<?php

function smarty_function_date_range($params, &$smarty)
{
    $emptyText = empty($params['emptyText']) ? '' : $params['emptyText'];
    if (empty($params['start'])) {
        return $emptyText;
    }

    $monthFormat = empty($params['monthFormat']) ? '%b.' : $params['monthFormat'];
    $dayFormat   = empty($params['dayFormat'])   ? '%e'  : $params['dayFormat'];
    $yearFormat  = empty($params['yearFormat'])  ? '%Y'  : $params['yearFormat'];

    $formats = array(
        'oneDay'     => "{m1} {d1}, {y1}",                   // Oct. 1, 2013
        'oneMonth'   => "{m1} {d1}-{d2}, {y1}",              // Oct. 1-20, 2013
        'oneYear'    => "{m1} {d1} - {m2} {d2}, {y1}",       // Oct. 1 - Dec. 20, 2013
        'multiYears' => "{m1} {d1}, {y1} - {m2} {d2}, {y2}", // Oct. 1, 2013 - Dec. 20, 2014
    );

    if (!empty($params['formats']) && is_array($params['formats'])) {
        $formats = array_merge($formats, $params['formats']);
    }

    $getDate = function($time, $index) use ($monthFormat, $dayFormat, $yearFormat) {
        return [
            "{m{$index}}" => strftime($monthFormat, $time),
            "{d{$index}}" => trim(strftime($dayFormat, $time)),
            "{y{$index}}" => strftime($yearFormat, $time),
        ];
    };

    $formatDate = function ($format, $startTime, $endTime = null) use ($getDate) {
        $map = $getDate($startTime, 1);
        if ($endTime) {
            $map = array_merge($map, $getDate($endTime, 2));
        }
        return str_replace(array_keys($map), array_values($map), $format);
    };

    $startTime = strtotime($params['start']);
    if (empty($params['end'])) {
        return $formatDate($formats['oneDay'], $startTime);
    }
    $endTime = strtotime($params['end']);

    if (idate('Y', $startTime) == idate('Y', $endTime)) {
        if (idate('m', $startTime) == idate('m', $endTime)) {
            if (idate('d', $startTime) == idate('d', $endTime)) {
                return $formatDate($formats['oneDay'], $startTime, $endTime);
            } else {
                return $formatDate($formats['oneMonth'], $startTime, $endTime);
            }
        } else {
            return $formatDate($formats['oneYear'], $startTime, $endTime);
        }
    }
    return $formatDate($formats['multiYears'], $startTime, $endTime);
}