"""Central YouTube Data API quota guard.

The whole app shares one daily budget (the API resets at midnight US Pacific time).
Steady-state work (RSS detection is free; enrichment of new videos is cheap) should
always be allowed; expensive backfill must yield to the remaining budget.
"""
from datetime import datetime
from zoneinfo import ZoneInfo

from sqlalchemy.dialects.postgresql import insert as pg_insert
from sqlalchemy.orm import Session

from app.config import settings
from app.models import ApiQuotaUsage

_PACIFIC = ZoneInfo("America/Los_Angeles")


def pacific_today():
    return datetime.now(_PACIFIC).date()


def units_used_today(db: Session) -> int:
    row = db.get(ApiQuotaUsage, pacific_today())
    return row.units_used if row else 0


def remaining_today(db: Session) -> int:
    return max(0, settings.quota_daily_budget - units_used_today(db))


def can_spend(db: Session, units: int) -> bool:
    return remaining_today(db) >= units


def record_usage(db: Session, units: int) -> None:
    """Atomically add `units` to today's counter (upsert)."""
    if units <= 0:
        return
    day = pacific_today()
    stmt = (
        pg_insert(ApiQuotaUsage)
        .values(day=day, units_used=units)
        .on_conflict_do_update(
            index_elements=[ApiQuotaUsage.day],
            set_={"units_used": ApiQuotaUsage.units_used + units},
        )
    )
    db.execute(stmt)
    db.commit()