// Earlier versions of a study. Just before a save replaces what the server holds, that copy can be kept, so a
// bad merge or an accidental delete can be undone. To stay small, a copy is kept at most once per window of
// editing, it is compressed, and only the newest few are kept.
import { gunzipSync, gzipSync } from 'zlib';

export const MIN_GAP_MS = 10 * 60 * 1000; // one version per ten minutes of editing history
export const MAX_VERSIONS = 30;

// `prevEditedAt` is when the copy about to be replaced was saved; `lastKeptAt` is when the newest kept version was.
export function shouldSnapshot({ prevEditedAt, lastKeptAt, force = false, minGap = MIN_GAP_MS }) {
  if (!Number.isFinite(prevEditedAt)) return false;
  if (force) return true;
  return !Number.isFinite(lastKeptAt) || prevEditedAt - lastKeptAt >= minGap;
}

export const pack = (json) => gzipSync(Buffer.from(typeof json === 'string' ? json : JSON.stringify(json)));
export const unpack = (buf) => JSON.parse(gunzipSync(buf).toString('utf8'));

const words = (s) => (String(s ?? '').trim() ? String(s).trim().split(/\s+/).length : 0);

// How big a study is: chunks and the words in its notes and scripts.
export function summarizeProject(project) {
  let chunks = 0;
  let noteWords = 0;
  for (const chapter of project?.chapters ?? []) {
    for (const chunk of chapter.chunks ?? []) {
      chunks += 1;
      for (const f of ['observation', 'interpretation', 'application', 'generalNotes', 'finalScript']) noteWords += words(chunk[f]);
    }
  }
  return { chunks, words: noteWords };
}