Generates a normalised email address, with support for extended latin as input

EmailAddressUtils.ts

function removeAccents (text: string) {
  return text.normalize('NFD').replace(/[\u0300-\u036f]/g, '');
}

/**
 * Converts a string, that may include extended latin characters
 * and accents, to the more limited range supported by the English
 * alphabet and 128 bit ASCII. 
 *
 * There may be some disagreement in the character mapping, but we
 * weren't able to find a good "go to" reference for this, to it is
 * based on discussing with people.
 *
 * @params text the input text
 * @return the flattened string
 */
function flattenString (text: string) {
  const extendedChar = ['ß', 'Œ', 'œ', 'æ', 'ø'];
  const englishChar = ['ss', 'oe', 'oe', 'ae', 'oe'];

  text = removeAccents('NFD');

  let newText = '';
  for (let i = 0; i < text.length; i++) {
    const charIdx = extendedChar.indexOf(text.charAt(i));
    if (charIdx > -1) {
      newText += englishChar[charIdx];
    } else {
      newText += text.charAt(i);
    }
  }

  return newText;
}

/**
 * Checks to see if the input string is a
 * valid latin name.
 *
 * The logic is based on eliminating characters
 * that aren't in the 'a-z' range and then seeing
 * if the string is not of zero length.
 *
 * @params text the input text
 * @return true if the name is valid
 */
function isValidLatinName (name: string) {
  name = removeAccents(name);
  name = name.replace(/[^a-z]+/gui, '')
  return name.length > 0;
}

/**
 * Creates an email address, based on normalising first name and last name, and
 * then joing the domain name. Support for normalising extended-latin, in the english
 * language subset, is also included.
 *
 * Output format: 
 * ```
 * <first character of first name>.<last name>@<domain name>
 * ```
 * 
 * Notes:
 *   - If the firstname is hyphenated, then the first name initial include each of
 *     hyphenated characters of the parts. For example: 'Marie-Claire' beceomes 'mc'.
 *   - In the case of a name clash, use the 'namePartSuffix' to provide a differentiator
 *   - This does not support names that do not contain latin characters. These will
 *     need to be transliterated before hand.
 *   - Domain names are used 'as is', without modification.
 *
 * @param firstName the person's first name
 * @param lastName the person's last name
 * @param domain the name of the domain
 * @param namePartSuffix an optional suffix to be provided in the case of geneated
 *        address clash.
 * @return the flattened string
 */
function createEmailAddress (firstName: string, lastName: string, domain: string, namePartSuffix: string = '') {
  if (!isValidLatinName(firstName) || !isValidLatinName(lastName)) {
    throw new Error('First name or last name did not have any valid latin characters');
  }

  firstName = firstName.trim();
  firstName = firstName.toLowerCase();
  firstName = flattenString(firstName);
  if (firstName.indexOf('-') > 0) {
    const parts = firstName.split('-');
    firstName = '';
    parts.forEach(part => firstName += part.charAt(0));
  } else {
    firstName = firstName.charAt(0);
  }
  firstName = firstName.replace(/[^a-z]+/gui, '');

  lastName = lastName.trim();
  lastName = lastName.toLowerCase();
  lastName = flattenString(lastName);
  lastName = lastName.replace(/[^a-z]+/gui, '');

  return `${firstName}.${lastName},${namePartSuffix}@${domain.toLowerCase()}`;
}

export { createEmailAddress };

EmailAddressUtilsTest.ts

import { createEmailAddress } from 'src/utils/EmailAddressUtils.ts';

const domain = 'mytestdomain.com';
const testData: string[][] = [
  ['Albert', 'Einstein', '[email protected]'],
  ['Jean-Marc', 'Chapeaux', '[email protected]'],
  ['Marc-André', 'Éléphant', '[email protected]'],
  ['Jager', 'Mozart-Shito', '[email protected]'],
  ['Édourd', 'Mazimbi!', '[email protected]'],
  ['士郎', '正宗', 'error'],
  ['Øyvind', 'Johansen', '[email protected]'],
  ['Aabjørn', 'Andersen', '[email protected]'],
  ['Adelbjørn', 'Jensen', '[email protected]'],
  ['Ásgerð', 'Abrahamsson', '[email protected]'],
  ['Auðbjörg', 'Berg', '[email protected]'],
  ['Emmý', 'Larsen', '[email protected]'],
  ['Aabjørn', 'Karlsson', '[email protected]'],
  ['Sælaug', 'Hämäläinen', '[email protected]'],
  ['Sæmann', 'Korhonen', '[email protected]'],
  ['Salvør', 'Mäkelä', '[email protected]'],
  ['Lara', 'Sælaugson', '[email protected]'],
]

let results: Record<string, unknown>[] = [];
for (let i = 0; i < testData.length; i++) {
  const resultObject: Record<string, unknown> = {
    firstName: testData[i][0],
    lastName: testData[i][1],
    expectedResult: testData[i][2],
  };

  try {
    const result = generateEmailAddress(testData[i][0], testData[i][1], domain);
    resultObject.actualResult = result;
    resultObject.success = result === testData[i][2];
  } catch (error) {
    if (testData[i][2] === 'error') {
      resultObject.actualResult = `error: ${error?.message}`;
      resultObject.success = testData[i][2] === 'error';
    } else {
      throw error;
    }
  }
  results.push(resultObject);
}

console.table(results, ['firstName', 'lastName', 'expectedResult', 'actualResult', 'success']);