// Package store persists small runtime state (terminal names, login sessions)
// to a JSON file with atomic writes.
package store

import (
	"encoding/json"
	"errors"
	"log"
	"os"
	"sync"
	"time"
)

type Terminal struct {
	ID   string `json:"id"`
	Name string `json:"name"`
}

type State struct {
	Terminals  []Terminal           `json:"terminals"`
	Sessions   map[string]time.Time `json:"sessions"`              // token -> expiry
	Dashboard  json.RawMessage      `json:"dashboard,omitempty"`   // UI layout prefs, opaque to the server
	UI         json.RawMessage      `json:"ui,omitempty"`          // theme etc., opaque to the server
	Alerts     json.RawMessage      `json:"alerts,omitempty"`      // rules, channels and recent events (internal/api/alerts.go)
	SamplerMs  int                  `json:"sampler_ms,omitempty"`  // how often this machine samples; the hub keeps every machine on the console's refresh rate
	HistorySec int                  `json:"history_sec,omitempty"` // how far back the graphs reach; the hub keeps every machine on the same one
}

type Store struct {
	mu    sync.Mutex
	path  string
	state State
}

func Open(path string) (*Store, error) {
	s := &Store{path: path}
	b, err := os.ReadFile(path)
	if err != nil && !errors.Is(err, os.ErrNotExist) {
		return nil, err
	}
	if err == nil {
		// State is conveniences (sessions, terminal names, layout). A file mangled by a power
		// cut must not keep the console down: set it aside and start clean.
		if err := json.Unmarshal(b, &s.state); err != nil {
			s.state = State{}
			_ = os.Rename(path, path+".corrupt")
			log.Printf("state: %s unreadable (%v); kept as %s.corrupt, starting fresh", path, err, path)
		}
	}
	if s.state.Sessions == nil {
		s.state.Sessions = map[string]time.Time{}
	}
	return s, nil
}

// Update applies fn under the lock and writes the result to disk.
func (s *Store) Update(fn func(*State)) error {
	s.mu.Lock()
	defer s.mu.Unlock()
	fn(&s.state)
	return s.save()
}

// View reads state under the lock.
func (s *Store) View(fn func(*State)) {
	s.mu.Lock()
	defer s.mu.Unlock()
	fn(&s.state)
}

func (s *Store) save() error {
	b, err := json.MarshalIndent(&s.state, "", "  ")
	if err != nil {
		return err
	}
	return WriteFileAtomic(s.path, b, 0o600)
}

// WriteFileAtomic writes beside path, syncs, then renames: after a crash the file is the
// old version or the new one, never empty or half-written.
func WriteFileAtomic(path string, data []byte, perm os.FileMode) error {
	tmp := path + ".tmp"
	f, err := os.OpenFile(tmp, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
	if err != nil {
		return err
	}
	_, err = f.Write(data)
	if err == nil {
		err = f.Sync()
	}
	if cerr := f.Close(); err == nil {
		err = cerr
	}
	if err != nil {
		os.Remove(tmp)
		return err
	}
	return os.Rename(tmp, path)
}