expression-parser.js

const moo = require('moo');
const Time = require('./time');

const parser = moo.compile({
  VAR: {
    match: /{[a-zA-Z_]\w*}/, 
    keywords: { PREDEF: ['{today}'] } // predefined keywords
  },
  OP: ['and', 'or', '+', 'at'],
  DAY: {
    match: /\d+d/, // 5d 12d
    value: s => parseInt(s) // it automatically cut off non digit symbols
  },
  HOUR: {
    match: /\d+h/, // 1h 433h
    value: s => parseInt(s) // it automatically cut off non digit symbols
  },
  TIME: [
    {
      match: 'noon', value: () => new Time(12, 0)
    }, {
      match: 'midnight', value: () => new Time(0, 0)
    }, {
      match: /(?:[0-9]|0[0-9]|1[0-9]|2[0-3])(?::[0-5][0-9])?[ap]m/, // 12am 3:45pm
      value: Time.parse12format
    }, {
      match: /(?:[0-9]|0[0-9]|1[0-9]|2[0-3]):[0-5][0-9]/, // 23:59 3:45
      value: Time.parse24format
    }
  ],
  STR: [
    /".*?"/, // double-quoted
    /'.*?'/  // single-quoted
  ],
  WS: { match: /\s+/, lineBreaks: true }
});
const str = `
"hello \'ere"
{today}
{my_var}
12h
3d
12am
12pm
5am
3:09pm
23:59`;
console.log('input: ', str, '\n\nparsed:');
for (const { type, value, text } of parser.reset(str)) {
  if (type !== 'WS') {
    console.log(type, `${value}`);
  }
}