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import type * as kv from '../kv/mod';import * as dag from '../dag/mod';import * as db from '../db/mod';import {Hash, isTempHash} from '../hash';
type OldHash = Hash;type NewHash = Hash;/** * Mappings are used to map from one hash to another. This is used when moving * chunks between two DAG stores that uses different hash functions. */type Mappings = ReadonlyMap<OldHash, NewHash>;
/** * This transformer is used to fixup the hashes we got from the source dag (the * perdag in our case) and rewrite the required chunks in the destination dag * (the memdag). */export class FixupTransformer extends db.Transformer {  private readonly _mappings: Mappings;
  constructor(dagWrite: dag.Write, mappings: Mappings) {    super(dagWrite);    this._mappings = mappings;  }
  override shouldSkip(hash: Hash): boolean {    if (isTempHash(hash)) {      return false;    }    return !this._mappings.has(hash);  }
  override shouldForceWrite(h: OldHash): boolean {    // If there is a mapping we need to write this chunk even if the data did    // not change. This happens for BTree data nodes for example because the    // hash it had in the memdag was using a temp hash but now we got a real    // hash from the perdag.    return this._mappings.has(h);  }
  protected override async writeChunk<D extends kv.Value>(    oldHash: OldHash,    data: D,    getRefs: (data: D) => readonly Hash[],  ): Promise<Hash> {    // We get here if the chunk changed or if we had a mapping for the hash.    const newHash = this._mappings.get(oldHash);    const refs = getRefs(data);    const newChunk = newHash      ? dag.createChunkWithHash(newHash, data, refs)      : this.dagWrite.createChunk(data, refs);    await this.dagWrite.putChunk(newChunk);    return newChunk.hash;  }}