php如何实现忘记密码找回密码的功能

<p><strong>输入您注册的电子邮箱，找回密码：</strong></p>
<p><input type="text" class="input" name="email" id="email"><span id="chkmsg"></span></p>
<p><input type="button" class="btn" id="sub_btn" value="提 交"></p>

$(function(){
$("#sub_btn").click(function(){
var email = $("#email").val();
var preg = /^\w+([-+.]\w+)*@\w+([-.]\w+)*\.\w+([-.]\w+)*/; //匹配Email
if(email=='' || !preg.test(email)){
$("#chkmsg").html("请填写正确的邮箱！");
}else{
$("#sub_btn").attr("disabled","disabled").val('提交中..').css("cursor","default");
$.post("sendmail.php",{mail:email},function(msg){
if(msg=="noreg"){
$("#chkmsg").html("该邮箱尚未注册！");
$("#sub_btn").removeAttr("disabled").val('提 交').css("cursor","pointer");
}else{
$(".demo").html("<h3>"+msg+"</h3>");
}
});
}
});
})

include_once("connect.php");//连接数据库
$email = stripslashes(trim($_POST['mail']));
$sql = "select id,username,password from `t_user` where `email`='$email'";
$query = mysql_query($sql);
$num = mysql_num_rows($query);
if($num==0){//该邮箱尚未注册！
echo 'noreg';
exit;
}else{
$row = mysql_fetch_array($query);
$getpasstime = time();
$uid = $row['id'];
$token = md5($uid.$row['username'].$row['password']);//组合验证码
$url = "http://www.helloweba.net/demo/resetpass/reset.php?email=".$email."
&token=".$token;//构造URL
$time = date('Y-m-d H:i');
$result = sendmail($time,$email,$url);
if($result==1){//邮件发送成功
$msg = &#39;系统已向您的邮箱发送了一封邮件<br/>请登录到您的邮箱及时重置您的密码！&#39;;
//更新数据发送时间
mysql_query("update `t_user` set `getpasstime`=&#39;$getpasstime&#39; where id=&#39;$uid &#39;");
}else{
$msg = $result;
}
echo $msg;
}
//发送邮件
function sendmail($time,$email,$url){
include_once("smtp.class.php");
$smtpserver = ""; //SMTP服务器，如smtp.163.com
    $smtpserverport = 25; //SMTP服务器端口
    $smtpusermail = ""; //SMTP服务器的用户邮箱
    $smtpuser = ""; //SMTP服务器的用户帐号
    $smtppass = ""; //SMTP服务器的用户密码
    $smtp = new Smtp($smtpserver, $smtpserverport, true, $smtpuser, $smtppass); 
    //这里面的一个true是表示使用身份验证,否则不使用身份验证.
    $emailtype = "HTML"; //信件类型，文本:text；网页：HTML
    $smtpemailto = $email;
    $smtpemailfrom = $smtpusermail;
    $emailsubject = "Helloweba.com - 找回密码";
    $emailbody = "亲爱的".$email."：<br/>您在".$time."提交了找回密码请求。请点击下面的链接重置密码
（按钮24小时内有效）。<br/><a href=&#39;".$url."&#39;target=&#39;_blank&#39;>".$url."</a>";
    $rs = $smtp->sendmail($smtpemailto, $smtpemailfrom, $emailsubject, $emailbody, $emailtype);
return $rs;
}

include_once("connect.php");//连接数据库
$token = stripslashes(trim($_GET['token']));
$email = stripslashes(trim($_GET['email']));
$sql = "select * from `t_user` where email='$email'";
$query = mysql_query($sql);
$row = mysql_fetch_array($query);
if($row){
$mt = md5($row['id'].$row['username'].$row['password']);
if($mt==$token){
if(time()-$row['getpasstime']>24*60*60){
$msg = '该链接已过期！';
}else{
//重置密码...
$msg = &#39;请重新设置密码，显示重置密码表单，<br/>这里只是演示，略过。&#39;;
}
}else{
$msg =  &#39;无效的链接&#39;;
}
}else{
$msg =  &#39;错误的链接！&#39;;
}
echo $msg;

CREATE TABLE `t_user` (
  `id` int(11) NOT NULL auto_increment,
  `username` varchar(30) NOT NULL,
  `password` varchar(32) NOT NULL,
  `email` varchar(50) NOT NULL,
  `getpasstime` int(10) NOT NULL,
  PRIMARY KEY  (`id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8;