please help to convert php to asp.net

session_start();
define('DB_SERVER', 'localhost');
define('DB_USERNAME', 'fb');
define('DB_PASSWORD', 'fb');
define('DB_DATABASE', 'fb');
$connection = mysql_connect(DB_SERVER, DB_USERNAME, DB_PASSWORD) or die(mysql_error());
$database = mysql_select_db(DB_DATABASE) or die(mysql_error());

if ($_GET['action'] == "chatheartbeat") { chatHeartbeat(); }
if ($_GET['action'] == "sendchat") { sendChat(); }
if ($_GET['action'] == "closechat") { closeChat(); }
if ($_GET['action'] == "startchatsession") { startChatSession(); }
if ($_GET['action'] == "chatname") { chatName(); }

if (!isset($_SESSION['chatHistory'])) {
    $_SESSION['chatHistory'] = array();
}

if (!isset($_SESSION['openChatBoxes'])) {
    $_SESSION['openChatBoxes'] = array();
}

function chatHeartbeat() {
    $sql = "select users.username,chat.from,chat.message,chat.to,chat.id,chat.sent,chat.recd from chat,users where (chat.to = '".mysql_real_escape_string($_SESSION['chatuser'])."' AND recd = 0) and chat.from=users.uid order by id ASC";

    $query = mysql_query($sql);
    $items = '';

    $chatBoxes = array();

    while ($chat = mysql_fetch_array($query)) {

        if (!isset($_SESSION['openChatBoxes'][$chat['from']]) && isset($_SESSION['chatHistory'][$chat['from']])) {
            $items = $_SESSION['chatHistory'][$chat['from']];
        }

        $chat['message'] = sanitize($chat['message']);

        $items .= &lt;&lt;<eod>
                       {
            "s": "0",
            "u": "{$chat['username']}",
            "f": "{$chat['from']}",
            "m": "{$chat['message']}"
       },
EOD;

    if (!isset($_SESSION['chatHistory'][$chat['from']])) {
        $_SESSION['chatHistory'][$chat['from']] = '';
    }

    $_SESSION['chatHistory'][$chat['from']] .= &lt;&lt;<eod>
                           {
            "s": "0",
            "u": "{$chat['username']}",
            "f": "{$chat['from']}",
            "m": "{$chat['message']}"
       },
EOD;

        unset($_SESSION['tsChatBoxes'][$chat['from']]);
        $_SESSION['openChatBoxes'][$chat['from']] = $chat['sent'];
    }

    if (!empty($_SESSION['openChatBoxes'])) {
    foreach ($_SESSION['openChatBoxes'] as $chatbox =&gt; $time) {
        if (!isset($_SESSION['tsChatBoxes'][$chatbox])) {
            $now = time()-strtotime($time);
            $time = date('g:iA M dS', strtotime($time));

            $message = "Sent at $time";
            if ($now &gt; 180) {
                $items .= &lt;&lt;<eod>
{
"s": "2",
"f": "$chatbox",
"m": "{$message}"
},
EOD;

    if (!isset($_SESSION['chatHistory'][$chatbox])) {
        $_SESSION['chatHistory'][$chatbox] = '';
    }

    $_SESSION['chatHistory'][$chatbox] .= &lt;&lt;<eod>
        {
"s": "2",
"f": "$chatbox",
"m": "{$message}"
},
EOD;
            $_SESSION['tsChatBoxes'][$chatbox] = 1;
        }
        }
    }
}

    $sql = "update chat set recd = 1 where chat.to = '".mysql_real_escape_string($_SESSION['chatuser'])."' and recd = 0";
    $query = mysql_query($sql);

    if ($items != '') {
        $items = substr($items, 0, -1);
    }
header('Content-type: application/json');
?&gt;
{
        "items": [
            <?php echo $items;??>
        ]
}

            exit(0);
}

function chatBoxSession($chatbox) {

    $items = '';

    if (isset($_SESSION['chatHistory'][$chatbox])) {
        $items = $_SESSION['chatHistory'][$chatbox];
    }

    return $items;
}

function startChatSession() {
    $items = '';
    if (!empty($_SESSION['openChatBoxes'])) {
        foreach ($_SESSION['openChatBoxes'] as $chatbox =&gt; $void) {
            $items .= chatBoxSession($chatbox);
        }
    }


    if ($items != '') {
        $items = substr($items, 0, -1);
    }

header('Content-type: application/json');
/*
$suser=$_SESSION['chatuser'];
$sc=mysql_query("select username from users where username='$su'");
while($row_sc=mysql_fetch_array($sc))
{
$_SESSION['current_chat_username']=$row_sc['username'];
}*/
?&gt;
{
        "username": "<?php echo $_SESSION['chatuser'];??>",
        "items": [
            <?php echo $items;??>
        ]
}

    exit(0);

}

function chatName() {
    $un = '';

$su=$_GET['usw'];
$sc2=mysql_query("select username from users where uid='$su' limit 1");
while($row_sc2=mysql_fetch_array($sc2))
{
$un=$row_sc2["username"];
}
?&gt;
{
        "unm": ["<?php echo $un;??>"]

}



    exit(0);
}



function sendChat() {
    $from = $_SESSION['chatuser'];
    $to = $_POST['to'];
    $message = $_POST['message'];
    $sql = "select users.username from users where users.uid='$from' limit 1";
    $uname = mysql_query($sql);
    $from_user='';
    while ($un = mysql_fetch_array($uname)) {
    $from_user=$un['username'];
    }


    $_SESSION['openChatBoxes'][$_POST['to']] = date('Y-m-d H:i:s', time());

    $messagesan = sanitize($message);

    if (!isset($_SESSION['chatHistory'][$_POST['to']])) {
        $_SESSION['chatHistory'][$_POST['to']] = '';
    }

    $_SESSION['chatHistory'][$_POST['to']] .= &lt;&lt;<eod>
                       {
            "s": "1",
            "u": "{$from_user}",
            "f": "{$to}",
            "m": "{$messagesan}"
       },
EOD;


    unset($_SESSION['tsChatBoxes'][$_POST['to']]);

    $sql = "insert into chat (chat.from,chat.to,message,sent) values ('".mysql_real_escape_string($from)."', '".mysql_real_escape_string($to)."','".mysql_real_escape_string($message)."',NOW())";
    $query = mysql_query($sql);
    echo "1";
    exit(0);
}

function closeChat() {

    unset($_SESSION['openChatBoxes'][$_POST['chatbox']]);

    echo "1";
    exit(0);
}

function sanitize($text) {
    $text = htmlspecialchars($text, ENT_QUOTES);
    $text = str_replace("\n\r","\n",$text);
    $text = str_replace("\r\n","\n",$text);
    $text = str_replace("\n","<br>",$text);
    return $text;
}