import fs from 'node:fs';
import { enrichFiles, walkUploadDir } from './lib/fs-tree.mjs';

export function createDriveRuntime(ctx) {
  const state = {
    ctx,
    listCache: { files: [], dirs: [], ts: 0, added: [], removed: [] },
    sseClients: new Set(),
    watchTimer: null,
    watcher: null,
  };

  async function refreshFileList() {
    const { files, dirs } = await walkUploadDir(ctx, ctx.uploadDir);
    const prevNames = new Set(state.listCache.files.map((f) => f.name));
    const added = files.filter((f) => !prevNames.has(f.name)).map((f) => f.name);
    const nextNames = new Set(files.map((f) => f.name));
    const removed = state.listCache.files.filter((f) => !nextNames.has(f.name)).map((f) => f.name);
    const enriched = await enrichFiles(ctx, files);
    state.listCache = {
      files: enriched,
      dirs,
      ts: Date.now(),
      added,
      removed,
      delta: added.length > 0 || removed.length > 0,
    };
    return state.listCache;
  }

  function broadcastList(payload) {
    const body = `data: ${JSON.stringify(payload)}\n\n`;
    for (const client of state.sseClients) {
      try {
        client.write(body);
      } catch {
        state.sseClients.delete(client);
      }
    }
  }

  async function notifyChange() {
    const payload = await refreshFileList();
    broadcastList(payload);
    return payload;
  }

  function scheduleNotify() {
    clearTimeout(state.watchTimer);
    state.watchTimer = setTimeout(() => {
      notifyChange().catch(console.error);
    }, 250);
  }

  function initWatcher() {
    if (state.watcher) return;
    try {
      state.watcher = fs.watch(ctx.uploadDir, { recursive: true }, scheduleNotify);
    } catch (err) {
      console.warn('[oa-drive] fs.watch unavailable:', err.message);
    }
  }

  async function bootstrap() {
    await refreshFileList();
    initWatcher();
  }

  function dispose() {
    clearTimeout(state.watchTimer);
    if (state.watcher) {
      state.watcher.close();
      state.watcher = null;
    }
    state.sseClients.clear();
  }

  return {
    ctx,
    getListCache: () => state.listCache,
    refreshFileList,
    notifyChange,
    addSseClient(res) {
      state.sseClients.add(res);
      return () => state.sseClients.delete(res);
    },
    bootstrap,
    dispose,
  };
}