class_name HttpChunkSource
extends Node
## HTTP-backed adapter for ChunkStreamManager.set_server_rpc().
##
## Implements docs/architecture/world_persistence_impl.md D6/§8.4: the
## playing client streams chunks from the FastAPI backend over HTTP (the
## same public routes the editor uses -- `backend/app/routers/world_content.py`),
## not over the dedicated server's ENet connection.
##
## `ChunkStreamManager` only requires an object with a `request_chunk(key)`
## method (see its `_server_rpc` seam); this adapter satisfies that and feeds
## results back through the manager's existing (previously dormant)
## `_on_chunk_data_received(key, bytes)` / `_on_chunk_load_error(coord, msg)`
## methods, and its `_instantiate_chunk_scene(coord)` for the "unwritten
## coordinate renders empty" case (§8.1).
##
## `ChunkStreamManager._load_chunk()` builds its request key with empty
## world/room components (`Chunk.build_key("", "", coord)`) because the
## manager itself has no notion of which world/room it's streaming --
## that's this adapter's job. `request_chunk(key)` only reads the
## coordinate out of the key it's given and rebuilds the real key from
## `world_id`/`room_slug` before touching the network, per the doc's note
## under §8.4.
##
## Must be added to the scene tree before use (it creates per-request
## HTTPRequest child nodes), e.g.:
##
##     var source := HttpChunkSource.new()
##     source.world_id = str(Session.world_id)
##     source.room_slug = "main"
##     source.stream_manager = stream_manager
##     stream_manager.add_child(source)
##     stream_manager.set_server_rpc(source)

## The world this source fetches chunks for (string form of the backend's
## numeric world id -- matches Chunk.build_key's world_id parameter type).
var world_id: String = ""

## The room slug within that world. world.md's default room is "main".
var room_slug: String = "main"

## The ChunkStreamManager to feed decoded results back into. Required.
var stream_manager: ChunkStreamManager = null

## In-memory ETag cache: chunk key -> last-known checksum (bare hex, no
## quotes). Backs the on-disk payload cache so re-fetching an unchanged
## chunk costs a 304, not a re-download (world_persistence_impl.md §8.1:
## "This is what makes the client's user://chunk_cache/ cache cheap").
var _etag_by_key: Dictionary = {}

const CACHE_DIR := "user://chunk_cache"


func _ready() -> void:
	DirAccess.make_dir_recursive_absolute(CACHE_DIR)


## Satisfies ChunkStreamManager's `_server_rpc.request_chunk(key)` seam.
func request_chunk(key: String) -> void:
	var coord: Variant = _coord_from_key(key)
	if coord == null:
		push_error("HttpChunkSource: malformed chunk key %s" % key)
		return
	_fetch(coord)


## world_persistence_impl.md §8.1 chunk index -- lists which chunks in a
## bounds actually exist without fetching their payloads. Not called by
## ChunkStreamManager's per-coordinate streaming loop today, but is the
## "bounds-query listing" half of this adapter's contract for future
## callers (e.g. a minimap, or a smarter prefetcher).
func list_chunks(cx_min: int, cx_max: int, cy_min: int, cy_max: int, cz: int = 0) -> Dictionary:
	var path := "/api/worlds/%s/rooms/%s/chunks?cx_min=%d&cx_max=%d&cy_min=%d&cy_max=%d&cz=%d" % [
		world_id, room_slug, cx_min, cx_max, cy_min, cy_max, cz
	]
	return await _api_client().request(HTTPClient.METHOD_GET, path, "", "application/json", true)


# ─────────────────────────── internals ───────────────────────────

## Resolved via an absolute node path rather than the bare `ApiClient`
## autoload identifier: bare autoload identifiers only resolve at GDScript
## compile time inside a scene the engine boots normally. Any script
## compiled while running headless via `godot --script ...` (as
## scripts/smoke_test_*.gd do) fails with "Identifier not found: ApiClient"
## on the bare form -- confirmed while writing
## scripts/smoke_test_http_chunk_source.gd. `get_node` resolves the same
## singleton correctly in both contexts (the same pattern game.gd already
## uses for AvatarSystem via `get_node_or_null("/root/AvatarSystem")`).
func _api_client() -> Node:
	return get_node("/root/ApiClient")


func _fetch(coord: Vector3i) -> void:
	var key := Chunk.build_key(world_id, room_slug, coord)

	var http := HTTPRequest.new()
	http.timeout = 10.0
	add_child(http)

	var api := _api_client()
	var headers := PackedStringArray()
	headers.append("Accept: application/octet-stream")
	if api.has_token():
		var bearer: String = api.bearer_token
		headers.append("Authorization: " + bearer)
	var cached_etag: String = _etag_by_key.get(key, "")
	if cached_etag != "":
		headers.append("If-None-Match: \"%s\"" % cached_etag)

	var base_url: String = api.base_url
	var url := "%s/api/worlds/%s/rooms/%s/chunks/%d/%d/%d" % [
		base_url, world_id, room_slug, coord.x, coord.y, coord.z
	]
	var err := http.request(url, headers, HTTPClient.METHOD_GET)
	if err != OK:
		http.queue_free()
		_fail(coord, "HttpChunkSource: failed to start request for %s (%d)" % [key, err])
		return

	var args: Array = await http.request_completed
	var result_code: int = args[0]
	var response_code: int = args[1]
	var response_headers: PackedStringArray = args[2]
	var body: PackedByteArray = args[3]
	http.queue_free()

	if result_code != HTTPRequest.RESULT_SUCCESS:
		_fail(coord, "HttpChunkSource: transport error fetching %s (code %d)" % [key, result_code])
		return

	match response_code:
		304:
			var cached := _read_cache(cached_etag)
			if cached.is_empty():
				# Cache miss despite a 304 (e.g. the user:// cache got
				# cleared) -- drop the stale ETag and refetch unconditionally
				# rather than deliver empty bytes to the decoder.
				_etag_by_key.erase(key)
				_fetch(coord)
				return
			_deliver(key, cached)
		200:
			var checksum := _etag_from_headers(response_headers)
			if checksum != "":
				_etag_by_key[key] = checksum
				_write_cache(checksum, body)
			_deliver(key, body)
		404:
			# world_persistence_impl.md §8.1: "an unwritten coordinate is not
			# an error to the streamer -- it renders empty."
			if stream_manager != null:
				stream_manager._instantiate_chunk_scene(coord)
		_:
			_fail(coord, "HttpChunkSource: HTTP %d fetching %s" % [response_code, key])


func _deliver(key: String, bytes: PackedByteArray) -> void:
	if stream_manager != null:
		stream_manager._on_chunk_data_received(key, bytes)


func _fail(coord: Vector3i, message: String) -> void:
	push_error(message)
	if stream_manager != null:
		stream_manager._on_chunk_load_error(coord, message)


func _coord_from_key(key: String) -> Variant:
	var parts: PackedStringArray = key.split(":")
	if parts.size() < 5:
		return null
	return Vector3i(int(parts[2]), int(parts[3]), int(parts[4]))


func _etag_from_headers(headers: PackedStringArray) -> String:
	for h in headers:
		if h.to_lower().begins_with("etag:"):
			var v := h.substr(h.find(":") + 1).strip_edges()
			return v.trim_prefix('"').trim_suffix('"')
	return ""


func _cache_path(checksum: String) -> String:
	return "%s/%s" % [CACHE_DIR, checksum]


func _write_cache(checksum: String, bytes: PackedByteArray) -> void:
	var f := FileAccess.open(_cache_path(checksum), FileAccess.WRITE)
	if f:
		f.store_buffer(bytes)
		f.close()


func _read_cache(checksum: String) -> PackedByteArray:
	if checksum == "":
		return PackedByteArray()
	var f := FileAccess.open(_cache_path(checksum), FileAccess.READ)
	if f == null:
		return PackedByteArray()
	var bytes := f.get_buffer(f.get_length())
	f.close()
	return bytes