<?php 

interface Identifier  { 
    public function setId($id); 
    public function getId(); 
} 

/** 
 * User class 
 * 
 */ 

class User implements Identifier { 

    private $id = NULL; 
    private $first_name; 
    private $last_name; 
    private $email;  

    // constructor (not implemented) 
    public function __construct(){
	} 

    //setter for id property
    public function setId($id) { 
        if (!is_numeric($id)) { 
            throw new Exception('ID must be a numeric value'); 
        } 
        $this->id = $id; 
    } 

    // getter for id property 
    public function getId() { 
        return $this->id; 
    }  

    // setter for first_name property 
    public function setFirstName($first_name) { 
        if (empty($first_name) || !is_string($first_name)) { 
            throw new Exception('First name must be a non-empty string.'); 
        } 
        $this->first_name = $first_name; 
    } 

    // getter for first_name property 
    public function getFirstName() { 
        return $this->first_name; 
    } 

    // setter for last_name property 
    public function setLastName($last_name) { 
        if (empty($last_name) || !is_string($last_name)) { 
            throw new Exception('Last name must be a non-empty string.'); 
        } 
        $this->last_name = $last_name;  
    } 

    // getter for last_name property 
    public function getLastName() { 
        return $this->last_name; 
    } 


    // setter for email property 
    public function setEmail($email) { 
        if (empty($email) || !is_string($email) || strpos($email, '@') === FALSE) { 
            throw new Exception('Email must be a well-formatted email address.'); 
        } 
        $this->email = $email;  
    } 

    // getter for email property 
    public function getEmail() { 
        return $this->email; 
    }          

} 

?>