crunchtime.js

function crunchtime(input) {
  // time should be a delta from some time Xa-Ya,
  // Xa-Y, Xp-Yp
  // This function parses the first non-numeric character
  // as an indication of whether it's receiving AM or PM, 
  // followed by a `-` to delimit between the starting time
  // and ending time. Our expected inputs, less formally, resemble
  // 4:45a-11a, 5p-12:30p, 6:45a-2p
  input = input.trim();
  if (input.toLowerCase() == "off") {
    return 0;
  }
  let [start, end] = input.split('-');
  let hours = 0;
  let minutes = 0;

  let startMin = timeToMin(start);
  let endMin = timeToMin(end);
  let delta = endMin - startMin;
  
  hours += Math.floor(delta / 60.0);
  minutes += delta - (hours * 60.0);
  hours += (minutes / 60.0);
  return hours;
}

function timeToMin(timestr) {
  
  const minPerHour = 60;
  const minPerTwelveHours = minPerHour * 12;
  let minutes = 0;
  
  if (!(timestr.includes(':'))) {
  
    let m = [...timestr].reverse().join("")[0].toLowerCase();
  
    switch (m) {
      case 'a': {
        let accum = timestr.replace('/a$/', '');
        accum = parseInt(accum, radix=10);
        if (accum == 12) {
          minutes += 2 * minPerTwelveHours;
        }
        else {
          minutes += accum * minPerHour;
        }
      };
      break;
      case 'p': {
        let accum = timestr.replace('/p$/', '');
        accum = parseInt(accum, radix=10);
        minutes += minPerTwelveHours;
        if (accum < 12) {
          minutes += accum * minPerHour;
        }
      };
      break;
      default: {
        return -1;
      };
      break;
    }
  }
  else 
  {
    let m = [...timestr].reverse().join("")[0].toLowerCase();
    switch (m) {
      case 'a': {
        let combined = timestr.replace('/a$/', '');
        let [h, s] = combined.split(':');
        let am_hours = parseInt(h, radix=10);
        let am_mins  = parseInt(s, radix=10);
        if (am_hours == 12) {
          minutes += 2 * minPerTwelveHours;
          minutes += am_mins;
        }
        else {
          minutes += am_hours * minPerHour;
          minutes += am_mins;
        }
      };
      break;
      case 'p': {
        let combined = timestr.replace('/p$/', '');
        let [h, s] = combined.split(':');
        let pm_hours = parseInt(h, radix=10);
        let pm_mins  = parseInt(s, radix=10);
        minutes += minPerTwelveHours;
        if (pm_hours < 12) {
          minutes += pm_mins * minPerHour;
        }
      };
      break;
      default: { return -2; };
      break;
    }
  }
  return minutes;
}