extends Node

# todo: Settle on whether connection should send Sums.Result or receiver should check stanza errors by itself.

class Connection extends Reference:
    var stream: StreamPeer
    var identity: String
    var domain: String
    var bare_jid: String
    var jid: String

    var _id_counter: int = 0
    var _pending_iqs: Dictionary # of id to GDScriptFunctionState
    var _presence_sinks: Dictionary # of Jid to [[WeakRef, String, String]]
    var _xml_parser := Xml.Parser.new()

    # todo: Route signals to particular receivers, based on 'from' or 'to'
    # warning-ignore:unused_signal
    signal presence_received(presence)
    # warning-ignore:unused_signal
    signal message_received(message)
    # warning-ignore:unused_signal
    signal iq_received(iq)

    # todo: Separate incremental hash to its own class.
    func generate_id() -> int:
        self._id_counter += 1
        return hash(self._id_counter)

    func promise_iq(to: String, type: String, payload: String, capture: GDScriptFunctionState) -> Sums.Promise:
        assert(type in ["get", "set"])

        var id := self.generate_id()
        if self.stream.put_data(
            """<iq from='{from}' id='{id}' to='{to}' type='{type}'>{payload}</iq>""".format({
                "from": self.jid.xml_escape(),
                "id": String(id).xml_escape(),
                "to": to.xml_escape(),
                "type": type,
                "payload": payload
                }).to_utf8()) != OK:
            return Sums.Promise.make_error(ERR_CONNECTION_ERROR)

        assert(not id in self._pending_iqs)
        self._pending_iqs[id] = capture

        return Sums.Promise.from(capture)

    func push_presence(to: String, type, payload: String) -> Sums.Result:
        assert(type == null or type is String)

        var message = Stanza.form_presence(
            String(self.generate_id()),
            self.jid, to, type, payload)

        if self.stream.put_data(message.to_utf8()) != OK:
                return Sums.Result.make_error(ERR_CONNECTION_ERROR)

        return Sums.Result.make_value(null)

    func presence_sink(p_base_jid: String, p_sink: Object, p_type: String, p_signal: String) -> void:
        self._presence_sinks[p_base_jid] = \
            self._presence_sinks.get(p_base_jid, []) + [[weakref(p_sink), p_type, p_signal]]

## Registry of connections used for poking of pending iqs.
var _connections: Array # of WeakRef to Connection

func _ready():
    # todo: Some better interval?
    if get_tree().connect("physics_frame", self, "_process_connections") != OK:
        assert("Bruh")

# todo: Collapse Result inside Promise.
func _process_connections() -> void:
    var to_remove := PoolIntArray()

    for idx in range(_connections.size()):
        var connection := _connections[idx].get_ref() as Connection
        if connection == null:
            to_remove.push_back(idx)
            continue

        var response = _wait_blocking_for_utf8_data(connection.stream, 0)
        if response == null:
            continue

        # todo: Move Result error into closure on connection failure?

        while connection._xml_parser.parse_a_bit(response):
            response = null

            var stanza := connection._xml_parser.take_root()

            if stanza.name == "iq":
                if "to" in stanza.attributes and stanza.attributes["to"] != connection.jid:
                    # todo: Server errors should not be raised in client.
                    push_error("Stanza is not addressed to assigned jid")

                if stanza.attributes["type"] in ["result", "error"]:
                    var id := int(stanza.attributes["id"]) # todo: Use strings directly instead?
                    connection._pending_iqs[id].resume(Sums.Result.make_value(stanza))
                    var was_present := connection._pending_iqs.erase(id)
                    assert(was_present)

                elif stanza.attributes["type"] in ["set", "get"]:
                    # todo: Emit in any way?
                    connection.emit_signal("iq_received", stanza)

            elif stanza.name == "message":
                connection.emit_signal("message_received", stanza)

            elif stanza.name == "presence":
                connection.emit_signal("presence_received", stanza)

                for base_jid in connection._presence_sinks.keys():
                    if not stanza.attributes["from"].begins_with(base_jid):
                        continue

                    var sink = connection._presence_sinks[base_jid]
                    var sink_idx := 0
                    while sink_idx < sink.size():
                        var ref = sink[sink_idx][0].get_ref()
                        if ref == null:
                            sink.remove(sink_idx)
                        else:
                            if sink[sink_idx][1] == "signal":
                                ref.emit_signal(sink[sink_idx][2], stanza)
                            else: ref.call(sink[sink_idx][2], stanza)
                            sink_idx += 1

    ## Collect dropped connections.
    for idx in range(to_remove.size() - 1, 0, -1):
        _connections.remove(to_remove[idx])

func establish_new_connection(domain: String, identity: String, password: String):
    var stream := StreamPeerTCP.new()
    if stream.connect_to_host(domain, 5222) != OK:
        push_error("Cannot establish connection to " + domain)
        return null

    while stream.get_status() == StreamPeerTCP.STATUS_CONNECTING:
        pass

    if stream.get_status() == StreamPeerTCP.STATUS_ERROR:
        push_error("Cannot establish connection to " + domain)
        return null

    var result := Connection.new()
    result.stream = stream
    result.identity = identity
    result.domain = domain
    result.bare_jid = identity + '@' + domain

    if _negotiate_connection(result, password) != OK:
        return null

    _connections.push_back(weakref(result))

    return result

# todo: Make it async
func _negotiate_connection(connection: Connection, password: String) -> int:
    ## See [9. Detailed Examples] of https://datatracker.ietf.org/doc/rfc6120/
    var error: int = OK

    error = _negotiate_tls(connection)
    if error != OK: return error

    error = _negotiate_sasl(connection, password)
    if error != OK: return error

    error = _bind_resource(connection)
    if error != OK: return error

    return OK

func _form_initial_message(domain: String, bare_jid: String) -> String:
    # todo: XML builder interface, writing by hand is extremely error prone.
    return """<?xml version='1.0'?><stream:stream
    from='{bare_jid}' to='{domain}' version='1.0'
    xml:lang='en' xmlns='jabber:client'
    xmlns:stream='http://etherx.jabber.org/streams'>""".format({
        "bare_jid": bare_jid.xml_escape(), "domain": domain.xml_escape()})

func _negotiate_tls(connection: Connection) -> int:
    var error: int = OK
    var response
    var parsed_response = Xml.Parser.new()

    ## Step 1: Client initiates stream to server:
    if connection.stream.put_data(_form_initial_message(
        connection.domain, connection.bare_jid).to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    ## Step 2: Server responds by sending a response stream header to client:
    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR
        # If <stream:stream> is closed, - connection is closed too.

    ## Check that server response corresponds to what we ask for.
    # todo: For conformity client must send closing stream tag on error.
    if parsed_response._root.name != "stream:stream": return ERR_CANT_CONNECT
    if parsed_response._root.attributes["from"] != connection.domain: return ERR_CANT_CONNECT
    if "to" in parsed_response._root.attributes:
        if parsed_response._root.attributes["to"] != connection.bare_jid: return ERR_CANT_CONNECT
    if parsed_response._root.attributes["version"] != "1.0": return ERR_CANT_CONNECT
    # todo: Assert for namespaces.

    ## Step 3: Server sends stream features to client (only the STARTTLS
    ## extension at this point, which is mandatory-to-negotiate):
    if parsed_response._root.children.size() == 0:
        response = _wait_blocking_for_utf8_data(connection.stream)
        if response == null: return ERR_CONNECTION_ERROR
        if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    var features = parsed_response._root.take_named_child_element("stream:features")
    if features == null: return ERR_CANT_CONNECT
    var starttls = features.take_named_child_element("starttls")
    if starttls == null or starttls.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-tls":
        push_error("Connection declined, TLS is not a listed feature")
        return ERR_CANT_CONNECT

    ## Step 4: Client sends STARTTLS command to server:
    if connection.stream.put_data("<starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>".to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    ## Step 5: Server informs client that it is allowed to proceed:
    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    # todo: Handle failure case.

    var proceed = parsed_response._root.take_named_child_element("proceed")
    if proceed == null: return ERR_CANT_CONNECT
    if proceed.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-tls": return ERR_CANT_CONNECT

    ## Step 6: Client and server attempt to complete TLS negotiation over
    ## the existing TCP connection (see [TLS] for details).
    var tls_stream := StreamPeerSSL.new()
    error = tls_stream.connect_to_stream(connection.stream, true, connection.domain)
    if error != OK:
        push_error("Cannot establish client->server TLS connection")
        return error

    connection.stream = tls_stream

    ## Step 7 (alt): If TLS negotiation is unsuccessful, server closes TCP
    ## connection (thus, the stream negotiation process ends unsuccessfully
    ## and the parties do not move on to the next step):

    return OK

func _negotiate_sasl(connection: Connection, password: String) -> int:
    var response
    var parsed_response = Xml.Parser.new()

    ## Step 7: If TLS negotiation is successful, client initiates a new
    ## stream to server over the TLS-protected TCP connection:
    if connection.stream.put_data(_form_initial_message(
        connection.domain, connection.bare_jid).to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    ## Step 8: Server responds by sending a stream header to client along
    ## with any available stream features:

    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    ## Check that server response corresponds to what we ask for.
    # todo: For conformity client must send closing stream tag on error.
    if parsed_response._root.name != "stream:stream": return ERR_CANT_CONNECT
    if parsed_response._root.attributes["from"] != connection.domain: return ERR_CANT_CONNECT
    if "to" in parsed_response._root.attributes:
        if parsed_response._root.attributes["to"] != connection.bare_jid: return ERR_CANT_CONNECT
    if parsed_response._root.attributes["version"] != "1.0": return ERR_CANT_CONNECT
    # todo: Assert for namespaces.

    if parsed_response._root.children.size() == 0:
        response = _wait_blocking_for_utf8_data(connection.stream)
        if response == null: return ERR_CONNECTION_ERROR
        if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    var features = parsed_response._root.take_named_child_element("stream:features")
    if features == null: return ERR_CANT_CONNECT
    var mechanisms = features.take_named_child_element("mechanisms")
    if mechanisms == null or mechanisms.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-sasl":
        push_error("Connection declined, mechanisms is not a listed feature")
        return ERR_CANT_CONNECT

    ## We only support PLAIN mechanism as it's sufficient over TLS.
    var plain_found := false
    for machanism in mechanisms.children:
        if machanism.is_element() and machanism.name == "mechanism":
            if machanism.children[0].data == "PLAIN":
                plain_found = true
                break

    if not plain_found:
        push_error("Connection declined, mechanisms don't include PLAIN method")
        return ERR_CANT_CONNECT

    ## Step 9: Client selects an authentication mechanism, including initial response data:
    ## https://datatracker.ietf.org/doc/html/rfc4616
    if connection.stream.put_data((
        "<auth xmlns='urn:ietf:params:xml:ns:xmpp-sasl' mechanism='PLAIN'>%s</auth>" %
            [_plain_auth_message(connection.identity, password)]).to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    ## (Skipped steps related to another auth machanism)

    ## Step 12: Server informs client of success, including additional data
    ## with success:
    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    var success = parsed_response._root.take_named_child_element("success")
    if success == null or success.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-sasl":
        return ERR_CANT_CONNECT

    return OK

func _bind_resource(connection: Connection, resource: String = "tochie-facade") -> int:
    var response
    var parsed_response = Xml.Parser.new()

    ## Step 13: Client initiates a new stream to server:
    if connection.stream.put_data(_form_initial_message(
        connection.domain, connection.bare_jid).to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    ## Step 14: Server responds by sending a stream header to client along
    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    ## Check that server response corresponds to what we ask for.
    # todo: For conformity client must send closing stream tag on error.
    if parsed_response._root.name != "stream:stream": return ERR_CANT_CONNECT
    if parsed_response._root.attributes["from"] != connection.domain: return ERR_CANT_CONNECT
    if "to" in parsed_response._root.attributes:
        if parsed_response._root.attributes["to"] != connection.bare_jid: return ERR_CANT_CONNECT
    if parsed_response._root.attributes["version"] != "1.0": return ERR_CANT_CONNECT
    # todo: Assert for namespaces.

    if parsed_response._root.children.size() == 0:
        response = _wait_blocking_for_utf8_data(connection.stream)
        if response == null: return ERR_CONNECTION_ERROR
        if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    var features = parsed_response._root.take_named_child_element("stream:features")
    if features == null: return ERR_CANT_CONNECT
    var bind = features.take_named_child_element("bind")
    if bind == null or bind.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-bind":
        push_error("Connection declined, bind is not a listed feature")
        return ERR_CANT_CONNECT

    ## Step 15: Client binds a resource:
    var iq_id := connection.generate_id()
    if connection.stream.put_data("""<iq id='{id}' type='set'>
    <bind xmlns='urn:ietf:params:xml:ns:xmpp-bind'>
        <resource>{resource}</resource>
    </bind></iq>""".format({
        "id": iq_id,
        "resource": resource.xml_escape()
    }).to_utf8()) != OK:
        return ERR_CONNECTION_ERROR

    response = _wait_blocking_for_utf8_data(connection.stream)
    if response == null: return ERR_CONNECTION_ERROR
    if parsed_response.parse_a_bit(response): return ERR_CONNECTION_ERROR

    ## Step 16: Server accepts submitted resourcepart and informs client of
    ## successful resource binding:
    var iq = parsed_response._root.take_named_child_element("iq")
    if iq.attributes["id"] != String(iq_id):
        push_error("iq id mismatch, expected: " + String(iq_id) + " but got: " + iq.attributes["id"])
        return ERR_CANT_CONNECT

    bind = iq.take_named_child_element("bind")
    if bind == null or bind.attributes["xmlns"] != "urn:ietf:params:xml:ns:xmpp-bind":
        return ERR_CANT_CONNECT

    var jid = bind.take_named_child_element("jid")
    if jid == null: return ERR_CANT_CONNECT

    connection.jid = jid.children[0].data

    return OK

func _plain_auth_message(identity: String, password: String) -> String:
    var raw = PoolByteArray([0])
    raw.append_array(identity.to_utf8() + PoolByteArray([0]))
    raw.append_array(password.to_utf8())
    return Marshalls.raw_to_base64(raw)

func _wait_blocking_for_utf8_data(stream: StreamPeer, timeout_ms: int = 1000): # -> String or null:
    var enter_time := OS.get_system_time_msecs()

    if stream is StreamPeerSSL: stream.poll()
    var available_bytes := stream.get_available_bytes()

    while available_bytes == 0:
        if OS.get_system_time_msecs() - enter_time >= timeout_ms:
            return null
        if stream is StreamPeerSSL: stream.poll()
        available_bytes = stream.get_available_bytes()

    return stream.get_utf8_string(available_bytes)