add Swedish validateNationalIdenityNumber()

Author: alexanbj

packages/validation/package.json

@@ -31,6 +31,7 @@
     "build": "bunchee"
   },
   "devDependencies": {
-    "nav-faker": "3.2.4"
+    "@personnummer/generate": "^1.0.3",
+    "nav-faker": "^3.2.4"
   }
 }

packages/validation/src/no.ts

@@ -1,5 +1,5 @@
 import type { ValidatorOptions } from './types';
-import { mod11, stripFormatting } from './utils';
+import { isValidDate, mod11, stripFormatting } from './utils';
 
 type PostalCodeOptions = ValidatorOptions;
 
@@ -161,8 +161,5 @@ export function validateNationalIdentityNumber(
     day = day - 40;
   }
 
-  // important to use UTC so the user's timezone doesn't affect the validation
-  const date = new Date(Date.UTC(year, month - 1, day));
-
-  return date && date.getUTCMonth() === month - 1 && date.getUTCDate() === day;
+  return isValidDate(year, month, day);
 }

packages/validation/src/se.ts

@@ -1,5 +1,5 @@
 import type { ValidatorOptions } from './types';
-import { stripFormatting } from './utils';
+import { isValidDate, mod10, stripFormatting } from './utils';
 
 type PostalCodeOptions = ValidatorOptions;
 
@@ -84,5 +84,54 @@ export function validateOrganizationNumber(
   return /^\d{10}$/.test(value);
 }
 
+type PersonalIdentityNumberOptions = ValidatorOptions;
+
+/**
+ * Validates that the input value is a Swedish national identity number (fødselsnummer or d-nummer).
+ *
+ * It validates the control digits and checks if the date of birth is valid.
+ *
+ * @example
+ * ```
+ * // Fødselsnummer
+ * validatePersonalIdentityNumber('21075417753') // => true
+ *
+ * // D-nummer
+ * validatePersonalIdentityNumber('53097248016') // => true
+ * ```
+ */
+export function validateNationalIdentityNumber(
+  value: string,
+  options: PersonalIdentityNumberOptions = {},
+): boolean {
+  if (options.allowFormatting) {
+    // biome-ignore lint/style/noParameterAssign:
+    value = stripFormatting(value);
+  }
+
+  const controlDigitCheck = mod10(value);
+  if (!controlDigitCheck) {
+    return false;
+  }
+
+  let add = 0;
+  if (value.length === 12) {
+    add = 2;
+  }
+
+  // copy/inspiration from NAV https://github.com/navikt/fnrvalidator/blob/77e57f0bc8e3570ddc2f0a94558c58d0f7259fe0/src/validator.ts#L108
+  let year = Number(value.substring(0, 2 + add));
+  const month = Number(value.substring(2 + add, 4 + add));
+  const day = Number(value.substring(4 + add, 6 + add));
+
+  // 1900 isn't a leap year, but 2000 is. Since JS two digits years to the Date constructor is an offset from the year 1900
+  // we need to special handle that case. For other cases it doesn't really matter if the year is 1925 or 2025.
+  if (year === 0) {
+    year = 2000;
+  }
+
+  return isValidDate(year, month, day);
+}
+
 // just reexport the no method for API feature parity
 export { validateObosMembershipNumber } from './no';

packages/validation/src/utils.ts

@@ -26,3 +26,49 @@ export function mod11(value: string, weights: number[]): boolean {
 
   return controlNumber === Number(value[value.length - 1]);
 }
+
+/**
+ * Also known as Luhn's algorithm.
+ * Used to validate Swedish national identity numbers.
+ * See https://no.wikipedia.org/wiki/MOD10
+ */
+export function mod10(value: string): boolean {
+  let sum = 0;
+
+  for (let i = 0; i < value.length; ++i) {
+    const weight = 2 - (i % 2);
+
+    let number = Number(value[i]);
+
+    number = weight * number;
+
+    // if the number is greater than 9, ie more than one digit, we reduce it to a single digit by adding the individual digits together
+    // 7 * 2 => 14 => 1 + 4 => 5
+    // instead of adding the digits together, we can subtract 9 for the same result
+    // 7 * 2 => 14 => 14 - 9 => 5
+    if (number > 9) {
+      number = number - 9;
+    }
+
+    sum += number;
+  }
+
+  return sum % 10 === 0;
+}
+
+export function isValidDate(year: number, month: number, day: number): boolean {
+  // months are zero indexed 🤷‍♂️
+  month -= 1;
+
+  // important to use UTC so the user's timezone doesn't affect the validation
+  const date = new Date(Date.UTC(year, month, day));
+
+  return (
+    date &&
+    // cannot do this for Norway
+    // maybe do it for Sweden?
+    // date.getUTCFullYear() === year &&
+    date.getUTCMonth() === month &&
+    date.getUTCDate() === day
+  );
+}

packages/validation/src/validation.test.ts

@@ -1,3 +1,4 @@
+import swedishPersonNummer from '@personnummer/generate';
 import navfaker from 'nav-faker/dist/index';
 import { describe, expect, test } from 'vitest';
 import * as no from './no';
@@ -178,4 +179,14 @@ describe('se', () => {
   ])('validateObosMembershipNumber(%s) -> %s', (input, expected, options) => {
     expect(se.validateObosMembershipNumber(input, options)).toBe(expected);
   });
+
+  test('validateNationalIdentityNumber() - validates leap years', () => {
+    for (let i = 0; i < 1000; ++i) {
+      const pnr = swedishPersonNummer({ format: 'short' });
+      expect(
+        se.validateNationalIdentityNumber(pnr, { allowFormatting: true }),
+        `${pnr} is valid`,
+      ).toBe(true);
+    }
+  });
 });