function test_form_X() {  // where X is the name of a form, in case there are multiple forms on the same page
  ok=true;
  msg='';
  first=1;
  $('#X .form_item').removeClass('error');  // jQuery/CSS magic!
 
  ...
  // let's assume we have a form element called form_element_N.
  if(is_form_element_N_ok()==false) {
    ok=false;
    msg+='Form element N is no good!\n';
    if(first) {
      form_element_N.focus();
      first=0;
    }
    // every input/select/textarea is inside an input_item inside a form_item.
    $('#form_element_N').parent.parent.addClass('error');  // jQuery/CSS magic!
  }
  ...
 
  if(ok==false) alert(msg);
  return ok;
}

function add_form_error($name,$message) {
  $str ="      if(first) {\n";
  $str.="        first=0;\n";
  $str.="        \$('#$name').focus();\n";
  $str.="      }\n";
  $str.="      \$('#$name').parent.parent.addClass('error');\n";
  $str.="      ok=false;\n";
  $str.="      msg+='".str_replace(array("'","\'"),$message)."';\n";
  return $str;
}

// Create a javascript error message for fields that can't be left blank.
function add_form_test_required($name,$label=null) {
  $test="    if(\$('$name').value==null || \$('$name').value.length==0) {\n"
       .add_form_error($name,"$label is required.\n")
       ."    }\n";
 
  add_form_test($test,$name);
}
 
function add_form_test($test,$name) {
  global $forms_to_validate,$last_form_name;
 
  $forms_to_validate[$last_form_name].=$test;
}
 
function create_form_start(name='form1',$classname='form',$action='',$method='post',$target='') {
  global $forms_to_validate,$last_form_name;
 
  $forms_to_validate[$name]='';
  $last_form_name=$name;
  return "
< form id="$name" class="$classname" action="$action" enctype="multipart/form-data" method="$method">\n";
}

function form_header() {
  global $forms_to_validate;
 
  echo "  <script type="'text/javascript'"><!--mce:0--></script>\n";
}

$body=create_form_start();
$body.=create_form_text('name','Name','','Your Name');
$body.=create_form_password('user_pass','Password','','Your Password. <a href="forgot.php">Did you forget your password?</a>');
$body.=create_form_required('name','Name');

//------------------------------------------------------------------------------
function create_form_price($name,$value=null,$label=null,$hint=null) {
  return create_form_row("\$<input type='text' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."'>",$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_password($name,$value=null,$label=null,$hint=null) {
  return create_form_row("<input type='password' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."'>",$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_password_confirm($name,$value=null,$label=null,$hint=null) {
  add_form_test_password_confirm("pass",$label);  // we'll cover this in part 3
 
  return create_form_row("<input type='password' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."'>",$label,$name,"").
  create_form_row("<input type='password' name='{$name}_confirm' value=''>"," ",$name."_confirm",$hint);
}
 
//------------------------------------------------------------------------------
function create_form_email($name,$value=null,$label=null,$hint=null) {
 // @TODO: add email validation.
 $test="    regex_{$name}=/^[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)*@[a-zA-Z0-9_-]+(\.[a-zA-Z0-9_-]+)*(\.[a-zA-Z]{2,4})$/\n"
 ."    compare_to=f.{$name}.value.replace(/^\s+|\s+$/g,'');\n"
 ."    if(compare_to!='' && !compare_to.match(regex_{$name})) {\n"
 .add_form_error($name,"$label does not appear to be a valid email.\n")
 ."    }\n";
 add_form_test($test,$name);
 
 return create_form_row("<input type='text' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."'>",$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_textarea($name,$value=null,$label=null,$hint=null) {
 return create_form_row("<textarea name='$name' rows='10' cols='80'>".htmlspecialchars($value,ENT_QUOTES)."</textarea>",$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_select_internal($name,$options,$value=null,$multiple=0,$extra='') {
 $sel="<select id='$name' name='$name' $extra";
 if($multiple>0) {
 $sel.=" multiple='yes' size='$multiple'";
 }
 $sel.=">\n";
 if(is_array($options)) {
 foreach($options as $k=>$v) {
 $k=htmlspecialchars($k,ENT_QUOTES);
 $v=htmlspecialchars($v,ENT_QUOTES);
 $sel.="  <option value='$k'>$v</option>\n";
 }
 }
 $sel.="</select>";
 $v=isset($value)?htmlspecialchars($value,ENT_QUOTES):"";
 return str_replace("value='$v'","value='$v' selected",$sel);
}
 
//------------------------------------------------------------------------------
function create_form_select($name,$options,$value=null,$label=null,$hint=null,$multiple=0,$extra='') {
 $sel=create_form_select_internal($name,$options,$value,$multiple,$extra);
 return create_form_row($sel,$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_bool($name,$value=null,$label=null,$hint=null,$extra='') {
 $sel="<select name='$name' $extra>\n";
 $sel.="  <option value='yes'>"._t("Yes")."</option>\n";
 $sel.="  <option value='no'>"._t("No")."</option>\n";
 $sel.="</select>";
 $v=isset($value)?htmlspecialchars($value,ENT_QUOTES):"";
 $sel=str_replace("value='$v'","value='$v' selected",$sel);
 return create_form_row($sel,$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_file($name,$label='',$hint='') {
 $inner="<input name='$name' type='file'>";
 
 return create_form_row($inner,$label,$name,$hint);
}
 
//------------------------------------------------------------------------------
function create_form_address($name,$value=null,$label=null,$hint=null) {
 if(!isset($value['address1'])) $value['address1']="";
 if(!isset($value['address2'])) $value['address2']="";
 if(!isset($value['city'])) $value['city']="";
 if(!isset($value['region'])) $value['region']="";
 if(!isset($value['country'])) $value['country']="";
 if(!isset($value['postalcode'])) $value['postalcode']="";
 
 $str =create_form_text($name."_address1",$value['address1'],"Street");
 $str.=create_form_text($name."_address2",$value['address2'],"");
 $str.=create_form_text($name."_city",$value['city'],"City");
 $str.=create_form_text($name."_region",$value['region'],"State/Province");
 $str.=create_form_text($name."_country",$value['country'],"Country");
 $str.=create_form_text($name."_postalcode",$value['postalcode'],"Postal Code");
 
 return create_form_row($str,$label,null,null);
}
 
//------------------------------------------------------------------------------
function create_form_hidden($name,$value=null) {
 return "  <input type='hidden' id='$name' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."'>\n";
}
 
//------------------------------------------------------------------------------
function create_form_submit($name,$value,$extra='') {
 global $last_form_name;  // we'll cover this is in part 3
 
 return "  <input type='submit' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."' onclick='javascript:return validate_$last_form_name(this.form);' $extra>\n";
}
 
//------------------------------------------------------------------------------
function create_form_cancel($name,$value,$redirect) {
 return "  <input type='button' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."' onclick='javascript:window.location=\"".htmlspecialchars($redirect,ENT_QUOTES)."\";'>\n";
}
 
//------------------------------------------------------------------------------
function create_form_submit_confirm($name,$value,$confirm="Are you sure?",$validate=0) {
 global $last_form_name;  // we'll cover this is in part 3
 
 $str="  <input type='submit' name='$name' value='".htmlspecialchars($value,ENT_QUOTES)."' onclick='javascript:return (confirm(\"".str_replace(array("'","\n"),array("\'","\\n"),$confirm)."\")";
 if($validate!=0) {
 $str.=" & validate_$last_form_name(this.form)";
 }
 $str.=");'>\n";
 return $str;
}

// I've already sanitized all GET, POST, and COOKIE data at this point.
function check_login() {
  global $DB;
 
  $login_justnow=false;
 
  // if the user isn't logged in and they're POSTing a login request, process it
  if(!get_session('user/id') && isset($_POST['login']) {
    $name=$_POST['login_name'];  $remember_me=isset($_POST['remember_me'])?1:0;
    $pass=md5($_POST['login_pass']);
    $user_id=$DB->QueryXY("SELECT id FROM `users` WHERE name='$name' AND pass='$pass' AND confirmed='1' LIMIT 1");
    if(isset($user_id)) {
      account_login($user_id,$remember_me);
      $login_justnow=true;
      $name=get_session("user/given_name")?', '.get_session("user/given_name"):'';
      add_notice("Welcome$name!");
    } else {
      add_error("Login failed.");
      account_logout();
    }
  }
 
  // if the user isn't logged in but has a COOKIE, process it
  if(!get_session("user/id") && isset($_COOKIE["remember_me"]) ) {
    list($user_id,$cookie_code)=@unserialize(stripslashes($_COOKIE["remember_me"]));
    if(isset($user_id) && isset($cookie_code)) {
      $cookie=md5($cookie_code);
      $result=$DB->QueryArray("SELECT * FROM `users` WHERE id='$user_id' AND cookie='$cookie' AND confirmed='1' LIMIT 1");
      if(count($result)) {
        account_login($user_id,true);
        $login_justnow=true;
        $name=get_session("user/given_name")?', '.get_session("user/given_name"):'';
        add_notice("Welcome$name!");
      }
    }
  }
 
  // if the user's session says they're logged in, process it
  if(get_session("user/id") && $login_justnow===false) {
    $user_id=get_session("user/id");
    $cookie=get_session("user/cookie");
    $ip=get_session("user/ip");
    $session=session_id();
 
    $query="SELECT * FROM `users` WHERE id='$user_id' AND ip='$ip' AND session='$session' AND cookie='$cookie' AND confirmed='1' LIMIT 1";
    $result=$DB->DoQuery($query);
 
    if($DB->NumRows($result)) {
      account_login($user_id,false);
    } else {
      add_error("Session security failed.");
      account_logout();
    }
    $DB->EndQuery($result);
  }
 
  // check if the user actually has rights to this part of the site - your implementation may vary
}
 
function account_login($user_id,$remember_me) {
  global $DB;
 
  if(user_is_logged_in())
    return;
 
  // update cookie
  if($remember_me==true) {
    $cookie_code=generate_random_string();
    $cookie_str=serialize(array($user_id, $cookie_code));
    setcookie('remember_me', $cookie_str, time() + 60*60*24*30, '/');
    add_session("user/cookie",$cookie_code);
  } else {
    remove_session("user/cookie");
  }
 
  // update session security
  $ip=$_SERVER['REMOTE_ADDR'];
  $session=session_id();
  $cookie_code=get_session("user/cookie");
  $cookie=md5($cookie_code);
  $DB->DoQuery("UPDATE `users` SET last_on=NOW(), session='$session'"
    .(($cookie_code!='')?", cookie='".$cookie."'":"")
    .", ip='$ip' WHERE id='$user_id' LIMIT 1");
 
  // update session info
  $result=$DB->DoQuery("SELECT * FROM `users` WHERE id='$user_id' LIMIT 1");
  $row=$DB->FetchAssoc($result);
  foreach($row as $k=>$v) {
    add_session("user/".$k,$v);
  }
  $DB->EndQuery($result);
 
  // check if any other part of your system needs to know about a user logging in.
}
 
function user_is_logged_in() {
 return get_session("user/id")!=0;
}
 
function generate_random_string($length=32) {
 $random="";
 srand((double)microtime()*1000000);
 $char_list = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
 $char_list.= "abcdefghijklmnopqrstuvwxyz";
 $char_list.= "1234567890";
 
 for($i=0;$i<$length;++$i) {
 $random.=substr($char_list,(rand()%(strlen($char_list))), 1);
 }
 
 return $random;
}

function save() {
  setcookie("username","foo",60*60*24*30);
}
 
function load() {
  return isset($_COOKIE["username"])?$_COOKIE["username"]:'';
}

function save() {
  $data=array('username'=>'foo', 'something else'=>'bar');
  $str=serialize($data);
  setcookie("userdata",$str,60*60*24*30);
}
 
function load() {
  $data=array('username'=>'','something else'=>'');
  if(isset($_COOKIE['userdata'])) {
     $data=unserialize($_COOKIE['userdata']);
  }
  return $data;
}

function save() {
  $data=array('version'='1.0', 'username'=>'foo', 'something else'=>'bar');
  $str=serialize($data);
  setcookie("userdata",$str,60*60*24*30);
}
 
function load() {
  $data=array('username'=>'','something else'=>'');
  $old=false;
  if(isset($_COOKIE['userdata'])) {
    try {
      $data=unserialize($_COOKIE['userdata']);
    }
    catch(Exception $e) {
      $old=true;  // this version is so old & busted we can't read it at all.
    }
    if(!$old) {
      // Use the $data['version'] to help us figure out what pieces of $data need to be filled in.
    }
  }
  return $data;
}