package sessions

import (
	"fmt"
	"sync"
	"time"

	"github.com/deneonet/benc"
	bstd "github.com/deneonet/benc/std"
)

// Session stores data for a single user session
type Session struct {
	ID        string
	Data      map[string]any
	CreatedAt time.Time
	UpdatedAt time.Time
	LastUsed  time.Time
	Expiry    time.Time
	dirty     bool
}

var (
	sessionPool = sync.Pool{
		New: func() any {
			return &Session{Data: make(map[string]any, 8)}
		},
	}
	bufPool = benc.NewBufPool(benc.WithBufferSize(4096))
)

// NewSession creates a new session with the given ID
func NewSession(id string, maxAge int) *Session {
	s := sessionPool.Get().(*Session)
	now := time.Now()
	*s = Session{
		ID:        id,
		Data:      s.Data, // Reuse map
		CreatedAt: now,
		UpdatedAt: now,
		LastUsed:  now,
		Expiry:    now.Add(time.Duration(maxAge) * time.Second),
	}
	return s
}

// Release returns the session to the pool
func (s *Session) Release() {
	for k := range s.Data {
		delete(s.Data, k)
	}
	sessionPool.Put(s)
}

// Get returns a deep copy of a value
func (s *Session) Get(key string) any {
	if v, ok := s.Data[key]; ok {
		return deepCopy(v)
	}
	return nil
}

// GetTable returns a value as a table
func (s *Session) GetTable(key string) map[string]any {
	if v := s.Get(key); v != nil {
		if t, ok := v.(map[string]any); ok {
			return t
		}
	}
	return nil
}

// GetAll returns a deep 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] = deepCopy(v)
	}
	return copy
}

// Set stores a value in the session
func (s *Session) Set(key string, value any) {
	if existing, ok := s.Data[key]; ok && deepEqual(existing, value) {
		return // No change
	}
	s.Data[key] = value
	s.UpdatedAt = time.Now()
	s.dirty = true
}

// SetSafe stores a value with validation
func (s *Session) SetSafe(key string, value any) error {
	if err := validate(value); err != nil {
		return fmt.Errorf("session.SetSafe: %w", err)
	}
	s.Set(key, value)
	return nil
}

// SetTable is a convenience method for setting table data
func (s *Session) SetTable(key string, table map[string]any) error {
	return s.SetSafe(key, table)
}

// 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
}

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

// UpdateLastUsed updates the last used time
func (s *Session) UpdateLastUsed() {
	now := time.Now()
	if now.Sub(s.LastUsed) > 5*time.Second {
		s.LastUsed = now
	}
}

// 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
}

// SizePlain calculates the size needed to marshal the session
func (s *Session) SizePlain() int {
	return bstd.SizeString(s.ID) +
		bstd.SizeMap(s.Data, bstd.SizeString, sizeAny) +
		bstd.SizeInt64()*4
}

// MarshalPlain serializes the session to binary
func (s *Session) MarshalPlain(n int, b []byte) int {
	n = bstd.MarshalString(n, b, s.ID)
	n = bstd.MarshalMap(n, b, s.Data, bstd.MarshalString, marshalAny)
	n = bstd.MarshalInt64(n, b, s.CreatedAt.Unix())
	n = bstd.MarshalInt64(n, b, s.UpdatedAt.Unix())
	n = bstd.MarshalInt64(n, b, s.LastUsed.Unix())
	return bstd.MarshalInt64(n, b, s.Expiry.Unix())
}

// UnmarshalPlain deserializes the session from binary
func (s *Session) UnmarshalPlain(n int, b []byte) (int, error) {
	var err error
	n, s.ID, err = bstd.UnmarshalString(n, b)
	if err != nil {
		return n, err
	}

	n, s.Data, err = bstd.UnmarshalMap[string, any](n, b, bstd.UnmarshalString, unmarshalAny)
	if err != nil {
		return n, err
	}

	var ts int64
	for _, t := range []*time.Time{&s.CreatedAt, &s.UpdatedAt, &s.LastUsed, &s.Expiry} {
		n, ts, err = bstd.UnmarshalInt64(n, b)
		if err != nil {
			return n, err
		}
		*t = time.Unix(ts, 0)
	}
	return n, nil
}

// Marshal serializes the session using benc
func (s *Session) Marshal() ([]byte, error) {
	return bufPool.Marshal(s.SizePlain(), func(b []byte) int {
		return s.MarshalPlain(0, b)
	})
}

// Unmarshal deserializes a session using benc
func Unmarshal(data []byte) (*Session, error) {
	s := sessionPool.Get().(*Session)
	if _, err := s.UnmarshalPlain(0, data); err != nil {
		s.Release()
		return nil, err
	}
	return s, nil
}

// Type identifiers
const (
	typeNull   byte = 0
	typeString byte = 1
	typeInt    byte = 2
	typeFloat  byte = 3
	typeBool   byte = 4
	typeBytes  byte = 5
	typeTable  byte = 6
	typeArray  byte = 7
)

// sizeAny calculates the size needed for any value
func sizeAny(v any) int {
	if v == nil {
		return 1
	}

	size := 1 // type byte
	switch v := v.(type) {
	case string:
		size += bstd.SizeString(v)
	case int:
		size += bstd.SizeInt64()
	case int64:
		size += bstd.SizeInt64()
	case float64:
		size += bstd.SizeFloat64()
	case bool:
		size += bstd.SizeBool()
	case []byte:
		size += bstd.SizeBytes(v)
	case map[string]any:
		size += bstd.SizeMap(v, bstd.SizeString, sizeAny)
	case []any:
		size += bstd.SizeSlice(v, sizeAny)
	default:
		size += bstd.SizeString("unknown")
	}
	return size
}

// marshalAny serializes any value
func marshalAny(n int, b []byte, v any) int {
	if v == nil {
		b[n] = typeNull
		return n + 1
	}

	switch v := v.(type) {
	case string:
		b[n] = typeString
		return bstd.MarshalString(n+1, b, v)
	case int:
		b[n] = typeInt
		return bstd.MarshalInt64(n+1, b, int64(v))
	case int64:
		b[n] = typeInt
		return bstd.MarshalInt64(n+1, b, v)
	case float64:
		b[n] = typeFloat
		return bstd.MarshalFloat64(n+1, b, v)
	case bool:
		b[n] = typeBool
		return bstd.MarshalBool(n+1, b, v)
	case []byte:
		b[n] = typeBytes
		return bstd.MarshalBytes(n+1, b, v)
	case map[string]any:
		b[n] = typeTable
		return bstd.MarshalMap(n+1, b, v, bstd.MarshalString, marshalAny)
	case []any:
		b[n] = typeArray
		return bstd.MarshalSlice(n+1, b, v, marshalAny)
	default:
		b[n] = typeString
		return bstd.MarshalString(n+1, b, "unknown")
	}
}

// unmarshalAny deserializes any value
func unmarshalAny(n int, b []byte) (int, any, error) {
	if len(b) <= n {
		return n, nil, benc.ErrBufTooSmall
	}

	switch b[n] {
	case typeNull:
		return n + 1, nil, nil
	case typeString:
		return bstd.UnmarshalString(n+1, b)
	case typeInt:
		n, v, err := bstd.UnmarshalInt64(n+1, b)
		return n, v, err
	case typeFloat:
		return bstd.UnmarshalFloat64(n+1, b)
	case typeBool:
		return bstd.UnmarshalBool(n+1, b)
	case typeBytes:
		return bstd.UnmarshalBytesCopied(n+1, b)
	case typeTable:
		return bstd.UnmarshalMap[string, any](n+1, b, bstd.UnmarshalString, unmarshalAny)
	case typeArray:
		return bstd.UnmarshalSlice[any](n+1, b, unmarshalAny)
	default:
		return n + 1, nil, nil
	}
}

// deepCopy creates a deep copy of any value
func deepCopy(v any) any {
	switch v := v.(type) {
	case map[string]any:
		cp := make(map[string]any, len(v))
		for k, val := range v {
			cp[k] = deepCopy(val)
		}
		return cp
	case []any:
		cp := make([]any, len(v))
		for i, val := range v {
			cp[i] = deepCopy(val)
		}
		return cp
	default:
		return v
	}
}

// validate ensures a value can be safely serialized
func validate(v any) error {
	switch v := v.(type) {
	case nil, string, int, int64, float64, bool, []byte:
		return nil
	case map[string]any:
		for k, val := range v {
			if err := validate(val); err != nil {
				return fmt.Errorf("invalid value for key %q: %w", k, err)
			}
		}
	case []any:
		for i, val := range v {
			if err := validate(val); err != nil {
				return fmt.Errorf("invalid value at index %d: %w", i, err)
			}
		}
	default:
		return fmt.Errorf("unsupported type: %T", v)
	}
	return nil
}

// deepEqual efficiently compares two values for deep equality
func deepEqual(a, b any) bool {
	if a == b {
		return true
	}

	if a == nil || b == nil {
		return false
	}

	switch va := a.(type) {
	case string:
		if vb, ok := b.(string); ok {
			return va == vb
		}
	case int:
		if vb, ok := b.(int); ok {
			return va == vb
		}
		if vb, ok := b.(int64); ok {
			return int64(va) == vb
		}
	case int64:
		if vb, ok := b.(int64); ok {
			return va == vb
		}
		if vb, ok := b.(int); ok {
			return va == int64(vb)
		}
	case float64:
		if vb, ok := b.(float64); ok {
			return va == vb
		}
	case bool:
		if vb, ok := b.(bool); ok {
			return va == vb
		}
	case []byte:
		if vb, ok := b.([]byte); ok {
			if len(va) != len(vb) {
				return false
			}
			for i, v := range va {
				if v != vb[i] {
					return false
				}
			}
			return true
		}
	case map[string]any:
		if vb, ok := b.(map[string]any); ok {
			if len(va) != len(vb) {
				return false
			}
			for k, v := range va {
				if bv, exists := vb[k]; !exists || !deepEqual(v, bv) {
					return false
				}
			}
			return true
		}
	case []any:
		if vb, ok := b.([]any); ok {
			if len(va) != len(vb) {
				return false
			}
			for i, v := range va {
				if !deepEqual(v, vb[i]) {
					return false
				}
			}
			return true
		}
	}

	return false
}

// IsEmpty returns true if the session has no data
func (s *Session) IsEmpty() bool {
	return len(s.Data) == 0
}