package auth

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"maps"
	"os"
	"sync"
	"time"
)

const (
	SessionCookieName = "dk_session"
	DefaultExpiration = 24 * time.Hour
	SessionIDLength   = 32
)

type Session struct {
	ID        string    `json:"id"`
	UserID    int       `json:"user_id"`
	Username  string    `json:"username"`
	Email     string    `json:"email"`
	CreatedAt time.Time `json:"created_at"`
	ExpiresAt time.Time `json:"expires_at"`
	LastSeen  time.Time `json:"last_seen"`
}

type SessionStore struct {
	mu           sync.RWMutex
	sessions     map[string]*Session
	filePath     string
	saveInterval time.Duration
	stopChan     chan struct{}
}

type persistedData struct {
	Sessions map[string]*Session `json:"sessions"`
	SavedAt  time.Time           `json:"saved_at"`
}

func NewSessionStore(filePath string) *SessionStore {
	store := &SessionStore{
		sessions:     make(map[string]*Session),
		filePath:     filePath,
		saveInterval: 5 * time.Minute,
		stopChan:     make(chan struct{}),
	}

	store.loadFromFile()
	store.startPeriodicSave()

	return store
}

func (s *SessionStore) generateSessionID() string {
	bytes := make([]byte, SessionIDLength)
	rand.Read(bytes)
	return hex.EncodeToString(bytes)
}

func (s *SessionStore) Create(userID int, username, email string) *Session {
	s.mu.Lock()
	defer s.mu.Unlock()

	session := &Session{
		ID:        s.generateSessionID(),
		UserID:    userID,
		Username:  username,
		Email:     email,
		CreatedAt: time.Now(),
		ExpiresAt: time.Now().Add(DefaultExpiration),
		LastSeen:  time.Now(),
	}

	s.sessions[session.ID] = session
	return session
}

func (s *SessionStore) Get(sessionID string) (*Session, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	session, exists := s.sessions[sessionID]
	if !exists {
		return nil, false
	}

	if time.Now().After(session.ExpiresAt) {
		delete(s.sessions, sessionID)
		return nil, false
	}

	return session, true
}

func (s *SessionStore) Update(sessionID string) bool {
	s.mu.Lock()
	defer s.mu.Unlock()

	session, exists := s.sessions[sessionID]
	if !exists {
		return false
	}

	if time.Now().After(session.ExpiresAt) {
		delete(s.sessions, sessionID)
		return false
	}

	session.LastSeen = time.Now()
	session.ExpiresAt = time.Now().Add(DefaultExpiration)
	return true
}

func (s *SessionStore) Delete(sessionID string) {
	s.mu.Lock()
	defer s.mu.Unlock()

	delete(s.sessions, sessionID)
}

func (s *SessionStore) Cleanup() {
	s.mu.Lock()
	defer s.mu.Unlock()

	now := time.Now()
	for id, session := range s.sessions {
		if now.After(session.ExpiresAt) {
			delete(s.sessions, id)
		}
	}
}

func (s *SessionStore) loadFromFile() {
	if s.filePath == "" {
		return
	}

	data, err := os.ReadFile(s.filePath)
	if err != nil {
		return // File might not exist yet
	}

	var persisted persistedData
	if err := json.Unmarshal(data, &persisted); err != nil {
		return
	}

	s.mu.Lock()
	defer s.mu.Unlock()

	now := time.Now()
	for id, session := range persisted.Sessions {
		if now.Before(session.ExpiresAt) {
			s.sessions[id] = session
		}
	}
}

func (s *SessionStore) saveToFile() error {
	if s.filePath == "" {
		return nil
	}

	s.mu.RLock()
	sessionsCopy := make(map[string]*Session)
	maps.Copy(sessionsCopy, s.sessions)
	s.mu.RUnlock()

	data := persistedData{
		Sessions: sessionsCopy,
		SavedAt:  time.Now(),
	}

	jsonData, err := json.MarshalIndent(data, "", "  ")
	if err != nil {
		return err
	}

	return os.WriteFile(s.filePath, jsonData, 0600)
}

func (s *SessionStore) startPeriodicSave() {
	go func() {
		ticker := time.NewTicker(s.saveInterval)
		defer ticker.Stop()

		for {
			select {
			case <-ticker.C:
				s.Cleanup()
				s.saveToFile()
			case <-s.stopChan:
				s.saveToFile()
				return
			}
		}
	}()
}

func (s *SessionStore) Close() error {
	close(s.stopChan)
	return s.saveToFile()
}

func (s *SessionStore) Stats() (total, active int) {
	s.mu.RLock()
	defer s.mu.RUnlock()

	now := time.Now()
	total = len(s.sessions)

	for _, session := range s.sessions {
		if now.Before(session.ExpiresAt) {
			active++
		}
	}

	return
}