"""Paid-tier access checks.

Two sources can grant paid access:

1. ``user.tier in {"paid", "enterprise"}`` — set by Paddle webhook in
   Phase D.3 once a subscription is active.
2. ``user.credit_until > now()`` — non-subscription credit. Currently
   populated by the admin CLI (`python -m app.cli grant-credit`) and, in
   D.3, by the referral-conversion path (3 months at 50% off).

Either is sufficient. We use a single ``paid_status`` function so the
Settings page can show *why* a user has paid access ("paid subscription"
vs "credit, 47 days left") without duplicating the rules.
"""
from __future__ import annotations

from dataclasses import dataclass
from datetime import datetime, timezone

from fastapi import Depends, HTTPException, status

from app.auth import CurrentUser, require_auth
from app.models import User

# How many hours of news the free tier sees. Paid sees whatever the
# endpoint's `since_hours` param requests (up to its own max).
FREE_NEWS_WINDOW_HOURS = 6.0


def _utcnow() -> datetime:
    return datetime.now(timezone.utc)


@dataclass(frozen=True)
class PaidStatus:
    """Snapshot of paid-tier status for one user."""
    active: bool
    source: str | None              # "tier" | "credit" | None
    expires_at: datetime | None     # only meaningful when source == "credit"
    days_remaining: int | None      # only meaningful when source == "credit"


def _aware(dt: datetime | None) -> datetime | None:
    """MariaDB round-trips DateTime(timezone=True) as a naive UTC value
    via aiomysql. Normalise to tz-aware so comparisons against utcnow()
    never raise."""
    if dt is None:
        return None
    if dt.tzinfo is None:
        return dt.replace(tzinfo=timezone.utc)
    return dt


def paid_status(user: User | None) -> PaidStatus:
    """Compute paid-tier status for a User row. ``user=None`` (anonymous
    or admin bearer-token) returns inactive — callers should special-case
    admin separately via ``is_paid_active``."""
    if user is None:
        return PaidStatus(False, None, None, None)
    if user.tier in ("paid", "enterprise"):
        return PaidStatus(True, "tier", None, None)
    cu = _aware(getattr(user, "credit_until", None))
    if cu is not None and cu > _utcnow():
        days = max(0, (cu - _utcnow()).days)
        return PaidStatus(True, "credit", cu, days)
    return PaidStatus(False, None, None, None)


def is_paid_active(principal: CurrentUser | User | None) -> bool:
    """True if the principal has paid-tier access right now. Admin
    bearer-token (``CurrentUser.is_admin=True``) always passes."""
    if principal is None:
        return False
    if isinstance(principal, CurrentUser):
        if principal.is_admin:
            return True
        return paid_status(principal.user).active
    return paid_status(principal).active


async def require_paid(
    principal: CurrentUser = Depends(require_auth),
) -> CurrentUser:
    """FastAPI dependency for paid-only endpoints. Returns the principal
    on success; raises 402 Payment Required otherwise.

    402 is the semantically-correct code for "auth succeeded but plan
    insufficient" — distinct from 401 (not authenticated) and 403
    (authenticated but forbidden by ACL). Frontends key off it to show
    the upgrade prompt rather than redirecting to /login."""
    if is_paid_active(principal):
        return principal
    raise HTTPException(
        status_code=status.HTTP_402_PAYMENT_REQUIRED,
        detail={
            "code": "paid_required",
            "message": "This feature requires an active paid plan or credit.",
        },
    )