reset tax rate to 0 if taxable amount is zero

.changeset/gold-dryers-talk.md

@@ -0,0 +1,9 @@
+---
+"app-avatax": patch
+---
+
+Changed behavior how tax rate is calculated. It was possible that AvaTax return a non-zero rate, while the actual tax was 0 (for example - product is normally taxable, but this transaction has tax exemption). 
+
+Previously, app returned original, non-zero tax rate as the response together with 0 tax. 
+
+Now, if taxableAmount or total net amount is 0, rate will be also zero

apps/avatax/src/modules/avatax/calculate-taxes/avatax-calculate-taxes-response-lines-transformer.test.ts

@@ -1,10 +1,12 @@
+import { TransactionModel } from "avatax/lib/models/TransactionModel";
 import { describe, expect, it } from "vitest";
 
 import { avataxMockFactory } from "../avatax-mock-factory";
 import { AvataxCalculateTaxesResponseLinesTransformer } from "./avatax-calculate-taxes-response-lines-transformer";
 
 const transformer = new AvataxCalculateTaxesResponseLinesTransformer();
 
+const TAXABLE_TRANSACTION_MOCK = avataxMockFactory.createMockTransaction("taxIncludedShipping");
 const NON_TAXABLE_TRANSACTION_MOCK = avataxMockFactory.createMockTransaction("nonTaxable");
 const NON_TAXABLE_TRANSACTION_MOCK_WITH_DISCOUNT =
   avataxMockFactory.createMockTransaction("nonTaxableWithDiscount");
@@ -85,4 +87,38 @@ describe("AvataxCalculateTaxesResponseLinesTransformer", () => {
       },
     ]);
   });
+
+  /**
+   * AvaTax will return non-zero rate even if item is not taxable or there is some tax exemption.
+   * That's why we overwrite the rate to be effectively zero too.
+   */
+  describe("GIVEN non-zero tax rate from AvaTax", () => {
+    const transaction = structuredClone(TAXABLE_TRANSACTION_MOCK);
+
+    // Assert only first line
+    transaction.lines![0].details![0].rate = 0.1;
+
+    describe("AND calculated tax from AvaTax is zero", () => {
+      const localTransaction = structuredClone(transaction);
+
+      localTransaction!.lines![0].taxCalculated = 0;
+
+      it("Should return tax rate as zero", () => {
+        const result = transformer.transform(localTransaction);
+
+        expect(result[0].tax_rate).toBe(0);
+      });
+    });
+    describe("AND taxableAmount from AvaTax is zero", () => {
+      const localTransaction = structuredClone(transaction);
+
+      localTransaction!.lines![0].taxableAmount = 0;
+
+      it("Should return tax rate as zero", () => {
+        const result = transformer.transform(localTransaction);
+
+        expect(result[0].tax_rate).toBe(0);
+      });
+    });
+  });
 });

apps/avatax/src/modules/avatax/calculate-taxes/avatax-calculate-taxes-response-lines-transformer.ts

@@ -44,7 +44,7 @@ export class AvataxCalculateTaxesResponseLinesTransformer {
           };
         }
 
-        const rate = extractIntegerRateFromTaxDetailsRates(
+        let rate = extractIntegerRateFromTaxDetailsRates(
           line.details?.map((details) => details.rate),
         );
 
@@ -69,6 +69,18 @@ export class AvataxCalculateTaxesResponseLinesTransformer {
           .toDecimalPlaces(2)
           .toNumber();
 
+        /**
+         * Avalara will return non-zero rate as a standard rate, but
+         * it's possible that there is a tax exemption. So the tax effectively
+         * is zero, but rate is not.
+         *
+         * In this scenario, we reset rate to 0, so Saleor properly apply such rate in further
+         * calculations
+         */
+        if (lineTaxCalculated === 0 || lineTotalNetAmount === 0) {
+          rate = 0;
+        }
+
         this.logger.info(
           "Transforming taxable product line from AvaTax to Saleor CalculateTaxesResponse",
           {