from datetime import datetime, time, timedelta
from zoneinfo import ZoneInfo

from app.bars.models import Timeframe

UTC = ZoneInfo("UTC")
EASTERN = ZoneInfo("America/New_York")
SESSION_OPEN = time(18, 0)
SESSION_CLOSE = time(17, 0)
FUTURE_SLOT_COUNT = 180


def _session_open_local(current: datetime) -> datetime:
    session_date = current.date() if current.timetz().replace(tzinfo=None) >= SESSION_OPEN else current.date() - timedelta(days=1)
    return datetime.combine(session_date, SESSION_OPEN, EASTERN)


def bucket_start(t: int, tf: Timeframe) -> int:
    # Everything below a day divides the hour evenly, so UTC boundaries are
    # correct and session anchoring is unnecessary. Only the daily bar needs to
    # know that the CME trading day runs 18:00 to 17:00 ET.
    if tf is not Timeframe.D1:
        return (t // tf.seconds) * tf.seconds

    current = datetime.fromtimestamp(t, UTC).astimezone(EASTERN)
    return int(_session_open_local(current).timestamp())


def bucket_duration(t: int, tf: Timeframe) -> int:
    """Wall-clock span of one logical bar bucket.

    Intraday buckets are fixed. A daily line advances only through the active
    18:00-17:00 ET session, not the settlement halt; constructing the close in
    Eastern keeps DST transitions correct without shifting stored UTC times.
    """
    if tf is not Timeframe.D1:
        return tf.seconds
    current = datetime.fromtimestamp(t, UTC).astimezone(EASTERN)
    next_close = datetime.combine(current.date() + timedelta(days=1), SESSION_CLOSE, EASTERN)
    return int(next_close.timestamp()) - t


def next_bucket_start(t: int, tf: Timeframe) -> int:
    """Next projected source-bar open, skipping known CME closures."""
    if tf is not Timeframe.D1:
        candidate = datetime.fromtimestamp(t + tf.seconds, UTC).astimezone(EASTERN)
        weekday = candidate.weekday()
        wall_time = candidate.timetz().replace(tzinfo=None)
        if weekday == 5:  # Saturday -> Sunday open.
            candidate = datetime.combine(candidate.date() + timedelta(days=1), SESSION_OPEN, EASTERN)
        elif weekday == 6 and wall_time < SESSION_OPEN:
            candidate = datetime.combine(candidate.date(), SESSION_OPEN, EASTERN)
        elif weekday in {0, 1, 2, 3} and SESSION_CLOSE <= wall_time < SESSION_OPEN:
            candidate = datetime.combine(candidate.date(), SESSION_OPEN, EASTERN)
        elif weekday == 4 and wall_time >= SESSION_CLOSE:
            candidate = datetime.combine(candidate.date() + timedelta(days=2), SESSION_OPEN, EASTERN)
        return int(candidate.timestamp())
    current = datetime.fromtimestamp(t, UTC).astimezone(EASTERN)
    candidate = current.date() + timedelta(days=1)
    # Daily futures sessions open Sunday through Thursday.
    while candidate.weekday() not in {6, 0, 1, 2, 3}:
        candidate += timedelta(days=1)
    return int(datetime.combine(candidate, SESSION_OPEN, EASTERN).timestamp())


def future_bucket_starts(t: int, tf: Timeframe, count: int = FUTURE_SLOT_COUNT) -> list[int]:
    values = []
    for _ in range(count):
        t = next_bucket_start(t, tf)
        values.append(t)
    return values