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import type * as kv from '../kv/mod';import {Store, Read, Write, mustGetChunk} from './store';import {  assertMeta,  Chunk,  createChunkWithHash,  createChunk,  ChunkHasher,} from './chunk';import {chunkDataKey, chunkMetaKey, headKey, chunkRefCountKey} from './key';import {assertHash, Hash} from '../hash';import {assertNumber} from '../asserts';import type {ReadonlyJSONValue} from '../json';import {computeRefCountUpdates} from './gc';
export class StoreImpl implements Store {  private readonly _kv: kv.Store;  private readonly _chunkHasher: ChunkHasher;  private readonly _assertValidHash: (hash: Hash) => void;
  constructor(    kv: kv.Store,    chunkHasher: ChunkHasher,    assertValidHash: (hash: Hash) => void,  ) {    this._kv = kv;    this._chunkHasher = chunkHasher;    this._assertValidHash = assertValidHash;  }
  async read(): Promise<Read> {    return new ReadImpl(await this._kv.read(), this._assertValidHash);  }
  async withRead<R>(fn: (read: Read) => R | Promise<R>): Promise<R> {    return this._kv.withRead(kvr =>      fn(new ReadImpl(kvr, this._assertValidHash)),    );  }
  async write(): Promise<Write> {    return new WriteImpl(      await this._kv.write(),      this._chunkHasher,      this._assertValidHash,    );  }
  async withWrite<R>(fn: (Write: Write) => R | Promise<R>): Promise<R> {    return this._kv.withWrite(kvw =>      fn(new WriteImpl(kvw, this._chunkHasher, this._assertValidHash)),    );  }
  async close(): Promise<void> {    await this._kv.close();  }}
export class ReadImpl implements Read {  protected readonly _tx: kv.Read;  readonly assertValidHash: (hash: Hash) => void;
  constructor(kv: kv.Read, assertValidHash: (hash: Hash) => void) {    this._tx = kv;    this.assertValidHash = assertValidHash;  }
  async hasChunk(hash: Hash): Promise<boolean> {    return await this._tx.has(chunkDataKey(hash));  }
  async getChunk(hash: Hash): Promise<Chunk | undefined> {    const data = await this._tx.get(chunkDataKey(hash));    if (data === undefined) {      return undefined;    }
    const refsVal = await this._tx.get(chunkMetaKey(hash));    let refs: readonly Hash[];    if (refsVal !== undefined) {      assertMeta(refsVal);      refs = refsVal;    } else {      refs = [];    }    return createChunkWithHash(hash, data, refs);  }
  async mustGetChunk(hash: Hash): Promise<Chunk> {    return mustGetChunk(this, hash);  }
  async getHead(name: string): Promise<Hash | undefined> {    const data = await this._tx.get(headKey(name));    if (data === undefined) {      return undefined;    }    assertHash(data);    return data;  }
  close(): void {    this._tx.release();  }
  get closed(): boolean {    return this._tx.closed;  }}
type HeadChange = {  new: Hash | undefined;  old: Hash | undefined;};
export class WriteImpl extends ReadImpl implements Write {  protected declare readonly _tx: kv.Write;  private readonly _chunkHasher: ChunkHasher;
  private readonly _putChunks = new Set<Hash>();  private readonly _changedHeads = new Map<string, HeadChange>();
  constructor(    kvw: kv.Write,    chunkHasher: ChunkHasher,    assertValidHash: (hash: Hash) => void,  ) {    super(kvw, assertValidHash);    this._chunkHasher = chunkHasher;  }
  createChunk = <V extends ReadonlyJSONValue>(    data: V,    refs: readonly Hash[],  ): Chunk<V> => createChunk(data, refs, this._chunkHasher);
  get kvWrite(): kv.Write {    return this._tx;  }
  async putChunk(c: Chunk): Promise<void> {    const {hash, data, meta} = c;    // We never want to write temp hashes to the underlying store.    this.assertValidHash(hash);    const key = chunkDataKey(hash);    const p1 = this._tx.put(key, data);    let p2;    if (meta.length > 0) {      for (const h of meta) {        this.assertValidHash(h);      }      p2 = this._tx.put(chunkMetaKey(hash), meta);    }    this._putChunks.add(hash);    await p1;    await p2;  }
  setHead(name: string, hash: Hash): Promise<void> {    return this._setHead(name, hash);  }
  removeHead(name: string): Promise<void> {    return this._setHead(name, undefined);  }
  private async _setHead(name: string, hash: Hash | undefined): Promise<void> {    const oldHash = await this.getHead(name);    const hk = headKey(name);
    let p1: Promise<void>;    if (hash === undefined) {      p1 = this._tx.del(hk);    } else {      p1 = this._tx.put(hk, hash);    }
    const v = this._changedHeads.get(name);    if (v === undefined) {      this._changedHeads.set(name, {new: hash, old: oldHash});    } else {      // Keep old if existing      v.new = hash;    }
    await p1;  }
  async commit(): Promise<void> {    const refCountUpdates = await computeRefCountUpdates(      this._changedHeads.values(),      this._putChunks,      this,    );    await this._applyRefCountUpdates(refCountUpdates);    await this._tx.commit();  }
  async getRefCount(hash: Hash): Promise<number | undefined> {    const value = await this._tx.get(chunkRefCountKey(hash));    if (value === undefined) {      return undefined;    }    assertNumber(value);    if (value < 0 || value > 0xffff || value !== (value | 0)) {      throw new Error(        `Invalid ref count ${value}. We expect the value to be a Uint16`,      );    }    return value;  }
  async getRefs(hash: Hash): Promise<readonly Hash[] | undefined> {    const meta = await this._tx.get(chunkMetaKey(hash));    if (meta !== undefined) {      assertMeta(meta);    }    return meta;  }
  private async _applyRefCountUpdates(    refCountCache: Map<Hash, number>,  ): Promise<void> {    const ps: Promise<void>[] = [];    refCountCache.forEach((count, hash) => {      if (count === 0) {        ps.push(this._removeAllRelatedKeys(hash));      } else {        const refCountKey = chunkRefCountKey(hash);        ps.push(this._tx.put(refCountKey, count));      }    });    await Promise.all(ps);  }
  private async _removeAllRelatedKeys(hash: Hash): Promise<void> {    await Promise.all([      this._tx.del(chunkDataKey(hash)),      this._tx.del(chunkMetaKey(hash)),      this._tx.del(chunkRefCountKey(hash)),    ]);
    this._putChunks.delete(hash);  }
  close(): void {    this._tx.release();  }}