Basic 2D Enemy Script including AI (Follow, Swarm)

This Script requires you create Enemy Node (Area2d) with Sprite, Collision2d Area, Timer, Tween and Visibility (see attached image) . Please note my attached image has specific names for my game and not the ones used in this generic code. It works in Godot v3. I have generified it as much as possible and commented it. It assumes you have created a player node as well that you control via inputs. I use it in my Batty Bat (Godot v3 version) game and thought I'd share it. The AI is basic but effective. I will be posting Batty Bat game (Godot V3 version) when engine is in stable release. Hope this helps someone out.

extends Area2D

signal enemy_killed
var direction = Vector2()
var screensize 
var follow = false
var distance
var speed = 0
var swarm = false
var enemySpeedMin = 50
var enemySpeedMax = 75
var enemyTimerMin = 5
var enemyTimerMax = 25
    
onready var player = get_node("/root/main/player")

func _ready():
	# Initiate Randomization
	randomize()
	# Init variables
	# get Screensize 
	screensize = screensize = get_viewport_rect().size
	# set speed between Min & Max values
	speed = rand_range(enemySpeedMin ,enemySpeedMax)
	# init AI variables 
	follow = false
	swarm = 0
	# setup Tween to shrink enemy when killed
	$effect.interpolate_property(self, "scale", self.get_scale(),Vector2(.3,.3),0.3,Tween.TRANS_QUAD,Tween.EASE_OUT)
	# set Enemy live time between Min & Max values
	$enemyTimer.wait_time = (rand_range(enemyTimerMin ,enemyTimerMax))
	# Start Enemy Life Timer
	$enemyTimer.start()
	
	
func _process(delta):	
	# AI rules
	# get direction / distance of player
	direction = player.position - self.position
	# Determine whether to flip enemy image to face player
	if direction.x > 0:
		# Set Enemy facing right
		self.get_node("enemy").set_flip_h(1)
	else:
		# Set Enemy facing left
		self.get_node("enemy").set_flip_h(0)
	# calculate distance from player
	distance = sqrt(direction.x * direction.x + direction.y * direction.y)
	#print(dist) # uncomment this to see distance from player
	# If distance less than 200 then start Enemy following player
	if distance < 200:
		follow = true
	else:
		follow = false
	# Move Enemy towards player if follow is true or swarm is true
	if follow == true or swarm > 100:	
		# increment swarm while enemy following
		swarm += 1
		#print(swarm) # uncomment this to check swarm 
		position += direction.normalized() * speed * delta
		position.x = clamp(position.x, 0, screensize.x)
		position.y = clamp(position.y, 0 , screensize.y)
	
		
func _on_enemy_area_enter( area ):
	#print(area.get_name()) # uncomment this to print name of area entering enemy collision2d
	if area.get_name()=="player":
		# limit collision to single time
		call_deferred("set_monitoring", false)
		# check if Tween active and if not activate it
		if not $effect.is_active():
			$effect.start()
		# emit a signal when enemy killed
		emit_signal("enemy_killed")

func _on_effect_tween_completed( object, key ):
	# remove enemy from memory after Tween finishes (enemy shrinks when killed)
	queue_free()

func _on_enemytimer_timeout():
	# if enemy time to live runs out activate Tween (enemy shrinks)
	if not $effect.is_active():
		$effect.start()

func _on_VisibilityNotifier2D_screen_exited():
	# if enemy goes outside of screen (shouldn't happen) then remove from memory
	queue_free()