class_name LocalBridge
## TCP transport with length-prefixed framing for IPC (D-020).
##
## Wraps StreamPeerTCP with 4-byte big-endian length-prefix framing
## matching server/src/bridge/framing.rs.

const MAX_MESSAGE_SIZE: int = 16 * 1024 * 1024  # 16 MB, matching server

var _stream: StreamPeerTCP
var _read_buffer: PackedByteArray = PackedByteArray()
var _pending_length: int = -1  # -1 = awaiting header, >= 0 = awaiting payload
var _corrupt: bool = false  # Set on unrecoverable framing error


func _init() -> void:
	_stream = StreamPeerTCP.new()


## Initiate connection to host:port. Non-blocking — poll get_status() for result.
func connect_to_server(host: String, port: int) -> Error:
	return _stream.connect_to_host(host, port)


## Poll the TCP stream. Call every frame to drive connection and reads.
func poll() -> void:
	_stream.poll()


## Current TCP connection status.
func get_status() -> StreamPeerTCP.Status:
	if _corrupt:
		return StreamPeerTCP.STATUS_ERROR
	return _stream.get_status()


## Whether the TCP stream is in the connected state.
func is_connected_to_server() -> bool:
	return not _corrupt and _stream.get_status() == StreamPeerTCP.STATUS_CONNECTED


## Send a framed message: [4-byte BE length][payload].
## Concatenates header and payload into a single put_data() call to avoid partial writes.
func send_message(payload: PackedByteArray) -> Error:
	if not is_connected_to_server():
		return ERR_CONNECTION_ERROR

	var len := payload.size()
	if len > MAX_MESSAGE_SIZE:
		push_error("LocalBridge: message too large: %d bytes (max %d)" % [len, MAX_MESSAGE_SIZE])
		return ERR_PARAMETER_RANGE_ERROR

	# Build complete frame: [4-byte BE length][payload]
	var frame := PackedByteArray()
	frame.resize(4 + len)
	frame[0] = (len >> 24) & 0xFF
	frame[1] = (len >> 16) & 0xFF
	frame[2] = (len >> 8) & 0xFF
	frame[3] = len & 0xFF
	for i in range(len):
		frame[4 + i] = payload[i]

	return _stream.put_data(frame)


## Non-blocking poll for a complete framed message.
## Returns the payload if a complete message is available, empty array otherwise.
## Call in a loop until empty to drain all buffered messages.
func poll_message() -> PackedByteArray:
	if not is_connected_to_server():
		return PackedByteArray()

	# Read any available bytes into the buffer
	var available := _stream.get_available_bytes()
	if available > 0:
		var result := _stream.get_data(available)
		if result[0] != OK:
			return PackedByteArray()
		_read_buffer.append_array(result[1])

	return _try_extract_message()


## Try to extract a complete message from the read buffer.
func _try_extract_message() -> PackedByteArray:
	# Phase 1: read 4-byte header if we don't have a pending length
	if _pending_length < 0:
		if _read_buffer.size() < 4:
			return PackedByteArray()
		_pending_length = (_read_buffer[0] << 24) | (_read_buffer[1] << 16) | \
				(_read_buffer[2] << 8) | _read_buffer[3]
		_read_buffer = _read_buffer.slice(4)

		if _pending_length > MAX_MESSAGE_SIZE:
			# Stream is corrupt — we can't find the next valid frame boundary.
			# Disconnect rather than silently discarding valid buffered data.
			push_error(
				"LocalBridge: incoming message too large: %d bytes (max %d) — disconnecting" % [_pending_length, MAX_MESSAGE_SIZE])
			_corrupt = true
			_pending_length = -1
			_read_buffer.clear()
			disconnect_from_server()
			return PackedByteArray()

	# Phase 2: read payload
	if _read_buffer.size() < _pending_length:
		return PackedByteArray()

	var payload := _read_buffer.slice(0, _pending_length)
	_read_buffer = _read_buffer.slice(_pending_length)
	_pending_length = -1
	return payload


## Close the connection and reset read state.
func disconnect_from_server() -> void:
	_stream.disconnect_from_host()
	_read_buffer.clear()
	_pending_length = -1


## Reset corrupt state (for reconnection after disconnect).
func reset() -> void:
	_corrupt = false
	_read_buffer.clear()
	_pending_length = -1


# -- Static helpers for D-030 Layer 2 testing ----------------------------------
# These exist for unit tests that verify framing logic without a live TCP
# connection. Not used in production code paths.

## Encode a payload into a framed byte array: [4-byte BE length][payload].
static func frame_encode(payload: PackedByteArray) -> PackedByteArray:
	var len := payload.size()
	var frame := PackedByteArray()
	frame.resize(4 + len)
	frame[0] = (len >> 24) & 0xFF
	frame[1] = (len >> 16) & 0xFF
	frame[2] = (len >> 8) & 0xFF
	frame[3] = len & 0xFF
	for i in range(len):
		frame[4 + i] = payload[i]
	return frame


## Decode the first framed message from raw bytes.
## Returns { "payload": PackedByteArray, "remainder": PackedByteArray } or null if incomplete.
static func frame_decode(data: PackedByteArray) -> Variant:
	if data.size() < 4:
		return null
	var len := (data[0] << 24) | (data[1] << 16) | (data[2] << 8) | data[3]
	if len > MAX_MESSAGE_SIZE:
		push_error("LocalBridge: frame too large: %d bytes" % len)
		return null
	if data.size() < 4 + len:
		return null
	return {
		"payload": data.slice(4, 4 + len),
		"remainder": data.slice(4 + len),
	}