CosmicClash/server/domain/proposal.go

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   `json:"player_id"`
	Response Response `json:"response"`
	Team     int      `json:"team"`
	Slot     int      `json:"slot"`
}

type Proposal struct {
	ProposalID   string
	Playlist     Playlist
	Region       string
	Protocol     int
	ArenaPath    string
	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
}

// HasParticipant is the read-side authorization check for proposal recovery.
// A proposal contains private matchmaking state, so non-participants must not
// be able to enumerate or observe it through the control plane.
func (p *Proposal) HasParticipant(playerID string) bool {
	return p != nil && playerID != "" && p.participantIndex(playerID) >= 0
}

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...)
	if p.idempotent != nil {
		clone.idempotent = make(map[string]proposalMutation, len(p.idempotent))
		for key, mutation := range p.idempotent {
			prior := mutation.proposal
			prior.Participants = append([]ProposalParticipant(nil), prior.Participants...)
			prior.idempotent = nil
			clone.idempotent[key] = proposalMutation{digest: mutation.digest, proposal: prior}
		}
	}
	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 {
		validKind := event.Kind == DeclinedResponse || event.Kind == TimedOutResponse
		if event.Playlist == playlist && validKind && !event.At.Before(cutoff) && !event.At.After(now) {
			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)
}