修改用户密码

我在开发登录系统时遇到了一个问题。我构建了一个处理多个用户登录的类。我还为admin用户创建了一个管理区域。他将能够添加新用户、更改密码、删除用户等。

现在我设法使添加新用户和更改密码部分。我现在遇到的问题是关于更改密码部分。

我有一个这样结构的表:

TABLE user
id int(11) AUTO INCREMENT
admin int(11) DEFAULT 0
username varchar(256)
password varchar(256)

表中的admin定义了用户的类型，0表示普通用户，1表示可以执行上面描述的操作的admin用户。

我有以下功能来修改用户密码:

public function changeUserPassword($cusrn,$oldPass,$newPass,$newPassConfirm) {
    if(strlen($newPass) < 4) {
        $error = true;
        $message['error'] = true;
        $message['message'] = "The Password is to short";
        return json_encode($message);
    }
        elseif($newPass != $newPassConfirm) {
            $error = true;
            $message['error'] = true;
            $message['message'] = "Confirmed Password doesn't match";
            return json_encode($message);
        }
            elseif(!(ALLOW_SPECIAL_CHARACTERS == true) && preg_match('/[''^£$%&*()}{@#~?><>,|=_+¬-]/', $newPass)) {
                $error = true;
                $message['error'] = true;
                $message['message'] = "Special characters are not allowed";
                return json_encode($message);
            }
                elseif(!(ALLOW_NUMBERS == true) && preg_match('#'d#',$newPass)) {
                    $error = true;
                    $message['error'] = true;
                    $message['message'] = "Numbers are not allowed";
                    return json_encode($message);
                }
                    elseif(!isset($error)) {
                        $oldPass = hash_hmac('sha512',$oldPass,$this -> salt($cusrn,$oldPass));
                        $newPass = hash_hmac('sha512',$newPass,$this -> salt($cusrn,$newPass));
                        $sql = 'SELECT username,password FROM user WHERE username = ? AND password = ?';
                        if($stmt = $this->conn->prepare($sql)) {
                            $stmt->bind_param('ss',$cusrn,$newPass);
                            $stmt->execute();
                            $stmt->bind_result($usrn,$passw);
                            if($stmt->fetch()) {
                                if( $cusrn == $usrn ) {
                                    if(!(strcmp($oldPass,$passw) == false)) {
                                        $error = true;
                                        $message['error'] = true;
                                        $message['message'] = "The current Password is incorrect";
                                        return json_encode($message);
                                    }
                                        elseif (!(strcmp($oldPass,$newPass) == false)) {
                                            $stmt->close();
                                            $sql = "UPDATE user SET password = ? WHERE username = '$usrn' LIMIT 1";
                                            if($stmt = $this->conn->prepare($sql)) {
                                                $stmt->bind_param('s',$newPass);
                                                $stmt->execute();
                                                $stmt->close();
                                                $error = false;
                                                $message['error'] = false;
                                                $message['message'] = "Password successfuly changed";
                                                return json_encode($message);
                                            }
                                                else {
                                                    $error = true;
                                                    $message['error'] = true;
                                                    $message['message'] = "Cannot connect to database for updating";
                                                    return json_encode($message);
                                                }
                                        }
                                            else {
                                                $error = true;
                                                $message['error'] = true;
                                                $message['message'] = "New Password must not match the old one";
                                                return json_encode($message);
                                            }
                                }
                                    else {
                                        $error = true;
                                        $message['error'] = true;
                                        $message['message'] = "The current Username is incorrect";
                                        return json_encode($message);   
                                    }
                                }
                                    else {
                                        $error = true;
                                        $message['error'] = true;
                                        $message['message'] = "Cannot fetch data from the database";
                                        return json_encode($message);
                                    }
                            }
                                else {
                                    $error = true;
                                    $message['error'] = true;
                                    $message['message'] = "Cannot prepare database connection";
                                    return json_encode($message);   
                                }
                    }
                        else {
                            $error = true;
                            $message['error'] = true;
                            $message['message'] = "Check the PHP syntax | Something went wrong";
                            return json_encode($message);
                        }
}

我遇到的问题是，如果我试图输入某个用户名它要么给我这个:

 "Cannot fetch data from the database" 

或者它一直告诉我:

 "The current Username is incorrect"

，即使用户名是正确的。虽然它适用于它存在于表中的最后一行，但我的意思是它适用于放在表中最后一行的用户名。

我确定我做错了什么，我问你我做错了什么