// Package devicehistory persists the set of devices that have ever logged in
// to the Go server, so the web UI can keep listing them after they go offline.
//
// It implements hub.EventHandler and is subscribed to the hub, which means the
// only wiring needed at startup is hub.Subscribe(store). Online events upsert
// the record (refreshing the display fields the client reports at login) and
// offline events merely refresh last_seen.
//
// Storage is a small JSON file, mirroring the wsauth users.json convention:
// atomic temp-file + fsync + rename, loaded once at startup and written back
// on a short debounce so a burst of reconnects doesn't rewrite it per device.
package devicehistory

import (
	"encoding/json"
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"sort"
	"sync"
	"time"

	"github.com/yuanyuanxiang/SimpleRemoter/server/go/hub"
	"github.com/yuanyuanxiang/SimpleRemoter/server/go/logger"
)

const (
	// fileVersion lets a future release migrate the on-disk shape. Unknown
	// versions are still parsed best-effort; only structurally invalid JSON
	// makes Open fail.
	fileVersion = 1

	// flushDelay coalesces updates. Device logins/disconnects are sparse, but
	// a server restart makes every agent reconnect at once; without the
	// debounce that would be one file write per device.
	flushDelay = 500 * time.Millisecond
)

// Record is one persisted device. The fields mirror hub.DeviceInfo so the
// offline list can be rendered with the same front-end card code; only the
// fields that are stable across sessions are kept (RTT / active window are
// live-only and would be stale noise on an offline card).
type Record struct {
	ID          string `json:"id"`
	Name        string `json:"name"`
	Group       string `json:"group,omitempty"`
	Version     string `json:"version,omitempty"`
	Capability  string `json:"capability,omitempty"`
	OS          string `json:"os,omitempty"`
	CPU         string `json:"cpu,omitempty"`
	FilePath    string `json:"file_path,omitempty"`
	InstallTime string `json:"install_time,omitempty"`
	Location    string `json:"location,omitempty"`
	PeerIP      string `json:"peer_ip,omitempty"`
	IP          string `json:"ip,omitempty"`
	Screen      string `json:"screen,omitempty"`

	FirstSeen int64 `json:"first_seen"`
	LastSeen  int64 `json:"last_seen"`
}

type fileShape struct {
	Version int                `json:"version"`
	Devices map[string]*Record `json:"devices"`
}

// Store is the in-memory device history plus its backing file. Safe for
// concurrent use.
type Store struct {
	path string
	max  int // 0 = unlimited
	log  *logger.Logger

	mu      sync.Mutex
	devices map[string]*Record
	// online is derived from hub events and used only by pruning: a device
	// that is still connected must keep its record even if its last login is
	// older than the 1000th offline device's. Not persisted — after a restart
	// every device is offline until it reconnects.
	online map[string]bool
	dirty  bool
	timer  *time.Timer
}

// Open loads the history at path. A missing file is an empty history, not an
// error. If the file exists but cannot be parsed, the returned store is still
// usable (empty) along with the error, so callers can log and continue — the
// next flush will replace the corrupt file.
func Open(path string, max int, log *logger.Logger) (*Store, error) {
	s := newStore(path, max, log)

	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return s, nil
		}
		return s, err
	}
	var f fileShape
	if err := json.Unmarshal(data, &f); err != nil {
		return s, fmt.Errorf("parse %s: %w", path, err)
	}
	for id, r := range f.Devices {
		if r == nil {
			continue
		}
		// The map key is authoritative; tolerate records written by a
		// future/older shape that omitted or disagreed with the id field.
		r.ID = id
		s.devices[id] = r
	}
	s.pruneLocked()
	return s, nil
}

// New returns an empty store for path without touching disk. Useful when Open
// failed and the caller still wants live recording to work.
func New(path string, max int, log *logger.Logger) *Store {
	return newStore(path, max, log)
}

func newStore(path string, max int, log *logger.Logger) *Store {
	return &Store{
		path:    path,
		max:     max,
		log:     log,
		devices: make(map[string]*Record),
		online:  make(map[string]bool),
	}
}

// OnDeviceOnline records a device that just logged in. It refreshes every
// display field because the agent reports its current name/group/version at
// each login, and preserves first_seen across reconnects.
func (s *Store) OnDeviceOnline(d hub.DeviceInfo) {
	s.upsertAt(d, time.Now())
}

func (s *Store) upsertAt(d hub.DeviceInfo, at time.Time) {
	if d.ID == "" {
		return
	}
	now := at.Unix()

	s.mu.Lock()
	rec, ok := s.devices[d.ID]
	if !ok {
		rec = &Record{ID: d.ID, FirstSeen: now}
		s.devices[d.ID] = rec
	}
	if rec.FirstSeen == 0 {
		rec.FirstSeen = now
	}
	rec.Name = d.Name
	rec.Group = d.Group
	rec.Version = d.Version
	rec.Capability = d.Capability
	rec.OS = d.OS
	rec.CPU = d.CPU
	rec.FilePath = d.FilePath
	rec.InstallTime = d.InstallTime
	rec.Location = d.Location
	rec.PeerIP = d.PeerIP
	rec.IP = d.IP
	rec.Screen = d.Screen
	rec.LastSeen = now
	s.online[d.ID] = true

	s.pruneLocked()
	s.markDirtyLocked()
	s.mu.Unlock()
}

// OnDeviceOffline refreshes last_seen. The record was created when the device
// logged in; an unknown ID is ignored (e.g. a device rejected by signing never
// reaches the hub).
func (s *Store) OnDeviceOffline(id string) {
	if id == "" {
		return
	}
	s.offlineAt(id, time.Now())
}

func (s *Store) offlineAt(id string, at time.Time) {
	s.mu.Lock()
	delete(s.online, id)
	if rec, ok := s.devices[id]; ok {
		rec.LastSeen = at.Unix()
		s.markDirtyLocked()
	}
	s.mu.Unlock()
}

// The remaining EventHandler methods are not relevant to device history.
func (s *Store) OnDeviceUpdate(string, int, string)  {}
func (s *Store) OnScreenFrame(string, []byte, bool)  {}
func (s *Store) OnResolutionChange(string, int, int) {}
func (s *Store) OnCursorChange(string, byte)         {}
func (s *Store) OnClipboardText(string, string)      {}
func (s *Store) OnTerminalReady(string, bool)        {}
func (s *Store) OnTerminalData(string, []byte)       {}
func (s *Store) OnTerminalClosed(string, string)     {}

// Offline returns the records whose IDs are not in online, newest last_seen
// first, converted to the hub's device payload shape with Online=false.
//
// Callers pass the hub's current online snapshot; the store deliberately does
// not know which device is online, so a reconnect that re-registers the same
// ID can never produce a duplicate row.
func (s *Store) Offline(online map[string]struct{}) []hub.DeviceInfo {
	s.mu.Lock()
	out := make([]hub.DeviceInfo, 0, len(s.devices))
	for id, rec := range s.devices {
		if _, ok := online[id]; ok {
			continue
		}
		out = append(out, hub.DeviceInfo{
			ID:          rec.ID,
			Name:        rec.Name,
			Group:       rec.Group,
			Version:     rec.Version,
			Capability:  rec.Capability,
			OS:          rec.OS,
			CPU:         rec.CPU,
			FilePath:    rec.FilePath,
			InstallTime: rec.InstallTime,
			Location:    rec.Location,
			IP:          rec.IP,
			PeerIP:      rec.PeerIP,
			Screen:      rec.Screen,
			LastSeen:    rec.LastSeen,
			Online:      false,
		})
	}
	s.mu.Unlock()

	sort.Slice(out, func(i, j int) bool {
		if out[i].LastSeen != out[j].LastSeen {
			return out[i].LastSeen > out[j].LastSeen
		}
		return out[i].ID < out[j].ID
	})
	return out
}

// Remove deletes the persisted record for id and reports whether one existed.
// This is the web UI's explicit "delete" for an offline device: an offline
// record has no live agent to uninstall, so forgetting it is all "delete" can
// mean. The caller decides when removal is appropriate; the store does not
// refuse to drop a record that happens to be marked online.
func (s *Store) Remove(id string) bool {
	if id == "" {
		return false
	}
	s.mu.Lock()
	_, existed := s.devices[id]
	if existed {
		delete(s.devices, id)
		delete(s.online, id)
		s.markDirtyLocked()
	}
	s.mu.Unlock()
	return existed
}

// Flush writes the current state synchronously. Normally the debounced timer
// does this; Flush exists for tests and graceful shutdown.
func (s *Store) Flush() error {
	s.mu.Lock()
	if s.timer != nil {
		s.timer.Stop()
		s.timer = nil
	}
	if !s.dirty {
		s.mu.Unlock()
		return nil
	}
	s.dirty = false
	data, err := s.marshalLocked()
	s.mu.Unlock()
	if err != nil {
		return err
	}
	if err := writeAtomic(s.path, data); err != nil {
		s.mu.Lock()
		s.dirty = true
		s.mu.Unlock()
		return err
	}
	return nil
}

// Close stops the debounce timer and flushes pending changes.
func (s *Store) Close() error {
	return s.Flush()
}

func (s *Store) markDirtyLocked() {
	s.dirty = true
	if s.timer == nil {
		s.timer = time.AfterFunc(flushDelay, s.flush)
	}
}

func (s *Store) flush() {
	if err := s.Flush(); err != nil && s.log != nil {
		s.log.Error("Failed to persist device history to %s: %v", s.path, err)
	}
}

func (s *Store) marshalLocked() ([]byte, error) {
	f := fileShape{Version: fileVersion, Devices: s.devices}
	return json.MarshalIndent(f, "", "  ")
}

// pruneLocked keeps the max most-recently-seen records. It runs after every
// online upsert, which is the only path that can grow the map; the O(n log n)
// sort only happens when the cap is actually exceeded.
func (s *Store) pruneLocked() {
	if s.max <= 0 || len(s.devices) <= s.max {
		return
	}
	ids := make([]string, 0, len(s.devices))
	for id := range s.devices {
		ids = append(ids, id)
	}
	sort.Slice(ids, func(i, j int) bool {
		oi, oj := s.online[ids[i]], s.online[ids[j]]
		if oi != oj {
			return !oi // evict offline records before online ones
		}
		return s.devices[ids[i]].LastSeen < s.devices[ids[j]].LastSeen
	})
	for _, id := range ids[:len(ids)-s.max] {
		delete(s.devices, id)
	}
}

// writeAtomic mirrors wsauth.writeUsersFile: temp file in the same directory,
// fsync, then rename over the destination.
func writeAtomic(path string, data []byte) error {
	dir := filepath.Dir(path)
	if dir != "" {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return err
		}
	}
	tmp, err := os.CreateTemp(dir, "devices-*.json.tmp")
	if err != nil {
		return err
	}
	tmpName := tmp.Name()
	if _, err := tmp.Write(data); err != nil {
		_ = tmp.Close()
		_ = os.Remove(tmpName)
		return err
	}
	if err := tmp.Sync(); err != nil {
		_ = tmp.Close()
		_ = os.Remove(tmpName)
		return err
	}
	if err := tmp.Close(); err != nil {
		_ = os.Remove(tmpName)
		return err
	}
	if err := os.Rename(tmpName, path); err != nil {
		_ = os.Remove(tmpName)
		return err
	}
	return nil
}