from django.core.cache import cache
from django.db import transaction
from django.db.models import F
from django.shortcuts import get_object_or_404
from drf_spectacular.types import OpenApiTypes
from drf_spectacular.utils import OpenApiParameter, extend_schema
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response
from rest_framework.throttling import ScopedRateThrottle
from rest_framework.views import APIView

from payment.models import Order
from payment.services import create_order

from .models import Plan, Subscription
from .serializers import (
    PlansListResponseSerializer,
    PurchaseRequestSerializer,
    PurchaseResponseSerializer,
    SubscriptionStatusResponseSerializer,
)


class GuestAwarePurchaseThrottle(ScopedRateThrottle):
    """همون الگوی GuestAwareAIThrottle/GuestAwareFamilyThrottle/etc: چرخشِ
    حساب مهمان نباید bucket تازه‌ی purchase بده — این endpoint حساسِ مالیه
    (Subscription می‌سازه/آپدیت می‌کنه، create_order رو صدا می‌زنه). برای
    مهمان‌ها کلیدِ cache بر اساسِ IP هست، نه pk."""

    def get_cache_key(self, request, view):
        user = request.user
        if user and user.is_authenticated and getattr(user, 'is_guest', False):
            ident = f'guest-ip:{self.get_ident(request)}'
        elif user and user.is_authenticated:
            ident = user.pk
        else:
            ident = self.get_ident(request)

        return self.cache_format % {'scope': self.scope, 'ident': ident}


# پلن‌ها تقریباً هیچ‌وقت عوض نمی‌شوند و روی صفحه‌ی اشتراک هر بار خوانده می‌شوند.
# با هر save/delete روی Plan کش باطل می‌شود (subscription/receivers.py).
PLANS_CACHE_KEY = 'subscription:plans:v1'
PLANS_CACHE_TTL = 3600


class PlansListView(APIView):
    """GET /api/subscription/plans — list available plans."""

    @extend_schema(responses=PlansListResponseSerializer, tags=['Subscription (subscription)'])
    def get(self, request):
        def build():
            return {
                'plans': [
                    {
                        'id': str(p.id),
                        'title': p.title,
                        'price': p.price,
                        'currency': p.currency,
                        'popular': p.popular,
                        'discountPercent': p.discount_percent,
                        'durationDays': p.duration_days,
                        'features': p.features or [],
                        'badge': p.badge,
                    }
                    for p in Plan.objects.all()
                ]
            }

        data = cache.get_or_set(PLANS_CACHE_KEY, build, PLANS_CACHE_TTL)
        return Response(PlansListResponseSerializer(data).data)


class PurchaseView(APIView):
    """POST /api/subscription/purchase — starts a purchase (Idempotency-Key
    header supported). Creates/updates a pending Subscription, then calls
    the payment app's service directly (in-process, not a separate HTTP call)
    to create an Order."""

    permission_classes = [IsAuthenticated]
    # این throttle مستقلِ Idempotency-Key است چون اون فقط جلوی تکرارِ *همون*
    # کلید رو می‌گیره، نه حجمِ درخواست‌های متفاوت. کاربرهای مهمان با هر
    # deviceId یک pk تازه می‌گیرن، پس کلیدِ per-user ساده قابل‌دورزدنه؛
    # GuestAwarePurchaseThrottle برای مهمان‌ها بر اساسِ IP کلید می‌سازه
    # (مثلِ GuestAwareAIThrottle/FamilyThrottle/DiscountThrottle) و برای
    # کاربرهای غیرمهمان رفتارِ per-user را حفظ می‌کنه.
    throttle_scope = 'purchase'
    throttle_classes = [GuestAwarePurchaseThrottle]

    @extend_schema(
        request=PurchaseRequestSerializer,
        responses=PurchaseResponseSerializer,
        parameters=[
            OpenApiParameter(
                'Idempotency-Key', OpenApiTypes.STR, OpenApiParameter.HEADER, required=False,
                description=(
                    'کلید یکتای idempotency برای جلوگیری از ساخت سفارش تکراری هنگام retry. '
                    'در صورت عدم ارسال، یک کلید تصادفی ساخته می‌شود.'
                ),
            ),
        ],
        tags=['Subscription (subscription)'],
    )
    def post(self, request):
        serializer = PurchaseRequestSerializer(data=request.data)
        serializer.is_valid(raise_exception=True)
        v = serializer.validated_data
        user = request.user

        plan = get_object_or_404(Plan, pk=v['planId'])
        idempotency_key = request.headers.get('Idempotency-Key')

        # Three-phase flow so create_order (which may call an external payment
        # gateway) never runs inside a DB transaction/lock: phase 1 creates/updates
        # the pending Subscription, phase 2 calls create_order and restores the
        # prior state on failure, phase 3 attaches order_id atomically.
        existing_order = None
        if idempotency_key:
            existing_order = Order.objects.filter(idempotency_key=idempotency_key).first()

        prior_subscription = Subscription.objects.filter(user_id=user.id).first()
        prior_snapshot = None
        if prior_subscription is not None:
            prior_snapshot = {
                'status': prior_subscription.status,
                'plan_id': prior_subscription.plan_id,
                'order_id': prior_subscription.order_id,
            }

        if existing_order is not None:
            # Retry path: leave an existing subscription untouched, only
            # create one if it's genuinely missing.
            if prior_subscription is None:
                # Fresh row: version starts at 1 to give it a CAS token.
                subscription = Subscription.objects.create(
                    user_id=user.id, plan=plan, status='pending', version=1,
                )
                subscription_is_new = True
            else:
                subscription = prior_subscription
                subscription_is_new = False
        else:
            subscription, subscription_is_new = Subscription.objects.update_or_create(
                user_id=user.id,
                defaults={'plan': plan, 'status': 'pending'},
            )
            # Two concurrent requests can reach an identical intermediate state,
            # so version is bumped atomically here to give this write a unique
            # CAS token the cleanup below can match against.
            Subscription.objects.filter(pk=subscription.pk).update(version=F('version') + 1)
            subscription.refresh_from_db(fields=['version'])

        try:
            order, payment_url = create_order(
                user_id=user.id,
                amount=plan.price,
                currency=plan.currency,
                subscription_id=subscription.id,
                idempotency_key=idempotency_key,
            )
        except Exception:
            # Guard by pk+status+plan_id+order_id+version so this cleanup only
            # matches the exact row state phase 1 wrote; any concurrent writer
            # (another request, a payment webhook, etc.) changes the match and
            # the delete/update below becomes a no-op instead of clobbering it.
            guard = {
                'pk': subscription.pk,
                'status': subscription.status,
                'plan_id': subscription.plan_id,
                'order_id': subscription.order_id,
                'version': subscription.version,
            }
            with transaction.atomic():
                if subscription_is_new:
                    Subscription.objects.filter(**guard).delete()
                elif prior_snapshot is not None:
                    Subscription.objects.filter(**guard).update(**prior_snapshot)
            raise

        if subscription.order_id != order.id:
            with transaction.atomic():
                subscription.order_id = order.id
                subscription.save(update_fields=['order_id'])

        data = {'orderId': str(order.id), 'paymentUrl': payment_url}
        return Response(PurchaseResponseSerializer(data).data)


class SubscriptionStatusView(APIView):
    """GET /api/subscription/status — current subscription status."""

    permission_classes = [IsAuthenticated]

    @extend_schema(responses=SubscriptionStatusResponseSerializer, tags=['Subscription (subscription)'])
    def get(self, request):
        subscription = Subscription.objects.filter(user_id=request.user.id).first()
        data = {
            'active': bool(subscription and subscription.status == 'active'),
            'planId': str(subscription.plan_id) if subscription and subscription.plan_id else None,
            'expiresAt': subscription.expires_at if subscription else None,
        }
        return Response(SubscriptionStatusResponseSerializer(data).data)