from django.db.models import ExpressionWrapper, F, FloatField, Q, Sum, Value, Window
from django.db.models.functions import Coalesce, Power, Rank

from events.models import Event

# points = 1000 * (1 / (remaining_seconds + 0.5)) ** 2, computed per press and
# summed per player. Never stored - always derived live from Press rows.
POINTS_BASE = 1000.0
POINTS_OFFSET = 0.5
POINTS_EXPONENT = -2.0


def _press_points_expression():
    base = ExpressionWrapper(
        F("clock_presses__remaining_before_press") + Value(POINTS_OFFSET),
        output_field=FloatField(),
    )
    return ExpressionWrapper(
        Value(POINTS_BASE) * Power(base, Value(POINTS_EXPONENT)),
        output_field=FloatField(),
    )


def ranked_players(event: Event):
    """All users annotated with their live total `clock_points` (not `points`,
    that one is the market balance field on CustomUser) for this event and
    DB-computed RANK(). Points only ever come from presses made in `event` -
    a player's history in another event never leaks into this leaderboard."""
    from accounts.models import CustomUser

    points = Coalesce(
        Sum(_press_points_expression(), filter=Q(clock_presses__event=event)),
        Value(0.0),
        output_field=FloatField(),
    )
    return CustomUser.objects.annotate(clock_points=points).annotate(
        rank=Window(expression=Rank(), order_by=F("clock_points").desc())
    )