// Хранение миров в IndexedDB (локально в браузере).
import type { World } from './types';

const DB = 'citygen';
const STORE = 'worlds';

function open(): Promise<IDBDatabase> {
  return new Promise((resolve, reject) => {
    const req = indexedDB.open(DB, 1);
    req.onupgradeneeded = () => req.result.createObjectStore(STORE);
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error);
  });
}

async function tx<T>(mode: IDBTransactionMode, fn: (s: IDBObjectStore) => IDBRequest<T>): Promise<T> {
  const db = await open();
  return new Promise((resolve, reject) => {
    const t = db.transaction(STORE, mode);
    const req = fn(t.objectStore(STORE));
    req.onsuccess = () => resolve(req.result);
    req.onerror = () => reject(req.error);
  });
}

export const saveWorld = (w: World) => tx('readwrite', (s) => s.put(w, 'last'));
export const loadWorld = () => tx<World | undefined>('readonly', (s) => s.get('last'));
export const hasWorld = async () => {
  try {
    return (await tx<number>('readonly', (s) => s.count('last'))) > 0;
  } catch {
    return false;
  }
};

/** Скачать мир файлом (.json.gz, если браузер умеет сжимать). */
export async function downloadWorld(w: World) {
  const json = JSON.stringify(w);
  let blob: Blob = new Blob([json], { type: 'application/json' });
  let ext = 'json';
  if ('CompressionStream' in window) {
    const cs = blob.stream().pipeThrough(new CompressionStream('gzip'));
    blob = await new Response(cs).blob();
    ext = 'json.gz';
  }
  const a = document.createElement('a');
  a.href = URL.createObjectURL(blob);
  a.download = `${(w.name || 'world').replace(/[^\p{L}\p{N}_-]+/gu, '_').slice(0, 40)}.${ext}`;
  a.click();
  setTimeout(() => URL.revokeObjectURL(a.href), 2000);
}

/** Прочитать файл мира или Overpass JSON (поддерживает .gz). */
export async function readJsonFile(file: File): Promise<any> {
  let stream: ReadableStream = file.stream();
  const head = new Uint8Array(await file.slice(0, 2).arrayBuffer());
  if (head[0] === 0x1f && head[1] === 0x8b) stream = stream.pipeThrough(new DecompressionStream('gzip'));
  return JSON.parse(await new Response(stream).text());
}