Enemy Spawner

extends Node2D

## Which scene to copy each time we spawn. Set to spawn_enemy.tscn in Godot.
@export var enemy_scene: PackedScene
## How many seconds to wait between spawns.
@export var spawn_interval: float = 1.5
## The most enemies allowed to be alive at the same time.
@export var max_enemies: int = 10

# How many enemies are alive right now.
var _enemy_count: int = 0

@onready var spawn_timer: Timer = %SpawnTimer
@onready var player: SpawnerPlayer = %SpawnerPlayer

func _ready() -> void:
	spawn_timer.wait_time = spawn_interval
	# "timeout" is a signal every Timer sends when it reaches zero. We put
	# "_on_spawn_timer_timeout" inside ".connect()". That is the function
	# Godot runs each time the timer finishes.
	spawn_timer.timeout.connect(_on_spawn_timer_timeout)
	# A Timer sits still until you start it.
	spawn_timer.start()

func _on_spawn_timer_timeout() -> void:
	# Already at the limit, so skip this one. "return" leaves early.
	if _enemy_count >= max_enemies:
		return
	# Nobody picked a scene in Godot, so there is nothing to copy.
	if enemy_scene == null:
		return

	# "instantiate()" makes one real copy of the saved scene. The copy exists
	# now, but it is NOT in the game until "add_child()" near the bottom.
	var enemy: SpawnEnemy = enemy_scene.instantiate()

	# Pick one of the four screen edges at random.
	# "randi()" gives a random whole number, and "% 4" chops it down to
	# 0, 1, 2, or 3. "match" then runs only the line that matches.
	var side: int = randi() % 4
	match side:
		0: enemy.global_position = Vector2(randf_range(50, 1100), 10)
		1: enemy.global_position = Vector2(randf_range(50, 1100), 638)
		2: enemy.global_position = Vector2(10, randf_range(50, 600))
		3: enemy.global_position = Vector2(1140, randf_range(50, 600))

	# Aim the new enemy at wherever the player is standing right now.
	enemy.direction = (player.global_position - enemy.global_position).normalized()
	# "tree_exiting" is a signal a node sends right before it gets erased.
	# That is how we find out to subtract one from our count.
	enemy.tree_exiting.connect(_on_enemy_removed)
	# NOW the enemy is really in the game and starts moving.
	add_child(enemy)
	_enemy_count += 1

# Runs when any enemy we made is about to be erased.
func _on_enemy_removed() -> void:
	_enemy_count -= 1

class_name SpawnerPlayer
extends CharacterBody2D

## How fast the player moves. "@export" puts "speed" at the top of the
## Inspector panel, so you can change it there instead of in this file.
@export var speed: float = 200.0

# "_physics_process()" runs about 60 times a second. Godot calls it for you.
func _physics_process(_delta: float) -> void:
	# "Input.get_vector(...)" checks all four keys at once and hands back
	# an arrow pointing where to go. The four names in quotes are ours.
	# See them under Project > Project Settings > Input Map.
	var direction: Vector2 = Input.get_vector(
		"move_left", "move_right", "move_up", "move_down"
	)
	# "direction" is only WHICH WAY (its length is always 1).
	# "direction * speed" stretches it, so "velocity" is also HOW FAST.
	velocity = direction * speed
	# Nothing moves until "move_and_slide()" runs.
	# "Slide" means we slide along walls instead of sticking to them.
	move_and_slide()

	# The warrior picture only faces right. Walking left mirrors it.
	if direction.x != 0.0:
		$Sprite2D.flip_h = direction.x < 0.0

class_name SpawnEnemy
extends CharacterBody2D

## How fast this enemy drifts along.
@export var speed: float = 80.0

# Which way to go. enemy_spawner.gd fills this in right after making us.
var direction: Vector2 = Vector2.ZERO

func _physics_process(delta: float) -> void:
	# We change "global_position" directly instead of using
	# "move_and_slide()". These enemies are meant to drift off the edge of
	# the screen in a straight line, not to bump into anything on the way.
	global_position += direction * speed * delta

	# Once an enemy is off screen nobody can see it, but it would keep
	# running forever and slowly clog the game up. "queue_free()" erases it.
	if global_position.x < -50 or global_position.x > 1200:
		queue_free()
	if global_position.y < -50 or global_position.y > 700:
		queue_free()