fix(vehicle): calculate VIN check digit

src/modules/vehicle/module.ts

@@ -1,5 +1,51 @@
 import { ModuleBase } from '../../internal/module-base';
 
+// NHTSA 49 CFR § 565.15(c), Tables III and IV define the transliteration
+// values and position weights used here:
+// https://www.govinfo.gov/content/pkg/CFR-2025-title49-vol6/pdf/CFR-2025-title49-vol6-sec565-15.pdf
+const vinWeights = [8, 7, 6, 5, 4, 3, 2, 10, 0, 9, 8, 7, 6, 5, 4, 3, 2];
+
+const vinTransliteration: Record<string, number> = {
+  A: 1,
+  B: 2,
+  C: 3,
+  D: 4,
+  E: 5,
+  F: 6,
+  G: 7,
+  H: 8,
+  J: 1,
+  K: 2,
+  L: 3,
+  M: 4,
+  N: 5,
+  P: 7,
+  R: 9,
+  S: 2,
+  T: 3,
+  U: 4,
+  V: 5,
+  W: 6,
+  X: 7,
+  Y: 8,
+  Z: 9,
+};
+
+/**
+ * Calculates a Vehicle Identification Number (VIN) check digit.
+ *
+ * @param vin The VIN to calculate the check digit for.
+ */
+export function vinCheckDigit(vin: string): string {
+  let checksum = 0;
+  for (const [index, character] of vin.split('').entries()) {
+    const value = vinTransliteration[character] ?? Number(character);
+    checksum += value * vinWeights[index];
+  }
+
+  return checksum % 11 === 10 ? 'X' : String(checksum % 11);
+}
+
 /**
  * Module to generate vehicle related entries.
  *
@@ -84,7 +130,7 @@ export class VehicleModule extends ModuleBase {
    */
   vin(): string {
     const exclude = ['o', 'i', 'q', 'O', 'I', 'Q'];
-    return `${this.faker.string.alphanumeric({
+    const vin = `${this.faker.string.alphanumeric({
       length: 10,
       casing: 'upper',
       exclude,
@@ -97,6 +143,8 @@ export class VehicleModule extends ModuleBase {
       casing: 'upper',
       exclude,
     })}${this.faker.string.numeric({ length: 5, allowLeadingZeros: true })}`;
+
+    return `${vin.slice(0, 8)}${vinCheckDigit(vin)}${vin.slice(9)}`;
   }
 
   /**

test/modules/__snapshots__/vehicle.spec.ts.snap

@@ -14,7 +14,7 @@ exports[`vehicle > 42 > type 1`] = `"Extended Cab Pickup"`;
 
 exports[`vehicle > 42 > vehicle 1`] = `"Jeep Wrangler"`;
 
-exports[`vehicle > 42 > vin 1`] = `"CYRK551VKPAZ82113"`;
+exports[`vehicle > 42 > vin 1`] = `"CYRK551V7PAZ82113"`;
 
 exports[`vehicle > 42 > vrm 1`] = `"JY75EEB"`;
 
@@ -32,7 +32,7 @@ exports[`vehicle > 1211 > type 1`] = `"Wagon"`;
 
 exports[`vehicle > 1211 > vehicle 1`] = `"Toyota Spyder"`;
 
-exports[`vehicle > 1211 > vin 1`] = `"XW7ZNNSBNTUM84882"`;
+exports[`vehicle > 1211 > vin 1`] = `"XW7ZNNSB8TUM84882"`;
 
 exports[`vehicle > 1211 > vrm 1`] = `"YX29RRT"`;
 
@@ -50,6 +50,6 @@ exports[`vehicle > 1337 > type 1`] = `"Coupe"`;
 
 exports[`vehicle > 1337 > vehicle 1`] = `"Fiat Aventador"`;
 
-exports[`vehicle > 1337 > vin 1`] = `"859FAH8ZR3JL19477"`;
+exports[`vehicle > 1337 > vin 1`] = `"859FAH8Z23JL19477"`;
 
 exports[`vehicle > 1337 > vrm 1`] = `"GE24ING"`;

test/modules/vehicle.spec.ts

@@ -1,11 +1,24 @@
 import { describe, expect, it } from 'vitest';
 import { faker } from '../../src';
+import { vinCheckDigit } from '../../src/modules/vehicle/module';
 import { seededTests } from '../support/seeded-runs';
 import { times } from '../support/times';
 
 const NON_SEEDED_BASED_RUN = 5;
 
 describe('vehicle', () => {
+  describe('vinCheckDigit()', () => {
+    it.each([
+      ['1M8GDM9AXKP042788', 'X'],
+      ['1HGCM82633A004352', '3'],
+      ['CYRK551V7PAZ82113', '7'],
+      ['XW7ZNNSB8TUM84882', '8'],
+      ['859FAH8Z23JL19477', '2'],
+    ])('calculates the check digit for %s', (vin, expected) => {
+      expect(vinCheckDigit(vin)).toBe(expected);
+    });
+  });
+
   seededTests(faker, 'vehicle', (t) => {
     t.itEach(
       'vehicle',
@@ -102,6 +115,12 @@ describe('vehicle', () => {
             /^([A-HJ-NPR-Z0-9]{10}[A-HJ-NPR-Z0-9]{1}[A-HJ-NPR-Z0-9]{1}\d{5})$/
           );
         });
+
+        it('should add the check digit at the correct position', () => {
+          const vin = faker.vehicle.vin();
+
+          expect(vin[8]).toBe(vinCheckDigit(vin));
+        });
       });
 
       describe('vrm()', () => {