package domain

import (
	"crypto/rand"
	"crypto/sha256"
	"crypto/subtle"
	"encoding/hex"
	"fmt"
	"sync"
	"time"
)

type SteamTicket struct {
	TicketID  string
	SteamID   string
	AppID     uint64
	ExpiresAt time.Time
}

type VerifiedIdentity struct {
	PlayerID string
	SteamID  string
}

type TicketVerifier struct {
	mu          sync.Mutex
	expectedApp uint64
	consumed    map[string]time.Time
}

var (
	ErrTicketRejected  = fmt.Errorf("steam ticket rejected")
	ErrSessionRejected = fmt.Errorf("session rejected")
)

func NewTicketVerifier(expectedApp uint64) (*TicketVerifier, error) {
	if expectedApp == 0 {
		return nil, ErrTicketRejected
	}
	return &TicketVerifier{expectedApp: expectedApp, consumed: make(map[string]time.Time)}, nil
}

// Verify consumes a backend-validated ticket exactly once. In production the
// adapter must obtain the Steam Web API response before calling this policy;
// callers never get to choose the verified SteamID independently.
func (v *TicketVerifier) Verify(ticket SteamTicket, resolve func(string) (string, bool), now time.Time) (VerifiedIdentity, error) {
	v.mu.Lock()
	defer v.mu.Unlock()
	if ticket.TicketID == "" || ticket.SteamID == "" || resolve == nil || ticket.AppID != v.expectedApp || ticket.ExpiresAt.IsZero() || !now.Before(ticket.ExpiresAt) {
		return VerifiedIdentity{}, ErrTicketRejected
	}
	if _, used := v.consumed[ticket.TicketID]; used {
		return VerifiedIdentity{}, ErrTicketRejected
	}
	playerID, ok := resolve(ticket.SteamID)
	if !ok || playerID == "" {
		return VerifiedIdentity{}, ErrTicketRejected
	}
	v.consumed[ticket.TicketID] = now
	return VerifiedIdentity{PlayerID: playerID, SteamID: ticket.SteamID}, nil
}

type Session struct {
	SessionID string
	PlayerID  string
	ExpiresAt time.Time
	RevokedAt time.Time
}

type SessionStore struct {
	mu       sync.Mutex
	sessions map[string]Session
	digests  map[string]string
}

func NewSessionStore() *SessionStore {
	return &SessionStore{sessions: make(map[string]Session), digests: make(map[string]string)}
}

func (s *SessionStore) Issue(playerID string, lifetime time.Duration, now time.Time) (Session, string, error) {
	if playerID == "" || lifetime <= 0 {
		return Session{}, "", ErrSessionRejected
	}
	token, err := randomToken()
	if err != nil {
		return Session{}, "", err
	}
	sessionID, err := randomToken()
	if err != nil {
		return Session{}, "", err
	}
	session := Session{SessionID: sessionID, PlayerID: playerID, ExpiresAt: now.Add(lifetime)}
	s.mu.Lock()
	s.sessions[sessionID] = session
	s.digests[sessionID] = digestToken(token)
	s.mu.Unlock()
	return session, token, nil
}

func (s *SessionStore) Authenticate(sessionID, token string, now time.Time) (Session, error) {
	s.mu.Lock()
	defer s.mu.Unlock()
	session, ok := s.sessions[sessionID]
	if !ok || session.RevokedAt != (time.Time{}) || !now.Before(session.ExpiresAt) || !constantTimeEqual(s.digests[sessionID], digestToken(token)) {
		return Session{}, ErrSessionRejected
	}
	return session, nil
}

func (s *SessionStore) Revoke(sessionID string, now time.Time) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	session, ok := s.sessions[sessionID]
	if !ok {
		return ErrSessionRejected
	}
	if session.RevokedAt.IsZero() {
		session.RevokedAt = now
		s.sessions[sessionID] = session
	}
	return nil
}

func randomToken() (string, error) {
	bytes := make([]byte, 32)
	if _, err := rand.Read(bytes); err != nil {
		return "", err
	}
	return hex.EncodeToString(bytes), nil
}

func digestToken(token string) string {
	digest := sha256.Sum256([]byte(token))
	return hex.EncodeToString(digest[:])
}

func constantTimeEqual(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	return subtle.ConstantTimeCompare([]byte(a), []byte(b)) == 1
}