#!/usr/bin/env bash
#
# Optimized script to batch prepend directories to PATH.
# For each given directory, it removes all duplicate occurrences from PATH
# and then prepends it. Directories that do not exist are skipped.
#
# Usage: x-path-prepend <directory1> [<directory2> ...]
#
# Enable verbose output by setting the environment variable VERBOSE=1.
#
# Author: Ismo Vuorinen <https://github.com/ivuorinen> 2024
# License: MIT

VERBOSE="${VERBOSE:-0}"

# Ensure that at least one argument is provided.
[ "$#" -lt 1 ] && {
  echo "Usage: $0 <directory> [<directory> ...]"
  exit 1
}

# Save the arguments in an array.
dirs=("$@")

# Process the directories in reverse order so that the first argument ends up leftmost in PATH.
for ((idx = ${#dirs[@]} - 1; idx >= 0; idx--)); do
  dir="${dirs[idx]}"

  # Check if the specified directory exists.
  if [ ! -d "$dir" ]; then
    [ "$VERBOSE" -eq 1 ] && echo "(?) Directory '$dir' does not exist. Skipping."
    continue
  fi

  # Remove all duplicate occurrences of the directory from PATH using built-in string operations.
  case ":$PATH:" in
    *":$dir:"*)
      PATH=":${PATH}:"
      PATH="${PATH//:$dir:/:}"
      PATH="${PATH#:}"
      PATH="${PATH%:}"
      [ "$VERBOSE" -eq 1 ] && echo "Removed duplicate occurrences of '$dir' from PATH."
      ;;
    *) ;;
  esac

  # Prepend the directory to PATH.
  export PATH="$dir${PATH:+":$PATH"}"
  [ "$VERBOSE" -eq 1 ] && echo "Prepended '$dir' to PATH."
done