add balance prediction page and make it the default

core/prediction.py

@@ -113,3 +113,66 @@ def predict_all(subjects: Iterable[Subject], past_days=30, future_days=60):
         prediction_list.append((subject, transactions, prediction_info))
 
     return prediction_list
+
+
+min_pos_color = (Decimal("50"), Decimal("150"), Decimal("220"))
+max_pos_color = (Decimal("50"), Decimal("170"), Decimal("20"))
+min_neg_color = (Decimal("220"), Decimal("70"), Decimal("30"))
+max_neg_color = (Decimal("180"), Decimal("160"), Decimal("30"))
+
+global_minimum = Decimal("-300")
+global_maximum = Decimal("300")
+
+
+def limit(amount: Decimal, first_bound: Decimal, second_bound: Decimal):
+    lower = min(first_bound, second_bound)
+    upper = max(first_bound, second_bound)
+    return max(min(amount, upper), lower)
+
+
+def get_color_for_amount(amount: Decimal, minimum: Decimal, maximum: Decimal):
+    if amount >= Decimal():
+        minimum = Decimal()
+        maximum = min(maximum, global_maximum)
+        rmin, gmin, bmin = min_pos_color
+        rmax, gmax, bmax = max_pos_color
+    else:
+        minimum = max(minimum, global_minimum)
+        maximum = Decimal()
+        rmin, gmin, bmin = min_neg_color
+        rmax, gmax, bmax = max_neg_color
+    assert minimum < maximum
+    percentage = (amount - minimum) / (maximum - minimum)
+    return "#%02x%02x%02x" % (
+        round(limit(rmin + (percentage * (rmax - rmin)), rmin, rmax)),
+        round(limit(gmin + (percentage * (gmax - gmin)), gmin, gmax)),
+        round(limit(bmin + (percentage * (bmax - bmin)), bmin, bmax)),
+    )
+
+
+def predict_balance(start_balance=Decimal("0")):
+    prediction_list = predict_all(Subject.objects.order_by("name"))
+    today = timezone.now().date()
+    future_transactions = []
+    minimum, maximum = Decimal(), Decimal()
+    for _, transactions, _ in prediction_list:
+        for transaction in transactions:
+            if transaction.booking_date > today:
+                future_transactions.append(transaction)
+                minimum = min(minimum, transaction.amount)
+                maximum = max(maximum, transaction.amount)
+
+    formatted_transactions = []
+    current_balance = start_balance
+    for transaction in sorted(future_transactions, key=lambda t: t.booking_date):
+        current_balance += transaction.amount
+        formatted_transactions.append({
+            "date": transaction.booking_date,
+            "subject": transaction.subject,
+            "amount": transaction.amount,
+            "balance": current_balance,
+            "predicted": transaction.pk is None,
+            "color": get_color_for_amount(transaction.amount, minimum, maximum),
+        })
+
+    return formatted_transactions