How to make an enemy follow a certain path - lua

Question

How do I make my enemy follow a certain path? This is all I have right now, I'm using Tiled for the images and such. I'm trying to make a game where the player enters an area, and has to avoid the enemy to get the coin so the door will open to the next area. But because my enemy is patrolling the enemy sometimes enters the hallway to the next area and that's not supposed to happen obviously.
I also had a problem with the door, it doesn't disappear when I pick up the coin. I thought that the easiest way to do this is that when I reach a certain score, the door is removed, but it doesnt disappear until the player touches the door. Any suggestions? Maybe link the coin with the door so that when it's picked up, they both disappear somehow?
Level.Load ("Game.tmx")
player = {
object = nil,
score = 0,
health = 100,
speed = 3,
}
function Start()
--Identify the objects, naming them
player.object = Level.GetObject ("Player")
enemy = Level.GetObject ("Enemy")
-- music = Sound.Load ("music.mp3", true, true)
Hud.Message ( " Start ", 2)
end
function DoPlayer()
player.object = Level.GetObject( "Player")
end
function DoEnemey()
enemy = Level.GetObjects( "Enemey" )
end
function DoSign()
Sign = Level.GetObject( "Sign" )
end
function DoDoor()
door = Level.GetObject( "door" )
end
function Update()
--HUD
Hud.Score ("Score : " ..player.score )
Hud.Health ("Health : " ..player.health )
--Controllers
Controller.Wasd (player.object, player.speed)
Controller.Patrol (enemy, 2)
Camera.Follow (player.object)
end
function info()
Hud.Message ("Pick up coins to proceed to the next area!", 3)
end
function CoinPickup( target, source)
if target == player.object then
player.score = player.score + 1
Level.RemoveObject( source )
end
end
function DoorOpen( target, source)
if target == player.object
and player.score == 2
then Level.RemoveObject ( source )
end
end