Email domain suggestion for typo prone user segments

popular-domain-suggestion.ts

import { default as curry } from 'ramda/src/curry';

function deleteChar(deleteCount: number, word: string): string[] {
  if (!(0 < deleteCount)) {
    return [word];
  }
  const accumulatedWordList = [];
  for (let wordIterator = 0; wordIterator < word.length; wordIterator++) {
    const deletedWord = `${
      word.substring(0, wordIterator)
      }${
      word.substring(wordIterator + 1, word.length)
      }`;
    accumulatedWordList.push(
      deleteChar(
        deleteCount - 1,
        deletedWord,
      ),
    );
  }
  return [].concat(...accumulatedWordList);
}

const deleteCharN = curry(deleteChar);
const deleteChar1 = deleteCharN(1);

const extractName = /^[-\w\d]+/i;
const generateIndex = (domain: string) => {
  const match = extractName.exec(domain);
  if (!match) {
    return [];
  }
  return [domain, deleteChar1(match[0])];
};

import { default as map } from 'ramda/src/map';

const extractDomain = /^(.+)@([-.\w\d]+)$/i;
const deleteChar2 = deleteCharN(2);
const nullSuggesting = {
  suggestOther: false,
  suggestedEmail: null,
  suggestedDomain: null,
};
const suggest = (
  domainList: string[],
) => {
  const index = map(generateIndex, domainList);
  return (
    testEmail: string,
  ) => {
    const domainMatching = extractDomain.exec(testEmail);
    if (!domainMatching) {
      return nullSuggesting;
    }
    const domainName = domainMatching[2].toLowerCase();
    for (const indexEntry of index) {
      if (indexEntry[0] === domainName) {
        return nullSuggesting;
      }
    }
    const providerNameMatching = extractName.exec(domainName);
    if (!providerNameMatching) {
      return nullSuggesting;
    }
    const checkingName = providerNameMatching[0];
    const checkingList = [
      checkingName,
      ...deleteChar1(checkingName),
      ...deleteChar2(checkingName),
    ];
    for (const checkingWord of checkingList) {
      for (const indexEntry of index) {
        for (const indexMatch of indexEntry[1]) {
          if (indexMatch === checkingWord) {
            const suggestedDomain = indexEntry[0];
            return {
              suggestOther: true,
              suggestedEmail: `${domainMatching[1]}@${suggestedDomain}`,
              suggestedDomain,
            };
          }
        }
      }
    }
    return nullSuggesting;
  };
};

// don't add 3-letter-or-less domain name here
const suggester = suggest([
  'hotmail.com',
  'yahoo.com',
  'yahoo.co.jp',
  'outlook.com',
  'gmail.com',
  'ymail.com',
  'live.com',
  'mail.com',
  'rocketmail.com',
  'icloud.com',
]);

console.log('index', suggester('hahaha@yaahoo.com'));