Conditional Logic for ATS Plugin

<?php
// Fetch theme options array
global $ats_plugin;
global $is_IE;

// Initialize the main variables
$ats_active = null;
$the_theme = null;

// We only want to run this fat chunk of logic on IE since it's IE with the issues
if ( $is_IE ) {

// Is a supported useragent active?
function checkActive($data) {
    global $ats_active;
    $user_agent = $_SERVER['HTTP_USER_AGENT'];

    switch($user_agent) {
        case strpos($user_agent, 'MSIE 5') :
            if ($data['ie5_switch'] == 1 && !empty($data['ie5_theme'])) {
                $ats_active = 'ie5';
            };
            break;
        case strpos($user_agent, 'MSIE 6') :
            if ($data['ie6_switch'] == 1 && !empty($data['ie6_theme'])) {
                $ats_active = 'ie6';
            };
            break;
        case strpos($user_agent, 'MSIE 7') :
            if ($data['ie7_switch'] == 1 && !empty($data['ie7_theme'])) {
                $ats_active = 'ie7';
            };
            break;
        case strpos($user_agent, 'MSIE 8') :
            if ($data['ie8_switch'] == 1 && !empty($data['ie8_theme'])) {
                $ats_active = 'ie8';
            };
            break;
        case strpos($user_agent, 'MSIE 9') :
            if ($data['ie9_switch'] == 1 && !empty($data['ie9_theme'])) {
                $ats_active = 'ie9';
            };
            break;
        default :
            $ats_active = null;
    }

    // Dev Mode Overide
    if(current_user_can('manage_options') && $data['dev_mode'] == 1) {
        $ats_active = 1;
    }

    return $ats_active;
}

// Run active agents check
checkActive($ats_plugin);

if(!empty($ats_active)) {

    function change_theme() {
        global $ats_plugin;
        global $ats_active;
        global $the_theme;

        if(!empty($ats_plugin['ie5_theme'])) {$ie5 = $ats_plugin['ie5_theme'];} else {$ie5 = null;}
        if(!empty($ats_plugin['ie6_theme'])) {$ie6 = $ats_plugin['ie6_theme'];} else {$ie6 = null;}
        if(!empty($ats_plugin['ie7_theme'])) {$ie7 = $ats_plugin['ie7_theme'];} else {$ie7 = null;}
        if(!empty($ats_plugin['ie8_theme'])) {$ie8 = $ats_plugin['ie8_theme'];} else {$ie8 = null;}
        if(!empty($ats_plugin['ie9_theme'])) {$ie9 = $ats_plugin['ie9_theme'];} else {$ie9 = null;}

        $theme_key = array(
            'ie5' => $ie5,
            'ie6' => $ie6,
            'ie7' => $ie7,
            'ie8' => $ie8,
            'ie9' => $ie9
        );

        // Only one value should return
        foreach ($theme_key as $browser => $selection ) {
            if ($ats_active == $browser) {
                $the_theme = $selection;
            }
        }

        // Add the dev mode override
        if( current_user_can('manage_options') && !empty($ats_plugin['dev_theme'])) {
            $the_theme = $ats_plugin['dev_theme'];
        }

        return $the_theme;
    }
    add_filter('template', 'change_theme');
    add_filter('option_template', 'change_theme');
    add_filter('option_stylesheet', 'change_theme');
}
}

// For non-IE browsers, we check if the user is an admin and enable developer mode
if ( !$is_IE && current_user_can('manage_options') ) {
    if($ats_plugin['dev_mode'] == 1 && !empty($ats_plugin['dev_theme'])) {
        $the_theme = $ats_plugin['dev_theme'];
    }

    function dev_theme() {
        global $the_theme;
        return $the_theme;
    }

    /* @todo if the theme is in developer mode, there should be a visual warning as a reminder */

    if ($ats_plugin['dev_mode'] == 1) {
        add_filter('template', 'dev_theme');
        add_filter('option_template', 'dev_theme');
        add_filter('option_stylesheet', 'dev_theme');
    }
}