WIP feature: Started adding discounts

Author: TreyWW

backend/migrations/0026_invoice_discount_amount_invoice_discount_percentage.py

@@ -0,0 +1,26 @@
+# Generated by Django 5.0.3 on 2024-03-29 20:00
+
+import django.core.validators
+from django.db import migrations, models
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ("backend", "0025_alter_invoiceonetimeschedule_stored_schedule_arn"),
+    ]
+
+    operations = [
+        migrations.AddField(
+            model_name="invoice",
+            name="discount_amount",
+            field=models.DecimalField(decimal_places=2, default=0, max_digits=15),
+        ),
+        migrations.AddField(
+            model_name="invoice",
+            name="discount_percentage",
+            field=models.DecimalField(
+                decimal_places=2, default=0, max_digits=5, validators=[django.core.validators.MaxValueValidator(100)]
+            ),
+        ),
+    ]

backend/models.py

@@ -1,7 +1,10 @@
+import decimal
+from decimal import Decimal
 from uuid import uuid4
 
 from django.contrib.auth.hashers import make_password, check_password
 from django.contrib.auth.models import UserManager, AbstractUser, AnonymousUser
+from django.core.validators import MaxValueValidator
 from django.db import models
 from django.db.models import Count
 from django.utils import timezone
@@ -303,6 +306,9 @@ class Invoice(models.Model):
     date_due = models.DateField()
     date_issued = models.DateField(blank=True, null=True)
 
+    discount_amount = models.DecimalField(max_digits=15, default=0, decimal_places=2)
+    discount_percentage = models.DecimalField(default=0, max_digits=5, decimal_places=2, validators=[MaxValueValidator(100)])
+
     class Meta:
         constraints = [USER_OR_ORGANIZATION_CONSTRAINT()]
 
@@ -345,10 +351,33 @@ def get_subtotal(self):
             subtotal += item.get_total_price()
         return round(subtotal, 2)
 
+    def get_tax(self, amount: float = 0.00) -> float:
+        amount = amount or self.get_subtotal()
+        if self.vat_number:
+            return round(amount * 0.2, 2)
+        return 0
+
+    def get_percentage_amount(self, subtotal: float = 0.00) -> Decimal:
+        total = subtotal or self.get_subtotal()
+
+        if self.discount_percentage > 0:
+            return round(total * (self.discount_percentage / 100), 2)
+        return Decimal(0)
+
     def get_total_price(self):
-        total = 0
-        subtotal = self.get_subtotal()
-        total = subtotal * 1.2 if self.vat_number else subtotal
+        total = self.get_subtotal() or 0.00
+
+        total -= self.get_percentage_amount()
+
+        discount_amount = self.discount_amount
+
+        total -= discount_amount
+
+        if 0 > total:
+            total = 0
+        else:
+            total -= self.get_tax(total)
+
         return round(total, 2)