Natural language duration parser

duration-parser.js

const units = [ 
  {
    names: ['day', 'dy', 'd'],
    seconds: 86400
  }, {
    names: ['hour', 'hr', 'h'],
    seconds: 3600
  }, {
    names: ['minute', 'min', 'm'],
    seconds: 60
  }, {
    names: ['second', 'sec', 's'],
    seconds: 1
  }
];

function pluralize(count, noun) {
  return count === 1 ? noun : `${noun}s`;
}

class Duration {
  constructor(number, name) {
    this.count = parseFloat(number);
    this.unit = units.find(u => u.names.includes(name));
    this.seconds = Math.floor(this.count * this.unit.seconds);
  }

  static detect(seconds) {
    let unit = units.find(unit => Math.floor(seconds) % unit.seconds === 0);

    return new Duration(seconds / unit.seconds, unit.names[0]);
  }

  toString() {
    return `${this.count} ${pluralize(this.count, this.unit.names[0])}`;
  }
}

function tokenizer() {
  let numbers = '[\\d.]+';
  let names = [].concat(...units.map(m => m.names)).join('|');

  return new RegExp(`(${numbers})(${names})s?`, 'g');
}

function parse(input) {
  let re = tokenizer();
  let durations = [];
  let result;

  input = input.replace(/\s/g, '');

  while (result = re.exec(input)) {
    let [, number, name] = result;

    durations.push(new Duration(number, name));
  }

  return durations;
}

let good = ['1 day', '1h 2 min', '1d12h', ' 3.5 dy ', '48h'];
let bad = ['', '1 day 5', 'potato 1d tomato', '555', 'day'];

for (let inputs of [good, bad]) {
  console.log(inputs.map(input => {
    let durations = parse(input);
    let seconds = durations.map(d => d.seconds).reduce((a, b) => a + b, 0);
    let total = Duration.detect(seconds);

    return {
      input,
      output: durations.join(' '),
      seconds,
      total: total.toString()
    };
  }));
}

output.md

Good inputs

input	output	seconds	total
"1 day"	"1 day"	86400	"1 day"
"1h 2 min"	"1 hour 2 minutes"	3720	"62 minutes"
"1d12h"	"1 day 12 hours"	129600	"36 hours"
" 3.5 dy "	"3.5 days"	302400	"84 hours"
"48h"	"48 hours"	172800	"2 days"

Bad inputs

input	output	seconds	total
"day"	""	0	"0 days"
"555"	""	0	"0 days"
"potato 1d tomato"	"1 day"	86400	"1 day"
"1 day 5"	"1 day"	86400	"1 day"
""	""	0	"0 days"