fix(inventory): preserve ledger chain continuity for legacy stock quantities (#1217)

main/services/inventory.ts

@@ -128,6 +128,17 @@ export function resolveInventoryDeduction(
   return null;
 }
 
+function getDecimalPlaces(value: number): number {
+  if (!Number.isFinite(value) || Math.floor(value) === value) return 0;
+  const str = value.toString();
+  if (str.includes('e-')) {
+    const [base, exp] = str.split('e-');
+    const baseDecimals = base.includes('.') ? base.split('.')[1].length : 0;
+    return baseDecimals + Number(exp);
+  }
+  return str.includes('.') ? str.split('.')[1].length : 0;
+}
+
 export function adjustProductStock(
   db: ReturnType<typeof getDatabase>,
   options: StockChangeOptions,
@@ -213,6 +224,10 @@ export function adjustProductStock(
     }
   }
   const stockBefore = Number(current?.stock_quantity ?? 0);
+  const targetPrecision = Math.max(
+    INVENTORY_QUANTITY_PRECISION,
+    Math.min(14, getDecimalPlaces(stockBefore)),
+  );
   const update = db.prepare(`
     UPDATE ${stockTable}
     SET stock_quantity = CASE
@@ -230,15 +245,15 @@ export function adjustProductStock(
     normalizedQuantityDelta,
     INVENTORY_QUANTITY_TOLERANCE,
     normalizedQuantityDelta,
-    INVENTORY_QUANTITY_PRECISION,
+    targetPrecision,
     updatedAt,
     ...stockIdArgs,
     normalizedQuantityDelta,
     INVENTORY_QUANTITY_TOLERANCE,
     normalizedQuantityDelta,
     INVENTORY_QUANTITY_TOLERANCE,
     normalizedQuantityDelta,
-    INVENTORY_QUANTITY_PRECISION,
+    targetPrecision,
   );
   if (result.changes !== 1) {
     if (!current) {
@@ -252,9 +267,7 @@ export function adjustProductStock(
 
   const updatedStock = readStock.get(...stockIdArgs) as { stock_quantity: number };
   const stockAfter = Number(updatedStock.stock_quantity);
-  const effectiveQuantityDelta = Number(
-    (stockAfter - stockBefore).toFixed(INVENTORY_QUANTITY_PRECISION),
-  );
+  const effectiveQuantityDelta = Number((stockAfter - stockBefore).toFixed(targetPrecision));
 
   db.prepare(`
     INSERT INTO inventory_movements (

tests/inventory-ledger.test.ts

@@ -25,6 +25,7 @@ const {
   closeDatabase,
   now,
   validateInventoryLedgerReplacement,
+  validateInventoryLedgerDatabase,
 } = require('../main/db');
 const { adjustProductStock } = require('../main/services/inventory');
 const {
@@ -456,6 +457,68 @@ async function main() {
       'movement delta reflects the clamped change (-2e-8)',
     );
 
+    // ── Legacy stock precision test: >8 decimal places ───────────────────────
+    const legacyStock = 10.123456789012;
+    db.prepare(`
+      INSERT INTO products (id, category_id, name, price, track_inventory, stock_quantity, created_at, updated_at)
+      VALUES ('p-legacy-precision', 'cat-ledger', 'Legacy Precision Item', 100, 1, ?, ?, ?)
+    `).run(legacyStock, now(), now());
+    db.prepare(`
+      INSERT INTO inventory_movements (
+        product_id, quantity_delta, movement_type, reference_type, stock_after, actor_user_id, created_at
+      ) VALUES ('p-legacy-precision', ?, 'adjustment', 'opening_balance', ?, ?, ?)
+    `).run(legacyStock, legacyStock, owner.userId, now());
+
+    assertEqual(
+      validateInventoryLedgerDatabase(db),
+      null,
+      'legacy stock with >8 decimals validates before adjustment',
+    );
+
+    // Negative adjustment
+    adjustProductStock(db, {
+      productId: 'p-legacy-precision',
+      quantityDelta: -0.5,
+      movementType: 'adjustment',
+      actorUserId: owner.userId,
+      reason: 'Legacy minus 0.5 adjustment',
+    });
+    assertEqual(
+      validateInventoryLedgerDatabase(db),
+      null,
+      'adjustProductStock preserves ledger chain continuity for legacy stock after decrease',
+    );
+    const legacyAfterDec = db
+      .prepare('SELECT stock_quantity FROM products WHERE id = ?')
+      .get('p-legacy-precision') as { stock_quantity: number };
+    assertEqual(
+      legacyAfterDec.stock_quantity,
+      9.623456789012,
+      'stock_quantity retains legacy decimal precision after decrease',
+    );
+
+    // Positive adjustment
+    adjustProductStock(db, {
+      productId: 'p-legacy-precision',
+      quantityDelta: 0.25,
+      movementType: 'adjustment',
+      actorUserId: owner.userId,
+      reason: 'Legacy plus 0.25 adjustment',
+    });
+    assertEqual(
+      validateInventoryLedgerDatabase(db),
+      null,
+      'adjustProductStock preserves ledger chain continuity for legacy stock after increase',
+    );
+    const legacyAfterInc = db
+      .prepare('SELECT stock_quantity FROM products WHERE id = ?')
+      .get('p-legacy-precision') as { stock_quantity: number };
+    assertEqual(
+      legacyAfterInc.stock_quantity,
+      9.873456789012,
+      'stock_quantity retains legacy decimal precision after increase',
+    );
+
     const manualIncrease = await api(baseUrl, `/api/products/${productId}/stock`, {
       method: 'POST',
       headers: owner.authHeader,