compath

#!/bin/bash

replace_home_with_tilda() {
  while read -r path; do
    abs_path="$(realpath -s "$path")"
    rel_path="$(realpath --relative-base "$HOME" "$abs_path")"
    if [ "$abs_path" = "$rel_path" ]; then
      echo "$abs_path"
    else
      # shellcheck disable=2088 # in this case I want literal ~
      echo "~/$rel_path"
    fi
  done
}

shorten_word() {
  if [[ "${#1}" -gt "$allow_len" ]]; then
    echo "${1:0:$trim_len}"
  else
    echo "$1"
  fi
}

compress_path() {
  local path path_element path_elements first_element last_element length
  while read -r path; do
    # shellcheck disable=2162 # in this case -r will cause havoc
    IFS=/ read -a path_elements <<<"$path"
    length="${#path_elements[*]}"
    first_element="${path_elements[0]}"
    last_element="${path_elements[$((length - 1))]}"

    # skip / if in home
    if ! [ "$first_element" = "~" ]; then
      printf "/"
    fi

    # shorten each part
    for index in $(seq 0 $((length - 2))); do
      path_element="${path_elements[$index]}"
      if [ -n "$path_element" ]; then
        printf "%s/" "$(shorten_word "$path_element")"
      fi
    done

    # last element gets special treatment
    if [ -n "$last_element" ]; then
      printf "%s" "$(allow_len="$last_allow_len" trim_len="$last_allow_len" shorten_word "$last_element")"
    fi
    printf "\n"
  done
}

expand_path() {
  while read -r path; do
    # shellcheck disable=2162 # in this case -r will cause havoc
    IFS=/ read -a path_elements <<<"$path"
    path=
    for path_element in "${path_elements[@]}"; do

      # expand tilda or append path elements
      if [ -z "$path_element" ]; then
        continue
      elif [ -z "$path" ] && [ "$path_element" = "~" ]; then
        path="$HOME"
      else
        path="$path/$path_element"
      fi

      # try to complete the path if it doesn't exist
      if ! [ -e "$path" ]; then
        globpath="$(compgen -G "$path*")"
        if ! [ "$globpath" = "$path" ]; then
          path="$globpath"
        fi
      fi
    done
    echo "$path"
  done
}

trim_len=3
last_allow_len=100
calc_allow_len=true
calc_allow_len_val=2
expand=false

print_help() {
  cat <<EOL
Usage: $0 [ [-t <trim-length>] [-a <allow-length>]) | -x | -h ] [<path>]

Path compression utility, created mostly with prompts in mind.
It can trim path elements to given sizes, with some wiggle room,
and it can also expand these paths if they exist.

If no path is provided, the application will attempt to capture standard input.

Options:
  -a    Set allow length, which is the max length before path element
        is trimmed (default:<trim-length>+$calc_allow_len_val).
  -h    Show this help
  -l    Allowed length for last path element (default:$last_allow_len).
  -t    Set trim length, the path elements will be trimmed to (default:$trim_len).
  -x    Expand path (reverse of default compression)

Examples:

    $ $0 /home/user/repositories/tools/compath
    ~/rep/tools/compath

    $ $0 -t 2 /home/user/repositories/tools/compath
    ~/re/to/compath

    $ $0 -t 2 -a 5 /home/user/repositories/tools/compath
    ~/re/tools/co

    $ $0 -t 2 -a 5 -l 2 /home/user/repositories/tools/compath
    ~/re/tools/co

    $ $0 -x ~/rep/tools/com
    /home/user/repositories/tools/compath
EOL
}

while getopts "a:h?l:x?t:" opt; do
  case $opt in
    a) calc_allow_len=false
       allow_len="$OPTARG" ;;
    h) print_help ;;
    l) last_allow_len="$OPTARG" ;;
    t) trim_len="$OPTARG" ;;
    x) expand=true ;;
    ?) continue ;;
  esac
done

if [ $OPTIND -ge 0 ]; then
  shift "$((OPTIND - 1))"
fi

if $calc_allow_len; then
  allow_len=$((trim_len + calc_allow_len_val))
fi

if [ -n "$1" ]; then
  echo "$@"
else
  cat
fi |
  if $expand; then
    expand_path
  else
    replace_home_with_tilda | compress_path | sed 's|/.$||'
  fi