feat(backend): add discount code (#52)

* feat(backend): add discount code

* fix(backend): only count paid payments in discount remaining capacity

* feat(backend): rollback discount on payment threshold

backend/backend_api/admin.py

@@ -3,6 +3,7 @@
 
 from backend_api import models
 from backend_api.email import MailerThread
+from backend_api.models import Discount
 
 
 def desc_creator(selected_model):
@@ -101,6 +102,15 @@ def execute_mailer(self, request, obj):
     actions = ['execute_mailer']
 
 
+class DiscountAdmin(admin.ModelAdmin):
+    list_display = ('__str__', 'is_active', 'discount_percent', 'capacity', 'expiration_date')
+    readonly_fields = ('participants',)
+
+    class Meta:
+        model = Discount
+        fields = '__all__'
+
+
 class PaymentAdmin(admin.ModelAdmin):
     rdfields = []
     for field in models.Payment._meta.get_fields():
@@ -123,6 +133,7 @@ class Meta:
 admin.site.register(models.Presenter, PresenterAdmin)
 admin.site.register(models.User, UserAdmin)
 admin.site.register(models.Mailer, MailerAdmin)
+admin.site.register(models.Discount, DiscountAdmin)
 admin.site.register(models.Payment, PaymentAdmin)
 admin.site.register(models.WorkshopRegistration)
 admin.site.register(models.PresentationParticipation)

backend/backend_api/migrations/0054_discount_payment_discount.py

@@ -0,0 +1,31 @@
+# Generated by Django 4.2.4 on 2023-12-03 20:08
+
+from django.db import migrations, models
+import django.db.models.deletion
+import django.utils.timezone
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('backend_api', '0053_alter_staff_role_alter_staff_section_name'),
+    ]
+
+    operations = [
+        migrations.CreateModel(
+            name='Discount',
+            fields=[
+                ('id', models.BigAutoField(auto_created=True, primary_key=True, serialize=False, verbose_name='ID')),
+                ('code', models.CharField(default='BTusxOmw', max_length=8, unique=True)),
+                ('discount_percent', models.IntegerField(default=0)),
+                ('is_active', models.BooleanField(default=False)),
+                ('capacity', models.IntegerField(default=0)),
+                ('expiration_date', models.DateTimeField(default=django.utils.timezone.now)),
+            ],
+        ),
+        migrations.AddField(
+            model_name='payment',
+            name='discount',
+            field=models.ForeignKey(default=None, null=True, on_delete=django.db.models.deletion.SET_NULL, to='backend_api.discount'),
+        ),
+    ]

backend/backend_api/models.py

@@ -9,6 +9,7 @@
 from django.db import models
 from django.template.loader import render_to_string
 from django.urls import reverse
+from django.utils import timezone
 from django.utils.translation import gettext_lazy as _
 from rest_framework.exceptions import ValidationError
 from rest_framework import status
@@ -21,6 +22,7 @@
 from utils.random import create_random_string
 from utils.renderers import new_detailed_response
 from urllib.parse import quote
+
 SMALL_MAX_LENGTH = 255
 BIG_MAX_LENGTH = 65535
 
@@ -173,7 +175,7 @@ class Presentation(models.Model):
     cost = models.PositiveIntegerField(default=0)
     capacity = models.PositiveIntegerField(default=50)
     has_project = models.BooleanField(default=False, blank=False)
-    
+
     NOT_ASSIGNED = 'NOT_ASSIGNED'
     ELEMENTARY = 'Elementary'
     INTERMEDIATE = 'Intermediate'
@@ -341,6 +343,44 @@ def __str__(self):
         return f"Mailer with id {self.id}: subject= {self.subject}"
 
 
+class Discount(models.Model):
+    _CODE_LENGTH = 8
+    code = models.CharField(max_length=_CODE_LENGTH, null=False, default=create_random_string(_CODE_LENGTH),
+                            unique=True)
+    discount_percent = models.IntegerField(default=0)
+    is_active = models.BooleanField(default=False)
+    capacity = models.IntegerField(default=0)
+    expiration_date = models.DateTimeField(default=timezone.now)
+
+    def __str__(self):
+        return self.code
+
+    @property
+    def participants(self):
+        users = []
+        for payment in self.payment_set.all():
+            users.append(payment.user)
+        return users
+
+    def _remaining_capacity(self) -> int:
+        return self.capacity - self.payment_set.filter(status=Payment.PaymentStatus.PAYMENT_CONFIRMED).count()
+
+    def is_usable(self, user: User) -> bool:
+        if not self.is_active:
+            raise ValidationError(new_detailed_response(status.HTTP_400_BAD_REQUEST,
+                                                        "Discount is not active"))
+        if self._remaining_capacity() <= 0:
+            raise ValidationError(new_detailed_response(status.HTTP_400_BAD_REQUEST,
+                                                        "Discount capacity is full"))
+        if self.expiration_date < timezone.now():
+            raise ValidationError(new_detailed_response(status.HTTP_400_BAD_REQUEST,
+                                                        "Discount has expired"))
+        if self.payment_set.filter(user=user).exists():
+            raise ValidationError(new_detailed_response(status.HTTP_400_BAD_REQUEST,
+                                                        "Discount has already been used by this user"))
+        return True
+
+
 class Payment(models.Model):
     class PaymentStatus(models.IntegerChoices):
         AWAITING_PAYMENT = 0, _('Awaiting payment')
@@ -361,6 +401,7 @@ class PaymentStatus(models.IntegerChoices):
                             default=datetime.datetime(year=2020, month=7, day=1, hour=0, minute=0, second=0,
                                                       microsecond=0))
     track_id = models.CharField(max_length=20, null=True, default=None)
+    discount = models.ForeignKey(Discount, on_delete=models.SET_NULL, null=True, default=None)
 
     def __str__(self):
         return f"Payment for {self.user.account} ({self.amount})  in {str(self.date)}"
@@ -385,7 +426,7 @@ def update_payment_status(self, payment_status: PaymentStatus):
         self.save()
 
     @staticmethod
-    def create_payment_for_user(user: User):
+    def create_payment_for_user(user: User, discount: Discount):
         total_cost = 0
         workshops: list[Workshop] = []
         presentations: list[Presentation] = []
@@ -419,15 +460,20 @@ def create_payment_for_user(user: User):
         if len(workshops) == 0 and len(presentations) == 0:
             raise ValidationError(
                 new_detailed_response(status.HTTP_400_BAD_REQUEST, f"User {user} has no unpaid registrations"))
-        if total_cost >= Payment._DISCOUNT_THRESHOLD:
-            total_cost = int(total_cost * (1 - Payment._DISCOUNT_PERCENTAGE / 100))
         payment = Payment.objects.create(user=user, amount=total_cost, year=datetime.date.today().year,
-                                         date=datetime.datetime.now())
+                                         date=datetime.datetime.now(), discount=discount)
         payment.workshops.set(workshops)
         payment.presentations.set(presentations)
         payment.save()
         return payment
 
+    @property
+    def discounted_amount(self):
+        if self.discount is None:
+            return self.amount if self.amount < self._DISCOUNT_THRESHOLD else int(
+                self.amount * (1 - self._DISCOUNT_PERCENTAGE / 100))
+        return int(self.amount * (1 - self.discount.discount_percent / 100))
+
 
 class Committee(models.Model):
     profile = models.ImageField(verbose_name='profile', null=True, blank=True)

backend/backend_api/views.py

@@ -2,7 +2,7 @@
 import os
 import urllib.parse
 
-from django.core.exceptions import ObjectDoesNotExist
+from django.core.exceptions import ObjectDoesNotExist, ValidationError
 from django.shortcuts import get_object_or_404, redirect
 from rest_framework import status, mixins
 from rest_framework import viewsets
@@ -17,7 +17,7 @@
 from aaiss_backend.settings import BASE_URL
 from backend_api import models
 from backend_api import serializers
-from backend_api.models import User, Account, Payment, Staff, WorkshopRegistration, PresentationParticipation
+from backend_api.models import User, Account, Payment, Staff, WorkshopRegistration, PresentationParticipation, Discount
 from backend_api.serializers import WorkshopRegistrationSerializer, PresentationParticipationSerializer
 from payment_backends.zify import ZIFYRequest, ZIFY_STATUS_OK
 from utils.renderers import new_detailed_response
@@ -215,17 +215,29 @@ class PaymentViewSet(viewsets.GenericViewSet):
     @action(methods=['POST'], detail=False, permission_classes=[IsAuthenticated])
     def payment(self, request):
         account = request.user
-        call_back = request.data.get('call_back')
-        if call_back is None:
-            return Response(new_detailed_response(status.HTTP_400_BAD_REQUEST, "call_back field is required"))
         try:
             user = User.objects.get(account=account)
         except ObjectDoesNotExist:
             return Response(new_detailed_response(
                 status.HTTP_400_BAD_REQUEST, "User not found"))
-
-        payment = Payment.create_payment_for_user(user)
-        response = ZIFYRequest().create_payment(str(payment.pk), payment.amount, user.name, user.phone_number,
+        call_back = request.data.get('call_back')
+        if call_back is None:
+            return Response(new_detailed_response(status.HTTP_400_BAD_REQUEST, "call_back field is required"))
+        discount = None
+        discount_code = request.data.get('discount_code')
+        if discount_code is not None:
+            try:
+                discount = Discount.objects.get(code=discount_code)
+            except ObjectDoesNotExist:
+                return Response(new_detailed_response(
+                    status.HTTP_400_BAD_REQUEST, "Discount code not found"))
+            try:
+                discount.is_usable(user)
+            except ValidationError as e:
+                return Response(e)
+        payment = Payment.create_payment_for_user(user, discount)
+        response = ZIFYRequest().create_payment(str(payment.pk), payment.discounted_amount, user.name,
+                                                user.phone_number,
                                                 user.account.email, call_back)
         if response['status'] == ZIFY_STATUS_OK:
             payment.track_id = response['data']['order']
@@ -250,7 +262,7 @@ def verify(self, request):
         response = ZIFYRequest().verify_payment(payment.track_id)
         if response['status'] == ZIFY_STATUS_OK:
             payment.update_payment_status(Payment.PaymentStatus.PAYMENT_CONFIRMED)
-            return Response(new_detailed_response(status.HTTP_200_OK, "Payment verified successfully",  payment.pk))
+            return Response(new_detailed_response(status.HTTP_200_OK, "Payment verified successfully", payment.pk))
         else:
             payment.update_payment_status(Payment.PaymentStatus.PAYMENT_REJECTED)
             return Response(
@@ -278,7 +290,7 @@ def list(self, request, *args, **kwargs):
                     }
 
                     section_data['people'].append(person_data)
-                
+
             if len(section_data['people']) != 0:
                 section_data['people'] = sorted(section_data['people'], key=lambda x: x['role'])[::-1]
                 data.append(section_data)