"""Trading window utilities for the autonomous trading engine.

Pure computation module that determines whether a given timestamp falls
within the allowed trading window (9:45 AM – 3:45 PM ET on weekdays),
whether the US market is open, and when the next trading window opens.

Uses ``zoneinfo.ZoneInfo("America/New_York")`` for Eastern Time handling.
Does not check market holidays (simplified).
"""

from __future__ import annotations

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

# US Eastern timezone
ET = ZoneInfo("America/New_York")

# Trading window boundaries (excludes first/last 15 min of market hours)
WINDOW_OPEN = time(9, 45)
WINDOW_CLOSE = time(15, 45)

# Full US market hours
MARKET_OPEN = time(9, 30)
MARKET_CLOSE = time(16, 0)

# Weekday range: Monday=0 … Friday=4
_WEEKDAYS = range(0, 5)


def is_within_trading_window(dt: datetime) -> bool:
    """Return True if *dt* is between 9:45 AM ET and 3:45 PM ET on a weekday.

    The timestamp is first converted to US/Eastern time.  Weekends are
    always outside the window.  Market holidays are **not** checked
    (simplified implementation).
    """
    et_dt = dt.astimezone(ET)
    if et_dt.weekday() not in _WEEKDAYS:
        return False
    t = et_dt.time()
    return WINDOW_OPEN <= t < WINDOW_CLOSE


def next_window_open(dt: datetime) -> datetime:
    """Return the next datetime when the trading window opens (9:45 AM ET).

    If *dt* is before 9:45 AM ET on a weekday the same day's open is
    returned.  Otherwise the next weekday's 9:45 AM ET is returned.
    """
    et_dt = dt.astimezone(ET)
    today_open = et_dt.replace(
        hour=WINDOW_OPEN.hour,
        minute=WINDOW_OPEN.minute,
        second=0,
        microsecond=0,
    )

    # If we haven't reached today's open yet and it's a weekday, return today
    if et_dt < today_open and et_dt.weekday() in _WEEKDAYS:
        return today_open

    # Otherwise advance to the next weekday
    candidate = et_dt + timedelta(days=1)
    candidate = candidate.replace(
        hour=WINDOW_OPEN.hour,
        minute=WINDOW_OPEN.minute,
        second=0,
        microsecond=0,
    )
    while candidate.weekday() not in _WEEKDAYS:
        candidate += timedelta(days=1)
    return candidate


def is_market_open(dt: datetime) -> bool:
    """Return True if *dt* is during US market hours (9:30 AM – 4:00 PM ET) on a weekday."""
    et_dt = dt.astimezone(ET)
    if et_dt.weekday() not in _WEEKDAYS:
        return False
    t = et_dt.time()
    return MARKET_OPEN <= t < MARKET_CLOSE