public async cloneDetector(files: File[]): Promise<Report> {
    const tokenizedFiles = files.map(f => this.tokenizer.tokenizeFile(f));
    const report = new Report(this.options);
    for (const file of tokenizedFiles) {
      let kgram = 0;
      for await (
        const { hash, start, stop  }
        of hashFilter.fingerprints(file.Ast)
      ) {

        // add kgram to file
        file.kgrams.push(new Range(start, stop));

        const location = Region.merge(
          file.mapping[start],
          file.mapping[stop]
        );

        const part: Occurrence = {
          file,
          side: { index: kgram, start, stop, data, location }
        };

        // look if the index already contains the given hashing
        const matches = this.index.get(hash);

        if (matches) {
          report.addOccurrences(hash, part, ...matches);
          matches.push(part);
        } else {
          this.index.set(hash, [part]);
        }
        kgram += 1;
      }
    }
    report.finish();
    return report;
  }