/**
     * Get a range of datetimes
     * Method 1: Get date ranges between $start_at and $end_at
     * Method 2: Get a specified number of dates by using $count
     * @param null $start_at
     * @param null $end_at
     * @param string $step
     * @param null $count
     * @param Y-m-d H:i:s $format_str
     * @return array
     * @throws \Exception
     */
    public static function getDatetimesArray($start_at = null, $end_at = null, $step = '+1 hour', $count = null, $format_str = 'Y-m-d H:i:s')
    {
        /**
         * Format all datetimes
         * @param $timestamp
         * @return false|string
         */
        $format = function($timestamp) use($format_str) {
            return date($format_str, $timestamp);
        };

        if($start_at == null) {
            $start_at = $format(time());
        }

        $datetimes = array();
        $datetimes[] = $format(strtotime($start_at));

        if($end_at !== null) {
            while($start_at < $end_at) {
                $datetimes[] = $format(strtotime($step, strtotime($start_at)));
                $start_at = $datetimes[count($datetimes) - 1];
            }
        }
        else if($count !== null) {
            for($i = 0; $i < $count; $i++) {
                $datetimes[] = $format(strtotime($step, strtotime($start_at)));
                $start_at = $datetimes[count($datetimes) - 1];
            }
        }
        else {
            throw new \Exception('Expecting parameter from $end_at or $count');
        }

        return $datetimes;
    }