feat(api): add endpoints for importing files and getting account balance

app/apps/accounts/services.py

@@ -0,0 +1,33 @@
+from decimal import Decimal
+
+from django.db import models
+
+from apps.accounts.models import Account
+from apps.transactions.models import Transaction
+
+
+def get_account_balance(account: Account, paid_only: bool = True) -> Decimal:
+    """
+    Calculate account balance (income - expense).
+
+    Args:
+        account: Account instance to calculate balance for.
+        paid_only: If True, only count paid transactions (current balance).
+                   If False, count all transactions (projected balance).
+
+    Returns:
+        Decimal: The calculated balance (income - expense).
+    """
+    filters = {"account": account}
+    if paid_only:
+        filters["is_paid"] = True
+
+    income = Transaction.objects.filter(
+        type=Transaction.Type.INCOME, **filters
+    ).aggregate(total=models.Sum("amount"))["total"] or Decimal("0")
+
+    expense = Transaction.objects.filter(
+        type=Transaction.Type.EXPENSE, **filters
+    ).aggregate(total=models.Sum("amount"))["total"] or Decimal("0")
+
+    return income - expense

app/apps/accounts/tests.py

@@ -1,3 +1,5 @@
+from datetime import date
+
 from django.test import TestCase
 
 from apps.accounts.models import Account, AccountGroup
@@ -39,3 +41,135 @@ class AccountTests(TestCase):
             exchange_currency=self.exchange_currency,
         )
         self.assertEqual(account.exchange_currency, self.exchange_currency)
+
+
+class GetAccountBalanceServiceTests(TestCase):
+    """Tests for the get_account_balance service function"""
+
+    def setUp(self):
+        """Set up test data"""
+        from apps.transactions.models import Transaction
+        self.Transaction = Transaction
+        
+        self.currency = Currency.objects.create(
+            code="BRL", name="Brazilian Real", decimal_places=2, prefix="R$ "
+        )
+        self.account_group = AccountGroup.objects.create(name="Service Test Group")
+        self.account = Account.objects.create(
+            name="Service Test Account", group=self.account_group, currency=self.currency
+        )
+
+    def test_balance_with_no_transactions(self):
+        """Test balance is 0 when no transactions exist"""
+        from apps.accounts.services import get_account_balance
+        from decimal import Decimal
+        
+        balance = get_account_balance(self.account, paid_only=True)
+        self.assertEqual(balance, Decimal("0"))
+
+    def test_current_balance_only_counts_paid(self):
+        """Test current balance only counts paid transactions"""
+        from apps.accounts.services import get_account_balance
+        from decimal import Decimal
+        
+        # Paid income
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("100.00"),
+            is_paid=True,
+            date=date(2025, 1, 1),
+            description="Paid income",
+        )
+        # Unpaid income (should not count)
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("50.00"),
+            is_paid=False,
+            date=date(2025, 1, 1),
+            description="Unpaid income",
+        )
+        # Paid expense
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.EXPENSE,
+            amount=Decimal("30.00"),
+            is_paid=True,
+            date=date(2025, 1, 1),
+            description="Paid expense",
+        )
+
+        balance = get_account_balance(self.account, paid_only=True)
+        self.assertEqual(balance, Decimal("70.00"))  # 100 - 30
+
+    def test_projected_balance_counts_all(self):
+        """Test projected balance counts all transactions"""
+        from apps.accounts.services import get_account_balance
+        from decimal import Decimal
+        
+        # Paid income
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("100.00"),
+            is_paid=True,
+            date=date(2025, 1, 1),
+            description="Paid income",
+        )
+        # Unpaid income
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("50.00"),
+            is_paid=False,
+            date=date(2025, 1, 1),
+            description="Unpaid income",
+        )
+        # Paid expense
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.EXPENSE,
+            amount=Decimal("30.00"),
+            is_paid=True,
+            date=date(2025, 1, 1),
+            description="Paid expense",
+        )
+        # Unpaid expense
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.EXPENSE,
+            amount=Decimal("20.00"),
+            is_paid=False,
+            date=date(2025, 1, 1),
+            description="Unpaid expense",
+        )
+
+        balance = get_account_balance(self.account, paid_only=False)
+        self.assertEqual(balance, Decimal("100.00"))  # (100 + 50) - (30 + 20)
+
+    def test_balance_defaults_to_paid_only(self):
+        """Test that paid_only defaults to True"""
+        from apps.accounts.services import get_account_balance
+        from decimal import Decimal
+        
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("100.00"),
+            is_paid=True,
+            date=date(2025, 1, 1),
+            description="Paid",
+        )
+        self.Transaction.objects.create(
+            account=self.account,
+            type=self.Transaction.Type.INCOME,
+            amount=Decimal("50.00"),
+            is_paid=False,
+            date=date(2025, 1, 1),
+            description="Unpaid",
+        )
+
+        balance = get_account_balance(self.account)  # defaults to paid_only=True
+        self.assertEqual(balance, Decimal("100.00"))
+

app/apps/accounts/views/balance.py

@@ -11,23 +11,13 @@ from django.utils.translation import gettext_lazy as _
 
 from apps.accounts.forms import AccountBalanceFormSet
 from apps.accounts.models import Account, Transaction
+from apps.accounts.services import get_account_balance
 from apps.common.decorators.htmx import only_htmx
 
 
 @only_htmx
 @login_required
 def account_reconciliation(request):
-    def get_account_balance(account):
-        income = Transaction.objects.filter(
-            account=account, type=Transaction.Type.INCOME, is_paid=True
-        ).aggregate(total=models.Sum("amount"))["total"] or Decimal("0")
-
-        expense = Transaction.objects.filter(
-            account=account, type=Transaction.Type.EXPENSE, is_paid=True
-        ).aggregate(total=models.Sum("amount"))["total"] or Decimal("0")
-
-        return income - expense
-
     initial_data = [
         {
             "account_id": account.id,