from decimal import Decimal

from rest_framework import generics, status, viewsets
from rest_framework.permissions import IsAuthenticated
from rest_framework.response import Response

from .models import Material, StockTransaction
from .serializers import (
    MaterialReadSerializer,
    MaterialWriteSerializer,
    StockSummarySerializer,
    StockTransactionSerializer,
)


class MaterialViewSet(viewsets.ModelViewSet):
    """資材マスタ CRUD"""

    permission_classes = [IsAuthenticated]

    def get_queryset(self):
        queryset = Material.objects.select_related(
            'fertilizer_profile',
            'pesticide_profile',
        ).prefetch_related('stock_transactions')

        material_type = self.request.query_params.get('material_type')
        if material_type:
            queryset = queryset.filter(material_type=material_type)

        active = self.request.query_params.get('active')
        if active is not None:
            queryset = queryset.filter(is_active=active.lower() == 'true')

        return queryset

    def get_serializer_class(self):
        if self.action in ['create', 'update', 'partial_update']:
            return MaterialWriteSerializer
        return MaterialReadSerializer

    def destroy(self, request, *args, **kwargs):
        instance = self.get_object()
        if instance.stock_transactions.exists():
            return Response(
                {'detail': 'この資材には入出庫履歴があるため削除できません。無効化してください。'},
                status=status.HTTP_400_BAD_REQUEST,
            )
        return super().destroy(request, *args, **kwargs)


class StockTransactionViewSet(viewsets.ModelViewSet):
    """入出庫履歴 CRUD"""

    serializer_class = StockTransactionSerializer
    permission_classes = [IsAuthenticated]
    http_method_names = ['get', 'post', 'put', 'patch', 'delete', 'head', 'options']

    def get_queryset(self):
        queryset = StockTransaction.objects.select_related('material')

        material_id = self.request.query_params.get('material_id')
        if material_id:
            queryset = queryset.filter(material_id=material_id)

        material_type = self.request.query_params.get('material_type')
        if material_type:
            queryset = queryset.filter(material__material_type=material_type)

        date_from = self.request.query_params.get('date_from')
        if date_from:
            queryset = queryset.filter(occurred_on__gte=date_from)

        date_to = self.request.query_params.get('date_to')
        if date_to:
            queryset = queryset.filter(occurred_on__lte=date_to)

        return queryset

    def update(self, request, *args, **kwargs):
        instance = self.get_object()
        if instance.fertilization_plan_id or instance.spreading_item_id:
            return Response(
                {'detail': '計画や実績に紐づく入出庫履歴は編集できません。'},
                status=status.HTTP_400_BAD_REQUEST,
            )
        return super().update(request, *args, **kwargs)

    def partial_update(self, request, *args, **kwargs):
        instance = self.get_object()
        if instance.fertilization_plan_id or instance.spreading_item_id:
            return Response(
                {'detail': '計画や実績に紐づく入出庫履歴は編集できません。'},
                status=status.HTTP_400_BAD_REQUEST,
            )
        return super().partial_update(request, *args, **kwargs)

    def destroy(self, request, *args, **kwargs):
        instance = self.get_object()
        if instance.fertilization_plan_id or instance.spreading_item_id:
            return Response(
                {'detail': '計画や実績に紐づく入出庫履歴は削除できません。'},
                status=status.HTTP_400_BAD_REQUEST,
            )
        return super().destroy(request, *args, **kwargs)


class StockSummaryView(generics.ListAPIView):
    """在庫集計一覧"""

    serializer_class = StockSummarySerializer
    permission_classes = [IsAuthenticated]

    def get_queryset(self):
        return Material.objects.none()

    def list(self, request, *args, **kwargs):
        queryset = Material.objects.prefetch_related('stock_transactions').order_by(
            'material_type',
            'name',
        )

        material_type = request.query_params.get('material_type')
        if material_type:
            queryset = queryset.filter(material_type=material_type)

        active = request.query_params.get('active')
        if active is not None:
            queryset = queryset.filter(is_active=active.lower() == 'true')

        results = []
        for material in queryset:
            results.append(_build_stock_summary(material))

        serializer = self.get_serializer(results, many=True)
        return Response(serializer.data)


class FertilizerStockView(generics.ListAPIView):
    """施肥計画画面用: 肥料の在庫情報を返す"""

    permission_classes = [IsAuthenticated]
    serializer_class = StockSummarySerializer

    def get_queryset(self):
        return Material.objects.none()

    def list(self, request, *args, **kwargs):
        queryset = Material.objects.filter(
            material_type=Material.MaterialType.FERTILIZER,
            is_active=True,
        ).prefetch_related('stock_transactions').order_by('name')

        results = [_build_stock_summary(material) for material in queryset]
        serializer = self.get_serializer(results, many=True)
        return Response(serializer.data)


def _build_stock_summary(material):
    transactions = list(material.stock_transactions.all())
    increase = sum(
        txn.quantity
        for txn in transactions
        if txn.transaction_type in StockTransaction.INCREASE_TYPES
    )
    decrease = sum(
        txn.quantity
        for txn in transactions
        if txn.transaction_type in StockTransaction.DECREASE_TYPES
    )
    reserved = sum(
        txn.quantity
        for txn in transactions
        if txn.transaction_type == StockTransaction.TransactionType.RESERVE
    )
    available = increase - decrease if transactions else Decimal('0')
    last_date = max((txn.occurred_on for txn in transactions), default=None)
    return {
        'material_id': material.id,
        'name': material.name,
        'material_type': material.material_type,
        'material_type_display': material.get_material_type_display(),
        'maker': material.maker,
        'stock_unit': material.stock_unit,
        'stock_unit_display': material.get_stock_unit_display(),
        'is_active': material.is_active,
        'current_stock': available + reserved,
        'reserved_stock': reserved,
        'available_stock': available,
        'last_transaction_date': last_date,
    }