from django.db.models import Count, F, Sum
from django.db.models.functions import TruncDate, TruncHour
from django.utils import timezone
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response
from rest_framework.views import APIView

from apps.core.permissions import IsStoreOwner
from apps.orders.models import Order, OrderItem

from .serializers import SellerAnalyticsSerializer

PERIOD_START = {
    'today': lambda now: now.replace(hour=0, minute=0, second=0, microsecond=0),
    'week': lambda now: now - timezone.timedelta(days=7),
    'month': lambda now: now - timezone.timedelta(days=30),
}


class SellerAnalyticsView(APIView):
    """Seller sales dashboard (S17): daily chart, stat cards, top-selling products."""

    schema_tags = ['Seller · Analytics']
    permission_classes = [IsAuthenticated, IsStoreOwner]
    serializer_class = SellerAnalyticsSerializer

    def get(self, request):
        period = request.query_params.get('period', 'today')
        start_fn = PERIOD_START.get(period, PERIOD_START['today'])
        start = start_fn(timezone.now())
        store = request.user.store

        period_orders = Order.objects.filter(store=store, created_at__gte=start)
        order_count = period_orders.count()
        cancelled_count = period_orders.filter(status=Order.Status.CANCELLED).count()
        cancellation_rate = round(cancelled_count / order_count * 100, 1) if order_count else 0

        delivered_orders = period_orders.filter(status=Order.Status.DELIVERED)
        total_sales = sum(o.total_amount for o in delivered_orders)
        delivered_count = delivered_orders.count()
        average_order_value = round(total_sales / delivered_count) if delivered_count else 0

        trunc = TruncHour if period == 'today' else TruncDate
        chart = list(
            delivered_orders
            .annotate(bucket=trunc('created_at'))
            .values('bucket')
            .annotate(sales=Sum(F('items_subtotal') + F('delivery_fee')))
            .order_by('bucket')
        )

        top_products = list(
            OrderItem.objects.filter(order__in=delivered_orders)
            .values('product_name_snapshot')
            .annotate(
                units_sold=Sum('quantity'),
                revenue=Sum(F('unit_price_snapshot') * F('quantity')),
            )
            .order_by('-revenue')[:5]
        )

        return Response({
            'period': period,
            'order_count': order_count,
            'total_sales': total_sales,
            'cancellation_rate': cancellation_rate,
            'average_order_value': average_order_value,
            'chart': [{'bucket': point['bucket'], 'sales': point['sales']} for point in chart],
            'top_products': [
                {
                    'name': p['product_name_snapshot'],
                    'units_sold': p['units_sold'],
                    'revenue': p['revenue'],
                }
                for p in top_products
            ],
        })