1 files changed, 145 insertions, 0 deletions
diff --git a/common/sequencer/sequencer.go b/common/sequencer/sequencer.go
new file mode 100644
index 0000000..fe83580
--- /dev/null
+++ b/common/sequencer/sequencer.go
@@ -0,0 +1,145 @@
+package sequencer
+
+import (
+	"errors"
+	"time"
+
+	"github.com/osm/quake/packet/command"
+)
+
+var ErrRateLimit = errors.New("rate limit reached")
+
+type State byte
+
+const (
+	Disconnected State = 0
+	Handshake    State = 1
+	Connecting   State = 2
+	Connected    State = 3
+)
+
+type Sequencer struct {
+	ping      int16
+	lastWrite time.Time
+
+	state State
+
+	incomingSeq     uint32
+	incomingAck     uint32
+	lastReliableSeq uint32
+	outgoingSeq     uint32
+
+	isIncomingAckReliable bool
+	isOutgoingSeqReliable bool
+	isIncomingSeqReliable bool
+
+	outgoingCommands    []command.Command
+	outgoingCommandsBuf []command.Command
+}
+
+func New(opts ...Option) *Sequencer {
+	s := Sequencer{
+		ping: 999,
+	}
+
+	for _, opt := range opts {
+		opt(&s)
+	}
+
+	return &s
+}
+
+func (s *Sequencer) SetState(state State) { s.state = state }
+func (s *Sequencer) GetState() State      { return s.state }
+func (s *Sequencer) SetPing(ping int16)   { s.ping = ping }
+func (s *Sequencer) GetPing() int16       { return s.ping }
+
+func (s *Sequencer) Reset() {
+	s.incomingSeq = 0
+	s.incomingAck = 0
+	s.lastReliableSeq = 0
+	s.outgoingSeq = 0
+
+	s.isIncomingAckReliable = false
+	s.isOutgoingSeqReliable = false
+	s.isIncomingSeqReliable = false
+
+	s.outgoingCommands = []command.Command{}
+	s.outgoingCommandsBuf = []command.Command{}
+}
+
+func (s *Sequencer) Process(
+	incomingSeq, incomingAck uint32,
+	cmds []command.Command,
+) (uint32, uint32, []command.Command, error) {
+	s.incoming(incomingSeq, incomingAck)
+	return s.outgoing(cmds)
+}
+
+func (s *Sequencer) incoming(incomingSeq, incomingAck uint32) {
+	isIncomingSeqReliable := incomingSeq>>31 == 1
+	isIncomingAckReliable := incomingAck>>31 == 1
+
+	incomingSeq = incomingSeq & 0x7fffffff
+	incomingAck = incomingAck & 0x7fffffff
+
+	if incomingSeq < s.incomingSeq {
+		return
+	}
+
+	if isIncomingAckReliable == s.isOutgoingSeqReliable {
+		s.outgoingCommandsBuf = []command.Command{}
+	}
+
+	if isIncomingSeqReliable {
+		s.isIncomingSeqReliable = !s.isIncomingSeqReliable
+	}
+
+	s.incomingSeq = incomingSeq
+	s.incomingAck = incomingAck
+	s.isIncomingAckReliable = isIncomingAckReliable
+}
+
+func (s *Sequencer) outgoing(cmds []command.Command) (uint32, uint32, []command.Command, error) {
+	s.outgoingCommands = append(s.outgoingCommands, cmds...)
+
+	if s.state == Connected && time.Since(s.lastWrite).Milliseconds() < int64(s.ping) {
+		return 0, 0, nil, ErrRateLimit
+	}
+
+	var isReliable bool
+
+	if s.incomingAck > s.lastReliableSeq &&
+		s.isIncomingAckReliable != s.isOutgoingSeqReliable {
+		isReliable = true
+	}
+
+	if len(s.outgoingCommandsBuf) == 0 && len(s.outgoingCommands) > 0 {
+		s.outgoingCommandsBuf = s.outgoingCommands
+		s.isOutgoingSeqReliable = !s.isOutgoingSeqReliable
+		isReliable = true
+		s.outgoingCommands = []command.Command{}
+	}
+
+	outgoingSeq := s.outgoingSeq
+	if isReliable {
+		outgoingSeq = s.outgoingSeq | (1 << 31)
+	}
+
+	outgoingAck := s.incomingSeq
+	if s.isIncomingSeqReliable {
+		outgoingAck = s.incomingSeq | (1 << 31)
+	}
+
+	outgoingCmds := []command.Command{}
+
+	s.outgoingSeq++
+
+	if isReliable {
+		outgoingCmds = append(outgoingCmds, s.outgoingCommandsBuf...)
+		s.lastReliableSeq = s.outgoingSeq
+	}
+
+	s.lastWrite = time.Now()
+	return outgoingSeq, outgoingAck, outgoingCmds, nil
+}