// 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"`
}

// Session is one signed-in browser. The map key is the cookie's token; ID is what the
// UI sees and revokes by, so a session list never shows a usable token.
type Session struct {
	ID       string    `json:"id"`
	User     string    `json:"user"`
	Expires  time.Time `json:"expires"`
	Created  time.Time `json:"created,omitempty"`
	LastSeen time.Time `json:"last_seen,omitempty"`
	IP       string    `json:"ip,omitempty"`
	Agent    string    `json:"agent,omitempty"`
}

// UnmarshalJSON also reads the pre-users form, a bare expiry time: such a session has no
// user yet; the server gives it to the migrated first account.
func (s *Session) UnmarshalJSON(b []byte) error {
	if len(b) > 0 && b[0] == '"' {
		return json.Unmarshal(b, &s.Expires)
	}
	type plain Session
	return json.Unmarshal(b, (*plain)(s))
}

// UserState is what follows an account rather than the machine: how the console looks
// to that person and how their dashboard is laid out.
type UserState struct {
	UI json.RawMessage `json:"ui,omitempty"` // theme, accents; opaque to the server
}

// RememberedMount is one bind mount of a container that was running when Ham Lab last
// looked. A compose stack records the path its file had *inside* whatever deployed it, so
// when that container is gone the path is the only way back to the file on disk.
type RememberedMount struct {
	Container string    `json:"container"`
	Dest      string    `json:"dest"` // the path inside the container
	Src       string    `json:"src"`  // the path on the machine
	Seen      time.Time `json:"seen"`
}

type State struct {
	Terminals []Terminal            `json:"terminals"`
	Sessions  map[string]Session    `json:"sessions"` // token -> session
	Users     map[string]*UserState `json:"users,omitempty"`
	// UI is the pre-users machine-wide look; on first boot with users it moves to the first
	// account. Kept so an old state file still reads.
	UI         json.RawMessage `json:"ui,omitempty"`
	Alerts     json.RawMessage `json:"alerts,omitempty"`      // rules, channels and recent events (internal/api/alerts.go)
	ZFS        json.RawMessage `json:"zfs,omitempty"`         // snapshot schedules (internal/api/zfs.go)
	DockerJobs json.RawMessage `json:"docker_jobs,omitempty"` // image-update schedules (internal/api/dockersched.go)
	// Mounts remembers where a container's bind mounts pointed, so a stack deployed by an
	// orchestrator that has since been removed can still be found on disk. See
	// internal/api/stacks.go.
	Mounts []RememberedMount `json:"mounts,omitempty"`
	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
}

// UserState returns the prefs of an account, making an empty one if needed.
func (st *State) UserState(name string) *UserState {
	if st.Users == nil {
		st.Users = map[string]*UserState{}
	}
	u := st.Users[name]
	if u == nil {
		u = &UserState{}
		st.Users[name] = u
	}
	return u
}

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]Session{}
	}
	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)
}