def fill_restrictive(multiworld: MultiWorld, base_state: CollectionState, locations: typing.List[Location],
                     item_pool: typing.List[Item], single_player_placement: bool = False, lock: bool = False,
                     swap: bool = True, on_place: typing.Optional[typing.Callable[[Location], None]] = None,
                     allow_partial: bool = False, allow_excluded: bool = False, one_item_per_player: bool = True,
                     name: str = "Unknown") -> None:
    """
    :param multiworld: Multiworld to be filled.
    :param base_state: State assumed before fill.
    :param locations: Locations to be filled with item_pool, gets mutated by removing locations that get filled.
    :param item_pool: Items to fill into the locations, gets mutated by removing items that get placed.
    :param single_player_placement: if true, can speed up placement if everything belongs to a single player
    :param lock: locations are set to locked as they are filled
    :param swap: if true, swaps of already place items are done in the event of a dead end
    :param on_place: callback that is called when a placement happens
    :param allow_partial: only place what is possible. Remaining items will be in the item_pool list.
    :param allow_excluded: if true and placement fails, it is re-attempted while ignoring excluded on Locations
    :param name: name of this fill step for progress logging purposes
    """
    unplaced_items: typing.List[Item] = []
    placements: typing.List[Location] = []
    cleanup_required = False
    swapped_items: typing.Counter[typing.Tuple[int, str, bool]] = Counter()
    reachable_items: typing.Dict[int, typing.Deque[Item]] = {}
    for item in item_pool:
        reachable_items.setdefault(item.player, deque()).append(item)

    # for progress logging
    total = min(len(item_pool), len(locations))
    placed = 0

    while any(reachable_items.values()) and locations:
        if one_item_per_player:
            # grab one item per player
            items_to_place = [items.pop()
                              for items in reachable_items.values() if items]
        else:
            next_player = multiworld.random.choice([player for player, items in reachable_items.items() if items])
            items_to_place = []
            if item_pool:
                items_to_place.append(reachable_items[next_player].pop())

        for item in items_to_place:
            for p, pool_item in enumerate(item_pool):
                if pool_item is item:
                    item_pool.pop(p)
                    break

        maximum_exploration_state = sweep_from_pool(
            base_state, item_pool + unplaced_items, multiworld.get_filled_locations(item.player)
            if single_player_placement else None)

        has_beaten_game = multiworld.has_beaten_game(maximum_exploration_state)

        while items_to_place:
            # if we have run out of locations to fill,break out of this loop
            if not locations:
                unplaced_items += items_to_place
                break
            item_to_place = items_to_place.pop(0)

            spot_to_fill: typing.Optional[Location] = None

            # if minimal accessibility, only check whether location is reachable if game not beatable
            if multiworld.worlds[item_to_place.player].options.accessibility == Accessibility.option_minimal:
                perform_access_check = not multiworld.has_beaten_game(maximum_exploration_state,
                                                                 item_to_place.player) \
                    if single_player_placement else not has_beaten_game
            else:
                perform_access_check = True

            for i, location in enumerate(locations):
                if (not single_player_placement or location.player == item_to_place.player) \
                        and location.can_fill(maximum_exploration_state, item_to_place, perform_access_check):
                    # popping by index is faster than removing by content,
                    spot_to_fill = locations.pop(i)
                    # skipping a scan for the element
                    break

            else:
                # we filled all reachable spots.
                if swap:
                    # try swapping this item with previously placed items in a safe way then in an unsafe way
                    swap_attempts = ((i, location, unsafe)
                                     for unsafe in (False, True)
                                     for i, location in enumerate(placements))
                    for (i, location, unsafe) in swap_attempts:
                        placed_item = location.item
                        # Unplaceable items can sometimes be swapped infinitely. Limit the
                        # number of times we will swap an individual item to prevent this
                        swap_count = swapped_items[placed_item.player, placed_item.name, unsafe]
                        if swap_count > 1:
                            continue

                        location.item = None
                        placed_item.location = None
                        swap_state = sweep_from_pool(base_state, [placed_item, *item_pool] if unsafe else item_pool,
                                                     multiworld.get_filled_locations(item.player)
                                                     if single_player_placement else None)
                        # unsafe means swap_state assumes we can somehow collect placed_item before item_to_place
                        # by continuing to swap, which is not guaranteed. This is unsafe because there is no mechanic
                        # to clean that up later, so there is a chance generation fails.
                        if (not single_player_placement or location.player == item_to_place.player) \
                                and location.can_fill(swap_state, item_to_place, perform_access_check):

                            # Verify placing this item won't reduce available locations, which would be a useless swap.
                            prev_state = swap_state.copy()
                            prev_loc_count = len(
                                multiworld.get_reachable_locations(prev_state))

                            swap_state.collect(item_to_place, True)
                            new_loc_count = len(
                                multiworld.get_reachable_locations(swap_state))

                            if new_loc_count >= prev_loc_count:
                                # Add this item to the existing placement, and
                                # add the old item to the back of the queue
                                spot_to_fill = placements.pop(i)

                                swap_count += 1
                                swapped_items[placed_item.player, placed_item.name, unsafe] = swap_count

                                reachable_items[placed_item.player].appendleft(
                                    placed_item)
                                item_pool.append(placed_item)

                                # cleanup at the end to hopefully get better errors
                                cleanup_required = True

                                break

                        # Item can't be placed here, restore original item
                        location.item = placed_item
                        placed_item.location = location

                    if spot_to_fill is None:
                        # Can't place this item, move on to the next
                        unplaced_items.append(item_to_place)
                        continue
                else:
                    unplaced_items.append(item_to_place)
                    continue
            multiworld.push_item(spot_to_fill, item_to_place, False)
            spot_to_fill.locked = lock
            placements.append(spot_to_fill)
            placed += 1
            if not placed % 1000:
                _log_fill_progress(name, placed, total)
            if on_place:
                on_place(spot_to_fill)

    if total > 1000:
        _log_fill_progress(name, placed, total)

    if cleanup_required:
        # validate all placements and remove invalid ones
        state = sweep_from_pool(
            base_state, [], multiworld.get_filled_locations(item.player)
            if single_player_placement else None)
        for placement in placements:
            if multiworld.worlds[placement.item.player].options.accessibility != "minimal" and not placement.can_reach(state):
                placement.item.location = None
                unplaced_items.append(placement.item)
                placement.item = None
                locations.append(placement)

    if allow_excluded:
        # check if partial fill is the result of excluded locations, in which case retry
        excluded_locations = [
            location for location in locations
            if location.progress_type == location.progress_type.EXCLUDED and not location.item
        ]
        if excluded_locations:
            for location in excluded_locations:
                location.progress_type = location.progress_type.DEFAULT
            fill_restrictive(multiworld, base_state, excluded_locations, unplaced_items, single_player_placement, lock,
                             swap, on_place, allow_partial, False)
            for location in excluded_locations:
                if not location.item:
                    location.progress_type = location.progress_type.EXCLUDED

    if not allow_partial and len(unplaced_items) > 0 and len(locations) > 0:
        # There are leftover unplaceable items and locations that won't accept them
        if multiworld.can_beat_game():
            logging.warning(
                f"Not all items placed. Game beatable anyway.\nCould not place:\n"
                f"{', '.join(str(item) for item in unplaced_items)}")
        else:
            raise FillError(f"No more spots to place {len(unplaced_items)} items. Remaining locations are invalid.\n"
                            f"Unplaced items:\n"
                            f"{', '.join(str(item) for item in unplaced_items)}\n"
                            f"Unfilled locations:\n"
                            f"{', '.join(str(location) for location in locations)}\n"
                            f"Already placed {len(placements)}:\n"
                            f"{', '.join(str(place) for place in placements)}", multiworld=multiworld)

    item_pool.extend(unplaced_items)


def remaining_fill(multiworld: MultiWorld,
                   locations: typing.List[Location],
                   itempool: typing.List[Item],
                   name: str = "Remaining", 
                   move_unplaceable_to_start_inventory: bool = False,
                   check_location_can_fill: bool = False) -> None:
    unplaced_items: typing.List[Item] = []
    placements: typing.List[Location] = []
    swapped_items: typing.Counter[typing.Tuple[int, str]] = Counter()
    total = min(len(itempool),  len(locations))
    placed = 0

    # Optimisation: Decide whether to do full location.can_fill check (respect excluded), or only check the item rule
    if check_location_can_fill:
        state = CollectionState(multiworld)

        def location_can_fill_item(location_to_fill: Location, item_to_fill: Item):
            return location_to_fill.can_fill(state, item_to_fill, check_access=False)
    else:
        def location_can_fill_item(location_to_fill: Location, item_to_fill: Item):
            return location_to_fill.item_rule(item_to_fill)

    while locations and itempool:
        item_to_place = itempool.pop()
        spot_to_fill: typing.Optional[Location] = None

        for i, location in enumerate(locations):
            if location_can_fill_item(location, item_to_place):
                # popping by index is faster than removing by content,
                spot_to_fill = locations.pop(i)
                # skipping a scan for the element
                break

        else:
            # we filled all reachable spots.
            # try swapping this item with previously placed items

            for (i, location) in enumerate(placements):
                placed_item = location.item
                # Unplaceable items can sometimes be swapped infinitely. Limit the
                # number of times we will swap an individual item to prevent this

                if swapped_items[placed_item.player,
                                 placed_item.name] > 1:
                    continue

                location.item = None
                placed_item.location = None
                if location_can_fill_item(location, item_to_place):
                    # Add this item to the existing placement, and
                    # add the old item to the back of the queue
                    spot_to_fill = placements.pop(i)

                    swapped_items[placed_item.player,
                                  placed_item.name] += 1

                    itempool.append(placed_item)

                    break

                # Item can't be placed here, restore original item
                location.item = placed_item
                placed_item.location = location

            if spot_to_fill is None:
                # Can't place this item, move on to the next
                unplaced_items.append(item_to_place)
                continue

        multiworld.push_item(spot_to_fill, item_to_place, False)
        placements.append(spot_to_fill)
        placed += 1
        if not placed % 1000:
            _log_fill_progress(name, placed, total)

    if total > 1000:
        _log_fill_progress(name, placed, total)

    if unplaced_items and locations:
        # There are leftover unplaceable items and locations that won't accept them
        if move_unplaceable_to_start_inventory:
            last_batch = []
            for item in unplaced_items:
                logging.debug(f"Moved {item} to start_inventory to prevent fill failure.")
                multiworld.push_precollected(item)
                last_batch.append(multiworld.worlds[item.player].create_filler())
            remaining_fill(multiworld, locations, unplaced_items, name + " Start Inventory Retry")
        else:
            raise FillError(f"No more spots to place {len(unplaced_items)} items. Remaining locations are invalid.\n"
                            f"Unplaced items:\n"
                            f"{', '.join(str(item) for item in unplaced_items)}\n"
                            f"Unfilled locations:\n"
                            f"{', '.join(str(location) for location in locations)}\n"
                            f"Already placed {len(placements)}:\n"
                            f"{', '.join(str(place) for place in placements)}", multiworld=multiworld)

    itempool.extend(unplaced_items)


def fast_fill(multiworld: MultiWorld,
              item_pool: typing.List[Item],
              fill_locations: typing.List[Location]) -> typing.Tuple[typing.List[Item], typing.List[Location]]:
    placing = min(len(item_pool), len(fill_locations))
    for item, location in zip(item_pool, fill_locations):
        multiworld.push_item(location, item, False)
    return item_pool[placing:], fill_locations[placing:]


def accessibility_corrections(multiworld: MultiWorld, state: CollectionState, locations, pool=[]):
    maximum_exploration_state = sweep_from_pool(state, pool)
    minimal_players = {player for player in multiworld.player_ids if multiworld.worlds[player].options.accessibility == "minimal"}
    unreachable_locations = [location for location in multiworld.get_locations() if location.player in minimal_players and
                             not location.can_reach(maximum_exploration_state)]
    for location in unreachable_locations:
        if (location.item is not None and location.item.advancement and location.address is not None and not
                location.locked and location.item.player not in minimal_players):
            pool.append(location.item)
            state.remove(location.item)
            location.item = None
            if location in state.advancements:
                state.advancements.remove(location)
            locations.append(location)
    if pool and locations:
        locations.sort(key=lambda loc: loc.progress_type != LocationProgressType.PRIORITY)
        fill_restrictive(multiworld, state, locations, pool, name="Accessibility Corrections")


def inaccessible_location_rules(multiworld: MultiWorld, state: CollectionState, locations):
    maximum_exploration_state = sweep_from_pool(state)
    unreachable_locations = [location for location in locations if not location.can_reach(maximum_exploration_state)]
    if unreachable_locations:
        def forbid_important_item_rule(item: Item):
            return not ((item.classification & 0b0011) and multiworld.worlds[item.player].options.accessibility != 'minimal')

        for location in unreachable_locations:
            add_item_rule(location, forbid_important_item_rule)


def distribute_early_items(multiworld: MultiWorld,
                           fill_locations: typing.List[Location],
                           itempool: typing.List[Item]) -> typing.Tuple[typing.List[Location], typing.List[Item]]:
    """ returns new fill_locations and itempool """
    early_items_count: typing.Dict[typing.Tuple[str, int], typing.List[int]] = {}
    for player in multiworld.player_ids:
        items = itertools.chain(multiworld.early_items[player], multiworld.local_early_items[player])
        for item in items:
            early_items_count[item, player] = [multiworld.early_items[player].get(item, 0),
                                               multiworld.local_early_items[player].get(item, 0)]
    if early_items_count:
        early_locations: typing.List[Location] = []
        early_priority_locations: typing.List[Location] = []
        loc_indexes_to_remove: typing.Set[int] = set()
        base_state = multiworld.state.copy()
        base_state.sweep_for_advancements(locations=(loc for loc in multiworld.get_filled_locations() if loc.address is None))
        for i, loc in enumerate(fill_locations):
            if loc.can_reach(base_state):
                if loc.progress_type == LocationProgressType.PRIORITY:
                    early_priority_locations.append(loc)
                else:
                    early_locations.append(loc)
                loc_indexes_to_remove.add(i)
        fill_locations = [loc for i, loc in enumerate(fill_locations) if i not in loc_indexes_to_remove]

        early_prog_items: typing.List[Item] = []
        early_rest_items: typing.List[Item] = []
        early_local_prog_items: typing.Dict[int, typing.List[Item]] = {player: [] for player in multiworld.player_ids}
        early_local_rest_items: typing.Dict[int, typing.List[Item]] = {player: [] for player in multiworld.player_ids}
        item_indexes_to_remove: typing.Set[int] = set()
        for i, item in enumerate(itempool):
            if (item.name, item.player) in early_items_count:
                if item.advancement:
                    if early_items_count[item.name, item.player][1]:
                        early_local_prog_items[item.player].append(item)
                        early_items_count[item.name, item.player][1] -= 1
                    else:
                        early_prog_items.append(item)
                        early_items_count[item.name, item.player][0] -= 1
                else:
                    if early_items_count[item.name, item.player][1]:
                        early_local_rest_items[item.player].append(item)
                        early_items_count[item.name, item.player][1] -= 1
                    else:
                        early_rest_items.append(item)
                        early_items_count[item.name, item.player][0] -= 1
                item_indexes_to_remove.add(i)
                if early_items_count[item.name, item.player] == [0, 0]:
                    del early_items_count[item.name, item.player]
                    if len(early_items_count) == 0:
                        break
        itempool = [item for i, item in enumerate(itempool) if i not in item_indexes_to_remove]
        for player in multiworld.player_ids:
            player_local = early_local_rest_items[player]
            fill_restrictive(multiworld, base_state,
                             [loc for loc in early_locations if loc.player == player],
                             player_local, lock=True, allow_partial=True, name=f"Local Early Items P{player}")
            if player_local:
                logging.warning(f"Could not fulfill rules of early items: {player_local}")
                early_rest_items.extend(early_local_rest_items[player])
        early_locations = [loc for loc in early_locations if not loc.item]
        fill_restrictive(multiworld, base_state, early_locations, early_rest_items, lock=True, allow_partial=True,
                         name="Early Items")
        early_locations += early_priority_locations
        for player in multiworld.player_ids:
            player_local = early_local_prog_items[player]
            fill_restrictive(multiworld, base_state,
                             [loc for loc in early_locations if loc.player == player],
                             player_local, lock=True, allow_partial=True, name=f"Local Early Progression P{player}")
            if player_local:
                logging.warning(f"Could not fulfill rules of early items: {player_local}")
                early_prog_items.extend(player_local)
        early_locations = [loc for loc in early_locations if not loc.item]
        fill_restrictive(multiworld, base_state, early_locations, early_prog_items, lock=True, allow_partial=True,
                         name="Early Progression")
        unplaced_early_items = early_rest_items + early_prog_items
        if unplaced_early_items:
            logging.warning("Ran out of early locations for early items. Failed to place "
                            f"{unplaced_early_items} early.")
            itempool += unplaced_early_items

        fill_locations.extend(early_locations)
        multiworld.random.shuffle(fill_locations)
    return fill_locations, itempool


def distribute_items_restrictive(multiworld: MultiWorld,
                                 panic_method: typing.Literal["swap", "raise", "start_inventory"] = "swap") -> None:
    fill_locations = sorted(multiworld.get_unfilled_locations())
    multiworld.random.shuffle(fill_locations)
    # get items to distribute
    itempool = sorted(multiworld.itempool)
    multiworld.random.shuffle(itempool)

    fill_locations, itempool = distribute_early_items(multiworld, fill_locations, itempool)

    progitempool: typing.List[Item] = []
    usefulitempool: typing.List[Item] = []
    filleritempool: typing.List[Item] = []

    for item in itempool:
        if item.advancement:
            progitempool.append(item)
        elif item.useful:
            usefulitempool.append(item)
        else:
            filleritempool.append(item)

    call_all(multiworld, "fill_hook", progitempool, usefulitempool, filleritempool, fill_locations)

    locations: typing.Dict[LocationProgressType, typing.List[Location]] = {
        loc_type: [] for loc_type in LocationProgressType}

    for loc in fill_locations:
        locations[loc.progress_type].append(loc)

    prioritylocations = locations[LocationProgressType.PRIORITY]
    defaultlocations = locations[LocationProgressType.DEFAULT]
    excludedlocations = locations[LocationProgressType.EXCLUDED]

    # can't lock due to accessibility corrections touching things, so we remember which ones got placed and lock later
    lock_later = []

    def mark_for_locking(location: Location):
        nonlocal lock_later
        lock_later.append(location)

    single_player = multiworld.players == 1 and not multiworld.groups

    if prioritylocations:
        # "priority fill"
        fill_restrictive(multiworld, multiworld.state, prioritylocations, progitempool,
                         single_player_placement=single_player, swap=False, on_place=mark_for_locking,
                         name="Priority", one_item_per_player=True, allow_partial=True)

        if prioritylocations:
            # retry with one_item_per_player off because some priority fills can fail to fill with that optimization
            fill_restrictive(multiworld, multiworld.state, prioritylocations, progitempool,
                            single_player_placement=single_player, swap=False, on_place=mark_for_locking,
                            name="Priority Retry", one_item_per_player=False)
        accessibility_corrections(multiworld, multiworld.state, prioritylocations, progitempool)
        defaultlocations = prioritylocations + defaultlocations

    if progitempool:
        # "advancement/progression fill"
        if panic_method == "swap":
            fill_restrictive(multiworld, multiworld.state, defaultlocations, progitempool, swap=True,
                             name="Progression", single_player_placement=single_player)
        elif panic_method == "raise":
            fill_restrictive(multiworld, multiworld.state, defaultlocations, progitempool, swap=False,
                             name="Progression", single_player_placement=single_player)
        elif panic_method == "start_inventory":
            fill_restrictive(multiworld, multiworld.state, defaultlocations, progitempool, swap=False,
                             allow_partial=True, name="Progression", single_player_placement=single_player)
            if progitempool:
                for item in progitempool:
                    logging.debug(f"Moved {item} to start_inventory to prevent fill failure.")
                    multiworld.push_precollected(item)
                    filleritempool.append(multiworld.worlds[item.player].create_filler())
                logging.warning(f"{len(progitempool)} items moved to start inventory,"
                                f" due to failure in Progression fill step.")
                progitempool[:] = []

        else:
            raise ValueError(f"Generator Panic Method {panic_method} not recognized.")
        if progitempool:
            raise FillError(
                f"Not enough locations for progression items. "
                f"There are {len(progitempool)} more progression items than there are available locations.\n"
                f"Unfilled locations:\n{multiworld.get_unfilled_locations()}.",
                multiworld=multiworld,
            )
        accessibility_corrections(multiworld, multiworld.state, defaultlocations)

    for location in lock_later:
        if location.item:
            location.locked = True
    del mark_for_locking, lock_later

    inaccessible_location_rules(multiworld, multiworld.state, defaultlocations)

    remaining_fill(multiworld, excludedlocations, filleritempool, "Remaining Excluded",
                   move_unplaceable_to_start_inventory=panic_method=="start_inventory")

    if excludedlocations:
        raise FillError(
            f"Not enough filler items for excluded locations. "
            f"There are {len(excludedlocations)} more excluded locations than excludable items.",
            multiworld=multiworld,
        )

    restitempool = filleritempool + usefulitempool

    remaining_fill(multiworld, defaultlocations, restitempool,
                   move_unplaceable_to_start_inventory=panic_method=="start_inventory")

    unplaced = restitempool
    unfilled = defaultlocations

    if unplaced or unfilled:
        logging.warning(
            f"Unplaced items({len(unplaced)}): {unplaced} - Unfilled Locations({len(unfilled)}): {unfilled}")
        items_counter = Counter(location.item.player for location in multiworld.get_filled_locations())
        locations_counter = Counter(location.player for location in multiworld.get_locations())
        items_counter.update(item.player for item in unplaced)
        print_data = {"items": items_counter, "locations": locations_counter}
        logging.info(f"Per-Player counts: {print_data})")

        more_locations = locations_counter - items_counter
        more_items = items_counter - locations_counter
        for player in multiworld.player_ids:
            if more_locations[player]:
                logging.error(
                    f"Player {multiworld.get_player_name(player)} had {more_locations[player]} more locations than items.")
            elif more_items[player]:
                logging.warning(
                    f"Player {multiworld.get_player_name(player)} had {more_items[player]} more items than locations.")
        if unfilled:
            raise FillError(
                f"Unable to fill all locations.\n" +
                f"Unfilled locations({len(unfilled)}): {unfilled}"
            )
        else:
            logging.warning(
                f"Unable to place all items.\n" +
                f"Unplaced items({len(unplaced)}): {unplaced}"
            )


def flood_items(multiworld: MultiWorld) -> None:
    # get items to distribute
    multiworld.random.shuffle(multiworld.itempool)
    itempool = multiworld.itempool
    progress_done = False

    # sweep once to pick up preplaced items
    multiworld.state.sweep_for_advancements()

    # fill multiworld from top of itempool while we can
    while not progress_done:
        location_list = multiworld.get_unfilled_locations()
        multiworld.random.shuffle(location_list)
        spot_to_fill = None
        for location in location_list:
            if location.can_fill(multiworld.state, itempool[0]):
                spot_to_fill = location
                break

        if spot_to_fill:
            item = itempool.pop(0)
            multiworld.push_item(spot_to_fill, item, True)
            continue

        # ran out of spots, check if we need to step in and correct things
        if len(multiworld.get_reachable_locations()) == len(multiworld.get_locations()):
            progress_done = True
            continue

        # need to place a progress item instead of an already placed item, find candidate
        item_to_place = None
        candidate_item_to_place = None
        for item in itempool:
            if item.advancement:
                candidate_item_to_place = item
                if multiworld.unlocks_new_location(item):
                    item_to_place = item
                    break

        # we might be in a situation where all new locations require multiple items to reach.
        # If that is the case, just place any advancement item we've found and continue trying
        if item_to_place is None:
            if candidate_item_to_place is not None:
                item_to_place = candidate_item_to_place
            else:
                raise FillError('No more progress items left to place.', multiworld=multiworld)

        # find item to replace with progress item
        location_list = multiworld.get_reachable_locations()
        multiworld.random.shuffle(location_list)
        for location in location_list:
            if location.item is not None and not location.item.advancement:
                # safe to replace
                replace_item = location.item
                replace_item.location = None
                itempool.append(replace_item)
                multiworld.push_item(location, item_to_place, True)
                itempool.remove(item_to_place)
                break


def balance_multiworld_progression(multiworld: MultiWorld) -> None:
    # A system to reduce situations where players have no checks remaining, popularly known as "BK mode."
    # Overall progression balancing algorithm:
    # Gather up all locations in a sphere.
    # Define a threshold value based on the player with the most available locations.
    # If other players are below the threshold value, swap progression in this sphere into earlier spheres,
    #   which gives more locations available by this sphere.
    balanceable_players: typing.Dict[int, float] = {
        player: multiworld.worlds[player].options.progression_balancing / 100
        for player in multiworld.player_ids
        if multiworld.worlds[player].options.progression_balancing > 0
    }
    if not balanceable_players:
        logging.info('Skipping multiworld progression balancing.')
    else:
        logging.info(f'Balancing multiworld progression for {len(balanceable_players)} Players.')
        logging.debug(balanceable_players)
        state: CollectionState = CollectionState(multiworld)
        checked_locations: typing.Set[Location] = set()
        unchecked_locations: typing.Set[Location] = set(multiworld.get_locations())

        total_locations_count: typing.Counter[int] = Counter(
            location.player
            for location in multiworld.get_locations()
            if not location.locked
        )
        reachable_locations_count: typing.Dict[int, int] = {
            player: 0
            for player in multiworld.player_ids
            if total_locations_count[player] and len(multiworld.get_filled_locations(player)) != 0
        }
        balanceable_players = {
            player: balanceable_players[player]
            for player in balanceable_players
            if total_locations_count[player]
        }
        sphere_num: int = 1
        moved_item_count: int = 0

        def get_sphere_locations(sphere_state: CollectionState,
                                 locations: typing.Set[Location]) -> typing.Set[Location]:
            return {loc for loc in locations if sphere_state.can_reach(loc)}

        def item_percentage(player: int, num: int) -> float:
            return num / total_locations_count[player]

        # If there are no locations that aren't locked, there's no point in attempting to balance progression.
        if len(total_locations_count) == 0:
            return

        while True:
            # Gather non-locked locations.
            # This ensures that only shuffled locations get counted for progression balancing,
            #   i.e. the items the players will be checking.
            sphere_locations = get_sphere_locations(state, unchecked_locations)
            for location in sphere_locations:
                unchecked_locations.remove(location)
                if not location.locked:
                    reachable_locations_count[location.player] += 1

            logging.debug(f"Sphere {sphere_num}")
            logging.debug(f"Reachable locations: {reachable_locations_count}")
            debug_percentages = {
                player: round(item_percentage(player, num), 2)
                for player, num in reachable_locations_count.items()
            }
            logging.debug(f"Reachable percentages: {debug_percentages}\n")
            sphere_num += 1

            if checked_locations:
                max_percentage = max(map(lambda p: item_percentage(p, reachable_locations_count[p]),
                                         reachable_locations_count))
                threshold_percentages = {
                    player: max_percentage * balanceable_players[player]
                    for player in balanceable_players
                }
                logging.debug(f"Thresholds: {threshold_percentages}")
                balancing_players = {
                    player
                    for player, reachables in reachable_locations_count.items()
                    if (player in threshold_percentages
                        and item_percentage(player, reachables) < threshold_percentages[player])
                }
                if balancing_players:
                    balancing_state = state.copy()
                    balancing_unchecked_locations = unchecked_locations.copy()
                    balancing_reachables = reachable_locations_count.copy()
                    balancing_sphere = sphere_locations.copy()
                    candidate_items: typing.Dict[int, typing.Set[Location]] = collections.defaultdict(set)
                    while True:
                        # Check locations in the current sphere and gather progression items to swap earlier
                        for location in balancing_sphere:
                            if location.advancement:
                                balancing_state.collect(location.item, True, location)
                                player = location.item.player
                                # only replace items that end up in another player's world
                                if (not location.locked and not location.item.skip_in_prog_balancing and
                                        player in balancing_players and
                                        location.player != player and
                                        location.progress_type != LocationProgressType.PRIORITY):
                                    candidate_items[player].add(location)
                                    logging.debug(f"Candidate item: {location.name}, {location.item.name}")
                        balancing_sphere = get_sphere_locations(balancing_state, balancing_unchecked_locations)
                        for location in balancing_sphere:
                            balancing_unchecked_locations.remove(location)
                            if not location.locked:
                                balancing_reachables[location.player] += 1
                        if multiworld.has_beaten_game(balancing_state) or all(
                                item_percentage(player, reachables) >= threshold_percentages[player]
                                for player, reachables in balancing_reachables.items()
                                if player in threshold_percentages):
                            break
                        elif not balancing_sphere:
                            raise RuntimeError('Not all required items reachable. Something went terribly wrong here.')
                    # Gather a set of locations which we can swap items into
                    unlocked_locations: typing.Dict[int, typing.Set[Location]] = collections.defaultdict(set)
                    for l in unchecked_locations:
                        if l not in balancing_unchecked_locations:
                            unlocked_locations[l.player].add(l)
                    items_to_replace: typing.List[Location] = []
                    for player in balancing_players:
                        locations_to_test = unlocked_locations[player]
                        items_to_test = list(candidate_items[player])
                        items_to_test.sort()
                        multiworld.random.shuffle(items_to_test)
                        while items_to_test:
                            testing = items_to_test.pop()
                            reducing_state = state.copy()
                            for location in itertools.chain((
                                l for l in items_to_replace
                                if l.item.player == player
                            ), items_to_test):
                                reducing_state.collect(location.item, True, location)

                            reducing_state.sweep_for_advancements(locations=locations_to_test)

                            if multiworld.has_beaten_game(balancing_state):
                                if not multiworld.has_beaten_game(reducing_state):
                                    items_to_replace.append(testing)
                            else:
                                reduced_sphere = get_sphere_locations(reducing_state, locations_to_test)
                                p = item_percentage(player, reachable_locations_count[player] + len(reduced_sphere))
                                if p < threshold_percentages[player]:
                                    items_to_replace.append(testing)

                    old_moved_item_count = moved_item_count

                    # sort then shuffle to maintain deterministic behaviour,
                    # while allowing use of set for better algorithm growth behaviour elsewhere
                    replacement_locations = sorted(l for l in checked_locations if not l.advancement and not l.locked)
                    multiworld.random.shuffle(replacement_locations)
                    items_to_replace.sort()
                    multiworld.random.shuffle(items_to_replace)

                    # Start swapping items. Since we swap into earlier spheres, no need for accessibility checks. 
                    while replacement_locations and items_to_replace:
                        old_location = items_to_replace.pop()
                        for i, new_location in enumerate(replacement_locations):
                            if new_location.can_fill(state, old_location.item, False) and \
                                    old_location.can_fill(state, new_location.item, False):
                                replacement_locations.pop(i)
                                swap_location_item(old_location, new_location)
                                logging.debug(f"Progression balancing moved {new_location.item} to {new_location}, "
                                              f"displacing {old_location.item} into {old_location}")
                                moved_item_count += 1
                                state.collect(new_location.item, True, new_location)
                                break
                        else:
                            logging.warning(f"Could not Progression Balance {old_location.item}")

                    if old_moved_item_count < moved_item_count:
                        logging.debug(f"Moved {moved_item_count} items so far\n")
                        unlocked = {fresh for player in balancing_players for fresh in unlocked_locations[player]}
                        for location in get_sphere_locations(state, unlocked):
                            unchecked_locations.remove(location)
                            if not location.locked:
                                reachable_locations_count[location.player] += 1
                            sphere_locations.add(location)

            for location in sphere_locations:
                if location.advancement:
                    state.collect(location.item, True, location)
            checked_locations |= sphere_locations

            if multiworld.has_beaten_game(state):
                break
            elif not sphere_locations:
                logging.warning("Progression Balancing ran out of paths.")
                break


def swap_location_item(location_1: Location, location_2: Location, check_locked: bool = True) -> None:
    """Swaps Items of locations. Does NOT swap flags like shop_slot or locked, but does swap event"""
    if check_locked:
        if location_1.locked:
            logging.warning(f"Swapping {location_1}, which is marked as locked.")
        if location_2.locked:
            logging.warning(f"Swapping {location_2}, which is marked as locked.")
    location_2.item, location_1.item = location_1.item, location_2.item
    location_1.item.location = location_1
    location_2.item.location = location_2


def distribute_planned(multiworld: MultiWorld) -> None:
    def warn(warning: str, force: typing.Union[bool, str]) -> None:
        if force in [True, 'fail', 'failure', 'none', False, 'warn', 'warning']:
            logging.warning(f'{warning}')
        else:
            logging.debug(f'{warning}')

    def failed(warning: str, force: typing.Union[bool, str]) -> None:
        if force in [True, 'fail', 'failure']:
            raise Exception(warning)
        else:
            warn(warning, force)

    swept_state = multiworld.state.copy()
    swept_state.sweep_for_advancements()
    reachable = frozenset(multiworld.get_reachable_locations(swept_state))
    early_locations: typing.Dict[int, typing.List[str]] = collections.defaultdict(list)
    non_early_locations: typing.Dict[int, typing.List[str]] = collections.defaultdict(list)
    for loc in multiworld.get_unfilled_locations():
        if loc in reachable:
            early_locations[loc.player].append(loc.name)
        else:  # not reachable with swept state
            non_early_locations[loc.player].append(loc.name)

    world_name_lookup = multiworld.world_name_lookup

    block_value = typing.Union[typing.List[str], typing.Dict[str, typing.Any], str]
    plando_blocks: typing.List[typing.Dict[str, typing.Any]] = []
    player_ids = set(multiworld.player_ids)
    for player in player_ids:
        for block in multiworld.plando_items[player]:
            block['player'] = player
            if 'force' not in block:
                block['force'] = 'silent'
            if 'from_pool' not in block:
                block['from_pool'] = True
            elif not isinstance(block['from_pool'], bool):
                from_pool_type = type(block['from_pool'])
                raise Exception(f'Plando "from_pool" has to be boolean, not {from_pool_type} for player {player}.')
            if 'world' not in block:
                target_world = False
            else:
                target_world = block['world']

            if target_world is False or multiworld.players == 1:  # target own world
                worlds: typing.Set[int] = {player}
            elif target_world is True:  # target any worlds besides own
                worlds = set(multiworld.player_ids) - {player}
            elif target_world is None:  # target all worlds
                worlds = set(multiworld.player_ids)
            elif type(target_world) == list:  # list of target worlds
                worlds = set()
                for listed_world in target_world:
                    if listed_world not in world_name_lookup:
                        failed(f"Cannot place item to {target_world}'s world as that world does not exist.",
                               block['force'])
                        continue
                    worlds.add(world_name_lookup[listed_world])
            elif type(target_world) == int:  # target world by slot number
                if target_world not in range(1, multiworld.players + 1):
                    failed(
                        f"Cannot place item in world {target_world} as it is not in range of (1, {multiworld.players})",
                        block['force'])
                    continue
                worlds = {target_world}
            else:  # target world by slot name
                if target_world not in world_name_lookup:
                    failed(f"Cannot place item to {target_world}'s world as that world does not exist.",
                           block['force'])
                    continue
                worlds = {world_name_lookup[target_world]}
            block['world'] = worlds

            items: block_value = []
            if "items" in block:
                items = block["items"]
                if 'count' not in block:
                    block['count'] = False
            elif "item" in block:
                items = block["item"]
                if 'count' not in block:
                    block['count'] = 1
            else:
                failed("You must specify at least one item to place items with plando.", block['force'])
                continue
            if isinstance(items, dict):
                item_list: typing.List[str] = []
                for key, value in items.items():
                    if value is True:
                        value = multiworld.itempool.count(multiworld.worlds[player].create_item(key))
                    item_list += [key] * value
                items = item_list
            if isinstance(items, str):
                items = [items]
            block['items'] = items

            locations: block_value = []
            if 'location' in block:
                locations = block['location']  # just allow 'location' to keep old yamls compatible
            elif 'locations' in block:
                locations = block['locations']
            if isinstance(locations, str):
                locations = [locations]

            if isinstance(locations, dict):
                location_list = []
                for key, value in locations.items():
                    location_list += [key] * value
                locations = location_list

            if "early_locations" in locations:
                locations.remove("early_locations")
                for target_player in worlds:
                    locations += early_locations[target_player]
            if "non_early_locations" in locations:
                locations.remove("non_early_locations")
                for target_player in worlds:
                    locations += non_early_locations[target_player]

            block['locations'] = list(dict.fromkeys(locations))

            if not block['count']:
                block['count'] = (min(len(block['items']), len(block['locations'])) if
                                  len(block['locations']) > 0 else len(block['items']))
            if isinstance(block['count'], int):
                block['count'] = {'min': block['count'], 'max': block['count']}
            if 'min' not in block['count']:
                block['count']['min'] = 0
            if 'max' not in block['count']:
                block['count']['max'] = (min(len(block['items']), len(block['locations'])) if
                                         len(block['locations']) > 0 else len(block['items']))
            if block['count']['max'] > len(block['items']):
                count = block['count']
                failed(f"Plando count {count} greater than items specified", block['force'])
                block['count'] = len(block['items'])
            if block['count']['max'] > len(block['locations']) > 0:
                count = block['count']
                failed(f"Plando count {count} greater than locations specified", block['force'])
                block['count'] = len(block['locations'])
            block['count']['target'] = multiworld.random.randint(block['count']['min'], block['count']['max'])

            if block['count']['target'] > 0:
                plando_blocks.append(block)

    # shuffle, but then sort blocks by number of locations minus number of items,
    # so less-flexible blocks get priority
    multiworld.random.shuffle(plando_blocks)
    plando_blocks.sort(key=lambda block: (len(block['locations']) - block['count']['target']
                                          if len(block['locations']) > 0
                                          else len(multiworld.get_unfilled_locations(player)) - block['count']['target']))

    for placement in plando_blocks:
        player = placement['player']
        try:
            worlds = placement['world']
            locations = placement['locations']
            items = placement['items']
            maxcount = placement['count']['target']
            from_pool = placement['from_pool']

            candidates = list(multiworld.get_unfilled_locations_for_players(locations, sorted(worlds)))
            multiworld.random.shuffle(candidates)
            multiworld.random.shuffle(items)
            count = 0
            err: typing.List[str] = []
            successful_pairs: typing.List[typing.Tuple[int, Item, Location]] = []
            claimed_indices: typing.Set[typing.Optional[int]] = set()
            for item_name in items:
                index_to_delete: typing.Optional[int] = None
                if from_pool:
                    try:
                        # If from_pool, try to find an existing item with this name & player in the itempool and use it
                        index_to_delete, item = next(
                            (i, item) for i, item in enumerate(multiworld.itempool)
                            if item.player == player and item.name == item_name and i not in claimed_indices
                        )
                    except StopIteration:
                        warn(
                        f"Could not remove {item_name} from pool for {multiworld.player_name[player]} as it's already missing from it.",
                        placement['force'])
                        item = multiworld.worlds[player].create_item(item_name)
                else:
                    item = multiworld.worlds[player].create_item(item_name)

                for location in reversed(candidates):
                    if (location.address is None) == (item.code is None):  # either both None or both not None
                        if not location.item:
                            if location.item_rule(item):
                                if location.can_fill(multiworld.state, item, False):
                                    successful_pairs.append((index_to_delete, item, location))
                                    claimed_indices.add(index_to_delete)
                                    candidates.remove(location)
                                    count = count + 1
                                    break
                                else:
                                    err.append(f"Can't place item at {location} due to fill condition not met.")
                            else:
                                err.append(f"{item_name} not allowed at {location}.")
                        else:
                            err.append(f"Cannot place {item_name} into already filled location {location}.")
                    else:
                        err.append(f"Mismatch between {item_name} and {location}, only one is an event.")

                if count == maxcount:
                    break
            if count < placement['count']['min']:
                m = placement['count']['min']
                failed(
                    f"Plando block failed to place {m - count} of {m} item(s) for {multiworld.player_name[player]}, error(s): {' '.join(err)}",
                    placement['force'])

            # Sort indices in reverse so we can remove them one by one
            successful_pairs = sorted(successful_pairs, key=lambda successful_pair: successful_pair[0] or 0, reverse=True)

            for (index, item, location) in successful_pairs:
                multiworld.push_item(location, item, collect=False)
                location.locked = True
                logging.debug(f"Plando placed {item} at {location}")
                if index is not None:  # If this item is from_pool and was found in the pool, remove it.
                    multiworld.itempool.pop(index)

        except Exception as e:
            raise Exception(
                f"Error running plando for player {player} ({multiworld.player_name[player]})") from e