class_name ChunkStreamManager
extends Node
## Manages loading and unloading of world chunks based on player position.
##
## This is the central orchestrator for the chunk streaming system. It monitors
## the player's position, determines which chunks should be loaded, requests
## chunk data from the server, instantiates ChunkScene nodes, and unloads
## chunks that fall outside the streaming radius.
##
## ## Design
##
## - **Streaming radius** defines how many chunks around the player are kept
##   loaded. Chunks beyond this radius are unloaded to save memory and CPU.
## - **Load priority** ensures chunks closer to the player are loaded first,
##   preventing visual pop-in at the edge of the view.
## - **Server communication** uses the RPCs defined in docs/architecture/world.md
##   (§5.3): `request_chunk`, `chunk_data`, `chunk_invalidated`.
##
## ## Usage
##
## Add this node to your scene tree and set the `player` reference:
## ```gdscript
## var stream_manager: ChunkStreamManager = $ChunkStreamManager
## stream_manager.player = $Player
## stream_manager.streaming_radius = 4  # chunks
## ```

## Number of chunks (radius) to keep loaded around the player.
## A radius of 2 means a 5x5 grid of chunks centered on the player.
## Higher values increase memory usage but reduce streaming pop-in.
@export var streaming_radius: int = 3

## Maximum number of chunks to load per frame. Prevents frame spikes during
## rapid movement or when entering a new area.
@export var max_loads_per_frame: int = 4

## Maximum number of chunks to unload per frame.
@export var max_unloads_per_frame: int = 4

## Distance (in chunks) from the streaming radius edge before a chunk is
## considered for unloading. Prevents rapid load/unload cycling.
@export var unload_margin: int = 1

## Emitted when a chunk finishes loading.
signal chunk_loaded(chunk_coord: Vector3i, chunk_scene: Node)

## Emitted when a chunk is unloaded.
signal chunk_unloaded(chunk_coord: Vector3i)

## Emitted when a chunk fails to load (e.g., server error).
signal chunk_load_failed(chunk_coord: Vector3i, error: String)

## Emitted when the player moves far enough to require a streaming update.
signal streaming_updated

## Reference to the player node. Must be set before the manager starts.
var player: Node3D = null

## The current player chunk coordinate.
var _player_chunk_coord: Vector3i = Vector3i.ZERO

## Map of loaded chunk coordinates to their scene nodes.
var _loaded_chunks: Dictionary = {}

## Queue of chunk coordinates pending load, sorted by distance from player.
var _load_queue: Array[Vector3i] = []

## Queue of chunk coordinates pending unload.
var _unload_queue: Array[Vector3i] = []

## Whether streaming is currently active (player is set and in game).
var is_active: bool = false

## The server RPC interface for chunk data. Set by the networking layer.
var _server_rpc: Object = null

## Internal: track which chunks are currently being loaded (to avoid duplicates).
var _loading_in_progress: Dictionary = {}

## Internal: time accumulator for throttled streaming updates.
var _update_accumulator: float = 0.0

## Internal: interval between streaming updates (seconds).
const UPDATE_INTERVAL: float = 0.1


func _ready() -> void:
	# Streaming is driven from _process (main thread) so we can safely
	# manipulate the scene tree. No background thread is used.
	set_process(true)


func _process(delta: float) -> void:
	if not is_active or player == null:
		return

	_update_accumulator += delta
	if _update_accumulator < UPDATE_INTERVAL:
		return
	_update_accumulator = 0.0

	_update_streaming()
	_process_load_queue()
	_process_unload_queue()
	streaming_updated.emit()


func _update_streaming() -> void:
	if player == null or not is_inside_tree():
		return

	var current_coord: Vector3i = Chunk.coord_for_position(player.global_position)
	if current_coord == _player_chunk_coord:
		return

	_player_chunk_coord = current_coord
	_rebuild_queues()


func _rebuild_queues() -> void:
	var target_set: Dictionary = _compute_target_chunks()

	# Determine which chunks need to be loaded
	var to_load: Array[Vector3i] = []
	for coord in target_set:
		if not _loaded_chunks.has(coord) and not _loading_in_progress.has(coord):
			to_load.append(coord)

	# Sort by distance from player (closest first)
	to_load.sort_custom(_compare_distance)
	_load_queue = to_load

	# Determine which chunks need to be unloaded
	var to_unload: Array[Vector3i] = []
	for coord in _loaded_chunks:
		if not target_set.has(coord):
			to_unload.append(coord)

	to_unload.sort_custom(_compare_distance)
	_unload_queue = to_unload


func _compute_target_chunks() -> Dictionary:
	"""Compute the set of chunk coordinates that should be loaded."""
	var target: Dictionary = {}
	var half: int = streaming_radius
	for dx in range(-half, half + 1):
		for dy in range(-half, half + 1):
			for dz in range(-half, half + 1):
				var coord: Vector3i = Vector3i(
					_player_chunk_coord.x + dx,
					_player_chunk_coord.y + dy,
					_player_chunk_coord.z + dz
				)
				target[coord] = coord
	return target


func _compare_distance(a: Vector3i, b: Vector3i) -> bool:
	"""Compare chunk coordinates by distance from player chunk."""
	var dist_a: int = _chunk_distance_squared(_player_chunk_coord, a)
	var dist_b: int = _chunk_distance_squared(_player_chunk_coord, b)
	return dist_a < dist_b


func _chunk_distance_squared(a: Vector3i, b: Vector3i) -> int:
	var dx: int = a.x - b.x
	var dy: int = a.y - b.y
	var dz: int = a.z - b.z
	return dx * dx + dy * dy + dz * dz


func _process_load_queue() -> void:
	var count: int = 0
	while count < max_loads_per_frame and not _load_queue.is_empty():
		var coord: Vector3i = _load_queue.pop_front()
		_load_chunk(coord)
		count += 1


func _process_unload_queue() -> void:
	var count: int = 0
	while count < max_unloads_per_frame and not _unload_queue.is_empty():
		var coord: Vector3i = _unload_queue.pop_front()
		_unload_chunk(coord)
		count += 1


func _load_chunk(coord: Vector3i) -> void:
	if _loading_in_progress.has(coord):
		return

	_loading_in_progress[coord] = true

	# Request chunk data from server via RPC
	if _server_rpc != null and _server_rpc.has_method("request_chunk"):
		_server_rpc.request_chunk(Chunk.build_key(
			"", "", coord
		))
	else:
		# Fallback: try to load from local cache or create empty chunk
		_instantiate_chunk_scene(coord)


func _on_chunk_data_received(key: String, binary_data: PackedByteArray) -> void:
	"""Called by the networking layer when chunk data arrives from server."""
	var coord: Vector3i = _parse_coord_from_key(key)
	if coord == null:
		return

	_loading_in_progress.erase(coord)

	# Decode the binary chunk data
	var chunk_data: ChunkDataDecoder.ChunkPayload = ChunkDataDecoder.decode_binary(binary_data)
	if chunk_data == null:
		chunk_load_failed.emit(coord, "Failed to decode chunk data")
		return

	# Instantiate the chunk scene with the decoded data
	_instantiate_chunk_scene_with_data(coord, chunk_data)


func _on_chunk_load_error(coord: Vector3i, error_msg: String) -> void:
	"""Called when the server reports a chunk load error."""
	_loading_in_progress.erase(coord)
	chunk_load_failed.emit(coord, error_msg)


func _instantiate_chunk_scene(coord: Vector3i) -> void:
	"""Create an empty chunk scene for the given coordinate."""
	var chunk_scene: ChunkScene = ChunkScene.new()
	chunk_scene.coord = coord
	chunk_scene.key = Chunk.build_key("", "", coord)
	chunk_scene.bounds = Chunk.compute_bounds(coord)
	_add_loaded_chunk(coord, chunk_scene)


func _instantiate_chunk_scene_with_data(coord: Vector3i, data: ChunkDataDecoder.ChunkPayload) -> void:
	"""Create a chunk scene populated with server data."""
	var chunk_scene: ChunkScene = ChunkScene.new()
	chunk_scene.coord = coord
	chunk_scene.key = data.key
	chunk_scene.bounds = data.bounds
	# ChunkDataDecoder.ChunkPayload's field is named `version`, not
	# `format_version` -- this was a hard crash ("Invalid access to
	# property or key 'format_version'") the first time real decoded data
	# ever reached this dormant method (via HttpChunkSource).
	chunk_scene.format_version = data.version
	chunk_scene.revision = data.revision

	# Add tiles
	for layer in data.tile_layers:
		var tile_layer: TileLayer = TileLayer.new()
		tile_layer.name = layer.name
		tile_layer.layer_id = layer.layer_id
		tile_layer.width = layer.width
		tile_layer.height = layer.height
		tile_layer.depth = layer.depth
		tile_layer.palette = layer.palette
		tile_layer.tiles = layer.tiles
		chunk_scene.add_tile_layer(tile_layer)

	# Add objects
	for obj_data in data.objects:
		var world_obj: WorldObject = WorldObject.new()
		world_obj.id = obj_data.id
		world_obj.type = obj_data.type
		world_obj.asset_id = obj_data.asset_id
		world_obj.position = obj_data.position
		world_obj.rotation = obj_data.rotation
		world_obj.scale = obj_data.scale
		world_obj.properties = obj_data.properties
		world_obj.is_dynamic = obj_data.dynamic
		world_obj.flags = obj_data.flags
		chunk_scene.add_object(world_obj)

	# Add content flags
	chunk_scene.content_flags = data.flags

	_add_loaded_chunk(coord, chunk_scene)


func _add_loaded_chunk(coord: Vector3i, chunk_scene: Node) -> void:
	_loaded_chunks[coord] = chunk_scene
	add_child(chunk_scene)
	_loading_in_progress.erase(coord)
	chunk_loaded.emit(coord, chunk_scene)


func _unload_chunk(coord: Vector3i) -> void:
	if not _loaded_chunks.has(coord):
		return

	var chunk_scene: Node = _loaded_chunks[coord]
	if is_instance_valid(chunk_scene):
		chunk_scene.queue_free()

	_loaded_chunks.erase(coord)
	chunk_unloaded.emit(coord)


func _on_player_position_changed() -> void:
	"""Call this when the player position changes significantly."""
	if player != null:
		_update_streaming()


func set_server_rpc(rpc_interface: Object) -> void:
	"""Set the server RPC interface for chunk requests."""
	_server_rpc = rpc_interface


func get_loaded_chunk(coord: Vector3i) -> Node:
	"""Get a loaded chunk scene by coordinate, or null if not loaded."""
	return _loaded_chunks.get(coord, null)


func is_chunk_loaded(coord: Vector3i) -> bool:
	"""Check if a chunk is currently loaded."""
	return _loaded_chunks.has(coord)


func get_loaded_chunk_count() -> int:
	"""Get the number of currently loaded chunks."""
	return _loaded_chunks.size()


func get_all_loaded_coords() -> Array[Vector3i]:
	"""Get all currently loaded chunk coordinates."""
	var coords: Array[Vector3i] = []
	for key in _loaded_chunks:
		coords.append(key)
	return coords


func force_reload_chunk(coord: Vector3i) -> void:
	"""Force reload a specific chunk (e.g., after server update)."""
	if _loaded_chunks.has(coord):
		_unload_chunk(coord)
	if not _loading_in_progress.has(coord):
		_load_chunk(coord)


func clear_all_chunks() -> void:
	"""Unload all chunks immediately."""
	var coords: Array[Vector3i] = get_all_loaded_coords()
	for coord in coords:
		_unload_chunk(coord)
	_load_queue.clear()
	_unload_queue.clear()


func _parse_coord_from_key(key: String) -> Variant:
	"""Parse chunk coordinate from a canonical chunk key."""
	# String.split() returns PackedStringArray, not Array[String] -- those
	# are different container types with no implicit conversion, so this
	# raised "Trying to assign a value of type 'PackedStringArray' to a
	# variable of type 'Array[String]'" the moment real data reached this
	# dormant method for the first time (via HttpChunkSource's
	# _on_chunk_data_received call -- nothing exercised this path before).
	var parts: PackedStringArray = key.split(":")
	if parts.size() < 5:
		return null
	return Vector3i(
		int(parts[2]),
		int(parts[3]),
		int(parts[4])
	)