fix: Balance now sums past-month (paid - expected) directly, ignoring current/future months

The previous calculation derived balance from total_balance (which includes
current/future-month activity and out-of-window credits) plus a one-sided
debt-only adjustment. Current-month surplus leaked through, making the balance
appear less negative than actual past-month debt (e.g. Mauric Daniel -1250 vs
correct -1750). Pay-All is now max(0, -balance) so the two values share a
single source and cannot disagree.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

CHANGELOG.md

@@ -1,5 +1,12 @@
 # Changelog
 
+## 2026-05-03 20:37 CEST — Fix Balance column to correctly reflect past-month debt
+
+- Balance (and Pay-All) are now computed as `sum(paid − expected)` over past months only, iterating directly over the ledger entries from `reconcile()`.
+- Previously the balance used `total_balance` (which includes current/future-month activity and out-of-window credits) plus a one-sided current-month debt adjustment. Current-month *surplus* leaked through, making the balance appear less negative than the actual past-month debt.
+- Pay-All is now `max(0, −balance)` so the two values are derived from a single source and can never disagree.
+- Affected: `adults_view()` and `juniors_view()` in `app.py`.
+
 ## 2026-05-03 19:26 CEST — Fee-aware allocation for multi-month payments
 
 - `reconcile()` no longer splits a multi-month payment evenly. Allocation is now per-member with two phases: greedy (if amount ≥ total expected, each month gets exactly its expected fee and overflow → credit) and proportional (otherwise distribute by each month's expected). Fixes the case where e.g. 1250 CZK covering 3 months with mixed fees (750/350/150) marked two months red.

app.py

@@ -192,7 +192,6 @@ def adults_view():
         row = {"name": name, "months": [], "balance": data["total_balance"], "unpaid_periods": "", "raw_unpaid_periods": ""}
         unpaid_months = []
         raw_unpaid_months = []
-        payable_amount = 0
         for m in sorted_months:
             mdata = data["months"].get(m, {"expected": 0, "original_expected": 0, "attendance_count": 0, "paid": 0, "exception": None})
             expected = mdata.get("expected", 0)
@@ -228,14 +227,12 @@ def adults_view():
                     if m < current_month:
                         unpaid_months.append(month_labels[m])
                         raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                        payable_amount += amount_to_pay
                 else:
                     status = "unpaid"
                     cell_text = f"0/{fee_display}"
                     if m < current_month:
                         unpaid_months.append(month_labels[m])
                         raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                        payable_amount += amount_to_pay
             elif paid > 0:
                 status = "surplus"
                 cell_text = f"PAID {paid}"
@@ -258,17 +255,17 @@ def adults_view():
                 "tooltip": tooltip
             })
 
-        # Compute balance excluding current/future months
-        current_month_debt = 0
-        for m in sorted_months:
+        # Balance = sum of (paid - expected) for past months only; current/future months ignored.
+        settled_balance = 0
+        for m, mdata in data["months"].items():
             if m >= current_month:
-                mdata = data["months"].get(m, {"expected": 0, "paid": 0})
+                continue
             exp = mdata.get("expected", 0)
-                pd = int(mdata.get("paid", 0))
-                current_month_debt += max(0, exp - pd)
-        settled_balance = data["total_balance"] + current_month_debt
+            if isinstance(exp, int):
+                settled_balance += int(mdata.get("paid", 0)) - exp
 
-        row["unpaid_periods"] = ", ".join(unpaid_months) if unpaid_months else ("Older debt" if settled_balance < 0 and payable_amount == 0 else "")
+        payable_amount = max(0, -settled_balance)
+        row["unpaid_periods"] = ", ".join(unpaid_months)
         row["raw_unpaid_periods"] = "+".join(raw_unpaid_months)
         row["balance"] = settled_balance
         row["payable_amount"] = payable_amount
@@ -293,8 +290,14 @@ def adults_view():
 
     def settled_balance(name):
         data = result["members"][name]
-        debt = sum(max(0, data["months"].get(m, {"expected": 0, "paid": 0}).get("expected", 0) - int(data["months"].get(m, {"expected": 0, "paid": 0}).get("paid", 0))) for m in sorted_months if m >= current_month)
-        return data["total_balance"] + debt
+        total = 0
+        for m, mdata in data["months"].items():
+            if m >= current_month:
+                continue
+            exp = mdata.get("expected", 0)
+            if isinstance(exp, int):
+                total += int(mdata.get("paid", 0)) - exp
+        return total
 
     credits = sorted([{"name": n, "amount": settled_balance(n)} for n in adult_names if settled_balance(n) > 0], key=lambda x: x["name"])
     debts = sorted([{"name": n, "amount": abs(settled_balance(n))} for n in adult_names if settled_balance(n) < 0], key=lambda x: x["name"])
@@ -373,7 +376,6 @@ def juniors_view():
         row = {"name": name, "months": [], "balance": data["total_balance"], "unpaid_periods": "", "raw_unpaid_periods": ""}
         unpaid_months = []
         raw_unpaid_months = []
-        payable_amount = 0
         for m in sorted_months:
             mdata = data["months"].get(m, {"expected": 0, "original_expected": 0, "attendance_count": 0, "paid": 0, "exception": None})
             expected = mdata.get("expected", 0)
@@ -429,7 +431,6 @@ def juniors_view():
                     if m < current_month:
                         unpaid_months.append(month_labels[m])
                         raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                        payable_amount += amount_to_pay
                 else:
                     status = "unpaid"
                     cell_text = f"0/{fee_display}"
@@ -437,7 +438,6 @@ def juniors_view():
                     if m < current_month:
                         unpaid_months.append(month_labels[m])
                         raw_unpaid_months.append(datetime.strptime(m, "%Y-%m").strftime("%m/%Y"))
-                        payable_amount += amount_to_pay
             elif paid > 0:
                 status = "surplus"
                 cell_text = f"PAID {paid}"
@@ -457,18 +457,17 @@ def juniors_view():
                 "tooltip": tooltip
             })
 
-        # Compute balance excluding current/future months
-        current_month_debt = 0
-        for m in sorted_months:
+        # Balance = sum of (paid - expected) for past months only; current/future months ignored.
+        settled_balance = 0
+        for m, mdata in data["months"].items():
             if m >= current_month:
-                mdata = data["months"].get(m, {"expected": 0, "paid": 0})
+                continue
             exp = mdata.get("expected", 0)
             if isinstance(exp, int):
-                    pd = int(mdata.get("paid", 0))
-                    current_month_debt += max(0, exp - pd)
-        settled_balance = data["total_balance"] + current_month_debt
+                settled_balance += int(mdata.get("paid", 0)) - exp
 
-        row["unpaid_periods"] = ", ".join(unpaid_months) if unpaid_months else ("Older debt" if settled_balance < 0 and payable_amount == 0 else "")
+        payable_amount = max(0, -settled_balance)
+        row["unpaid_periods"] = ", ".join(unpaid_months)
         row["raw_unpaid_periods"] = "+".join(raw_unpaid_months)
         row["balance"] = settled_balance
         row["payable_amount"] = payable_amount
@@ -494,14 +493,14 @@ def juniors_view():
     # Format credits and debts
     def junior_settled_balance(name):
         data = result["members"][name]
-        debt = 0
-        for m in sorted_months:
+        total = 0
+        for m, mdata in data["months"].items():
             if m >= current_month:
-                mdata = data["months"].get(m, {"expected": 0, "paid": 0})
+                continue
             exp = mdata.get("expected", 0)
             if isinstance(exp, int):
-                    debt += max(0, exp - int(mdata.get("paid", 0)))
-        return data["total_balance"] + debt
+                total += int(mdata.get("paid", 0)) - exp
+        return total
 
     junior_all_names = [name for name, _, _ in adapted_members]
     credits = sorted([{"name": n, "amount": junior_settled_balance(n)} for n in junior_all_names if junior_settled_balance(n) > 0], key=lambda x: x["name"])