package sessions

import (
	"sync"
	"time"

	"github.com/VictoriaMetrics/fastcache"
	gonanoid "github.com/matoous/go-nanoid/v2"
	"github.com/valyala/fasthttp"
)

const (
	DefaultMaxSessions = 10000
	DefaultCookieName  = "MoonsharkSID"
	DefaultCookiePath  = "/"
	DefaultMaxAge      = 86400 // 1 day in seconds
	CleanupInterval    = 5 * time.Minute
)

// SessionManager handles multiple sessions
type SessionManager struct {
	cache          *fastcache.Cache
	cookieName     string
	cookiePath     string
	cookieDomain   string
	cookieSecure   bool
	cookieHTTPOnly bool
	cookieMaxAge   int
	cookieMu       sync.RWMutex
	cleanupTicker  *time.Ticker
	cleanupDone    chan struct{}
}

// NewSessionManager creates a new session manager
func NewSessionManager(maxSessions int) *SessionManager {
	if maxSessions <= 0 {
		maxSessions = DefaultMaxSessions
	}

	sm := &SessionManager{
		cache:          fastcache.New(maxSessions * 4096),
		cookieName:     DefaultCookieName,
		cookiePath:     DefaultCookiePath,
		cookieDomain:   "",
		cookieSecure:   false,
		cookieHTTPOnly: true,
		cookieMaxAge:   DefaultMaxAge,
		cleanupDone:    make(chan struct{}),
	}

	// Pre-populate session pool
	for range 100 {
		s := NewSession("", 0)
		s.Release()
	}

	sm.cleanupTicker = time.NewTicker(CleanupInterval)
	go sm.cleanupRoutine()

	return sm
}

// Stop shuts down the session manager's cleanup routine
func (sm *SessionManager) Stop() {
	close(sm.cleanupDone)
}

func (sm *SessionManager) cleanupRoutine() {
	for {
		select {
		case <-sm.cleanupTicker.C:
			sm.CleanupExpired()
		case <-sm.cleanupDone:
			sm.cleanupTicker.Stop()
			return
		}
	}
}

// GetSession retrieves a session by ID, or creates a new one if it doesn't exist
func (sm *SessionManager) GetSession(id string) *Session {
	if id != "" {
		if data := sm.cache.Get(nil, []byte(id)); len(data) > 0 {
			if s, err := Unmarshal(data); err == nil && !s.IsExpired() {
				s.UpdateLastUsed()
				s.ResetDirty()
				return s
			}
			sm.cache.Del([]byte(id))
		}
	}
	return sm.CreateSession()
}

// CreateSession generates a new session with a unique ID
func (sm *SessionManager) CreateSession() *Session {
	id, _ := gonanoid.New()

	// Ensure uniqueness (max 3 attempts)
	for i := 0; i < 3 && sm.cache.Has([]byte(id)); i++ {
		id, _ = gonanoid.New()
	}

	s := NewSession(id, sm.cookieMaxAge)
	if data, err := s.Marshal(); err == nil {
		sm.cache.Set([]byte(id), data)
	}
	s.ResetDirty()
	return s
}

// DestroySession removes a session
func (sm *SessionManager) DestroySession(id string) {
	if data := sm.cache.Get(nil, []byte(id)); len(data) > 0 {
		if s, err := Unmarshal(data); err == nil {
			s.Release()
		}
	}
	sm.cache.Del([]byte(id))
}

// CleanupExpired removes all expired sessions
func (sm *SessionManager) CleanupExpired() int {
	// fastcache doesn't support iteration
	return 0
}

// SetCookieOptions configures cookie parameters
func (sm *SessionManager) SetCookieOptions(name, path, domain string, secure, httpOnly bool, maxAge int) {
	sm.cookieMu.Lock()
	sm.cookieName = name
	sm.cookiePath = path
	sm.cookieDomain = domain
	sm.cookieSecure = secure
	sm.cookieHTTPOnly = httpOnly
	sm.cookieMaxAge = maxAge
	sm.cookieMu.Unlock()
}

// GetSessionFromRequest extracts the session from a request
func (sm *SessionManager) GetSessionFromRequest(ctx *fasthttp.RequestCtx) *Session {
	sm.cookieMu.RLock()
	name := sm.cookieName
	sm.cookieMu.RUnlock()

	if cookie := ctx.Request.Header.Cookie(name); len(cookie) > 0 {
		return sm.GetSession(string(cookie))
	}
	return sm.CreateSession()
}

// ApplySessionCookie adds the session cookie to the response
func (sm *SessionManager) ApplySessionCookie(ctx *fasthttp.RequestCtx, session *Session) {
	if session.IsDirty() {
		if data, err := session.Marshal(); err == nil {
			sm.cache.Set([]byte(session.ID), data)
		}
		session.ResetDirty()
	}

	cookie := fasthttp.AcquireCookie()
	defer fasthttp.ReleaseCookie(cookie)

	sm.cookieMu.RLock()
	cookie.SetKey(sm.cookieName)
	cookie.SetPath(sm.cookiePath)
	cookie.SetHTTPOnly(sm.cookieHTTPOnly)
	cookie.SetMaxAge(sm.cookieMaxAge)
	if sm.cookieDomain != "" {
		cookie.SetDomain(sm.cookieDomain)
	}
	cookie.SetSecure(sm.cookieSecure)
	sm.cookieMu.RUnlock()

	cookie.SetValue(session.ID)
	ctx.Response.Header.SetCookie(cookie)
}

// CookieOptions returns the cookie options for this session manager
func (sm *SessionManager) CookieOptions() map[string]any {
	sm.cookieMu.RLock()
	defer sm.cookieMu.RUnlock()

	return map[string]any{
		"name":      sm.cookieName,
		"path":      sm.cookiePath,
		"domain":    sm.cookieDomain,
		"secure":    sm.cookieSecure,
		"http_only": sm.cookieHTTPOnly,
		"max_age":   sm.cookieMaxAge,
	}
}

// GetCacheStats returns statistics about the session cache
func (sm *SessionManager) GetCacheStats() map[string]uint64 {
	if sm == nil || sm.cache == nil {
		return map[string]uint64{}
	}

	var stats fastcache.Stats
	sm.cache.UpdateStats(&stats)

	return map[string]uint64{
		"entries":   stats.EntriesCount,
		"bytes":     stats.BytesSize,
		"max_bytes": stats.MaxBytesSize,
		"gets":      stats.GetCalls,
		"sets":      stats.SetCalls,
		"misses":    stats.Misses,
	}
}