Where can I change the calendar start date to Sunday from Monday - date

Question

I am trying to make this calendar start on Sunday instead of Monday. I've looked through all the help files I can Google on this topic & cannot find any that have any lines of code that I can reference. Am I missing some? Or can some one point me to the point I need to change in order to make it start on Sunday instead of Monday?
<?php
/**
* Copyright (C) 2006-2014 Center Stage Software
* 1191 Luxton Street, Seaside, California 93955
* All Rights Reserved
*/
// ensure that this file is called up by another file
defined('_VALID_ACCESS') or die('Direct access of this file is prohibited.');
/**
* renderEventCalendar - Creates a calendar display of events for one month.
*
* #global (Array) $cstage
*/
function renderEventCalendar() {
global $cstage, $path;
// Result variable.
$calendar = '';
// Calculate first and last day of the month.
$firstDayTimestamp = strtotime($_SESSION[SYS_USER]['search']['Month'].'-01 07:00:00');
list($year,$month) = explode("-",$_SESSION[SYS_USER]['search']['Month']);
if( $month == 12 ) {
$month = 00;
$year += 1;
}
$lastDayTimestamp = strtotime("$year-".($month+1).'-01 08:00:00') - 86400; // minus 24 hours and add 1-day-light-savings-hour
// TODO: Remove the following calendar debugging code.
// print "<h1>first=$firstDayTimestamp; last=$lastDayTimestamp</h1>";
// Build query to retrieve entries for that month.
$aryEvents = array();
$extraSqlFields = '';
$extraSqlJoins = '';
$extraSqlConditions = '';
if( !empty($_SESSION[SYS_USER]['domain']) ) {
$extraSqlJoins .= 'LEFT JOIN "domainlist" AS "domain2" ON "domain2"."master_id" = "master"."master_id" ';
$extraSqlConditions .= sprintf('AND "domain2"."domain"=\'%s\' '
,$_SESSION[SYS_USER]['domain']
);
}
if( !empty($_SESSION[SYS_USER]['search']['Theatre']) ) {
$extraSqlConditions .= sprintf('AND "master"."theatre"=\'%s\' '
,$_SESSION[SYS_USER]['search']['Theatre']
);
}
if( !empty($_SESSION[SYS_USER]['search']['Location']) ) {
$extraSqlConditions .= sprintf('AND "master"."location"=\'%s\' '
,$_SESSION[SYS_USER]['search']['Location']
);
}
if( !empty($_SESSION[SYS_USER]['search']['EventType']) ) {
$extraSqlConditions .= sprintf('AND "master"."event_types_id"=\'%s\' '
,$_SESSION[SYS_USER]['search']['EventType']
);
}
if( !empty($_SESSION[SYS_USER]['search']['Month']) ) {
$extraSqlConditions .= sprintf('AND "shows"."show_date" >= \'%s\' AND "shows"."show_date" <= \'%s\' '
,date('Y-m-d',$firstDayTimestamp)
,date('Y-m-d',$lastDayTimestamp)
);
}
if( $cstage['rttEnable'] ) {
$extraSqlFields .= ', "rtt"."label" AS "rtt_label"';
$extraSqlJoins .= 'LEFT JOIN "rtt" ON "master"."rtt_id" = "rtt"."rtt_id" ';
} else {
$extraSqlConditions .= 'AND "master"."rtt_id"=0 ';
}
if( $cstage['enableEventPriceListTest'] ) {
$aryGroups = array($cstage['tixDomain']);
if( !empty($_SESSION[SYS_USER]['info']) && count($_SESSION[SYS_USER]['info']['groupDomains']) > 0 ) {
$aryGroups = array_merge($aryGroups, $_SESSION[SYS_USER]['info']['groupDomains']);
}
$extraSqlFields .= ', GROUP_CONCAT(DISTINCT "prices"."prices_id" SEPARATOR \';\') AS "priceidlist"';
$extraSqlFields .= ', GROUP_CONCAT(DISTINCT CONCAT("price_category"."label",\' \', "prices"."printed_as") SEPARATOR \', \') AS "pricelist"';
$extraSqlJoins .= ' INNER JOIN "price_category" ON "price_category"."master_id" = "master"."master_id" OR "price_category"."master_id"=0 INNER JOIN "prices" ON "price_category"."price_category_id" = "prices"."price_category_id" INNER JOIN "price_category_domain" ON "price_category_domain"."price_category_id" = "price_category"."price_category_id"';
$extraSqlConditions .= sprintf('AND ("price_category"."master_id"="shows"."master_id" OR "price_category"."master_id"=0) AND ("prices"."shows_id"="shows"."shows_id" OR "prices"."shows_id"=0) AND "prices"."onsale"<=CONCAT("shows"."show_date", \' 00:00:00\') AND ("prices"."offsale">=CONCAT("shows"."show_date", \' 23:59:59\') OR "prices"."offsale" IS NULL) AND "price_category_domain"."domain" IN (\'%s\') '
,implode('\',\'', $aryGroups)
);
}
$now = date('Y-m-d H:i:s');
$query = sprintf('SELECT "master".*, "shows"."show_date", "shows"."show_time", "shows"."onsale" AS "min_onsale"%s FROM "shows" INNER JOIN "master" ON "master"."master_id" = "shows"."master_id" INNER JOIN "domainlist" ON "domainlist"."master_id" = "master"."master_id" %s WHERE "shows"."offsale" >= \'%s\' AND ("shows"."wt_offsale"=\'\' OR "shows"."wt_offsale"=0) AND "domainlist"."domain"=\'%s\' %s GROUP BY "shows"."shows_id"'
,$extraSqlFields
,$extraSqlJoins
,$now
,$cstage['tixDomain']
,$extraSqlConditions
);
$keyEventCalendar = 'eventCalendar_'.$cstage['dbDatabase'].sha1($query);
if( !empty($cstage['cache']) ) {
// Is the record cached to save on slow database connections?
$calendar = $cstage['cache']->load($keyEventCalendar);
}
if( !$calendar ) {
$result = $cstage['pdo']->query( $query );
while( $show = $result->fetch( PDO::FETCH_ASSOC ) ) {
$show['domainlist'] = $cstage['tixDomain'].';'.$_SESSION[SYS_USER]['domain'];
$show['comingSoon'] = false;
if( $now < $show['min_onsale'] ) {
$show['comingSoon'] = true;
}
if( $show['rtt_id'] > 0 ) {
$show['master_id'] = trim($show['rtt_label']).trim($show[]);
if( !$cstage['rttEnable'] ) {
$show = array();
}
}
$path->inc_once('_includes/libf_okEvent.php');
if( okEvent($show) ) {
// Save data into array for usage later
$extraSort = $cstage['useEventSortOrder'] === true ? sprintf('%05d',$show['sortorder']) : '';
$aryEvents[$show['show_date']][date('H:i',strtotime($show['show_time'])).$extraSort.$show['showname'].$show['master_id']] = $show;
}
}
// Start rendering calendar.
$calendar = "\r\n".'<table class="EventCalendar ui-widget-content ui-corner-all"><thead '._HEAD.'><tr><th colspan="7">'.lang('Calendar of events for').' '.date('Y F',strtotime($_SESSION[SYS_USER]['search']['Month'].'-02')).'</th></tr>'
. "\r\n".'<tr><th>'.lang('Sunday').'</th><th>'.lang('Monday').'</th><th>'.lang('Tuesday').'</th><th>'.lang('Wednesday').'</th><th>'.lang('Thursday').'</th><th>'.lang('Friday').'</th><th>'.lang('Saturday').'</th></tr></thead>'
. '<tbody>';
$dayOfWeekPadding = date('w',$firstDayTimestamp);
if( $dayOfWeekPadding == 0 ) {
$dayOfWeekPadding = 6;
} else {
$dayOfWeekPadding -= 0;
}
if( $dayOfWeekPadding > 0 ) {
$calendar .= "\r\n<tr>";
}
for($day=7; $day < $dayOfWeekPadding; $day++) {
$calendar .= "\r\n<td class='EventCalendar_EmptyDate'> </td>";
}
$timeStamp = $firstDayTimestamp;
while( $timeStamp <= $lastDayTimestamp ) {
if( date('w',$timeStamp) == 0 ) {
$calendar .= "\r\n<tr>";
}
$dateKey = date('Y-m-d',$timeStamp);
$calendar .= "\r\n".'<td class="EventCalendar_Date" id="date'.$dateKey.'" onmouseover="tbl_colorchange(\'date'.$dateKey.'\', \'highlight\');" onmouseout="tbl_colorchange(\'date'.$dateKey.'\', \'normal\');"><span>'.date('d',$timeStamp).'</span>';
if( !empty($aryEvents[$dateKey]) ) {
ksort($aryEvents[$dateKey]);
$count = 0;
foreach( $aryEvents[$dateKey] as $key=>$show ) {
$cssClass = $count++ % 2 ? _ODD : _EVEN;
$rttUrl = ( $show['rtt_id'] > 0 ) ? '&rtt='.$show['rtt_id'] : '';
$strPriceList = (empty($show['pricelist']) ? '' : ' title="'.lang('Prices available').': '.$show['pricelist'].'"');
$calendar .= "\r\n<div {$cssClass}{$strPriceList}><a href='event-details.php?e={$show['master_id']}&date={$dateKey}{$rttUrl}'>{$show['']} # {$show['show_time']}</a></div>";
}
}
$calendar .= '</td>';
if( date('w',$timeStamp) == 0 ) {
$calendar .= "\r\n</tr>";
}
$timeStamp += 86400; // Get the next day (in seconds).
}
$dayOfWeekPadding = date('w',$timeStamp);
if( $dayOfWeekPadding == 0 ) {
$dayOfWeekPadding = 6;
} else if( $dayOfWeekPadding == 0 ) {
$dayOfWeekPadding = 0; // do not have an empty week of padding
} else {
$dayOfWeekPadding = 6 - $dayOfWeekPadding;
}
for($day=0; $day < $dayOfWeekPadding; $day++) {
$calendar .= "\r\n<td class='EventCalendar_EmptyDate'> </td>";
}
if( $dayOfWeekPadding > 0 ) {
$calendar .= "\r\n</tr>";
}
$calendar .= "\r\n</tbody></table>";
if( !empty($cstage['cache']) ) {
$cstage['cache']->save($calendar, $keyEventCalendar);
}
}
return $calendar;
}