feat(insights): add Categories Overview

Closes #94

app/apps/insights/utils/category_overview.py

@@ -0,0 +1,165 @@
+from decimal import Decimal
+
+from django.db import models
+from django.db.models import Sum, Case, When, Value, DecimalField
+from django.db.models.functions import Coalesce
+
+from apps.transactions.models import Transaction
+from apps.currencies.models import Currency
+from apps.currencies.utils.convert import convert
+
+
+def get_categories_totals(transactions_queryset, ignore_empty=False):
+    # Get metrics for each category and currency in a single query
+    category_currency_metrics = (
+        transactions_queryset.values(
+            "category",
+            "category__name",
+            "account__currency",
+            "account__currency__code",
+            "account__currency__name",
+            "account__currency__decimal_places",
+            "account__currency__prefix",
+            "account__currency__suffix",
+            "account__currency__exchange_currency",
+        )
+        .annotate(
+            expense_current=Coalesce(
+                Sum(
+                    Case(
+                        When(
+                            type=Transaction.Type.EXPENSE, is_paid=True, then="amount"
+                        ),
+                        default=Value(0),
+                        output_field=models.DecimalField(),
+                    )
+                ),
+                Decimal("0"),
+            ),
+            expense_projected=Coalesce(
+                Sum(
+                    Case(
+                        When(
+                            type=Transaction.Type.EXPENSE, is_paid=False, then="amount"
+                        ),
+                        default=Value(0),
+                        output_field=models.DecimalField(),
+                    )
+                ),
+                Decimal("0"),
+            ),
+            income_current=Coalesce(
+                Sum(
+                    Case(
+                        When(type=Transaction.Type.INCOME, is_paid=True, then="amount"),
+                        default=Value(0),
+                        output_field=models.DecimalField(),
+                    )
+                ),
+                Decimal("0"),
+            ),
+            income_projected=Coalesce(
+                Sum(
+                    Case(
+                        When(
+                            type=Transaction.Type.INCOME, is_paid=False, then="amount"
+                        ),
+                        default=Value(0),
+                        output_field=models.DecimalField(),
+                    )
+                ),
+                Decimal("0"),
+            ),
+        )
+        .order_by("category__name")
+    )
+
+    # Process the results to structure by category
+    result = {}
+
+    for metric in category_currency_metrics:
+        # Skip empty categories if ignore_empty is True
+        if ignore_empty and all(
+            metric[field] == Decimal("0")
+            for field in [
+                "expense_current",
+                "expense_projected",
+                "income_current",
+                "income_projected",
+            ]
+        ):
+            continue
+
+        # Calculate derived totals
+        total_current = metric["income_current"] - metric["expense_current"]
+        total_projected = metric["income_projected"] - metric["expense_projected"]
+        total_income = metric["income_current"] + metric["income_projected"]
+        total_expense = metric["expense_current"] + metric["expense_projected"]
+        total_final = total_current + total_projected
+
+        category_id = metric["category"]
+        currency_id = metric["account__currency"]
+
+        if category_id not in result:
+            result[category_id] = {"name": metric["category__name"], "currencies": {}}
+
+        # Add currency data
+        currency_data = {
+            "currency": {
+                "code": metric["account__currency__code"],
+                "name": metric["account__currency__name"],
+                "decimal_places": metric["account__currency__decimal_places"],
+                "prefix": metric["account__currency__prefix"],
+                "suffix": metric["account__currency__suffix"],
+            },
+            "expense_current": metric["expense_current"],
+            "expense_projected": metric["expense_projected"],
+            "total_expense": total_expense,
+            "income_current": metric["income_current"],
+            "income_projected": metric["income_projected"],
+            "total_income": total_income,
+            "total_current": total_current,
+            "total_projected": total_projected,
+            "total_final": total_final,
+        }
+
+        # Add exchanged values if exchange_currency exists
+        if metric["account__currency__exchange_currency"]:
+            from_currency = Currency.objects.get(id=currency_id)
+            exchange_currency = Currency.objects.get(
+                id=metric["account__currency__exchange_currency"]
+            )
+
+            exchanged = {}
+            for field in [
+                "expense_current",
+                "expense_projected",
+                "income_current",
+                "income_projected",
+                "total_income",
+                "total_expense",
+                "total_current",
+                "total_projected",
+                "total_final",
+            ]:
+                amount, prefix, suffix, decimal_places = convert(
+                    amount=currency_data[field],
+                    from_currency=from_currency,
+                    to_currency=exchange_currency,
+                )
+                if amount is not None:
+                    exchanged[field] = amount
+                    if "currency" not in exchanged:
+                        exchanged["currency"] = {
+                            "prefix": prefix,
+                            "suffix": suffix,
+                            "decimal_places": decimal_places,
+                            "code": exchange_currency.code,
+                            "name": exchange_currency.name,
+                        }
+            if exchanged:
+                currency_data["exchanged"] = exchanged
+
+        result[category_id]["currencies"][currency_id] = currency_data
+
+    return result