feat: add matchmaking proposal policy

server/domain/proposal.go

@@ -0,0 +1,130 @@
+package domain
+
+import (
+	"crypto/sha256"
+	"errors"
+	"fmt"
+	"sort"
+	"time"
+)
+
+const ProposalWindow = 10 * time.Second
+
+var (
+	ErrProposalClosed = errors.New("proposal is no longer open")
+	ErrNotParticipant = errors.New("player is not a proposal participant")
+)
+
+type Playlist string
+
+const (
+	Casual Playlist = "casual"
+	Ranked Playlist = "ranked"
+)
+
+type Response string
+
+const (
+	Pending Response = "PENDING"
+	AcceptedResponse Response = "ACCEPTED"
+	DeclinedResponse Response = "DECLINED"
+	TimedOutResponse Response = "TIMED_OUT"
+)
+
+type ProposalParticipant struct {
+	PlayerID string
+	Response Response
+}
+
+type Proposal struct {
+	ProposalID string
+	Playlist Playlist
+	Participants []ProposalParticipant
+	State State
+	Revision uint64
+	ExpiresAt time.Time
+	idempotent map[string]proposalMutation
+}
+
+type proposalMutation struct {
+	digest [32]byte
+	proposal Proposal
+}
+
+func NewProposal(id string, playlist Playlist, playerIDs []string, now time.Time) (Proposal, error) {
+	if id == "" || (playlist != Casual && playlist != Ranked) { return Proposal{}, fmt.Errorf("%w: invalid proposal", ErrConflict) }
+	if playlist == Ranked && len(playerIDs) != 6 { return Proposal{}, fmt.Errorf("%w: ranked requires exactly six players", ErrConflict) }
+	if len(playerIDs) < 2 || len(playerIDs) > 6 { return Proposal{}, fmt.Errorf("%w: proposal requires 2 through 6 players", ErrConflict) }
+	seen := make(map[string]bool, len(playerIDs))
+	participants := make([]ProposalParticipant, 0, len(playerIDs))
+	for _, playerID := range playerIDs {
+		if playerID == "" || seen[playerID] { return Proposal{}, fmt.Errorf("%w: duplicate or empty player", ErrConflict) }
+		seen[playerID] = true
+		participants = append(participants, ProposalParticipant{PlayerID: playerID, Response: Pending})
+	}
+	sort.Slice(participants, func(i, j int) bool { return participants[i].PlayerID < participants[j].PlayerID })
+	return Proposal{ProposalID: id, Playlist: playlist, Participants: participants, State: Open, ExpiresAt: now.Add(ProposalWindow), idempotent: make(map[string]proposalMutation)}, nil
+}
+
+func (p *Proposal) Respond(playerID, idempotencyKey string, accept bool, expectedRevision uint64, now time.Time) (Proposal, error) {
+	digest := sha256.Sum256([]byte(fmt.Sprintf("%s:%t:%d", playerID, accept, expectedRevision)))
+	if prior, ok := p.idempotent[idempotencyKey]; ok {
+		if prior.digest != digest { return Proposal{}, fmt.Errorf("%w: proposal response payload changed", ErrConflict) }
+		return prior.proposal, nil
+	}
+	if idempotencyKey == "" { return Proposal{}, fmt.Errorf("%w: empty proposal response key", ErrConflict) }
+	if p.State != Open || !now.Before(p.ExpiresAt) { return Proposal{}, ErrProposalClosed }
+	if p.Revision != expectedRevision { return Proposal{}, ErrStaleRevision }
+	index := p.participantIndex(playerID)
+	if index < 0 { return Proposal{}, ErrNotParticipant }
+	if p.Participants[index].Response != Pending { return Proposal{}, fmt.Errorf("%w: participant already responded", ErrConflict) }
+	if accept { p.Participants[index].Response = AcceptedResponse } else { p.Participants[index].Response = DeclinedResponse; p.State = Declined }
+	if accept && p.allAccepted() { p.State = Accepted }
+	p.Revision++
+	p.idempotent[idempotencyKey] = proposalMutation{digest: digest, proposal: p.copy()}
+	return p.copy(), nil
+}
+
+func (p *Proposal) Expire(now time.Time) bool {
+	if p.State != Open || now.Before(p.ExpiresAt) { return false }
+	for i := range p.Participants { if p.Participants[i].Response == Pending { p.Participants[i].Response = TimedOutResponse } }
+	p.State = Expired
+	p.Revision++
+	return true
+}
+
+func (p *Proposal) participantIndex(playerID string) int {
+	for i, participant := range p.Participants { if participant.PlayerID == playerID { return i } }
+	return -1
+}
+
+func (p *Proposal) allAccepted() bool {
+	for _, participant := range p.Participants { if participant.Response != AcceptedResponse { return false } }
+	return true
+}
+
+func (p *Proposal) copy() Proposal {
+	clone := *p
+	clone.Participants = append([]ProposalParticipant(nil), p.Participants...)
+	clone.idempotent = nil
+	return clone
+}
+
+type CooldownEvent struct { At time.Time; Playlist Playlist; Kind Response }
+
+func CooldownUntil(events []CooldownEvent, playlist Playlist, now time.Time) time.Time {
+	window := 30 * time.Minute
+	cutoff := now.Add(-window)
+	filtered := make([]CooldownEvent, 0, len(events))
+	for _, event := range events { if event.Playlist == playlist && !event.At.Before(cutoff) { filtered = append(filtered, event) } }
+	sort.Slice(filtered, func(i, j int) bool { return filtered[i].At.Before(filtered[j].At) })
+	var duration time.Duration
+	if len(filtered) > 0 {
+		if playlist == Casual { if filtered[len(filtered)-1].Kind == DeclinedResponse { duration = 30 * time.Second } else { duration = 60 * time.Second } } else {
+			if filtered[len(filtered)-1].Kind == DeclinedResponse { duration = 2 * time.Minute } else { duration = 5 * time.Minute }
+			if len(filtered) >= 3 { duration = 15 * time.Minute }
+		}
+	}
+	if duration == 0 { return time.Time{} }
+	return filtered[len(filtered)-1].At.Add(duration)
+}