Prepared view to calculate the previous data

expenses_manager/expenses/templates/expenses/dashboard.html

@@ -81,6 +81,12 @@
         <!-- Chart -->
         <!-- ========================= -->
 
+        <label>
+            <input type="checkbox" name="compare" value="1"
+                {% if compare %}checked{% endif %}>
+            Comparar con periodo anterior
+        </label>
+        
         <canvas id="expensesChart"></canvas>
 
         <script>
@@ -101,5 +107,8 @@
             });
         </script>   
         
+        <hr>
+
+    
 </body>
 </html>

expenses_manager/expenses/views.py

@@ -1,7 +1,7 @@
 from datetime import date
-from re import M
 from .models import Expense
 from .forms import ExpenseForm
+# from dateutli.relativedelta import relativedelta
 
 from django.db.models import Sum
 from django.contrib.auth import login
@@ -117,6 +117,8 @@ def dashboard(request):
     selected_year = year or current_year
     selected_month = month    
         
+    compare = request.GET.get("compare") == "1"
+    
     # ------------------
     # Queryset base
     # -----------------
@@ -188,10 +190,61 @@ def dashboard(request):
         .order_by('year')
     )
     
-    # Prepare data fot ploting in chart
+    # ------------------
+    # Chart
+    # -----------------
     chart_labels = months
     chart_totals = [row['total'] for row in by_month]
     
+    # ------------------
+    # Compare period
+    # -----------------
+    
+    previous_expenses = expenses
+    
+    if month and year:
+        if month == 1:
+            prev_year = year - 1
+            prev_month = 12
+        else:
+            prev_year = year
+            prev_month = month - 1
+        previous_expenses = previous_expenses.filter(
+            date__year=prev_year,
+            date__month=prev_month
+        )
+    elif year and month is None:
+        prev_year = year - 1
+        previous_expenses = previous_expenses.filter(
+            date__year=prev_year
+        )
+    else:
+        today = date.today()
+        year = today.year
+        month = today.month
+        
+        if month == 1:
+            prev_year = year - 1
+            prev_month = 12
+        else:
+            prev_year = year
+            prev_month = month - 1
+        
+        previous_expenses = previous_expenses.filter(
+            date__year=prev_year,
+            date__month=prev_month
+        )
+
+    previous_total = (
+        previous_expenses.aggregate(total=Sum('amount'))['total'] or 0
+    )
+    
+    difference = total_amount - previous_total
+    precentage = (
+        (difference / previous_total) * 100 if previous_total else None
+    )
+
+    
     # Send the data to the dashboard
     return render(request, 'expenses/dashboard.html', {
         'by_category': by_category,