package store

import (
	"context"
	"sort"
	"sync"
	"time"

	"filefast/backend/internal/model"
)

type Persistence interface {
	PersistDevice(context.Context, model.Device) error
	PersistRoom(context.Context, model.Room) error
	PersistTransfer(context.Context, model.Transfer) error
	PersistFallbackObject(context.Context, model.FallbackObject) error
	PersistRuntimeConfig(context.Context, model.RuntimeConfig) error
}

type Snapshot struct {
	Devices         []model.Device
	Rooms           []model.Room
	Transfers       []model.Transfer
	FallbackObjects []model.FallbackObject
	Runtime         *model.RuntimeConfig
}

type MemoryStore struct {
	mu              sync.RWMutex
	devices         map[string]model.Device
	rooms           map[string]model.Room
	transfers       map[string]model.Transfer
	fallbackObjects map[string]model.FallbackObject
	adminSessions   map[string]model.AdminSession
	deviceSessions  map[string]model.DeviceSession
	runtime         model.RuntimeConfig
	persistence     Persistence
	persistTimeout  time.Duration
	onPersistError  func(kind, id string, err error)
}

const (
	activeDeviceWindow         = 2 * time.Minute
	activeTransferWindow       = 30 * time.Minute
	recentTerminalTransferWind = 24 * time.Hour
)

func NewMemoryStore(runtime model.RuntimeConfig) *MemoryStore {
	return &MemoryStore{
		devices:         make(map[string]model.Device),
		rooms:           make(map[string]model.Room),
		transfers:       make(map[string]model.Transfer),
		fallbackObjects: make(map[string]model.FallbackObject),
		adminSessions:   make(map[string]model.AdminSession),
		deviceSessions:  make(map[string]model.DeviceSession),
		runtime:         runtime,
	}
}

func (s *MemoryStore) UpsertDevice(device model.Device) model.Device {
	s.mu.Lock()
	s.devices[device.ID] = device
	s.mu.Unlock()
	s.persistDevice(device)
	return device
}

func (s *MemoryStore) GetDevice(id string) (model.Device, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	device, ok := s.devices[id]
	return device, ok
}

func (s *MemoryStore) ListDevices() []model.Device {
	s.mu.RLock()
	defer s.mu.RUnlock()

	devices := make([]model.Device, 0, len(s.devices))
	for _, device := range s.devices {
		devices = append(devices, device)
	}

	return devices
}

func (s *MemoryStore) UpsertRoom(room model.Room) model.Room {
	s.mu.Lock()
	s.rooms[room.Code] = room
	s.mu.Unlock()
	s.persistRoom(room)
	return room
}

func (s *MemoryStore) GetRoom(code string) (model.Room, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	room, ok := s.rooms[code]
	return room, ok
}

func (s *MemoryStore) UpsertTransfer(transfer model.Transfer) model.Transfer {
	s.mu.Lock()
	s.transfers[transfer.ID] = transfer
	s.mu.Unlock()
	s.persistTransfer(transfer)
	return transfer
}

func (s *MemoryStore) GetTransfer(id string) (model.Transfer, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	transfer, ok := s.transfers[id]
	return transfer, ok
}

func (s *MemoryStore) ListRecentTransfers(limit int) []model.Transfer {
	s.mu.RLock()
	defer s.mu.RUnlock()

	now := time.Now()
	transfers := make([]model.Transfer, 0, len(s.transfers))
	for _, transfer := range s.transfers {
		if !isTransferVisible(transfer, now) {
			continue
		}
		transfers = append(transfers, transfer)
	}

	sort.Slice(transfers, func(i, j int) bool {
		return transfers[i].UpdatedAt.After(transfers[j].UpdatedAt)
	})

	if limit > 0 && len(transfers) > limit {
		return transfers[:limit]
	}

	return transfers
}

func (s *MemoryStore) ListPendingFallbackDownloads(receiverDeviceID string, limit int) []model.PendingFallbackDownload {
	s.mu.RLock()
	defer s.mu.RUnlock()

	if receiverDeviceID == "" {
		return nil
	}

	now := time.Now()
	downloads := make([]model.PendingFallbackDownload, 0, len(s.transfers))

	for _, transfer := range s.transfers {
		if transfer.ReceiverDeviceID != receiverDeviceID || transfer.ObjectKey == "" || transfer.FinalStatus != model.TransferCompleted {
			continue
		}
		if transfer.ExpiresAt == nil || !transfer.ExpiresAt.After(now) {
			continue
		}

		object, ok := s.fallbackObjects[transfer.ID]
		if !ok || object.CleanedAt != nil || object.ExpiresAt.Before(now) || object.CleanupState != "ready" {
			continue
		}

		downloads = append(downloads, model.PendingFallbackDownload{
			TransferID:     transfer.ID,
			Name:           transfer.Name,
			SizeBytes:      transfer.SizeBytes,
			CreatedAt:      transfer.CreatedAt,
			ExpiresAt:      object.ExpiresAt,
			DownloadPath:   "/api/transfers/" + transfer.ID + "/fallback/download",
			SenderDeviceID: transfer.SenderDeviceID,
		})
	}

	sort.Slice(downloads, func(i, j int) bool {
		return downloads[i].CreatedAt.After(downloads[j].CreatedAt)
	})

	if limit > 0 && len(downloads) > limit {
		return downloads[:limit]
	}

	return downloads
}

func (s *MemoryStore) SaveFallbackObject(object model.FallbackObject) model.FallbackObject {
	s.mu.Lock()
	s.fallbackObjects[object.TransferID] = object
	s.mu.Unlock()
	s.persistFallbackObject(object)
	return object
}

func (s *MemoryStore) GetFallbackObject(transferID string) (model.FallbackObject, bool) {
	s.mu.RLock()
	defer s.mu.RUnlock()
	object, ok := s.fallbackObjects[transferID]
	return object, ok
}

func (s *MemoryStore) ListExpiredFallbackObjects(now time.Time) []model.FallbackObject {
	s.mu.RLock()
	defer s.mu.RUnlock()

	var objects []model.FallbackObject
	for _, object := range s.fallbackObjects {
		if object.CleanedAt == nil && !object.ExpiresAt.After(now) {
			objects = append(objects, object)
		}
	}

	return objects
}

func (s *MemoryStore) SaveAdminSession(session model.AdminSession) model.AdminSession {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.adminSessions[session.Token] = session
	return session
}

func (s *MemoryStore) SaveDeviceSession(session model.DeviceSession) model.DeviceSession {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.deviceSessions[session.DeviceID] = session
	return session
}

func (s *MemoryStore) HasAdminSession(token string) bool {
	s.mu.RLock()
	defer s.mu.RUnlock()
	_, ok := s.adminSessions[token]
	return ok
}

func (s *MemoryStore) ValidateDeviceSession(deviceID, token string) bool {
	s.mu.RLock()
	session, ok := s.deviceSessions[deviceID]
	s.mu.RUnlock()
	if !ok {
		return false
	}
	if session.ExpiresAt.Before(time.Now()) {
		s.mu.Lock()
		delete(s.deviceSessions, deviceID)
		s.mu.Unlock()
		return false
	}
	return session.Token == token
}

func (s *MemoryStore) RuntimeConfig() model.RuntimeConfig {
	s.mu.RLock()
	defer s.mu.RUnlock()
	return s.runtime
}

func (s *MemoryStore) UpdateRuntimeConfig(runtime model.RuntimeConfig) model.RuntimeConfig {
	s.mu.Lock()
	s.runtime = runtime
	s.mu.Unlock()
	s.persistRuntimeConfig(runtime)
	return runtime
}

func (s *MemoryStore) SnapshotStats() map[string]int {
	s.mu.RLock()
	defer s.mu.RUnlock()

	now := time.Now()
	onlineDevices := 0
	activeDevices := 0
	for _, device := range s.devices {
		if isDeviceActive(device, now) {
			activeDevices++
		}
		if device.IsOnline && isDeviceActive(device, now) {
			onlineDevices++
		}
	}

	waitingRooms := 0
	for _, room := range s.rooms {
		if room.Status == model.RoomStatusWaiting && room.ExpiresAt.After(now) {
			waitingRooms++
		}
	}

	fallbackPending := 0
	for _, object := range s.fallbackObjects {
		if object.CleanedAt == nil && object.CleanupState == "ready" {
			fallbackPending++
		}
	}

	validTransfers := 0
	for _, transfer := range s.transfers {
		if isTransferVisible(transfer, now) {
			validTransfers++
		}
	}

	return map[string]int{
		"devices_total":    activeDevices,
		"devices_online":   onlineDevices,
		"rooms_waiting":    waitingRooms,
		"transfers_total":  validTransfers,
		"transfers_cumulative": len(s.transfers),
		"fallback_pending": fallbackPending,
		"admin_sessions":   len(s.adminSessions),
	}
}

func (s *MemoryStore) SnapshotMinIOStorage() model.MinIOStorageOverview {
	s.mu.RLock()
	defer s.mu.RUnlock()

	now := time.Now()
	usedBytes := int64(0)
	objectCount := 0

	for _, object := range s.fallbackObjects {
		if object.CleanedAt != nil || !object.ExpiresAt.After(now) || object.CleanupState != "ready" {
			continue
		}

		usedBytes += object.SizeBytes
		objectCount++
	}

	capacityBytes := s.runtime.MinIOCapacityBytes
	if capacityBytes < 0 {
		capacityBytes = 0
	}

	remainingBytes := capacityBytes - usedBytes
	if remainingBytes < 0 {
		remainingBytes = 0
	}

	usagePercent := 0
	if capacityBytes > 0 {
		usagePercent = int((usedBytes * 100) / capacityBytes)
		if usagePercent > 100 {
			usagePercent = 100
		}
	}

	return model.MinIOStorageOverview{
		Enabled:        s.runtime.MinIOFallbackEnabled,
		UsedBytes:      usedBytes,
		CapacityBytes:  capacityBytes,
		RemainingBytes: remainingBytes,
		UsagePercent:   usagePercent,
		ObjectCount:    objectCount,
	}
}

func isDeviceActive(device model.Device, now time.Time) bool {
	if device.LastSeenAt.IsZero() {
		return false
	}

	return device.LastSeenAt.After(now.Add(-activeDeviceWindow))
}

func isTransferVisible(transfer model.Transfer, now time.Time) bool {
	if transfer.UpdatedAt.IsZero() {
		transfer.UpdatedAt = transfer.CreatedAt
	}

	if isTerminalTransferStatus(transfer.FinalStatus) {
		return transfer.UpdatedAt.After(now.Add(-recentTerminalTransferWind))
	}

	return transfer.UpdatedAt.After(now.Add(-activeTransferWindow))
}

func isTerminalTransferStatus(status string) bool {
	switch status {
	case model.TransferCompleted, model.TransferFailed, model.TransferCancelled:
		return true
	default:
		return false
	}
}

func (s *MemoryStore) SetPersistence(persistence Persistence, timeout time.Duration, onError func(kind, id string, err error)) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.persistence = persistence
	s.persistTimeout = timeout
	s.onPersistError = onError
}

func (s *MemoryStore) LoadSnapshot(snapshot Snapshot) {
	s.mu.Lock()
	defer s.mu.Unlock()

	s.devices = make(map[string]model.Device, len(snapshot.Devices))
	for _, device := range snapshot.Devices {
		s.devices[device.ID] = device
	}

	s.rooms = make(map[string]model.Room, len(snapshot.Rooms))
	for _, room := range snapshot.Rooms {
		s.rooms[room.Code] = room
	}

	s.transfers = make(map[string]model.Transfer, len(snapshot.Transfers))
	for _, transfer := range snapshot.Transfers {
		s.transfers[transfer.ID] = transfer
	}

	s.fallbackObjects = make(map[string]model.FallbackObject, len(snapshot.FallbackObjects))
	for _, object := range snapshot.FallbackObjects {
		s.fallbackObjects[object.TransferID] = object
	}

	if snapshot.Runtime != nil {
		s.runtime = *snapshot.Runtime
	}
}

func (s *MemoryStore) persistDevice(device model.Device) {
	s.persist(device.ID, "device", func(ctx context.Context, persistence Persistence) error {
		return persistence.PersistDevice(ctx, device)
	})
}

func (s *MemoryStore) persistRoom(room model.Room) {
	s.persist(room.Code, "room", func(ctx context.Context, persistence Persistence) error {
		return persistence.PersistRoom(ctx, room)
	})
}

func (s *MemoryStore) persistTransfer(transfer model.Transfer) {
	s.persist(transfer.ID, "transfer", func(ctx context.Context, persistence Persistence) error {
		return persistence.PersistTransfer(ctx, transfer)
	})
}

func (s *MemoryStore) persistFallbackObject(object model.FallbackObject) {
	s.persist(object.TransferID, "fallback_object", func(ctx context.Context, persistence Persistence) error {
		return persistence.PersistFallbackObject(ctx, object)
	})
}

func (s *MemoryStore) persistRuntimeConfig(runtime model.RuntimeConfig) {
	s.persist("transfer_policy", "runtime_config", func(ctx context.Context, persistence Persistence) error {
		return persistence.PersistRuntimeConfig(ctx, runtime)
	})
}

func (s *MemoryStore) persist(id, kind string, fn func(context.Context, Persistence) error) {
	s.mu.RLock()
	persistence := s.persistence
	timeout := s.persistTimeout
	onError := s.onPersistError
	s.mu.RUnlock()

	if persistence == nil {
		return
	}

	if timeout <= 0 {
		timeout = 5 * time.Second
	}

	ctx, cancel := context.WithTimeout(context.Background(), timeout)
	defer cancel()

	if err := fn(ctx, persistence); err != nil && onError != nil {
		onError(kind, id, err)
	}
}