"""Gateway operations and durable verification scheduling."""

from datetime import timedelta

from django.conf import settings
from django.db import transaction
from django.utils import timezone
import requests


class PaymentVerificationUncertain(Exception):
    """The gateway response does not prove either payment success or failure."""


class PaymentReversalUncertain(Exception):
    """The gateway did not give a conclusive response to a reversal request."""


class PaymentReversalRejected(Exception):
    """The gateway definitively rejected the reversal and needs human review."""


def request_payment_verification(payment):
    try:
        response = requests.post(
            settings.ZARINPAL_VERIFY_URL,
            json={
                "merchant_id": settings.ZARINPAL_MERCHANT_ID,
                "amount": payment.amount,
                "authority": payment.authority,
            },
            headers={"accept": "application/json", "content-type": "application/json"},
            timeout=15,
        )
        status_code = getattr(response, "status_code", 200)
        if isinstance(status_code, int) and status_code >= 400:
            raise PaymentVerificationUncertain(
                f"ZarinPal verification returned HTTP {status_code}"
            )
        body = response.json()
    except PaymentVerificationUncertain:
        raise
    except Exception as exc:
        raise PaymentVerificationUncertain("ZarinPal verification request failed") from exc

    if not isinstance(body, dict) or not isinstance(body.get("data"), dict):
        raise PaymentVerificationUncertain("ZarinPal returned an invalid verification response")

    code = body["data"].get("code")
    try:
        code = int(code)
    except (TypeError, ValueError) as exc:
        raise PaymentVerificationUncertain("ZarinPal returned no verification code") from exc

    if code not in (100, 101, -51):
        raise PaymentVerificationUncertain(
            f"ZarinPal returned an inconclusive verification code: {code}"
        )

    return code, body["data"]


def request_payment_reversal(payment):
    """Reverse a paid transaction through ZarinPal's transaction reversal API."""
    try:
        response = requests.post(
            settings.ZARINPAL_REVERSE_URL,
            json={
                "merchant_id": settings.ZARINPAL_MERCHANT_ID,
                "authority": payment.authority,
            },
            headers={"accept": "application/json", "content-type": "application/json"},
            timeout=15,
        )
        status_code = getattr(response, "status_code", 200)
        if isinstance(status_code, int) and status_code >= 500:
            raise PaymentReversalUncertain(
                f"ZarinPal reversal returned HTTP {status_code}"
            )
        if isinstance(status_code, int) and status_code >= 400:
            raise PaymentReversalRejected(
                f"ZarinPal reversal was rejected with HTTP {status_code}"
            )
        body = response.json()
    except (PaymentReversalUncertain, PaymentReversalRejected):
        raise
    except Exception as exc:
        raise PaymentReversalUncertain("ZarinPal reversal request failed") from exc

    if not isinstance(body, dict) or not isinstance(body.get("data"), dict):
        if isinstance(body, dict) and isinstance(body.get("errors"), dict):
            raise PaymentReversalRejected("ZarinPal rejected the reversal request")
        raise PaymentReversalUncertain("ZarinPal returned an invalid reversal response")

    code = body["data"].get("code")
    try:
        code = int(code)
    except (TypeError, ValueError) as exc:
        raise PaymentReversalUncertain("ZarinPal returned no reversal status code") from exc

    if code != 100:
        raise PaymentReversalRejected(f"ZarinPal rejected the reversal with code {code}")
    return body["data"]


def claim_payment_verification(
    payment_id: int,
    *,
    lease_seconds: int = 120,
    allow_terminal: bool = False,
    allow_manual_review: bool = False,
):
    """Claim one bounded verification attempt using the database as the lock."""
    from apps.payments.models import Payment

    with transaction.atomic():
        try:
            payment = Payment.objects.select_for_update().get(pk=payment_id)
        except Payment.DoesNotExist:
            return None, False

        if payment.status == Payment.OrderStatusChoices.PAID or (
            payment.status in (
                Payment.OrderStatusChoices.FAILED,
                Payment.OrderStatusChoices.CANCELED,
            )
            and not allow_terminal
        ):
            return payment, False

        now = timezone.now()
        if payment.verification_manual_review_at is not None and not allow_manual_review:
            return payment, False
        if not payment.authority:
            _mark_payment_manual_review(payment, now)
            return payment, False
        if payment.verification_lease_until and payment.verification_lease_until > now:
            return payment, False

        was_dispatched = bool(
            payment.verification_dispatch_expires_at
            and payment.verification_dispatch_expires_at > now
        )
        if (
            payment.verification_next_attempt_at
            and payment.verification_next_attempt_at > now
            and not was_dispatched
        ):
            return payment, False

        max_attempts = getattr(settings, "PAYMENT_VERIFICATION_MAX_ATTEMPTS", 6)
        if payment.verification_attempts >= max_attempts and not allow_manual_review:
            _mark_payment_manual_review(payment, now)
            return payment, False

        payment.verification_attempts += 1
        payment.verification_last_attempt_at = now
        payment.verification_next_attempt_at = None
        payment.verification_lease_until = now + timedelta(seconds=lease_seconds)
        payment.verification_dispatch_expires_at = None
        payment.verification_manual_review_at = None
        payment.save(update_fields=[
            "verification_attempts",
            "verification_last_attempt_at",
            "verification_next_attempt_at",
            "verification_lease_until",
            "verification_dispatch_expires_at",
            "verification_manual_review_at",
        ])
        return payment, True


def schedule_payment_verification_retry(payment_id: int):
    """Persist the next backoff step or stop at manual review after exhaustion."""
    from apps.payments.models import Payment

    with transaction.atomic():
        try:
            payment = Payment.objects.select_for_update().get(pk=payment_id)
        except Payment.DoesNotExist:
            return None

        payment.verification_lease_until = None
        payment.verification_dispatch_expires_at = None
        if payment.status in (
            Payment.OrderStatusChoices.PAID,
            Payment.OrderStatusChoices.FAILED,
            Payment.OrderStatusChoices.CANCELED,
        ):
            payment.verification_next_attempt_at = None
            payment.verification_manual_review_at = None
            payment.save(update_fields=[
                "verification_lease_until",
                "verification_dispatch_expires_at",
                "verification_next_attempt_at",
                "verification_manual_review_at",
            ])
            return None

        max_attempts = getattr(settings, "PAYMENT_VERIFICATION_MAX_ATTEMPTS", 6)
        if payment.verification_attempts >= max_attempts:
            _mark_payment_manual_review(payment, timezone.now())
            return None

        attempt_index = max(payment.verification_attempts - 1, 0)
        delay = min(60 * (2 ** attempt_index), 15 * 60)
        payment.verification_next_attempt_at = timezone.now() + timedelta(seconds=delay)
        payment.verification_manual_review_at = None
        payment.save(update_fields=[
            "verification_lease_until",
            "verification_dispatch_expires_at",
            "verification_next_attempt_at",
            "verification_manual_review_at",
        ])
        return delay


def mark_payment_manual_review(payment_id: int):
    """Keep an unresolved payment pending and make support review durable."""
    from apps.payments.models import Payment

    with transaction.atomic():
        try:
            payment = Payment.objects.select_for_update().get(pk=payment_id)
        except Payment.DoesNotExist:
            return None
        _mark_payment_manual_review(payment, timezone.now())
        return payment


def _mark_payment_manual_review(payment, now):
    payment.verification_manual_review_at = payment.verification_manual_review_at or now
    payment.verification_next_attempt_at = None
    payment.verification_lease_until = None
    payment.verification_dispatch_expires_at = None
    payment.save(update_fields=[
        "verification_manual_review_at",
        "verification_next_attempt_at",
        "verification_lease_until",
        "verification_dispatch_expires_at",
    ])