fix(billing): stop double-counting history a BALANCE FORWARD already carries

BALANCE FORWARD rows are not movements. Access materialized one per
customer per year, dated Jan 1, holding the closing balance of everything
before it — that is what let the portal keep each year in its own table and
still show a correct running balance from one year's rows.

The platform imported those rows AND the real pre-cutover history they
summarize, and every balance aggregate summed the lot. NUMid 501 read
-10,469.29 on the receivables worklist against -14,065.29 on the customer's
own statement and on the legacy portal; the gap was two cash receipts from
2009 and 2012 that the 2026 opening balance had already absorbed.

The scale settles what it is: summed the old way the whole book came to
+20,605,447.86 MXN — the office owing its customers 20.6 million pesos.
Floored, it is -56,855.90. A receivables ledger cannot be 20M in credit.

Adds BALANCE_FLOOR_JOIN + NOT_SUPERSEDED and applies them to balances()
(page and count queries, which must agree), to stats()'s per-currency and
per-domain figures, and to the owing/in-credit split. The four stats()
aggregates moved from Prisma groupBy to raw SQL because groupBy cannot
express a per-customer floor.

statement() takes the same floor as a scalar, which is also what stops
FEE ANUAL and fee15 leaking in. Those are not in
STATEMENT_EXCLUDED_SOURCE_TABLES — that list reproduces legacy's
DATOS2-only `datosfreak` — and they were putting 2,092 pre-cutover fee rows
across 1,062 customers into the statement, skewing it by -5,129,764 against
the number those customers have been quoted for years. Dating rather than
source is the right test: a fee row *after* the opening balance is a real
charge and still counts.

movements() is deliberately left alone. It is a browser over captured rows
— "how much water did we capture in April" — and staff need the historical
rows visible, so it keeps totalling everything, the same asymmetry
NOT_OUTSTANDING already has.

stats() now separates the two questions it was mixing: movements,
ledgerCustomers, crossLineCustomers and the date range stay unfloored
inventory; everything under byCurrency/byDomain is a balance and is floored.

BillingService had no tests. Adds 13 covering the floor's failure modes —
it fails silently, so MIN-vs-MAX, `>` vs `>=`, the NULL branch for customers
with no opening balance, and the join/predicate alias pairing are each
pinned, plus the 501 arithmetic as a regression.

Verified through the real service against the live ledger: balances() and
statement() both return -14,065.29 for 501, matching the portal.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

apps/api/src/billing/balance-floor.spec.ts

@@ -0,0 +1,180 @@
+import { Prisma } from "@jorgecuadros/database";
+import {
+  BALANCE_FLOOR_JOIN,
+  BALANCE_FORWARD_TYPE,
+  BillingService,
+  NOT_SUPERSEDED,
+} from "./billing.service";
+
+/**
+ * The balance floor drops rows a later BALANCE FORWARD already accounts for.
+ *
+ * It is worth testing because it fails silently: nothing throws, the numbers are
+ * just wrong, and they were wrong for years — the whole book read +20.6M MXN in
+ * credit because every customer's pre-cutover history was counted twice, once
+ * inside their opening balance and once as itself.
+ */
+describe("balance floor", () => {
+  describe("SQL fragments", () => {
+    it("binds the type name rather than interpolating it", () => {
+      // A literal would be a second place to edit if the label ever changes,
+      // and this string reaches SQL from a module constant.
+      expect(BALANCE_FLOOR_JOIN.values).toEqual([BALANCE_FORWARD_TYPE]);
+    });
+
+    it("keys the floor to the row's own customer", () => {
+      // Without this the derived table cross-joins and every customer inherits
+      // the earliest BALANCE FORWARD in the book.
+      expect(BALANCE_FLOOR_JOIN.sql).toContain(
+        "bfloor ON bfloor.customerId = t.customerId",
+      );
+    });
+
+    it("takes the most recent opening balance, not the first", () => {
+      // A customer accumulates one BALANCE FORWARD per year. MIN would floor at
+      // the oldest and leave every intervening year double-counted.
+      expect(BALANCE_FLOOR_JOIN.sql).toContain("MAX(bf.transactionDate)");
+      expect(BALANCE_FLOOR_JOIN.sql).not.toContain("MIN(bf.transactionDate)");
+    });
+
+    it("ignores voided opening balances when locating the floor", () => {
+      expect(BALANCE_FLOOR_JOIN.sql).toContain("bf.voidedAt IS NULL");
+    });
+
+    it("is inclusive of the opening balance row itself", () => {
+      // `>` instead of `>=` would drop the carried balance and understate every
+      // customer by exactly that amount.
+      expect(NOT_SUPERSEDED.sql).toContain("t.transactionDate >= bfloor.floorDate");
+      expect(NOT_SUPERSEDED.sql).not.toMatch(/transactionDate\s*>\s*bfloor/);
+    });
+
+    it("leaves customers with no opening balance untouched", () => {
+      // NULL comparisons are never true, so without the explicit IS NULL branch
+      // a customer who has no BALANCE FORWARD row loses their entire ledger.
+      expect(NOT_SUPERSEDED.sql).toContain("bfloor.floorDate IS NULL");
+    });
+
+    it("only ever references the alias the join defines", () => {
+      // The predicate is useless without the join; pairing them wrongly is a
+      // runtime "unknown column", so keep the alias identical in both.
+      const aliases = NOT_SUPERSEDED.sql.match(/bfloor\.\w+/g) ?? [];
+      expect(aliases.length).toBeGreaterThan(0);
+      for (const ref of aliases) {
+        expect(BALANCE_FLOOR_JOIN.sql).toContain(ref.split(".")[1]);
+      }
+    });
+  });
+
+  describe("statement()", () => {
+    /**
+     * One customer means one floor date, so the statement uses a scalar lookup
+     * instead of the join. Asserting on the `where` Prisma is handed is the only
+     * way to see it without a database.
+     */
+    function serviceWith(floor: Date | null) {
+      const findMany = jest.fn().mockResolvedValue([]);
+      const prisma = {
+        customer: {
+          findUnique: jest.fn().mockResolvedValue({
+            id: "c1",
+            name: "CUADROS, JORGE H.",
+            preferredCurrency: "USD",
+            _count: { properties: 0, policies: 0 },
+          }),
+        },
+        transaction: {
+          findFirst: jest
+            .fn()
+            .mockResolvedValue(floor ? { transactionDate: floor } : null),
+          findMany,
+        },
+      };
+
+      return {
+        service: new BillingService(prisma as never),
+        prisma,
+        findMany,
+      };
+    }
+
+    it("looks the floor up from the customer's newest opening balance", async () => {
+      const { service, prisma } = serviceWith(new Date("2026-01-01T00:00:00Z"));
+
+      await service.statement("c1");
+
+      expect(prisma.transaction.findFirst).toHaveBeenCalledWith(
+        expect.objectContaining({
+          where: {
+            customerId: "c1",
+            voidedAt: null,
+            type: { nameEn: BALANCE_FORWARD_TYPE },
+          },
+          orderBy: { transactionDate: "desc" },
+          select: { transactionDate: true },
+        }),
+      );
+    });
+
+    it("bounds the statement at the floor, inclusive", async () => {
+      const floor = new Date("2026-01-01T00:00:00Z");
+      const { service, findMany } = serviceWith(floor);
+
+      await service.statement("c1");
+
+      expect(findMany.mock.calls[0][0].where).toMatchObject({
+        customerId: "c1",
+        transactionDate: { gte: floor },
+      });
+    });
+
+    it("applies no date bound when the customer has no opening balance", async () => {
+      const { service, findMany } = serviceWith(null);
+
+      await service.statement("c1");
+
+      expect(findMany.mock.calls[0][0].where).not.toHaveProperty(
+        "transactionDate",
+      );
+    });
+
+    it("keeps the source-table exclusion alongside the floor", async () => {
+      // The two guards answer different questions — one reproduces legacy's
+      // DATOS2-only materialization, the other drops superseded history — and
+      // dropping either one changes the customer's balance.
+      const { service, findMany } = serviceWith(new Date("2026-01-01T00:00:00Z"));
+
+      await service.statement("c1");
+
+      const where = findMany.mock.calls[0][0].where;
+      expect(where.OR).toEqual([
+        { legacySourceTable: null },
+        { legacySourceTable: { notIn: expect.arrayContaining(["EFECTIVO"]) } },
+      ]);
+    });
+  });
+
+  describe("regression: NUMid 501", () => {
+    /**
+     * The arithmetic that exposed the bug, pinned so it cannot silently return.
+     * Figures measured against the live ledger on 2026-08-05.
+     */
+    const openingBalance = new Prisma.Decimal("-6732.29");
+    const activitySinceOpening = new Prisma.Decimal("-7333.00");
+    const preCutoverCashAlreadyInOpening = new Prisma.Decimal("3596.00");
+
+    it("matches the legacy portal once superseded rows are dropped", () => {
+      expect(openingBalance.plus(activitySinceOpening).toFixed(2)).toBe(
+        "-14065.29",
+      );
+    });
+
+    it("reproduces the wrong figure when they are not", () => {
+      expect(
+        openingBalance
+          .plus(activitySinceOpening)
+          .plus(preCutoverCashAlreadyInOpening)
+          .toFixed(2),
+      ).toBe("-10469.29");
+    });
+  });
+});

apps/api/src/billing/billing.service.ts

@@ -104,24 +104,31 @@ interface BalanceRow {
   nameMissing: number;
   city: string | null;
   state: string | null;
-  movements: bigint | number | string;
+  movements: RawCount;
   balanceMxn: Prisma.Decimal | null;
   balanceUsd: Prisma.Decimal | null;
   chargesMxn: Prisma.Decimal | null;
   creditsMxn: Prisma.Decimal | null;
   chargesUsd: Prisma.Decimal | null;
   creditsUsd: Prisma.Decimal | null;
-  utilityMovements: bigint | number | string;
+  utilityMovements: RawCount;
-  insuranceMovements: bigint | number | string;
+  insuranceMovements: RawCount;
   lastMovement: Date | null;
 }
 
 /**
- * Raw-query counts come back in three shapes depending on the aggregate:
+ * Every shape a raw-query count can arrive in. `COUNT(*)` is a bigint,
- * `COUNT(*)` as bigint, `SUM(bool)` as a decimal *string*, and plain numbers.
+ * `SUM(bool)` is a Prisma.Decimal, and plain numbers occur too — none of which
- * Normalize all of them before they reach the client as JSON.
+ * survive JSON serialization the way the client expects.
  */
-function num(v: bigint | number | string | null | undefined): number {
+type RawCount = bigint | number | string | Prisma.Decimal;
+
+/**
+ * Normalizes a raw-query count before it reaches the client as JSON. A bigint
+ * throws on JSON.stringify and a Decimal serializes to a *string*, so counts
+ * must not be passed through untouched.
+ */
+function num(v: RawCount | null | undefined): number {
   if (v === null || v === undefined) return 0;
   return typeof v === "number" ? v : Number(v);
 }
@@ -152,6 +159,56 @@ const NOT_VOIDED: Prisma.TransactionWhereInput = { voidedAt: null };
  */
 const NOT_OUTSTANDING: Prisma.TransactionWhereInput = { outstanding: false };
 
+/**
+ * The legacy type name for a carried-forward opening balance.
+ *
+ * These rows are not movements. Access materialized one per customer per year,
+ * dated Jan 1, holding the closing balance of everything before it — that is
+ * what let the portal keep each year in its own table (`datosfreak` = current,
+ * `2025`, `2024`, ...) and still show a correct running balance from a single
+ * year's rows.
+ */
+export const BALANCE_FORWARD_TYPE = "BALANCE FORWARD";
+
+/**
+ * Per-customer date of the most recent BALANCE FORWARD row.
+ *
+ * Joined rather than correlated: one small derived table (1,170 rows) beats a
+ * subquery evaluated per ledger row.
+ */
+export const BALANCE_FLOOR_JOIN = Prisma.sql`
+  LEFT JOIN (
+    SELECT bf.customerId, MAX(bf.transactionDate) AS floorDate
+    FROM transactions bf
+    JOIN type_transactions bft ON bft.id = bf.typeId
+    WHERE bft.nameEn = ${BALANCE_FORWARD_TYPE} AND bf.voidedAt IS NULL
+    GROUP BY bf.customerId
+  ) bfloor ON bfloor.customerId = t.customerId`;
+
+/**
+ * Excludes rows a later BALANCE FORWARD already accounts for.
+ *
+ * WHY THIS EXISTS. The platform holds both the synthetic BALANCE FORWARD rows
+ * and the real pre-cutover history they summarize, so summing a customer's
+ * whole ledger counts that history twice — once inside the opening balance,
+ * once as itself. NUMid 501 read -10,469.29 on the worklist against -14,065.29
+ * on the customer's own statement and on the legacy portal, the gap being two
+ * cash receipts from 2009 and 2012 that the 2026 opening balance had already
+ * absorbed.
+ *
+ * The scale is what settles it: summed the old way the entire book came to
+ * +20,605,447.86 MXN — the office owing its customers 20.6 million pesos.
+ * Floored, it is -56,855.90, a modest net receivable. A receivables ledger
+ * cannot be 20M in credit.
+ *
+ * Applies to BALANCES ONLY, in the same spirit as NOT_OUTSTANDING: the movement
+ * browser still totals every captured row, because "how much water did we
+ * capture in April" is a question about what was recorded, not about what is
+ * owed. Customers with no BALANCE FORWARD row (the floor is NULL) are
+ * unaffected.
+ */
+export const NOT_SUPERSEDED = Prisma.sql`(bfloor.floorDate IS NULL OR t.transactionDate >= bfloor.floorDate)`;
+
 /**
  * Source tables excluded from the customer-facing statement.
  *
@@ -402,22 +459,24 @@ export class BillingService {
         MAX(t.transactionDate)                                                     AS lastMovement
       FROM customers c
       JOIN transactions t ON t.customerId = c.id
-      WHERE t.voidedAt IS NULL AND t.outstanding = 0 ${nameFilter} ${txFilter}
+      ${BALANCE_FLOOR_JOIN}
+      WHERE t.voidedAt IS NULL AND t.outstanding = 0 AND ${NOT_SUPERSEDED} ${nameFilter} ${txFilter}
       GROUP BY c.id, c.name, c.nameSource, c.nameMissing, c.city, c.state
       ${having}
       ${orderBy}
       LIMIT ${pageSize} OFFSET ${(page - 1) * pageSize}
     `;
 
-    const counted = await this.prisma.$queryRaw<{ total: bigint | number | string }[]>`
+    const counted = await this.prisma.$queryRaw<{ total: RawCount }[]>`
       SELECT COUNT(*) AS total FROM (
         SELECT c.id
         FROM customers c
         JOIN transactions t ON t.customerId = c.id
+        ${BALANCE_FLOOR_JOIN}
         -- Must match the page query's filters exactly, or the total disagrees
         -- with the rows. (The void exclusion was missing here before the
         -- outstanding work; a voided-only customer inflated the count.)
-        WHERE t.voidedAt IS NULL AND t.outstanding = 0 ${nameFilter} ${txFilter}
+        WHERE t.voidedAt IS NULL AND t.outstanding = 0 AND ${NOT_SUPERSEDED} ${nameFilter} ${txFilter}
         GROUP BY c.id
         ${having}
       ) x
@@ -458,9 +517,18 @@ export class BillingService {
     };
   }
 
-  /** Top-line figures for the billing page header. */
+  /**
+   * Top-line figures for the billing page header.
+   *
+   * Two different questions live here and they use different row sets.
+   * `movements`, `ledgerCustomers`, `crossLineCustomers` and the date range are
+   * INVENTORY — what is stored — and count everything not voided. Everything
+   * under `byCurrency` / `byDomain` is a BALANCE, so it applies NOT_SUPERSEDED
+   * and drops rows an opening balance already accounts for. The four aggregates
+   * moved from Prisma groupBy to raw SQL to express that join; groupBy cannot.
+   */
   async stats() {
-    const [movements, ledgerCustomers, byCurrency, byDomain] = await Promise.all([
+    const [movements, ledgerCustomers] = await Promise.all([
       this.prisma.transaction.count({ where: NOT_VOIDED }),
       this.prisma.transaction
         .findMany({
@@ -469,34 +537,47 @@ export class BillingService {
           select: { customerId: true },
         })
         .then((r) => r.length),
-      this.prisma.transaction.groupBy({
-        by: ["currency"],
-        where: NOT_VOIDED,
-        _sum: { amount: true },
-        _count: { _all: true },
-      }),
-      this.prisma.transaction.groupBy({
-        by: ["domain", "currency"],
-        where: NOT_VOIDED,
-        _sum: { amount: true },
-        _count: { _all: true },
-      }),
     ]);
 
-    const charges = await this.prisma.transaction.groupBy({
+    const byCurrency = await this.prisma.$queryRaw<
-      by: ["currency"],
+      {
-      where: { AND: [{ amount: { lt: 0 } }, NOT_VOIDED] },
+        currency: string;
-      _sum: { amount: true },
+        net: Prisma.Decimal | null;
-      _count: { _all: true },
+        count: RawCount;
-    });
+        charges: Prisma.Decimal | null;
-    const credits = await this.prisma.transaction.groupBy({
+        chargeCount: RawCount;
-      by: ["currency"],
+        credits: Prisma.Decimal | null;
-      where: { AND: [{ amount: { gt: 0 } }, NOT_VOIDED] },
+        creditCount: RawCount;
-      _sum: { amount: true },
+      }[]
-      _count: { _all: true },
+    >`
-    });
+      SELECT t.currency                                             AS currency,
-    const chargeMap = new Map(charges.map((c) => [c.currency, c]));
+             SUM(t.amount)                                          AS net,
-    const creditMap = new Map(credits.map((c) => [c.currency, c]));
+             COUNT(*)                                               AS count,
+             SUM(CASE WHEN t.amount < 0 THEN t.amount ELSE 0 END)   AS charges,
+             SUM(t.amount < 0)                                      AS chargeCount,
+             SUM(CASE WHEN t.amount > 0 THEN t.amount ELSE 0 END)   AS credits,
+             SUM(t.amount > 0)                                      AS creditCount
+      FROM transactions t
+      ${BALANCE_FLOOR_JOIN}
+      WHERE t.voidedAt IS NULL AND ${NOT_SUPERSEDED}
+      GROUP BY t.currency
+    `;
+
+    const byDomain = await this.prisma.$queryRaw<
+      {
+        domain: string;
+        currency: string;
+        net: Prisma.Decimal | null;
+        count: RawCount;
+      }[]
+    >`
+      SELECT t.domain AS domain, t.currency AS currency,
+             SUM(t.amount) AS net, COUNT(*) AS count
+      FROM transactions t
+      ${BALANCE_FLOOR_JOIN}
+      WHERE t.voidedAt IS NULL AND ${NOT_SUPERSEDED}
+      GROUP BY t.domain, t.currency
+    `;
 
     // How many customers sit on each side of the line, per currency — the
     // headline for a receivables view. Counted in SQL; a customer can be
@@ -504,16 +585,19 @@ export class BillingService {
     const sides = await this.prisma.$queryRaw<
       {
         currency: string;
-        owing: bigint | number | string;
+        owing: RawCount;
-        inCredit: bigint | number | string;
+        inCredit: RawCount;
       }[]
     >`
       SELECT currency,
              SUM(bal < -0.005) AS owing,
              SUM(bal >  0.005) AS inCredit
       FROM (
-        SELECT customerId, currency, SUM(amount) AS bal
+        SELECT t.customerId, t.currency, SUM(t.amount) AS bal
-        FROM transactions WHERE voidedAt IS NULL GROUP BY customerId, currency
+        FROM transactions t
+        ${BALANCE_FLOOR_JOIN}
+        WHERE t.voidedAt IS NULL AND ${NOT_SUPERSEDED}
+        GROUP BY t.customerId, t.currency
       ) x
       GROUP BY currency
     `;
@@ -534,7 +618,7 @@ export class BillingService {
 
     // Customers whose ledger spans both business lines — the whole reason this
     // module is one view instead of two.
-    const crossLine = await this.prisma.$queryRaw<{ n: bigint | number | string }[]>`
+    const crossLine = await this.prisma.$queryRaw<{ n: RawCount }[]>`
       SELECT COUNT(*) AS n FROM (
         SELECT customerId FROM transactions WHERE voidedAt IS NULL
         GROUP BY customerId HAVING COUNT(DISTINCT domain) > 1
@@ -549,20 +633,20 @@ export class BillingService {
       lastMovement: lastRow?.transactionDate ?? null,
       byCurrency: byCurrency.map((c) => ({
         currency: c.currency,
-        net: c._sum.amount,
+        net: c.net,
-        count: c._count._all,
+        count: num(c.count),
-        charges: chargeMap.get(c.currency)?._sum.amount ?? null,
+        charges: c.charges,
-        chargeCount: chargeMap.get(c.currency)?._count._all ?? 0,
+        chargeCount: num(c.chargeCount),
-        credits: creditMap.get(c.currency)?._sum.amount ?? null,
+        credits: c.credits,
-        creditCount: creditMap.get(c.currency)?._count._all ?? 0,
+        creditCount: num(c.creditCount),
         owing: num(sideMap.get(c.currency)?.owing),
         inCredit: num(sideMap.get(c.currency)?.inCredit),
       })),
       byDomain: byDomain.map((d) => ({
         domain: d.domain,
         currency: d.currency,
-        net: d._sum.amount,
+        net: d.net,
-        count: d._count._all,
+        count: num(d.count),
       })),
     };
   }
@@ -589,7 +673,7 @@ export class BillingService {
     });
 
     const years = await this.prisma.$queryRaw<
-      { year: number; count: bigint | number | string }[]
+      { year: number; count: RawCount }[]
     >`
       SELECT YEAR(transactionDate) AS year, COUNT(*) AS count
       FROM transactions WHERE voidedAt IS NULL GROUP BY year ORDER BY year DESC
@@ -647,9 +731,32 @@ export class BillingService {
       throw new NotFoundException(`Customer ${customerId} not found`);
     }
 
+    // One customer, so the balance floor is a single date rather than the
+    // derived table the aggregate queries join. See NOT_SUPERSEDED: rows before
+    // the opening balance are already inside it, and showing them would both
+    // double the total and make every balanceAfter below wrong.
+    //
+    // This is also what stops FEE ANUAL and fee15 leaking in. They are not in
+    // STATEMENT_EXCLUDED_SOURCE_TABLES — that list exists to reproduce legacy's
+    // DATOS2-only `datosfreak`, and it was letting 2,092 pre-cutover fee rows
+    // across 1,062 customers through, skewing the statement by -5,129,764
+    // against the number those customers have been quoted for years. Dating
+    // rather than source is the right test: a FEE ANUAL row *after* the opening
+    // balance is a real charge and still counts.
+    const floor = await this.prisma.transaction.findFirst({
+      where: {
+        customerId,
+        voidedAt: null,
+        type: { nameEn: BALANCE_FORWARD_TYPE },
+      },
+      orderBy: { transactionDate: "desc" },
+      select: { transactionDate: true },
+    });
+
     const rows = await this.prisma.transaction.findMany({
       where: {
         customerId,
+        ...(floor ? { transactionDate: { gte: floor.transactionDate } } : {}),
         // NULL-safe exclusion. `notIn` alone compiles to SQL `NOT IN`, and
         // `NULL NOT IN (...)` is NULL, not true — so every app-captured row
         // (which has no legacySourceTable) silently vanished from the