// 자동 백업: versioned INP (+ asset attributes) copies of the model kept in a
// separate IndexedDB, so a bad edit hours ago can still be undone after the
// autosave (which keeps only the latest state) has overwritten it.
import type { AssetStore } from './assets';

const DB_NAME = 'spipe-backups';
const STORE = 'backups';
export const MAX_BACKUPS = 30;

export interface BackupRecord {
  id: string;
  savedAt: string;
  fileName: string;
  reason: 'auto' | 'manual';
  inp: string;
  assets?: AssetStore;
  nodes: number;
  links: number;
}

function open(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB_NAME, 1);
    req.onupgradeneeded = () => {
      if (!req.result.objectStoreNames.contains(STORE)) req.result.createObjectStore(STORE, { keyPath: 'id' });
    };
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error ?? new Error('백업 저장소를 열 수 없습니다.'));
  });
}

async function withStore<T>(mode: IDBTransactionMode, fn: (store: IDBObjectStore) => IDBRequest<T> | void): Promise<T | undefined> {
  const db = await open();
  try {
    return await new Promise<T | undefined>((resolve, reject) => {
      const tx = db.transaction(STORE, mode);
      const req = fn(tx.objectStore(STORE));
      tx.oncomplete = () => resolve(req ? req.result : undefined);
      tx.onerror = () => reject(tx.error ?? new Error('백업 저장소 오류'));
      tx.onabort = () => reject(tx.error ?? new Error('백업 저장 중단'));
    });
  } finally {
    db.close();
  }
}

export async function listBackups(): Promise<BackupRecord[]> {
  const all = ((await withStore<BackupRecord[]>('readonly', (s) => s.getAll())) ?? []) as BackupRecord[];
  return all.sort((a, b) => (a.savedAt < b.savedAt ? 1 : -1));
}

/** Save a backup unless it is identical to the newest one; trims to MAX_BACKUPS. */
export async function saveBackup(rec: Omit<BackupRecord, 'id' | 'savedAt'>): Promise<boolean> {
  const existing = await listBackups();
  const last = existing[0];
  if (last && last.inp === rec.inp && JSON.stringify(last.assets ?? null) === JSON.stringify(rec.assets ?? null)) return false;
  const savedAt = new Date().toISOString();
  await withStore('readwrite', (s) => {
    s.put({ ...rec, id: `${savedAt}_${Math.random().toString(36).slice(2, 7)}`, savedAt });
    for (const old of existing.slice(MAX_BACKUPS - 1)) s.delete(old.id);
  });
  return true;
}

export async function deleteBackup(id: string): Promise<void> {
  await withStore('readwrite', (s) => {
    s.delete(id);
  });
}