Google Drive - Remove duplicate files (files with the same name) from a folder and its subfolders. Keeps only one copy. Also, deletes a folder if it becomes empty

removeDuplicateFiles.gs

// Put the ID of the folder you want to process
// https://drive.google.com/drive/folders/abcdefgh
const id = "abcdefgh";

// we will store file names in this dictionary.
// using Set could be more efficient to check if it contains file (time complexity: O(1))
// App Script does not support Set
const allFiles = [];

// Keep deleted file URLs and report in the end
const deletedURLs = [];

function start() {
  const folder = DriveApp.getFolderById(id);

  iterateFolder(folder);
  handleSubFolders(folder);

  prune(folder);

  Logger.log("Deleted file and folder URLs:\n" + deletedURLs);
}

function handleSubFolders(parent) {
  const subFolders = parent.getFolders();

  if (subFolders.hasNext()) {
    while (subFolders.hasNext()) {
      const subFolder = subFolders.next();
      iterateFolder(subFolder);
      handleSubFolders(subFolder);
    }
  }
}

// Iterate files in a folder
function iterateFolder(folder) {
  const files = folder.getFiles();
  if (files.hasNext()) {
    while (files.hasNext()) {
      const file = files.next();
      const fileName = file.getName();

      if (allFiles.includes(fileName)) {
        deletedURLs.push(file.getUrl());
        file.setTrashed(true);
      } else {
        allFiles.push(fileName);
      }
    }
  }
}

// Delete folders if they do not have any folder or file after operations above
function prune(folder) {
  const subFolders = folder.getFolders();

  while (subFolders.hasNext()) {
    prune(subFolders.next());
  }

  if (!folder.getFiles().hasNext() && !subFolders.hasNext()) {
    folder.setTrashed(true);
    deletedURLs.push(folder.getUrl());
  }
}