Need help with programming an enemy for a platformer

I am trying to make an enemy for a side-scrolling platformer game that is similar to the green turtle in Super Mario. It needs to go 1 direction 1st then either turn when hitting a wall or fall if it walks over the edge. I am programming using separate as files connected together and so far have come up with the following code files.

enemy_test.as:

package
{
import flash.display.MovieClip;
import flash.utils.Timer;
import flash.events.TimerEvent;
public class inkman_enTest extends MovieClip
{

    public var Enemy:enemy;
    public var walls:Array;
    public var gtimer:Timer;
    public function inkman_enTest()
    {
        walls = new Array();
        Enemy = new enemy();
        addChild( Enemy );
        
        gtimer= new Timer(25);
        gtimer.addEventListener(TimerEvent.TIMER, gameLoop);
        gtimer.start();
    }
    
    function gameLoop(loop:TimerEvent):void 
    {
        Enemy.en_move(); 
    }
}

}

enemy.as:

package
{
import flash.display.MovieClip;
public class enemy extends MovieClip
{
public function en_start()
{
x= 100; // Variables for enemy starting place.
y= 10;//
}
public function en_move():void
{
this.x +=3;// Initial movement

    }
}

}

wall.as:

package
{
import flash.display.MovieClip;
public class Wall extends MovieClip
{
public var WIDTH:int = 32;

    public var HEIGHT:int = 32; 
    
}

}

Any help would be appreciated. If not can I you point me to a website or forum where I can get more information. Thanks.