Fix historical FY sundry creditors FIFO ageing from accounting mirror

app/modules/accounting/accounting_mirror_service.py

@@ -272,11 +272,10 @@ def sundry_creditors_aging(
     At a reporting date, the unpaid closing balance is therefore represented by
     the *latest* credit-side additions, with any residual carried from opening.
 
-    We reconstruct that closing composition backwards from the authoritative
-    ledger closing balance.  This is algebraically the same FIFO result as a
-    complete forward replay, but it is materially safer for an extracted mirror:
-    it cannot mis-age a closing balance merely because the opening balance is a
-    brought-forward aggregate rather than individual bills.
+    We first reconstruct the selected FY closing balance from the mirror opening
+    balance and selected-period movements, then reconstruct its unpaid composition
+    backwards.  This avoids using ledger_master.closing_balance for a historical FY
+    because that master value can reflect a different/current reporting period.
 
     Tally bill-allocation references are not yet persisted in the .act mirror, so
     this remains a transparent FIFO analysis rather than Agst Ref/New Ref matching.
@@ -358,20 +357,36 @@ def sundry_creditors_aging(
         key = party_name.casefold()
         meta = ledger_meta.get(key) or {}
 
-        # Sundry Creditor liability balances in the canonical mirror are credit
-        # balances (positive).  Debit/zero closing balances are deliberately not
-        # reported as closing creditors.
-        closing_balance = max(0.0, _money(meta.get("closing_balance")))
+        rows = by_ledger.get(key, [])
+
+        # IMPORTANT: ledger_master.closing_balance is a master-level snapshot and
+        # is not reliable as the closing balance for an arbitrary historical FY.
+        # Reconstruct the selected FY closing from the mirror's opening balance and
+        # the selected-period creditor movements.  This is the same balance control
+        # used by the first mirror implementation and keeps historical FY analysis
+        # tied to the voucher stream rather than the current ledger-master closing.
+        opening_balance = _money(meta.get("opening_balance"))
+        period_credit = round(sum(
+            _money(row.get("amount")) for row in rows
+            if str(row.get("dr_cr") or "").upper() == "CR"
+        ), 2)
+        period_debit = round(sum(
+            _money(row.get("amount")) for row in rows
+            if str(row.get("dr_cr") or "").upper() == "DR"
+        ), 2)
+        historical_closing = round(opening_balance + period_credit - period_debit, 2)
+
+        # Only credit closing balances are Sundry Creditors for this report.
+        closing_balance = max(0.0, historical_closing)
         if closing_balance <= 0.009:
             continue
 
-        rows = by_ledger.get(key, [])
         credit_rows = [
             row for row in rows
             if str(row.get("dr_cr") or "").upper() == "CR" and _money(row.get("amount")) > 0.009
         ]
 
-        # Reverse reconstruction of the closing balance under FIFO:
+        # Reverse reconstruction of the selected FY closing balance under FIFO:
         # oldest balances are settled first, therefore the newest credits remain.
         amount_to_allocate = closing_balance
         lots_newest_first: list[dict[str, Any]] = []
@@ -488,7 +503,7 @@ def sundry_creditors_aging(
                 "age_bucket": bucket,
                 "paid_subsequently": paid,
                 "balance_after_follow_up": after,
-                "allocation_basis": "FIFO reconstructed from Accounting Mirror closing balance",
+                "allocation_basis": "FIFO from selected-FY Accounting Mirror movements",
             })
 
         # Date on which the party's >180 FY-end component became fully paid.
@@ -499,12 +514,12 @@ def sundry_creditors_aging(
                 final_payment_date = max(dates)
 
         reconstructed = round(within_180 + over_180, 2)
-        # Maintain the mirror ledger closing balance as the authoritative control.
+        # Maintain the selected-FY movement-derived closing balance as the control.
         variance = round(closing_balance - reconstructed, 2)
         if abs(variance) > 0.01:
             raise AccountingMirrorError(
                 f"FIFO reconstruction does not reconcile for {party_name}: "
-                f"mirror closing {closing_balance:.2f}, reconstructed {reconstructed:.2f}."
+                f"selected-FY closing {closing_balance:.2f}, reconstructed {reconstructed:.2f}."
             )
 
         parties.append({
@@ -530,9 +545,9 @@ def sundry_creditors_aging(
         "parties": parties,
         "details": details,
         "allocation_basis": (
-            "FIFO reconstructed from the Accounting Mirror closing balance; "
-            "newest credit-side additions form the unpaid closing balance and "
-            "debit-side settlements are deemed to clear the oldest balance first"
+            "FIFO from selected-FY Accounting Mirror movements; the historical "
+            "closing balance is reconstructed from opening balance plus FY credits "
+            "less FY debits, and newest credit-side additions form the unpaid closing balance"
         ),
         "current_mirror": current.get("mirror") or {},
         "follow_up_mirror": later.get("mirror") or {},

app/modules/accounting/templates/accounting/sundry_creditors_aging.html

@@ -5,7 +5,7 @@
     <div>
       <p class="text-xs font-semibold uppercase tracking-[0.16em] text-brand-600">Accounting · Audit Analysis</p>
       <h1 class="mt-1 text-2xl font-semibold text-slate-900">Sundry Creditors – 180 Day Analysis</h1>
-      <p class="mt-1 max-w-4xl text-sm text-slate-500">Analyses closing Sundry Creditors into ≤180 days and &gt;180 days from the local Accounting Mirror. The closing balance is reconstructed on FIFO: debit-side settlements clear the oldest balances first, so the newest credit-side additions form the unpaid closing balance. Bill-reference allocations are not yet stored in the .act mirror.</p>
+      <p class="mt-1 max-w-4xl text-sm text-slate-500">Analyses closing Sundry Creditors into ≤180 days and &gt;180 days from the local Accounting Mirror. The selected-FY closing balance and ageing are reconstructed from the Accounting Mirror on FIFO: debit-side settlements clear the oldest balances first, so the newest credit-side additions form the unpaid closing balance. Bill-reference allocations are not yet stored in the .act mirror.</p>
     </div>
     <a href="/tools/tally{% if selected_client %}?client_id={{ selected_client.id }}{% endif %}" class="rounded-xl border border-slate-300 bg-white px-4 py-2 text-sm font-semibold text-slate-700 hover:bg-slate-50">Back to Tally Accounting</a>
   </div>