extends Node2D

# Spawns slow-drifting asteroids inside ASTEROID_FIELD biome chunks near
# the fleet, and despawns them once the fleet has moved far enough away -
# keeps the scene from accumulating unbounded nodes over a long session
# while still populating newly-entered asteroid regions on the fly.

@export var check_interval: float = 1.0
@export var spawn_radius_chunks: int = 2
# No asteroid may be created within this distance of the fleet. At cruise
# speed this is well over a second of warning, so anything that reaches the
# fleet was visible on its way in.
@export var safe_spawn_radius: float = 420.0
@export var despawn_radius_chunks: int = 4
@export var asteroids_per_chunk: int = 6
@export var min_speed: float = 12.0
@export var max_speed: float = 35.0

@onready var fleet: Node2D = get_node("../Fleet")

var asteroid_scene: PackedScene = preload("res://Asteroid.tscn")
var populated_chunks: Dictionary = {}
var timer: float = 0.0


func _ready() -> void:
	randomize()


func _process(delta: float) -> void:
	timer += delta
	if timer < check_interval:
		return
	timer = 0.0
	update_chunks()


func update_chunks() -> void:
	# Public (not just called from _process's own timer): also invoked
	# once synchronously right after the fleet is positioned on a fresh
	# Main.tscn load, so nearby asteroids exist immediately instead of
	# only appearing ~check_interval seconds later - most noticeable as a
	# jarring pop-in right after returning from a planet's surface.
	var center_chunk: Vector2i = WorldGen.chunk_coords(fleet.get_centroid())

	for dx in range(-spawn_radius_chunks, spawn_radius_chunks + 1):
		for dy in range(-spawn_radius_chunks, spawn_radius_chunks + 1):
			var chunk: Vector2i = center_chunk + Vector2i(dx, dy)
			if populated_chunks.has(chunk):
				continue
			if WorldGen.biome_at_chunk(chunk) != WorldGen.Biome.ASTEROID_FIELD:
				continue
			_spawn_chunk_asteroids(chunk)

	var to_remove: Array = []
	for chunk in populated_chunks.keys():
		if _chebyshev_chunk_distance(chunk, center_chunk) > despawn_radius_chunks:
			for asteroid in populated_chunks[chunk]:
				if is_instance_valid(asteroid):
					asteroid.queue_free()
			to_remove.append(chunk)
	for chunk in to_remove:
		populated_chunks.erase(chunk)


func _chebyshev_chunk_distance(a: Vector2i, b: Vector2i) -> int:
	return max(abs(a.x - b.x), abs(a.y - b.y))


func _safe_position(candidate: Vector2, centre: Vector2) -> Vector2:
	# Nothing may materialise on top of the fleet. Chunks are populated around
	# wherever the fleet happens to be - including the chunk it is standing in
	# - so without this an asteroid could appear directly on a ship and
	# destroy it with no chance to react. That is worst on the frame a scene
	# loads: arriving back from a planet could cost a ship instantly.
	if candidate.distance_to(centre) >= safe_spawn_radius:
		return candidate
	# Push it out to the edge of the bubble rather than dropping it, so the
	# field keeps its density near the fleet instead of thinning out.
	var away: Vector2 = candidate - centre
	if away.length() < 0.001:
		away = Vector2.RIGHT.rotated(randf() * TAU)
	return centre + away.normalized() * safe_spawn_radius


func _spawn_chunk_asteroids(chunk: Vector2i) -> void:
	var origin: Vector2 = WorldGen.chunk_origin(chunk)
	var spawned: Array = []
	var fleet_centre: Vector2 = fleet.get_centroid()

	for i in range(asteroids_per_chunk):
		var local_pos: Vector2 = Vector2(randf() * WorldGen.CHUNK_SIZE, randf() * WorldGen.CHUNK_SIZE)
		var asteroid: Node2D = asteroid_scene.instantiate()
		asteroid.position = _safe_position(origin + local_pos, fleet_centre)
		var angle: float = randf() * TAU
		var speed: float = randf_range(min_speed, max_speed)
		asteroid.velocity = Vector2(cos(angle), sin(angle)) * speed
		asteroid.rotation_speed = randf_range(-0.4, 0.4)
		# Deferred: update_chunks() can run synchronously from inside a
		# parent's own _ready() chain (forced once right after the fleet
		# is positioned, to avoid a pop-in on scene load) - Godot refuses
		# a direct add_child() while the tree is still "busy setting up
		# children" in that situation, so this must be deferred either way.
		get_parent().add_child.call_deferred(asteroid)
		spawned.append(asteroid)

	populated_chunks[chunk] = spawned