99bottles.js

import { downTo } from './helpers';

export class Bottles {
  song() {
    return this.verses(99,0);
  }

  verses(start, end) {
    const versesToSing = [];

    let currentVerse = start;
    let text = '';

    while (currentVerse > end - 1) {
      versesToSing.push(currentVerse);
      currentVerse--;
    }

    versesToSing.forEach((verseToSing, index) => {
      const connector = index + 1 < versesToSing.length ? '\n' : '';
      text += this.verse(verseToSing) + connector;
    });

    return text;
  }

  verse(currentBottles) {
    const [current, next] = downTo(currentBottles, currentBottles - 1);
    const nextText = next === 0 ? 'no more' : next;

    if (currentBottles === 0) {
      return (
        'No more bottles of beer on the wall, ' +
        'no more bottles of beer.\n' +
        'Go to the store and buy some more, ' +
        '99 bottles of beer on the wall.\n'
      );
    }

    return (
      `${current} bottle${current !== 1 ? 's' : ''} of beer on the wall, ` +
      `${current} bottle${current !== 1 ? 's' : ''} of beer.\n` +
      `Take ${current == 1 ? 'it' : 'one'} down and pass it around, ` +
      `${nextText} bottle${next !== 1 ? 's' : ''} of beer on the wall.\n`
    );
  }
}