flatten

#!/bin/bash
set -eo pipefail

throw() {
  printf '%s: %s\n' "${0##*/}" "$1" >&2
  return 1
}

if [[ $# == 0 || $1 =~ ^(--help|-h)$ ]]; then
  cat >&2 <<EOF
Usage: flatten [-p|--prefix <prefix>] [-s|--suffix <suffix>]
               [-d|--delimiter <delimiter>] [-n|--dry-run] <directory>

Flattens the contents of a directory "dir" such that "dir/foo/bar/file.jpg" is
renamed to "dir/foo - bar - file.jpg" with the empty directories "bar" and
"foo" removed afterward. Existing files are never overwritten.

Options:

  -p, --prefix <prefix>          Optional string prepended to filenames.

  -s, --suffix <suffix>          Optional string appended to filenames (before
                                 the file extension).

  -d, --delimiter <delimiter>    Separator added between path components.
                                 Defaults to " - ".

  -n, --dry-run                  Show how files would be renamed and exit.
EOF
  exit 1
fi

paths=()
prefix=
suffix=
delimiter=' - '
dry_run=
while (( $# > 0 )); do
  case $1 in
    --)
      shift
      paths+=("$@")
      break
      ;;
    # prefix
    -p|--prefix)
      shift
      prefix=$1
      ;;
    -p*)
      prefix=${1#-p}
      ;;
    --prefix=*)
      prefix=${1#--prefix=}
      ;;
    # suffix
    -s|--suffix)
      shift
      suffix=$1
      ;;
    -s*)
      suffix=${1#-s}
      ;;
    --suffix=*)
      suffix=${1#--suffix=}
      ;;
    # delimiter
    -d|--delimiter)
      shift
      delimiter=$1
      ;;
    -d*)
      delimiter=${1#-d}
      ;;
    --delimiter=*)
      delimiter=${1#--delimiter=}
      ;;
    # dry run
    -n|--dry-run)
      dry_run=1
      ;;
    -*)
      throw "unknown option: $1"
      ;;
    *)
      paths+=("$1")
      ;;
  esac
  shift
done
if (( ${#paths[@]} == 0 )); then
  throw 'no directory given'
elif (( ${#paths[@]} > 1 )); then
  throw 'too many directories given'
elif [[ ! -d ${paths[0]} ]]; then
  throw "not a directory: ${paths[0]}"
fi
directory=${paths[0]}

echo 'Scanning directory...'
file_list=$(cd "$directory" && find . -type f | sed 's/^.\///')
count_not_moved=0

while read -r orig_path; do
  orig_path_without_ext=${orig_path%.*}
  ext=
  if [[ $orig_path == *.* ]]; then
    ext=.${orig_path##*.}
  fi
  new_path="${prefix}${orig_path_without_ext//\//${delimiter}}${suffix}${ext}"

  full_orig_path="$directory/$orig_path"
  full_new_path="$directory/$new_path"

  if [[ $full_orig_path == "$full_new_path" ]]; then
    continue
  fi

  echo

  if [[ -e $full_new_path ]]; then
    printf '\e[31mAlready exists: %s\e[m\n' "$new_path"
    (( count_not_moved += 1 ))
    continue
  fi

  if [[ $dry_run ]]; then
    printf 'Would rename \e[32m%s\e[m\n' "$orig_path"
    printf '          to \e[32m%s\e[m\n' "$new_path"
    continue
  fi

  printf 'Renaming \e[32m%s\e[m\n' "$orig_path"
  printf '      to \e[32m%s\e[m\n' "$new_path"
  mv -n "$full_orig_path" "$full_new_path" 2> >(sed $'s/.*/\e[31m&\e[m/')
done <<<"$file_list"

echo
if [[ ! $dry_run ]]; then
  echo 'Removing empty directories...'
  find "$directory" -mindepth 1 -depth -type d -empty -exec rmdir -- {} \;
fi
echo 'Done.'

if (( count_not_moved > 0 )); then
  (( count_not_moved == 1 )) && plural= || plural=s
  printf '\n\e[31m%s file%s skipped to avoid overwriting existing files.\e[m\n' "$count_not_moved" "$plural"
fi

exit $((count_not_moved > 255 ? 255 : count_not_moved))