public function login(){
		$options = ['cost' => 12,];
		$username = $this->input->post('username');
		$password = $this->input->post('password');

		$this->db->where('email',$username);
		$user = $this->db->get('app_users');

		if ($user->num_rows() < 1){
			echo $this->jsonify(array('status'=>'failed', 'error' => 'invalid email id'));
			exit;
		}
		else {
			$user_data = $user->result()[0];

			if(hash('SHA256',$password) != $user_data->password){
				echo $this->jsonify(array('status'=>'failed', 'error' => 'invalid password'));
				exit;
			}

			unset($user_data->password);
			$new_login_token = $this->random_text();
			$user_data->login_token = $new_login_token;

			$this->db->where('id',$user_data->id);
			$this->db->set('last_activity',date('Y-m-d H:i:s',time()));
			$this->db->set('last_activity_ip',$_SERVER['REMOTE_ADDR']);
			$this->db->set('login_token',$new_login_token);
			$this->db->set('token_issued_on',date('Y-m-d H:i:s',time()));
			$this->db->update('app_users');

			echo $this->jsonify(
					array(
						'status'=>'logged in',
						'user' => (array) $user_data
					)
				);
		}

	}








	public function keepalive(){

		sleep(2);

		$token = $this->input->post('login_token');

		if(!$token){
			echo $this->jsonify(array('status'=>'not logged in'));
			exit;
		}

		$this->db->where('login_token',$token);
		$user = $this->db->get('app_users');

		if ($user->num_rows() < 1){
			echo $this->jsonify(array('status'=>'not logged in'));
			exit;
		}
		else {
			$user_data = $user->result()[0];

			$time_diff = (time() - strtotime($user_data->token_issued_on));
			if($time_diff > 1296000){
				echo $this->jsonify(array('status'=>'not logged in'));
				log_message('info', "Token expired for user id {$user_data->id}");
				exit;
			}

			// user is valid and good to go.
			// update old login token on both client and server ends
			// update last activity time, token issued on and last activity ip fields.

			unset($user_data->password);
			$new_login_token = $this->random_text();
			$user_data->login_token = $new_login_token;

			$this->db->where('id',$user_data->id);
			$this->db->set('last_activity',date('Y-m-d H:i:s',time()));
			$this->db->set('last_activity_ip',$_SERVER['REMOTE_ADDR']);
			$this->db->set('login_token',$new_login_token);
			$this->db->set('token_issued_on',date('Y-m-d H:i:s',time()));
			$this->db->update('app_users');

			echo $this->jsonify(
					array(
						'status'=>'logged in',
						'user' => (array) $user_data
					)
				);
		}
	}