class_name TileLayerNode
extends Node3D
## A visual representation of a single tile layer within a chunk.
##
## This node is instantiated by [ChunkScene] for each tile layer in a chunk.
## It renders the layer's tiles as instanced meshes (one per tile definition
## in the palette) using [MultiMeshInstance3D] for efficiency.
##
## ## Structure
##
## ```
## TileLayerNode (Node3D)
##  └── MultiMeshInstance3D  # one per palette entry (tile definition)
## ```

## The tile layer data this node renders.
var tile_layer: TileLayer = null

## The chunk coordinate this layer belongs to (for world positioning).
var chunk_coord: Vector3i = Vector3i.ZERO

## Tile size in world units (each tile is 1x1x1).
const TILE_SIZE: float = 1.0

## Cache of MultiMeshInstance3D nodes, keyed by tile definition id.
var _mesh_instances: Dictionary = {}


func _ready() -> void:
	if tile_layer == null:
		return
	_build_meshes()


## Build the MultiMesh instances for each tile definition in the palette.
func _build_meshes() -> void:
	for tile_def in tile_layer.palette:
		if tile_def.id == 0:
			continue  # Tile 0 is "empty/air", no mesh needed
		_create_mesh_for_tile(tile_def)


func _create_mesh_for_tile(tile_def: TileDef) -> void:
	# Count how many cells use this tile definition
	var count := 0
	for tile_id in tile_layer.tiles:
		if tile_id == tile_def.id:
			count += 1

	if count == 0:
		return

	var multi_mesh := MultiMesh.new()
	multi_mesh.transform_format = MultiMesh.TRANSFORM_3D
	multi_mesh.mesh = _make_unit_cube_mesh()
	multi_mesh.instance_count = count

	var instance_idx := 0
	for z in range(tile_layer.depth):
		for y in range(tile_layer.height):
			for x in range(tile_layer.width):
				var tile_id := tile_layer.get_tile(x, y, z)
				if tile_id != tile_def.id:
					continue
				var world_pos := _tile_to_world(x, y, z)
				var xform := Transform3D(Basis(), world_pos)
				multi_mesh.set_instance_transform(instance_idx, xform)
				instance_idx += 1

	var mesh_instance := MultiMeshInstance3D.new()
	mesh_instance.multimesh = multi_mesh
	mesh_instance.name = "tiles_%d" % tile_def.id
	add_child(mesh_instance)
	_mesh_instances[tile_def.id] = mesh_instance


## Convert a tile grid coordinate to a world-space position (center of tile).
func _tile_to_world(x: int, y: int, z: int) -> Vector3:
	var origin := Vector3(
		chunk_coord.x * tile_layer.width,
		chunk_coord.y * tile_layer.height,
		chunk_coord.z * tile_layer.depth
	)
	return origin + Vector3(
		x * TILE_SIZE + TILE_SIZE * 0.5,
		y * TILE_SIZE + TILE_SIZE * 0.5,
		z * TILE_SIZE + TILE_SIZE * 0.5
	)


## Create a simple unit cube mesh for tile rendering.
func _make_unit_cube_mesh() -> Mesh:
	var mesh := BoxMesh.new()
	mesh.size = Vector3(TILE_SIZE, TILE_SIZE, TILE_SIZE)
	return mesh


## Get the tile definition at a grid position, or null if empty.
func get_tile_def_at(x: int, y: int, z: int = 0) -> TileDef:
	if tile_layer == null:
		return null
	var tile_id := tile_layer.get_tile(x, y, z)
	if tile_id == 0:
		return null
	return tile_layer.get_tile_def(tile_id)


## Clear all rendered meshes.
func clear() -> void:
	for child in get_children():
		child.queue_free()
	_mesh_instances.clear()