package service

import (
	"context"
	"sort"
	"strings"
	"time"

	"filefast/backend/internal/model"
	"filefast/backend/internal/store"

	"github.com/google/uuid"
)

type DeviceService struct {
	store         *store.MemoryStore
	presenceStore devicePresenceStore
	sessionStore  deviceSessionStore
	presenceTTL   time.Duration
	sessionTTL    time.Duration
}

type devicePresenceStore interface {
	SetDevicePresence(context.Context, string, bool, time.Time, time.Duration) error
	GetDevicePresence(context.Context, []string) (map[string]bool, error)
}

type deviceSessionStore interface {
	SaveDeviceSession(context.Context, model.DeviceSession, time.Duration) error
	ValidateDeviceSession(context.Context, string, string) (bool, error)
}

type RegisterDeviceInput struct {
	DeviceID        string `json:"device_id"`
	Name            string `json:"name" binding:"required"`
	Type            string `json:"type" binding:"required"`
	NetworkGroupKey string `json:"network_group_key"`
	PublicIPHash    string `json:"public_ip_hash"`
}

func NewDeviceService(store *store.MemoryStore, presenceStore devicePresenceStore, sessionStore deviceSessionStore) *DeviceService {
	return &DeviceService{
		store:         store,
		presenceStore: presenceStore,
		sessionStore:  sessionStore,
		presenceTTL:   45 * time.Second,
		sessionTTL:    30 * 24 * time.Hour,
	}
}

func (s *DeviceService) Register(input RegisterDeviceInput, userAgent, claimedToken string) (model.Device, model.DeviceSession) {
	now := time.Now()
	id := strings.TrimSpace(input.DeviceID)
	if id == "" {
		id = uuid.NewString()
	}

	device, exists := s.store.GetDevice(id)
	if exists && !s.ValidateSession(id, strings.TrimSpace(claimedToken)) {
		id = uuid.NewString()
		exists = false
	}
	if !exists {
		device = model.Device{
			ID:        id,
			CreatedAt: now,
		}
	}

	device.Name = input.Name
	device.Type = input.Type
	device.UserAgent = userAgent
	device.NetworkGroupKey = input.NetworkGroupKey
	device.PublicIPHash = input.PublicIPHash
	device.LastSeenAt = now
	device.IsOnline = true

	device = s.store.UpsertDevice(device)
	session := s.issueSession(device.ID)
	s.syncPresence(device)
	return device, session
}

func (s *DeviceService) Heartbeat(deviceID string) (model.Device, bool) {
	device, ok := s.store.GetDevice(deviceID)
	if !ok {
		return model.Device{}, false
	}

	device.LastSeenAt = time.Now()
	device.IsOnline = true
	device = s.store.UpsertDevice(device)
	s.syncPresence(device)
	return device, true
}

func (s *DeviceService) SetOnline(deviceID string, online bool) (model.Device, bool) {
	device, ok := s.store.GetDevice(deviceID)
	if !ok {
		return model.Device{}, false
	}

	device.IsOnline = online
	device.LastSeenAt = time.Now()
	device = s.store.UpsertDevice(device)
	s.syncPresence(device)
	return device, true
}

func (s *DeviceService) ListCandidates(currentDeviceID string) []model.Device {
	current, _ := s.store.GetDevice(currentDeviceID)
	currentNetworkGroupKey := strings.TrimSpace(current.NetworkGroupKey)
	if currentNetworkGroupKey == "" {
		return []model.Device{}
	}

	devices := s.store.ListDevices()
	s.applyPresence(devices)
	candidates := make([]model.Device, 0, len(devices))

	for _, device := range devices {
		if device.ID == currentDeviceID || !device.IsOnline {
			continue
		}
		if strings.TrimSpace(device.NetworkGroupKey) != currentNetworkGroupKey {
			continue
		}
		candidates = append(candidates, device)
	}

	sort.SliceStable(candidates, func(i, j int) bool {
		return candidates[i].LastSeenAt.After(candidates[j].LastSeenAt)
	})

	return candidates
}

func (s *DeviceService) ValidateSession(deviceID, token string) bool {
	deviceID = strings.TrimSpace(deviceID)
	token = strings.TrimSpace(token)
	if deviceID == "" || token == "" {
		return false
	}

	if s.store.ValidateDeviceSession(deviceID, token) {
		return true
	}

	if s.sessionStore == nil {
		return false
	}

	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	ok, err := s.sessionStore.ValidateDeviceSession(ctx, deviceID, token)
	return err == nil && ok
}

func (s *DeviceService) issueSession(deviceID string) model.DeviceSession {
	session := model.DeviceSession{
		DeviceID:  deviceID,
		Token:     uuid.NewString(),
		CreatedAt: time.Now(),
		ExpiresAt: time.Now().Add(s.sessionTTL),
	}
	session = s.store.SaveDeviceSession(session)

	if s.sessionStore != nil {
		ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
		defer cancel()
		_ = s.sessionStore.SaveDeviceSession(ctx, session, s.sessionTTL)
	}

	return session
}

func (s *DeviceService) syncPresence(device model.Device) {
	if s.presenceStore == nil {
		return
	}

	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()
	_ = s.presenceStore.SetDevicePresence(ctx, device.ID, device.IsOnline, device.LastSeenAt, s.presenceTTL)
}

func (s *DeviceService) applyPresence(devices []model.Device) {
	if s.presenceStore == nil || len(devices) == 0 {
		return
	}

	deviceIDs := make([]string, 0, len(devices))
	for _, device := range devices {
		if device.ID != "" {
			deviceIDs = append(deviceIDs, device.ID)
		}
	}

	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	statuses, err := s.presenceStore.GetDevicePresence(ctx, deviceIDs)
	if err != nil {
		return
	}

	for index := range devices {
		if online, ok := statuses[devices[index].ID]; ok {
			devices[index].IsOnline = online
		}
	}
}