package session

import (
	"encoding/json"
	"fmt"
	"os"
	"path/filepath"
	"sort"

	"agentu/internal/safeio"
)

const sessionIndexFile = "index.json"

type sessionIndex struct {
	Sessions []SessionMeta `json:"sessions"`
}

func metaFromSession(sess *Session) SessionMeta {
	return SessionMeta{
		ID:           sess.ID,
		Name:         sess.Name,
		CreatedAt:    sess.CreatedAt,
		UpdatedAt:    sess.UpdatedAt,
		Provider:     sess.Provider,
		Model:        sess.Model,
		MessageCount: len(sess.Messages),
	}
}

func (s *Store) saveIndexFromSessions(metas []SessionMeta) error {
	sort.Slice(metas, func(i, j int) bool {
		return metas[i].UpdatedAt.After(metas[j].UpdatedAt)
	})
	idx := sessionIndex{Sessions: metas}
	data, err := json.MarshalIndent(idx, "", "  ")
	if err != nil {
		return fmt.Errorf("marshal session index: %w", err)
	}
	path := filepath.Join(s.dir, sessionIndexFile)
	return safeio.AtomicWriteFile(path, data, 0o644)
}

func (s *Store) loadIndex() ([]SessionMeta, error) {
	path := filepath.Join(s.dir, sessionIndexFile)
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, err
	}
	var idx sessionIndex
	if err := json.Unmarshal(data, &idx); err != nil {
		return nil, err
	}
	sort.Slice(idx.Sessions, func(i, j int) bool {
		return idx.Sessions[i].UpdatedAt.After(idx.Sessions[j].UpdatedAt)
	})
	return idx.Sessions, nil
}