package domain

import (
	"fmt"
	"sort"
	"time"
)

const RankedReconnectGrace = 60 * time.Second

var rankedAbandonCooldowns = [...]time.Duration{
	5 * time.Minute,
	15 * time.Minute,
	time.Hour,
	24 * time.Hour,
}

var (
	ErrJoinAuthorisation = fmt.Errorf("invalid join authorisation")
	ErrConnectionFenced  = fmt.Errorf("connection generation is fenced")
	ErrReconnectExpired  = fmt.Errorf("reconnect grace expired")
)

// JoinAuthorisation is the signed payload an adapter obtains from the secure
// backend. Signature verification is deliberately outside this pure policy
// package; every identity, match, slot, server and protocol field is still
// checked here before a lease can be admitted.
type JoinAuthorisation struct {
	MatchID    string
	ServerID   string
	PlayerID   string
	SteamID    string
	Slot       int
	Team       int
	Protocol   string
	Generation uint64
	ExpiresAt  time.Time
}

type rankedConnection struct {
	PlayerID    string
	Slot        int
	Team        int
	SteamID     string
	Generation  uint64
	ConnectedAt time.Time
	LostAt      time.Time
	Abandoned   bool
}

type RankedConnections struct {
	MatchID  string
	ServerID string
	Protocol string
	players  map[string]rankedConnection
}

func NewRankedConnections(matchID, serverID, protocol string, players []JoinAuthorisation) (*RankedConnections, error) {
	if matchID == "" || serverID == "" || protocol == "" || len(players) != 6 {
		return nil, fmt.Errorf("%w: invalid ranked match", ErrJoinAuthorisation)
	}
	r := &RankedConnections{MatchID: matchID, ServerID: serverID, Protocol: protocol, players: make(map[string]rankedConnection, len(players))}
	for _, auth := range players {
		if err := r.validate(auth, time.Time{}); err != nil || auth.Generation != 1 || auth.ExpiresAt.IsZero() {
			return nil, fmt.Errorf("%w: invalid initial roster", ErrJoinAuthorisation)
		}
		if _, exists := r.players[auth.PlayerID]; exists {
			return nil, fmt.Errorf("%w: duplicate player", ErrJoinAuthorisation)
		}
		for _, existing := range r.players {
			if existing.Slot == auth.Slot {
				return nil, fmt.Errorf("%w: duplicate slot", ErrJoinAuthorisation)
			}
		}
		r.players[auth.PlayerID] = rankedConnection{PlayerID: auth.PlayerID, SteamID: auth.SteamID, Slot: auth.Slot, Team: auth.Team, Generation: 1}
	}
	return r, nil
}

func (r *RankedConnections) validate(auth JoinAuthorisation, now time.Time) error {
	if auth.MatchID != r.MatchID || auth.ServerID != r.ServerID || auth.Protocol != r.Protocol || auth.PlayerID == "" || auth.SteamID == "" || auth.Slot < 0 || auth.Team < 0 || auth.ExpiresAt.IsZero() {
		return ErrJoinAuthorisation
	}
	if !now.IsZero() && !now.Before(auth.ExpiresAt) {
		return ErrJoinAuthorisation
	}
	return nil
}

// Admit accepts the current generation or atomically reclaims a disconnected
// slot with the next server-owned generation. A newer generation fences every
// older connection, even if the backend is temporarily unavailable.
func (r *RankedConnections) Admit(auth JoinAuthorisation, now time.Time) (uint64, error) {
	if err := r.validate(auth, now); err != nil {
		return 0, err
	}
	player, ok := r.players[auth.PlayerID]
	if !ok || player.SteamID != auth.SteamID || player.Slot != auth.Slot || player.Team != auth.Team {
		return 0, ErrJoinAuthorisation
	}
	// Generation in the authorisation identifies the backend-issued assignment
	// (currently 1); player.Generation is the server-owned live connection
	// generation and changes on every reclaim.
	if auth.Generation != 1 {
		return 0, ErrConnectionFenced
	}
	if player.Abandoned {
		return 0, ErrReconnectExpired
	}
	if !player.LostAt.IsZero() {
		if now.Sub(player.LostAt) > RankedReconnectGrace {
			return 0, ErrReconnectExpired
		}
		player.Generation++
	}
	player.ConnectedAt = now
	player.LostAt = time.Time{}
	r.players[auth.PlayerID] = player
	return player.Generation, nil
}

func (r *RankedConnections) Disconnect(playerID string, generation uint64, now time.Time) error {
	player, ok := r.players[playerID]
	if !ok {
		return ErrJoinAuthorisation
	}
	if generation != player.Generation {
		return ErrConnectionFenced
	}
	if player.Abandoned {
		return ErrReconnectExpired
	}
	player.LostAt = now
	r.players[playerID] = player
	return nil
}

type Abandonment struct {
	PlayerID    string
	Cooldown    time.Duration
	AbandonedAt time.Time
}

// ExpireGrace marks every disconnected player whose 60-second reclaim window
// has elapsed. The returned list is lexical for stable audit/event ordering.
func (r *RankedConnections) ExpireGrace(now time.Time, priorAbandons map[string][]time.Time) []Abandonment {
	result := make([]Abandonment, 0)
	for id, player := range r.players {
		if player.Abandoned || player.LostAt.IsZero() || now.Sub(player.LostAt) <= RankedReconnectGrace {
			continue
		}
		player.Abandoned = true
		r.players[id] = player
		result = append(result, Abandonment{PlayerID: id, Cooldown: abandonCooldown(priorAbandons[id], now), AbandonedAt: now})
	}
	sort.Slice(result, func(i, j int) bool { return result[i].PlayerID < result[j].PlayerID })
	return result
}

func abandonCooldown(history []time.Time, now time.Time) time.Duration {
	cutoff := now.Add(-7 * 24 * time.Hour)
	count := 0
	for _, at := range history {
		if !at.Before(cutoff) && !at.After(now) {
			count++
		}
	}
	index := count
	if index >= len(rankedAbandonCooldowns) {
		index = len(rankedAbandonCooldowns) - 1
	}
	return rankedAbandonCooldowns[index]
}