分配計画機能を実装

施肥計画の圃場を配置場所単位でグループ化し、グループ×肥料の集計表を
表示・PDF出力できる機能を追加。

- Backend: DistributionPlan/Group/GroupField モデル (migration 0003)
- API: GET/POST/PUT/DELETE/PDF (/api/fertilizer/distribution/)
- Frontend: 一覧・新規作成・編集画面 (/distribution)
- Navbar に分配計画メニューを追加
- 集計プレビューはクライアントサイド計算（API不要）

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/apps/fertilizer/views.py

@@ -11,11 +11,14 @@ from weasyprint import HTML
 
 from apps.fields.models import Field
 from apps.plans.models import Plan, Variety
-from .models import Fertilizer, FertilizationPlan
+from .models import Fertilizer, FertilizationPlan, DistributionPlan
 from .serializers import (
     FertilizerSerializer,
     FertilizationPlanSerializer,
     FertilizationPlanWriteSerializer,
+    DistributionPlanListSerializer,
+    DistributionPlanReadSerializer,
+    DistributionPlanWriteSerializer,
 )
 
 
@@ -194,3 +197,128 @@ class CalculateView(APIView):
             return Response({'error': 'method は nitrogen / even / per_tan のいずれかです'}, status=status.HTTP_400_BAD_REQUEST)
 
         return Response(results)
+
+
+class DistributionPlanViewSet(viewsets.ModelViewSet):
+    permission_classes = [IsAuthenticated]
+
+    def get_queryset(self):
+        qs = DistributionPlan.objects.select_related(
+            'fertilization_plan', 'fertilization_plan__variety', 'fertilization_plan__variety__crop'
+        ).prefetch_related(
+            'groups', 'groups__field_assignments', 'groups__field_assignments__field',
+            'fertilization_plan__entries', 'fertilization_plan__entries__field',
+            'fertilization_plan__entries__fertilizer',
+            'distributiongroupfield_set',
+        )
+        year = self.request.query_params.get('year')
+        if year:
+            qs = qs.filter(fertilization_plan__year=year)
+        return qs
+
+    def get_serializer_class(self):
+        if self.action in ['create', 'update', 'partial_update']:
+            return DistributionPlanWriteSerializer
+        if self.action == 'list':
+            return DistributionPlanListSerializer
+        return DistributionPlanReadSerializer
+
+    @action(detail=True, methods=['get'])
+    def pdf(self, request, pk=None):
+        dist_plan = self.get_object()
+        fert_plan = dist_plan.fertilization_plan
+
+        # 施肥計画の肥料一覧（名前順）
+        fert_ids = fert_plan.entries.values_list('fertilizer_id', flat=True).distinct()
+        fertilizers = sorted(
+            Fertilizer.objects.filter(id__in=fert_ids),
+            key=lambda f: f.name
+        )
+
+        # entries を (field_id, fertilizer_id) → bags のマトリクスに変換
+        entry_map = {}
+        for e in fert_plan.entries.all():
+            entry_map[(e.field_id, e.fertilizer_id)] = e.bags
+
+        # グループ行の構築
+        groups = dist_plan.groups.prefetch_related('field_assignments__field').all()
+        group_rows = []
+        for group in groups:
+            fields_in_group = [
+                a.field for a in group.field_assignments.select_related('field').order_by('field__display_order', 'field__id')
+            ]
+            # グループ合計（肥料ごと）
+            group_totals = []
+            for fert in fertilizers:
+                total = sum(
+                    entry_map.get((f.id, fert.id), Decimal('0'))
+                    for f in fields_in_group
+                )
+                group_totals.append(total)
+            group_row_total = sum(group_totals)
+
+            # 圃場サブ行
+            field_rows = []
+            for field in fields_in_group:
+                cells = [entry_map.get((field.id, fert.id), '') for fert in fertilizers]
+                row_total = sum(v for v in cells if v != '')
+                field_rows.append({'field': field, 'cells': cells, 'total': row_total})
+
+            group_rows.append({
+                'name': group.name,
+                'totals': group_totals,
+                'row_total': group_row_total,
+                'field_rows': field_rows,
+            })
+
+        # 未割り当て圃場
+        assigned_ids = dist_plan.distributiongroupfield_set.values_list('field_id', flat=True)
+        plan_field_ids = fert_plan.entries.values_list('field_id', flat=True).distinct()
+        unassigned_fields = Field.objects.filter(
+            id__in=plan_field_ids
+        ).exclude(id__in=assigned_ids).order_by('display_order', 'id')
+
+        unassigned_rows = []
+        if unassigned_fields.exists():
+            ua_totals = []
+            for fert in fertilizers:
+                total = sum(
+                    entry_map.get((f.id, fert.id), Decimal('0'))
+                    for f in unassigned_fields
+                )
+                ua_totals.append(total)
+            unassigned_rows = [{
+                'name': '未割り当て',
+                'totals': ua_totals,
+                'row_total': sum(ua_totals),
+                'field_rows': [
+                    {
+                        'field': f,
+                        'cells': [entry_map.get((f.id, fert.id), '') for fert in fertilizers],
+                        'total': sum(entry_map.get((f.id, fert.id), Decimal('0')) for fert in fertilizers),
+                    }
+                    for f in unassigned_fields
+                ],
+            }]
+
+        all_group_rows = group_rows + unassigned_rows
+        fert_totals = [
+            sum(r['totals'][i] for r in all_group_rows)
+            for i in range(len(fertilizers))
+        ]
+
+        context = {
+            'dist_plan': dist_plan,
+            'fert_plan': fert_plan,
+            'fertilizers': fertilizers,
+            'group_rows': all_group_rows,
+            'fert_totals': fert_totals,
+            'grand_total': sum(fert_totals),
+        }
+        html_string = render_to_string('fertilizer/distribution_pdf.html', context)
+        pdf_file = HTML(string=html_string).write_pdf()
+        response = HttpResponse(pdf_file, content_type='application/pdf')
+        response['Content-Disposition'] = (
+            f'attachment; filename="distribution_{fert_plan.year}_{dist_plan.id}.pdf"'
+        )
+        return response