"""Service for charging the unified credit wallet per successful web crawl.

Deliberately mirrors :class:`app.services.etl_credit_service.EtlCreditService`:
a simple **gate -> pre-check -> post-charge** model (no reserve/finalize),
because a crawl has no LLM token accumulator to settle against. The billable
unit is one *successful* crawl (``CrawlOutcomeStatus.SUCCESS``).

The price is **fully config-driven** — there is no hardcoded rate anywhere.
``config.WEB_CRAWL_MICROS_PER_SUCCESS`` is the single source of truth (default
``1000`` micro-USD == $1 / 1000 crawls); retune it via env + restart, no code
change. When ``config.WEB_CRAWL_CREDIT_BILLING_ENABLED`` is False (the default
for self-hosted / OSS installs) every check/charge is a no-op, preserving the
prior effectively-free crawl behaviour.

``billing_enabled()`` and ``successes_to_micros()`` are exposed as static
helpers so the capability biller (``app/capabilities/core/billing.py``, the
``web.crawl`` verb) can share the flag/price math when gating and charging a
crawl run.
"""

from uuid import UUID

from sqlalchemy.ext.asyncio import AsyncSession

from app.config import config

# Wallet math (spendable / check / debit) is shared with the platform-scrape
# biller — see app/services/wallet_credit.py.
from app.services import wallet_credit

# Reuse the ETL service's error type so callers (and tests) have one exception
# to catch for "out of credit" across every per-unit wallet biller.
from app.services.etl_credit_service import InsufficientCreditsError

__all__ = ["InsufficientCreditsError", "WebCrawlCreditService"]


class WebCrawlCreditService:
    """Checks and charges the credit wallet for successful web crawls."""

    def __init__(self, session: AsyncSession):
        self.session = session

    @staticmethod
    def billing_enabled() -> bool:
        return config.WEB_CRAWL_CREDIT_BILLING_ENABLED

    @staticmethod
    def successes_to_micros(successes: int) -> int:
        """Convert a successful-crawl count to USD micro-credits.

        Reads ``config.WEB_CRAWL_MICROS_PER_SUCCESS`` — the single, env-tunable
        source of truth for crawl price.
        """
        return int(successes) * config.WEB_CRAWL_MICROS_PER_SUCCESS

    @staticmethod
    def captcha_billing_enabled() -> bool:
        """Phase 3d: whether captcha *solves* are metered.

        Independent of crawl billing: a deployment may bill solves without
        billing crawls (or vice-versa). Off by default.
        """
        return config.WEB_CRAWL_CAPTCHA_BILLING_ENABLED

    @staticmethod
    def captcha_solves_to_micros(attempts: int) -> int:
        """Convert a captcha *attempt* count to USD micro-credits.

        Reads ``config.WEB_CRAWL_CAPTCHA_MICROS_PER_SOLVE`` (single source of
        truth). Charged per attempt — not per success — because the solver
        vendor bills every attempt regardless of crawl outcome.
        """
        return int(attempts) * config.WEB_CRAWL_CAPTCHA_MICROS_PER_SOLVE

    async def _spendable_micros(self, user_id: str | UUID) -> int:
        """Raw ``balance - reserved`` read, **ungated** by any billing flag.

        Used by :meth:`check_balance` for combined (crawl + captcha) pre-flight,
        where the relevant gate is decided by the caller, not by a single flag.
        """
        return await wallet_credit.spendable_micros(self.session, user_id)

    async def get_available_micros(self, user_id: str | UUID) -> int | None:
        """Return spendable credit in micro-USD (``balance - reserved``).

        Returns ``None`` when crawl billing is disabled, which callers treat as
        "unlimited" (no blocking, no charge).
        """
        if not config.WEB_CRAWL_CREDIT_BILLING_ENABLED:
            return None
        return await self._spendable_micros(user_id)

    async def check_balance(self, user_id: str | UUID, required_micros: int) -> None:
        """Raise :class:`InsufficientCreditsError` if the wallet can't cover
        ``required_micros`` (a combined crawl + worst-case captcha estimate).

        Generic and **ungated** — the caller computes ``required_micros`` from
        whichever billers are enabled and only calls this when at least one is.
        No-op for a non-positive requirement.
        """
        await wallet_credit.check_balance(self.session, user_id, required_micros)

    async def check_credits(
        self, user_id: str | UUID, estimated_successes: int = 1
    ) -> None:
        """Raise :class:`InsufficientCreditsError` if the user can't afford
        ``estimated_successes`` crawls.

        No-op when crawl billing is disabled. ``estimated_successes`` is a safe
        upper bound (``len(urls)``) — actual successes are always <=, so a
        passing pre-flight guarantees the wallet can never go negative.
        """
        if not config.WEB_CRAWL_CREDIT_BILLING_ENABLED:
            return

        required = self.successes_to_micros(estimated_successes)
        available = await self.get_available_micros(user_id)
        if available is None:
            return

        if required > available:
            raise InsufficientCreditsError(
                message=(
                    "This crawl would exceed your available credit. "
                    f"Available: ${available / 1_000_000:.2f}. "
                    f"Up to {estimated_successes} URL(s) cost about "
                    f"${required / 1_000_000:.2f}. Add more credits to continue."
                ),
                balance_micros=available,
                required_micros=required,
            )

    async def _apply_debit(self, user_id: str | UUID, cost_micros: int) -> int | None:
        """Debit ``cost_micros`` from the wallet and commit (shared by all
        charge paths). Flushes any audit row the caller staged before this.

        Mirrors ``EtlCreditService.charge_credits``' commit-then-refresh +
        best-effort auto-reload. No-op for a non-positive cost.
        """
        return await wallet_credit.apply_debit(self.session, user_id, cost_micros)

    async def charge_credits(self, user_id: str | UUID, successes: int) -> int | None:
        """Debit the wallet for ``successes`` successful crawls.

        No-op when crawl billing is disabled or ``successes <= 0``. Returns the
        new balance in micros, or ``None`` when nothing was charged.
        """
        if not config.WEB_CRAWL_CREDIT_BILLING_ENABLED:
            return None
        if successes <= 0:
            return None
        return await self._apply_debit(user_id, self.successes_to_micros(successes))

    async def charge_captcha(self, user_id: str | UUID, attempts: int) -> int | None:
        """Debit the wallet for ``attempts`` captcha solves (Phase 3d).

        Per-attempt (not per-success): the solver charges for every attempt even
        when the crawl ultimately fails. No-op when captcha billing is disabled
        or ``attempts <= 0``.
        """
        if not config.WEB_CRAWL_CAPTCHA_BILLING_ENABLED:
            return None
        if attempts <= 0:
            return None
        return await self._apply_debit(user_id, self.captcha_solves_to_micros(attempts))