(5 kyu) Ninety Nine Thousand Nine Hundred Ninety Nine.ts

export function numberToEnglish(x: number): string {
  let n = x.toString();

  if (x < 0 || x > 99999 || n.indexOf('.') !== -1) {
    return '';
  }

  const value: {[id: string]: string} = {
    '0': 'zero',
    '1': 'one',
    '2': 'two',
    '3': 'three',
    '4': 'four',
    '5': 'five',
    '6': 'six',
    '7': 'seven',
    '8': 'eight',
    '9': 'nine',
    '10': 'ten',
    '11': 'eleven',
    '12': 'twelve',
    '13': 'thirteen',
    '14': 'fourteen',
    '15': 'fifteen',
    '16': 'sixteen',
    '17': 'seventeen',
    '18': 'eighteen',
    '19': 'nineteen',
    '20': 'twenty',
    '30': 'thirty',
    '40': 'forty',
    '50': 'fifty',
    '60': 'sixty',
    '70': 'seventy',
    '80': 'eighty',
    '90': 'ninety',
  };

  const getDozens = (n: number) =>
    n <= 20
      ? value[n.toString()]
      : `${value[n.toString()[0] + '0']} ${value[n.toString()[1]]}`;
  const getHundreds = (n: number) =>
    n > 0 ? `${value[n.toString()]} hundred ` : '';
  const getThousands = (n: number) => getDozens(n) + ' thousand ';
  let string: string;

  if (x <= 99) {
    string = getDozens(+n).replace(/\szero/g, '');
  } else if (x === 100) {
    string = getHundreds(+n[0]);
  } else if (x > 100 && x < 999) {
    string = `${getHundreds(+n[0])}${getDozens(+n.slice(-2))}`;
  } else {
    const z = x < 9999 ? 1 : 2;
    string = `${getThousands(+n.slice(0, z))}${getHundreds(
      +n.slice(-3, -2),
    )}${getDozens(+n.slice(-2))}`;
  }

  return string.trim().replace(/\szero/g, '');
}