extends Node2D

# Spawns "Big Stable Asteroid" planets in ASTEROID_FIELD biome chunks near
# the fleet where WorldGen says one belongs, and despawns them once the
# fleet has moved far enough away - mirrors AsteroidField's chunk-lifecycle
# pattern, but at a sparser, larger-radius scale since planets are rare
# landmarks rather than common decoration.

@export var check_interval: float = 1.0
@export var spawn_radius_chunks: int = 3
@export var despawn_radius_chunks: int = 6

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

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


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


func get_planet_fleet_is_on() -> Node2D:
	# Fleet centroid distance, not per-ship Area2D overlap - a single
	# stable number instead of many independently-noisy ship positions.
	# See Planet.gd for why this matters.
	var fleet_centroid: Vector2 = fleet.get_centroid()
	for chunk in populated_chunks.keys():
		for planet in populated_chunks[chunk]:
			if is_instance_valid(planet) and planet.position.distance_to(fleet_centroid) <= planet.landing_radius:
				return planet
	return null


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 a nearby planet exists 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 not WorldGen.has_planet_at_chunk(chunk):
				continue
			_spawn_chunk_planet(chunk)

	var to_remove: Array = []
	for chunk in populated_chunks.keys():
		if _chebyshev_chunk_distance(chunk, center_chunk) > despawn_radius_chunks:
			for planet in populated_chunks[chunk]:
				if is_instance_valid(planet):
					planet.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 _spawn_chunk_planet(chunk: Vector2i) -> void:
	# WorldGen.planet_data_at_chunk() is seeded purely from the chunk's own
	# coordinates, so a given chunk always produces the exact same planet -
	# name, position within the chunk, and shape - no matter how many times
	# it's despawned and respawned across a scene reload. It's also the
	# same function the world map uses to place a marker for a
	# not-currently-loaded explored chunk, so the two never disagree.
	var data: Dictionary = WorldGen.planet_data_at_chunk(chunk)
	var origin: Vector2 = WorldGen.chunk_origin(chunk)

	var planet: Node2D = planet_scene.instantiate()
	planet.position = origin + data.local_pos
	planet.planet_name = data.name
	planet.shape_seed = data.shape_seed
	# 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(planet)

	populated_chunks[chunk] = [planet]