class_name ServerControl
extends Node

# Small loopback HTTP control surface for lifecycle-managed servers. The Go
# supervisor uses GET /ready as the explicit process-ready probe and POST
# /drain during a controlled termination. Direct/community servers outside
# Agones do not start this node.

signal drain_requested
signal initial_connect_ready

var _listener := TCPServer.new()
var _peers: Array = []
var _ready_for_connections := false
var _draining := false
var _drain_token := ""


func start(port: int, drain_token: String = "") -> Error:
	if port < 1 or port > 65535:
		return ERR_INVALID_PARAMETER
	_drain_token = drain_token
	return _listener.listen(port, "127.0.0.1")


func stop() -> void:
	_listener.stop()
	for peer in _peers:
		if is_instance_valid(peer):
			peer.disconnect_from_host()
	_peers.clear()


func set_process_ready(value: bool) -> void:
	_ready_for_connections = value and not _draining


func is_draining() -> bool:
	return _draining


func _exit_tree() -> void:
	stop()


func _process(_delta: float) -> void:
	while _listener.is_connection_available():
		_peers.append(_listener.take_connection())
	for i in range(_peers.size() - 1, -1, -1):
		var peer: StreamPeerTCP = _peers[i]
		if peer.get_status() != StreamPeerTCP.STATUS_CONNECTED:
			_peers.remove_at(i)
			continue
		var available := peer.get_available_bytes()
		if available <= 0:
			continue
		var request := peer.get_utf8_string(available)
		if "\r\n\r\n" not in request:
			continue
		_respond(peer, request)
		_peers.remove_at(i)


func _respond(peer: StreamPeerTCP, request: String) -> void:
	var lines := request.split("\r\n")
	var first := lines[0].split(" ") if not lines.is_empty() else PackedStringArray()
	var method := String(first[0]) if first.size() > 0 else ""
	var path := String(first[1]) if first.size() > 1 else ""
	var status := 404
	var reason := "Not Found"
	var body := ""
	if method in ["GET", "POST"] and path == "/ready":
		status = 200 if _ready_for_connections else 503
		reason = "OK" if status == 200 else "Service Unavailable"
	elif method in ["GET", "POST"] and path == "/health":
		status = 200
		reason = "OK"
	elif method == "POST" and path == "/drain":
		var supplied := ""
		for line in lines:
			if line.begins_with("Authorization: Bearer "):
				supplied = line.substr("Authorization: Bearer ".length())
		if _drain_token.is_empty() or not _constant_time_equal(supplied, _drain_token):
			status = 401
			reason = "Unauthorized"
		else:
			_draining = true
			_ready_for_connections = false
			drain_requested.emit()
			status = 202
			reason = "Accepted"
	elif method == "POST" and path == "/initial-connect-ready":
		var supplied := ""
		for line in lines:
			if line.begins_with("Authorization: Bearer "):
				supplied = line.substr("Authorization: Bearer ".length())
		if _drain_token.is_empty() or not _constant_time_equal(supplied, _drain_token):
			status = 401
			reason = "Unauthorized"
		else:
			initial_connect_ready.emit()
			status = 202
			reason = "Accepted"
	else:
		status = 405 if method in ["GET", "POST"] else 400
		reason = "Method Not Allowed" if status == 405 else "Bad Request"
	body = "{\"status\":\"%s\"}" % ("ready" if status == 200 else "not_ready")
	var response := "HTTP/1.1 %d %s\r\nContent-Type: application/json\r\nContent-Length: %d\r\nConnection: close\r\n\r\n%s" % [status, reason, body.to_utf8_buffer().size(), body]
	peer.put_data(response.to_utf8_buffer())
	peer.disconnect_from_host()


func _constant_time_equal(a: String, b: String) -> bool:
	var left := a.to_utf8_buffer()
	var right := b.to_utf8_buffer()
	var difference := left.size() ^ right.size()
	var length := mini(left.size(), right.size())
	for i in length:
		difference |= left[i] ^ right[i]
	return difference == 0