A helper to play with Dates

Date_helper.php

/*
$dateStart = "2016/12/14"; 
$dateFin =   "2017/04/21"

[2016/12/14 - 2016/12/31] => 17 days
[2017/01/01 - 2017/01/31] => 31 days
[2017/02/01 - 2017/02/28] => 28 days
[2017/03/01 - 2017/03/30] => 31 days
[2017/04/01 - 2017/04/21] => 21 days
*/
<?php
function how_many_days($firstDate, $lastDate)
{
  $dateStart = new DateTime($firstDate);
  $dateFin = new DateTime($lastDate);
  $totalMonths = $dateStart->diff($dateFin)->m + ($dateStart->diff($dateFin)->y*12);
  $result = [];
  for ($i = 0; $i <= $totalMonths; $i++)
  {
    if ($i != 0){
      $obj = $dateStart->modify('first day of next month');
    }

    $firstDay = $dateStart->format('Y/m/d');
      if ($i == $totalMonths){
        $lastDay = $dateFin->format('Y/m/d');
      } else {
      $lastDay = $dateStart->format('Y/m/t');
      }
      $firstDayObj = strtotime($firstDay);
      $lastDayObj = strtotime($lastDay);
      $totalDays = (int) ceil(($lastDayObj - $firstDayObj) / 86400);
      $totalDays = ((int) $dateStart->format('d') == 1) ? $totalDays + 1 : $totalDays;
      $result["$firstDay - $lastDay"] = $totalDays;
  }
  return $result;
}