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import {IndexRead} from './index';import type * as dag from '../dag/mod';import {  Commit,  DEFAULT_HEAD_NAME,  fromHash as commitFromHash,  Meta,} from './commit';import type {ReadonlyJSONValue} from '../json';import {BTreeRead, BTreeWrite} from '../btree/mod';import type {Hash} from '../hash';
export class Read {  private readonly _dagRead: dag.Read;  map: BTreeRead;  readonly indexes: Map<string, IndexRead>;  shouldDeepClone = false;
  constructor(    dagRead: dag.Read,    map: BTreeRead,    indexes: Map<string, IndexRead>,  ) {    this._dagRead = dagRead;    this.map = map;    this.indexes = indexes;  }
  has(key: string): Promise<boolean> {    return this.map.has(key);  }
  get(key: string): Promise<ReadonlyJSONValue | undefined> {    return this.map.get(key);  }
  isEmpty(): Promise<boolean> {    return this.map.isEmpty();  }
  async getMapForIndex(indexName: string): Promise<BTreeRead> {    const idx = this.indexes.get(indexName);    if (idx === undefined) {      throw new Error(`Unknown index name: ${indexName}`);    }    return idx.withMap(this._dagRead, map => map);  }
  get closed(): boolean {    return this._dagRead.closed;  }
  close(): void {    this._dagRead.close();  }}
const enum WhenceType {  Head,  Hash,}
export type Whence =  | {      type: WhenceType.Hash;      hash: Hash;    }  | {      type: WhenceType.Head;      name: string;    };
export function whenceHead(name: string): Whence {  return {    type: WhenceType.Head,    name,  };}
export function whenceHash(hash: Hash): Whence {  return {    type: WhenceType.Hash,    hash,  };}
export function readFromDefaultHead(dagRead: dag.Read): Promise<Read> {  return fromWhence(whenceHead(DEFAULT_HEAD_NAME), dagRead);}
export async function fromWhence(  whence: Whence,  dagRead: dag.Read,): Promise<Read> {  const [, basis, map] = await readCommitForBTreeRead(whence, dagRead);  const indexes = readIndexesForRead(basis);  return new Read(dagRead, map, indexes);}
export async function readCommit(  whence: Whence,  dagRead: dag.Read,): Promise<[Hash, Commit<Meta>]> {  let hash: Hash;  switch (whence.type) {    case WhenceType.Hash:      hash = whence.hash;      break;    case WhenceType.Head: {      const h = await dagRead.getHead(whence.name);      if (h === undefined) {        throw new Error(`Unknown head: ${whence.name}`);      }      hash = h;      break;    }  }
  const commit = await commitFromHash(hash, dagRead);  return [hash, commit];}
export async function readCommitForBTreeRead(  whence: Whence,  dagRead: dag.Read,): Promise<[Hash, Commit<Meta>, BTreeRead]> {  const [hash, commit] = await readCommit(whence, dagRead);  return [hash, commit, new BTreeRead(dagRead, commit.valueHash)];}
export async function readCommitForBTreeWrite(  whence: Whence,  dagWrite: dag.Write,): Promise<[Hash, Commit<Meta>, BTreeWrite]> {  const [hash, commit] = await readCommit(whence, dagWrite);  return [hash, commit, new BTreeWrite(dagWrite, commit.valueHash)];}
export function readIndexesForRead(  commit: Commit<Meta>,): Map<string, IndexRead> {  const m = new Map();  for (const index of commit.indexes) {    m.set(index.definition.name, new IndexRead(index, undefined));  }  return m;}