"""Validate-promo endpoint — gives the frontend a preview of price + discount."""

from django.shortcuts import get_object_or_404
from drf_spectacular.utils import OpenApiResponse, extend_schema, inline_serializer
from rest_framework import serializers
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response
from rest_framework.views import APIView

from apps.courses.models import Course, CourseStatus
from apps.enrollments.api.permissions import IsStudent
from apps.payments.services.orders import OrderError, _resolve_discount


class PromoPreviewRequestSerializer(serializers.Serializer):
    promo_code = serializers.CharField(required=False, allow_blank=True)
    referral_code = serializers.CharField(required=False, allow_blank=True)


class PromoPreviewResponseSerializer(serializers.Serializer):
    course_slug = serializers.CharField()
    base_amount_toman = serializers.IntegerField()
    discount_amount_toman = serializers.IntegerField()
    final_amount_toman = serializers.IntegerField()
    promo_code_applied = serializers.CharField(allow_null=True)
    referrer_code_applied = serializers.CharField(allow_null=True)


class CheckoutPreviewView(APIView):
    """`POST /api/courses/<slug>/checkout/preview/` — dry-run price computation."""

    permission_classes = [IsAuthenticated, IsStudent]

    @extend_schema(
        tags=["payments"],
        summary="Preview checkout price (apply promo / referral code without committing)",
        request=PromoPreviewRequestSerializer,
        responses={
            200: PromoPreviewResponseSerializer,
            400: OpenApiResponse(description="Code invalid / not applicable / both supplied / course is free."),
            404: OpenApiResponse(description="Course not found or not published."),
        },
    )
    def post(self, request, slug):
        course = get_object_or_404(Course, slug=slug, status=CourseStatus.PUBLISHED)
        if course.is_free:
            return Response(
                {"detail": "Course is free; no checkout needed."},
                status=400,
            )
        ser = PromoPreviewRequestSerializer(data=request.data)
        ser.is_valid(raise_exception=True)
        base = int(course.price_toman or 0)
        try:
            discount, pc_obj, referrer, _credit = _resolve_discount(
                course, base,
                promo_code=ser.validated_data.get("promo_code") or None,
                referral_code=ser.validated_data.get("referral_code") or None,
                buyer=request.user,
            )
        except OrderError as e:
            return Response({"detail": str(e)}, status=400)
        final = max(0, base - discount)
        body = {
            "course_slug": course.slug,
            "base_amount_toman": base,
            "discount_amount_toman": discount,
            "final_amount_toman": final,
            "promo_code_applied": pc_obj.code if pc_obj else None,
            "referrer_code_applied": referrer.referral_code if referrer else None,
        }
        return Response(PromoPreviewResponseSerializer(body).data)