Question that can't fit in the title

How can i make a sprite move left and rigth but just rigth when it sees the player? If you make events for both it keeps moving left and rigth even after it seen the player. How can i make it translate from moving left and rigth to moving just rigth. I also want to know how you can alter events depending on which side the player is in contrast to the enemy. I want the enemy to charge to the left if the player is on the left of the enemy and to the rigth if the enemy is to the rigth of the enemy.

You can add invisible big sprite to the player, and if the enemy overlap this sprite then will follow the player, if not will charge left and right.

i think this is the best idea, event best of using line of sight.