// Package subdisc persists the sub-discussion entries managed by the
// create-sub-discussion / close-sub-discussion tools (port of openclaw
// plugin's sub-discussion-store.ts). State lives under
// <profile>/state/plugin-kv/fabric-sub-discussions.json — the
// Plexum-host's standard plugin KV dir.
//
// One entry = one sub-discussion channel. Lifetime: from
// create-sub-discussion until close-sub-discussion (or the operator
// nukes the JSON file).
package subdisc

import (
	"encoding/json"
	"errors"
	"fmt"
	"io/fs"
	"os"
	"path/filepath"
	"sync"
	"time"
)

// FileName under <profile>/state/plugin-kv/.
const FileName = "fabric-sub-discussions.json"

// Entry is the on-disk shape of one sub-discussion.
type Entry struct {
	SubChannelID        string   `json:"sub_channel_id"`
	HostAgentID         string   `json:"host_agent_id"`
	HostUserID          string   `json:"host_user_id"`
	GuestUserIDs        []string `json:"guest_user_ids"`
	HostGuide           string   `json:"host_guide,omitempty"`
	GuestGuide          string   `json:"guest_guide,omitempty"`
	CallbackGuildNodeID string   `json:"callback_guild_node_id"`
	CallbackChannelID   string   `json:"callback_channel_id"`
	CreatedAt           string   `json:"created_at"`
}

// Store wraps the on-disk file. Thread-safe.
type Store struct {
	mu      sync.Mutex
	path    string
	entries map[string]*Entry // by SubChannelID
}

// Open loads (or creates empty) the store at path.
func Open(path string) (*Store, error) {
	s := &Store{path: path, entries: map[string]*Entry{}}
	raw, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, fs.ErrNotExist) {
			return s, nil
		}
		return nil, fmt.Errorf("subdisc: read %s: %w", path, err)
	}
	if len(raw) == 0 {
		return s, nil
	}
	var wire struct {
		Entries []*Entry `json:"entries"`
	}
	if err := json.Unmarshal(raw, &wire); err != nil {
		// Tolerate corruption — start empty; first write will overwrite.
		return s, nil
	}
	for _, e := range wire.Entries {
		if e != nil && e.SubChannelID != "" {
			s.entries[e.SubChannelID] = e
		}
	}
	return s, nil
}

// Lookup returns the entry for subChannelID or nil.
func (s *Store) Lookup(subChannelID string) *Entry {
	s.mu.Lock()
	defer s.mu.Unlock()
	if e, ok := s.entries[subChannelID]; ok {
		copyE := *e
		return &copyE
	}
	return nil
}

// LookupForHost returns the entry IF subChannelID exists AND the entry
// was created by hostAgentID. Used by close-sub-discussion to enforce
// "only the host can close".
func (s *Store) LookupForHost(subChannelID, hostAgentID string) *Entry {
	e := s.Lookup(subChannelID)
	if e == nil || e.HostAgentID != hostAgentID {
		return nil
	}
	return e
}

// Add inserts a new entry; CreatedAt is auto-set if empty.
func (s *Store) Add(e Entry) error {
	if e.SubChannelID == "" {
		return errors.New("subdisc: SubChannelID required")
	}
	if e.CreatedAt == "" {
		e.CreatedAt = time.Now().UTC().Format(time.RFC3339)
	}
	s.mu.Lock()
	s.entries[e.SubChannelID] = &e
	s.mu.Unlock()
	return s.persist()
}

// Remove drops the entry; returns true iff it was present.
func (s *Store) Remove(subChannelID string) bool {
	s.mu.Lock()
	_, ok := s.entries[subChannelID]
	if ok {
		delete(s.entries, subChannelID)
	}
	s.mu.Unlock()
	if !ok {
		return false
	}
	_ = s.persist() // best-effort
	return true
}

// All returns a snapshot copy of every entry (for diagnostic tools).
func (s *Store) All() []Entry {
	s.mu.Lock()
	defer s.mu.Unlock()
	out := make([]Entry, 0, len(s.entries))
	for _, e := range s.entries {
		out = append(out, *e)
	}
	return out
}

func (s *Store) persist() error {
	s.mu.Lock()
	entries := make([]*Entry, 0, len(s.entries))
	for _, e := range s.entries {
		entries = append(entries, e)
	}
	s.mu.Unlock()

	if err := os.MkdirAll(filepath.Dir(s.path), 0o755); err != nil {
		return err
	}
	data, err := json.MarshalIndent(struct {
		Entries []*Entry `json:"entries"`
	}{entries}, "", "  ")
	if err != nil {
		return err
	}
	tmp := s.path + ".tmp"
	if err := os.WriteFile(tmp, data, 0o600); err != nil {
		return err
	}
	return os.Rename(tmp, s.path)
}

// DefaultPath returns the canonical path under
// $PLEXUM_PROFILE_ROOT/state/plugin-kv (or ~/.plexum/...).
func DefaultPath() string {
	root := os.Getenv("PLEXUM_PROFILE_ROOT")
	if root == "" {
		home, _ := os.UserHomeDir()
		root = filepath.Join(home, ".plexum")
	}
	return filepath.Join(root, "state", "plugin-kv", FileName)
}