class_name Chunk
extends Node2D
## A single loaded chunk in the world.
##
## A chunk is a fixed-size, axis-aligned region of a room. It is the atomic
## unit of load, save, and stream. This node is instantiated by the
## [ChunkStreamer] when a chunk is loaded from the server and freed when the
## chunk is unloaded.

## World-space size of a chunk along X (world units / tiles).
const CHUNK_SIZE_X := 32.0
## World-space size of a chunk along Y (world units / tiles).
const CHUNK_SIZE_Y := 32.0
## World-space size of a chunk along Z (world units / tiles).
const CHUNK_SIZE_Z := 1.0

## Canonical chunk key: "{world_id}:{room_id}:{cx}:{cy}:{cz}".
var key: String = ""
## World id this chunk belongs to.
var world_id: String = ""
## Room id this chunk belongs to.
var room_id: String = ""
## Integer chunk coordinate along X.
var cx: int = 0
## Integer chunk coordinate along Y.
var cy: int = 0
## Integer chunk coordinate along Z.
var cz: int = 0

## Whether this chunk is currently loaded and active in the scene tree.
var is_loaded := false

## Emitted when the chunk has finished loading its content.
signal chunk_loaded(chunk: Chunk)
## Emitted when the chunk is about to be unloaded.
signal chunk_unloaded(chunk: Chunk)


## Build the canonical chunk key from the chunk's coordinates.
func build_key() -> String:
	return "%s:%s:%d:%d:%d" % [world_id, room_id, cx, cy, cz]


## Compute the world-space origin (min corner) of this chunk.
func world_origin() -> Vector2:
	return Vector2(cx * CHUNK_SIZE_X, cy * CHUNK_SIZE_Y)


## Compute the world-space bounding box of this chunk.
func world_bounds() -> Rect2:
	var origin := world_origin()
	return Rect2(origin, Vector2(CHUNK_SIZE_X, CHUNK_SIZE_Y))


## Compute the integer chunk coordinate for a world-space position.
static func coord_for_position(pos: Vector2) -> Vector2i:
	return Vector2i(
		floori(pos.x / CHUNK_SIZE_X),
		floori(pos.y / CHUNK_SIZE_Y)
	)


## Compute the canonical key for a world-space position.
static func key_for_position(pos: Vector2, p_world_id: String, p_room_id: String) -> String:
	var c := coord_for_position(pos)
	return "%s:%s:%d:%d:0" % [p_world_id, p_room_id, c.x, c.y]


## Load this chunk's content. In a real deployment this would fetch the chunk
## payload from the server (see world.md §5.3 `request_chunk` / `chunk_data`)
## and instantiate tiles/objects. For now it just marks the chunk loaded.
func load_chunk() -> void:
	is_loaded = true
	chunk_loaded.emit(self)


## Unload this chunk's content and free any child nodes.
func unload_chunk() -> void:
	chunk_unloaded.emit(self)
	for child in get_children():
		child.queue_free()
	is_loaded = false