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"""Functions for computing an anticipated draw."""

import itertools

from breakqual.utils import calculate_live_thresholds, determine_liveness
from draw.generator.utils import ispow2, partial_break_round_split
from participants.prefetch import populate_win_counts

def calculate_anticipated_draw(round):
    """Calculates an anticipated draw for the next round, based on the draw for
    the last round. Returns a list of tuples
        `(bracket_min, bracket_max, liveness)`,
    being the minimum and maximum brackets possible for that room, and the
    maximum number of teams that might be live in it. If the previous round's
    draw doesn't exist, it will just return an empty list.

      1. Take the (actual) draw of the last round, with team points
      2. For each room, compute a (min, max) of outcomes for each team.
      3. Take the min, divide into rooms to make the `bracket_min` for each room.
      4. Take the max, divide into rooms to make the `bracket_max` for each room.

    `round` should be the round for which you want an anticipated draw (the
    "next round").

    nteamsindebate = 4 if round.tournament.pref('teams_in_debate') == 'bp' else 2

    if round.prev is None or not round.prev.debate_set.exists() or round.is_break_round:
        # Special cases: If this is the first round, everyone will be on zero.
        # Just take all teams, rounded down -- if this is done, it'll typically
        # be done before availability is locked down. Also do this if the last
        # round hasn't yet been drawn, since that's premature for bracket
        # predictions.
        # Also occurs for elimination rounds as everyone is just as live.

        nteams = 0
        if round.is_break_round:
            break_size = round.break_category.break_size
            nprev_rounds = round.break_category.round_set.filter(seq__lt=round.seq).count()
            partial_two = nteamsindebate == 2 and not ispow2(break_size)
            partial_bp = nteamsindebate == 4 and ispow2(break_size // 6)
            if nprev_rounds > 0 and (partial_two or partial_bp):
                # If using partial elimination rounds, the second round is the first for
                # the powers of two, so start counting from here.
                nprev_rounds -= 1

            if nprev_rounds == 0 and nteamsindebate == 2:
                nteams = partial_break_round_split(break_size)[0] * 2
                # Subsequent rounds are half the previous, but always a power of 2
                nteams = 1 << (break_size.bit_length() - 1 - nprev_rounds)
            nteams = round.tournament.team_set.count()

        npanels = nteams // nteamsindebate
        return [(0, 0, 0) for i in range(npanels)]

    # 1. Take the (actual) draw of the last round, with team points
    debates = round.prev.debate_set_with_prefetches(ordering=('room_rank',),
        teams=True, adjudicators=False, speakers=False, venues=False)
    if round.prev.prev:
        populate_win_counts([team for debate in debates for team in debate.teams],
        # just say everyone is on zero (since no rounds have finished yet)
        for debate in debates:
            for team in debate.teams:
                team._points = 0

    # 2. Compute a (min, max) of outcomes for each team
    team_points_after = []
    points_available = [round.prev.weight * i for i in range(nteamsindebate)]
    for debate in debates:
        points_now = [team.points_count for team in debate.teams]
        highest = max(points_now)
        lowest = min(points_now)

        # Most cases will be single-point rooms or rooms with pull-ups from only
        # one bracket; in these cases it's easy to prove this closed-form
        # guarantee for what the teams in that room will look like afterwards.
        if highest - lowest <= 1:
            points_after = [(lowest+i, highest+i) for i in points_available]

        # For more complicated rooms (e.g. [9, 8, 8, 7]), it gets harder; just
        # use brute force. For few enough rooms this won't be too bad a hit.
            possible_outcomes = []
            for result in itertools.permutations(points_available):
                outcome = [n + r for n, r in zip(points_now, result)]
            points_after = [(min(team_after), max(team_after)) for team_after in zip(*possible_outcomes)]


    # 3. Take the min, divide into rooms to make the `bracket_min` for each room.
    # 4. Take the max, divide into rooms to make the `bracket_max` for each room.
    lowers, uppers = [sorted(x, reverse=True) for x in zip(*team_points_after)]
    brackets_min = [max(r) for r in zip(*([iter(lowers)] * nteamsindebate))]
    brackets_max = [max(r) for r in zip(*([iter(uppers)] * nteamsindebate))]

    open_category = round.tournament.breakcategory_set.filter(is_general=True).first()
    if open_category:
        live_thresholds = calculate_live_thresholds(open_category, round.tournament, round)
        liveness_by_lower = [determine_liveness(live_thresholds, x) for x in lowers]
        liveness_by_upper = [determine_liveness(live_thresholds, x) for x in uppers]
        liveness_by_team = [x == 'live' or y == 'live' for x, y in zip(liveness_by_lower, liveness_by_upper)]
        liveness = [x.count(True) for x in zip(*([iter(liveness_by_team)] * nteamsindebate))]
        liveness = [0] * len(debates)

    return zip(brackets_min, brackets_max, liveness)