Add movement variables for:

direction

speed

changing direction

a brief cooldown before

changing direction

(to prevent infinite flipping)

When the enemy is hit

it should briefly be invulnerable

create variables to manage this

and finally grab a reference to the player

Physics process will:  

add gravity

handle all state changes

and call the associated functions

call move_and_slide()

to enable movement

and if the enemy is patrolling

check for direction changes