Drush command to move files into a custom parent and child subfolders.

migration_filepath_custom.drush.inc

<?php
/**
 * @file
 * Drush command to move files into a custom parent and child subfolders.
 */

/**
 * Implements hook_drush_command().
 */
function migration_filepath_custom_drush_command() {
  $items = array();

  $items['migration_filepath_custom'] = array(
    'description' => "Move files to custom subdirectories",
    'callback' => 'drush_migration_filepath_custom',
    // We are using options rather than arguments so the source can be omitted
    // if needed (e.g. files are just directly under sites/default/files).
    'arguments' => array(
      'number' => 'Number of buckets to create under the parent folder.',
    ),
    'options' => array(
      'source' => array(
        'description' => 'The directory under files where the to be relocated files are.',
        'example_value' => 'field/image',
      ),
      'target' => array(
        'description' => 'The target directory where the files will be moved to and restructured.',
        'example_value' => 'pictures',
      ),
    ),
    'examples' => array(
      'drush migration_filepath_custom' => 'Moves all files located in a source subfolder to iterated style subdirectory.',
    ),
    'bootstrap' => DRUSH_BOOTSTRAP_DRUPAL_FULL,
  );

  return $items;
}

/**
 * Command callback to perform the file migration.
 *
 * The two optional options are the source and target directories. By default
 * assumes that these are under the default path, e.g. sites/default/files.
 */
function drush_migration_filepath_custom($number = 10) {
  // Source directory to be cleaned up.
  // All images in this directory will be relocated.
  $source_directory = rtrim(drush_get_option('source', ''), '/');
  // Directory to place the new structure under.
  // If does not exist will be created.
  $target_directory = rtrim(drush_get_option('target', ''), '/');
  // Set the target directory if it's not specified.
  if (empty($target_directory)) {
    if (strpos($source_directory, '/') !== false) {
      $source_directory_string = $source_directory;
      $source_directory_string = str_replace('/','-',$source_directory_string);
      $target_directory = $source_directory_string . '_parent';
      $target_child_directory = $source_directory_string;
    }
    else {
      $target_directory = $source_directory . '_parent';
      $target_child_directory = $source_directory;
    }
  }

  // Regular expression to find files in the source directory.
  // For now assume public files only.
  $extensions = array('jpeg', 'jpg', 'JPG', 'gif', 'png');

  // Construct a expression to find images located in the source directory.
  // Finds anything that does not contain "/", should be fine.
  $file_pattern = "[^\/]*";

  // Append the trailing slash for the regular expression.
  // Note, in some instances drupal places under public:/// (three slashes)
  // even when no folder specified. Reason for this is not known yet.
  $source_pattern = $source_directory ? $source_directory . "\/" : '';

  $regex = "^public:\/\/" . $source_pattern . "(" . $file_pattern . ")\.(" . implode($extensions, '|') . ")$";

  // Query the database for files that match this pattern.
  $filetypes = array('image/jpeg', 'image/jpg', 'image/gif', 'image/png');
  $query = db_select('file_managed', 'f')
    ->condition('filemime', $filetypes, 'IN')
    ->condition('uri', $regex, 'REGEXP');
  $total_count = $query->countQuery()->execute()->fetchField();

  drush_print(dt('@count entries are to be moved.', array('@count' => $total_count)));

  // Select the files to be moved.
  $files = $query->fields('f', array('fid', 'filename', 'uri', 'timestamp'))
    ->execute()
    ->fetchAll();

  // Divide total number of files into n buckets.
  $total_files = count($files);
  $loops_per_bucket_raw = $total_files / $number;
  $loops_per_bucket = ceil($loops_per_bucket_raw);
  // Initialize some variables.
  $target_subfolder = $target_child_directory . '_1';
  $count = 1;
  $bucket_count = 1;
  // Keep a list of files that have not been moved.
  $files_not_moved = array();

  // Create the 1st directory.
  $target_directory_for_file = $target_directory . '/' . $target_subfolder;
  $new_directory = file_build_uri($target_directory_for_file);
  $wrapper = file_stream_wrapper_get_instance_by_uri($new_directory);
  $wrapper->mkdir($new_directory, 0755, TRUE);

  // Loop thru files and move them.
  foreach ($files as $file) {
    // Note, $file->filename can be the SAME for different uri-s!
    $source_pattern = $source_directory ? $source_directory . "/" : '';
    $regex = "^public:\/\/" . str_replace("/", "\/", $source_pattern) . "(" . $file_pattern . ")\.(" . implode($extensions, '|') . ")$";
    preg_match_all("/$regex/i", $file->uri, $matches);
    $filename = $matches[1][0] . "." . $matches[2][0];
    // Get the file wrapper of the file to be moved.
    $old_file_wrapper = file_stream_wrapper_get_instance_by_uri($file->uri);

    // If the file has already been moved, or does not exist in the
    // filesystem, move on.
    if (FALSE === ($status = $old_file_wrapper->url_stat($file->uri, STREAM_URL_STAT_QUIET))) {
      $files_not_moved[] = $file->uri;
      drush_log("File entry in the database does not exist on the filesystem.", 'notice');
      continue;
    }
    // Increment the bucket appended folder number if we've filled the previous
    // bucket with the number of files in $loops_per_bucket.
    if ($count % $loops_per_bucket == 0) {
      $bucket_count++;
      $target_subfolder = $target_child_directory . '_' . $bucket_count;
      // Each file should go to the directory based on its timestamp.
      $target_directory_for_file = $target_directory . '/' . $target_subfolder;
      // Construct a dummy URI for it so we can use the stream wrappers.
      $new_directory = file_build_uri($target_directory_for_file);
      $wrapper = file_stream_wrapper_get_instance_by_uri($new_directory);

      // Make sure that the new directory exists.
      if (!$wrapper->mkdir($new_directory, 0755, TRUE)) {
        drush_print(dt('cannot make @newdir', array('@newdir' => $new_directory)));
        continue;
      }
    }

    // Construct the new directory.
    $wrapper = file_stream_wrapper_get_instance_by_uri($file->uri);
    $new_uri = file_build_uri($target_directory_for_file . '/' . $filename);
    if (!$wrapper->rename($file->uri, $new_uri)) {
      $files_not_moved[] = $file->uri;
      continue;
    }
    // Update the file_managed table and track progress, count.
    $progress = round(($count / $total_count) * 100);
    drush_print($progress . '%');
    $query = db_update('file_managed')
      ->fields(array('uri' => $new_uri))
      ->condition('fid', $file->fid)
      ->execute();

    $count++;
  }
  $not_moved = count($files_not_moved) ? count($files_not_moved) : 0;
  // Output count of files that couldn't be moved.
  drush_print(dt('(' . ($total_files - $not_moved) . '/' . $total_files . ') ' . 'files moved.'));
  if ($not_moved) {
    drush_print(dt($not_moved . ' files do not exist in the filesystem.'));
  }
}