package sessions

import (
	"sync"
	"time"

	"github.com/goccy/go-json"
)

// Session stores data for a single user session
type Session struct {
	ID        string         `json:"id"`
	Data      map[string]any `json:"data"`
	CreatedAt time.Time      `json:"created_at"`
	UpdatedAt time.Time      `json:"updated_at"`
	LastUsed  time.Time      `json:"last_used"`
	Expiry    time.Time      `json:"expiry"`
	dirty     bool           // Tracks if session has changes, not serialized
}

// Session pool to reduce allocations
var sessionPool = sync.Pool{
	New: func() any {
		return &Session{
			Data: make(map[string]any, 8),
		}
	},
}

// GetFromPool retrieves a session from the pool
func GetFromPool() *Session {
	return sessionPool.Get().(*Session)
}

// ReturnToPool returns a session to the pool after cleaning it
func ReturnToPool(s *Session) {
	if s == nil {
		return
	}

	// Clean the session for reuse
	s.ID = ""
	for k := range s.Data {
		delete(s.Data, k)
	}
	s.CreatedAt = time.Time{}
	s.UpdatedAt = time.Time{}
	s.LastUsed = time.Time{}
	s.Expiry = time.Time{}
	s.dirty = false

	sessionPool.Put(s)
}

// NewSession creates a new session with the given ID
func NewSession(id string, maxAge int) *Session {
	now := time.Now()

	// Get from pool or create new
	session := GetFromPool()

	// Initialize
	session.ID = id
	session.CreatedAt = now
	session.UpdatedAt = now
	session.LastUsed = now
	session.Expiry = now.Add(time.Duration(maxAge) * time.Second)
	session.dirty = false

	return session
}

// Get retrieves a value from the session
func (s *Session) Get(key string) any {
	return s.Data[key]
}

// Set stores a value in the session
func (s *Session) Set(key string, value any) {
	s.Data[key] = value
	s.UpdatedAt = time.Now()
	s.dirty = true
}

// Delete removes a value from the session
func (s *Session) Delete(key string) {
	delete(s.Data, key)
	s.UpdatedAt = time.Now()
	s.dirty = true
}

// Clear removes all data from the session
func (s *Session) Clear() {
	s.Data = make(map[string]any, 8)
	s.UpdatedAt = time.Now()
	s.dirty = true
}

// GetAll returns a copy of all session data
func (s *Session) GetAll() map[string]any {
	copy := make(map[string]any, len(s.Data))
	for k, v := range s.Data {
		copy[k] = v
	}
	return copy
}

// IsExpired checks if the session has expired
func (s *Session) IsExpired() bool {
	return time.Now().After(s.Expiry)
}

// UpdateLastUsed updates the last used time
// Only updates if at least 5 seconds have passed since last update
func (s *Session) UpdateLastUsed() {
	now := time.Now()
	if now.Sub(s.LastUsed) > 5*time.Second {
		s.LastUsed = now
		// Not marking dirty for LastUsed updates to reduce writes
	}
}

// IsDirty returns if the session has unsaved changes
func (s *Session) IsDirty() bool {
	return s.dirty
}

// ResetDirty marks the session as clean after saving
func (s *Session) ResetDirty() {
	s.dirty = false
}

// Marshal serializes the session to JSON
func (s *Session) Marshal() ([]byte, error) {
	return json.Marshal(s)
}

// Unmarshal deserializes a session from JSON
func Unmarshal(data []byte) (*Session, error) {
	session := GetFromPool()
	err := json.Unmarshal(data, session)
	if err != nil {
		ReturnToPool(session)
		return nil, err
	}
	return session, nil
}