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import {expect} from '@esm-bundle/chai';import type {Chain} from '../db/test-helpers';import type * as dag from '../dag/mod';import * as db from '../db/mod';import * as sync from '../sync/mod';import type {SnapshotMeta} from '../db/commit';
// See db.test_helpers for addLocal, addSnapshot, etc. We can't put addLocalRebase// there because sync depends on db, and addLocalRebase depends on sync.
// addSyncSnapshot adds a sync snapshot off of the main chain's base snapshot and// returns it (in chain order). Caller needs to supply which commit to take indexes// from because it is context dependent (they should come from the parent of the// first commit to rebase, or from head if no commits will be rebased).
export async function addSyncSnapshot(  chain: Chain,  store: dag.Store,  takeIndexesFrom: number,): Promise<Chain> {  expect(chain.length >= 2).to.be.true;
  let maybeBaseSnapshot: db.Commit<SnapshotMeta> | undefined;  for (let i = chain.length - 1; i > 0; i--) {    const commit = chain[i - 1];    if (commit.isSnapshot()) {      maybeBaseSnapshot = commit;      break;    }  }  if (maybeBaseSnapshot === undefined) {    throw new Error('main chain doesnt have a snapshot or local commit');  }  const baseSnapshot = maybeBaseSnapshot;  const syncChain: Chain = [];
  // Add sync snapshot.  const cookie = `sync_cookie_${chain.length}`;  const indexes = db.readIndexesForWrite(chain[takeIndexesFrom]);  await store.withWrite(async dagWrite => {    const w = await db.Write.newSnapshot(      db.whenceHash(baseSnapshot.chunk.hash),      baseSnapshot.mutationID,      cookie,      dagWrite,      indexes,    );    await w.commit(sync.SYNC_HEAD_NAME);  });  const [, commit] = await store.withRead(async dagRead => {    return await db.readCommit(db.whenceHead(sync.SYNC_HEAD_NAME), dagRead);  });  syncChain.push(commit);
  return syncChain;}