@ocfl/ocfl/lib/extensions/0004-hashed-n-tuple-storage-layout.js

Oxford Common File Layout (OCFL) JS library

const { OcflStorageLayout } = require("../extension");
const { OcflDigest } = require("../digest");
const path = require("path");
const { enumeration } = require("../enum");

const DefaultConfig = {
  extensionName: '0004-hashed-n-tuple-storage-layout',
  digestAlgorithm: 'sha256',
  tupleSize: 3,
  numberOfTuples: 3,
  shortObjectRoot: false
};
/** @typedef {Partial<typeof DefaultConfig>} HashedNTupleStorageLayoutConfig */
/**
 * @extends {OcflStorageLayout<typeof DefaultConfig>}
 */
class HashedNTupleStorageLayout extends OcflStorageLayout {
  static get NAME() { return DefaultConfig.extensionName; }
  static get DESCRIPTION() {
    return "OCFL object identifiers are hashed and encoded as lowercase hex strings." +
      " These digests are then divided into N n-tuple segments," +
      " which are used to create nested paths under the OCFL storage root.";
  }

  /**
   * 
   * @param {HashedNTupleStorageLayoutConfig} [config] 
   */
  constructor(config) {
    super(config, DefaultConfig);
    let c = this.parameters;
    const algo = enumeration.of(OcflDigest.FIXITY, c.digestAlgorithm)?.name;
    if (!algo) throw new Error('Invalid digestAlgorithm');
    let digestLength = OcflDigest.getHexDigestLength(algo);
    let p = c.numberOfTuples * c.tupleSize
    if (p > digestLength) throw new Error('Product of numberOfTuples and tupleSize is greater than the number of characters in the hex encoded digest.');
    else if (p === digestLength && c.shortObjectRoot) throw new Error('shortObjectRoot cannot be set to true');
  }

  /**
   * @param {string} id
   * @return {string} 
   */
  map(id) {
    let digest = OcflDigest.digestSync(this.parameters.digestAlgorithm, id);
    let segments = [];
    let s = this.parameters.tupleSize;
    let n = this.parameters.numberOfTuples;
    let i;
    for (i = 0; i < n; ++i) {
      segments.push(digest.slice(s * i, s * i + s));
    }
    if (this.parameters.shortObjectRoot) {
      segments.push(digest.slice(s * i));
    } else {
      segments.push(digest);
    }
    return segments.join(path.sep);
  }

}

module.exports = { HashedNTupleStorageLayout };