#!/usr/bin/env bash
#
# x-path: A unified script to manipulate the PATH variable.
#
# This script supports four subcommands:
#   - append (or a): Remove duplicates and append one or more directories.
#   - prepend (or p): Remove duplicates and prepend one or more directories.
#   - remove: Remove one or more directories from PATH.
#   - check:  Check if the directories (or all directories in PATH if none provided) are valid.
#
# All directory arguments are normalized (trailing slashes removed, except for "/"),
# and the current PATH is normalized before any operations.
#
# Usage:
#   x-path <command> <directory1> [<directory2> ...]
#
# Examples:
#   x-path append /usr/local/bin /opt/bin
#   x-path p /home/user/bin
#   x-path remove /usr/local/bin
#   x-path check            # Check all directories in PATH
#   x-path check /usr/local/bin /bin
#
# Enable verbose output by setting:
#   export VERBOSE=1

VERBOSE="${VERBOSE:-0}"

#######################################
# Normalize a directory by removing a trailing slash (unless the directory is "/").
# Globals:
#   None
# Arguments:
#   $1 - Directory path to normalize
# Returns:
#   Echoes the normalized directory.
#######################################
normalize_dir()
{
  local d="$1"
  if [ "$d" != "/" ]; then
    d="${d%/}"
  fi
  echo "$d"
}

#######################################
# Normalize the PATH variable by normalizing each of its components.
# Globals:
#   PATH
# Arguments:
#   None
# Returns:
#   Updates and exports PATH.
#######################################
normalize_path_var()
{
  local new_path=""
  local d
  IFS=':' read -r -a arr <<< "$PATH"
  for d in "${arr[@]}"; do
    d=$(normalize_dir "$d")
    if [ -z "$new_path" ]; then
      new_path="$d"
    else
      new_path="$new_path:$d"
    fi
  done
  PATH="$new_path"
  export PATH
}

#######################################
# Remove all occurrences of a normalized directory from PATH.
# Globals:
#   PATH
# Arguments:
#   $1 - Normalized directory to remove from PATH.
# Returns:
#   Updates PATH.
#######################################
remove_from_path()
{
  local d="$1"
  PATH=":${PATH}:"
  PATH="${PATH//:$d:/:}"
  PATH="${PATH#:}"
  PATH="${PATH%:}"
}

#######################################
# Append one or more directories to PATH.
# Globals:
#   PATH, VERBOSE
# Arguments:
#   One or more directory paths.
# Returns:
#   Updates PATH.
#######################################
do_append()
{
  local processed=""
  local d
  for arg in "$@"; do
    d=$(normalize_dir "$arg")
    if [[ " $processed " == *" $d "* ]]; then
      continue
    else
      processed="$processed $d"
    fi

    if [ ! -d "$d" ]; then
      [ "$VERBOSE" -eq 1 ] && echo "(?) Directory '$d' does not exist. Skipping."
      continue
    fi

    remove_from_path "$d"
    PATH="${PATH:+"$PATH:"}$d"
    [ "$VERBOSE" -eq 1 ] && echo "Appended '$d' to PATH."
  done
  export PATH
}

#######################################
# Prepend one or more directories to PATH.
# Directories are processed in reverse order so that the first argument ends up leftmost.
# Globals:
#   PATH, VERBOSE
# Arguments:
#   One or more directory paths.
# Returns:
#   Updates PATH.
#######################################
do_prepend()
{
  local processed=""
  local d
  local -a arr=("$@")
  local i
  for ((i = ${#arr[@]} - 1; i >= 0; i--)); do
    d=$(normalize_dir "${arr[i]}")
    if [[ " $processed " == *" $d "* ]]; then
      continue
    else
      processed="$processed $d"
    fi

    if [ ! -d "$d" ]; then
      [ "$VERBOSE" -eq 1 ] && echo "(?) Directory '$d' does not exist. Skipping."
      continue
    fi

    remove_from_path "$d"
    PATH="$d${PATH:+":$PATH"}"
    [ "$VERBOSE" -eq 1 ] && echo "Prepended '$d' to PATH."
  done
  export PATH
}

#######################################
# Remove one or more directories from PATH.
# Globals:
#   PATH, VERBOSE
# Arguments:
#   One or more directory paths.
# Returns:
#   Updates PATH.
#######################################
do_remove()
{
  local processed=""
  local d
  for arg in "$@"; do
    d=$(normalize_dir "$arg")
    if [[ " $processed " == *" $d "* ]]; then
      continue
    else
      processed="$processed $d"
    fi

    case ":$PATH:" in
      *":$d:"*)
        remove_from_path "$d"
        [ "$VERBOSE" -eq 1 ] && echo "Removed '$d' from PATH."
        ;;
      *)
        [ "$VERBOSE" -eq 1 ] && echo "(?) '$d' is not in PATH."
        ;;
    esac
  done
  export PATH
}

#######################################
# Check the validity of directories.
# If arguments are provided, check those directories; otherwise, check all directories in PATH.
# Globals:
#   PATH
# Arguments:
#   Zero or more directory paths.
# Returns:
#   Outputs the validity status of each directory.
#######################################
do_check()
{
  local d
  if [ "$#" -eq 0 ]; then
    echo "Checking all directories in PATH:"
    IFS=':' read -r -a arr <<< "$PATH"
    for d in "${arr[@]}"; do
      d=$(normalize_dir "$d")
      if [ -d "$d" ]; then
        echo "Valid:   $d"
      else
        echo "Invalid: $d"
      fi
    done
  else
    for arg in "$@"; do
      d=$(normalize_dir "$arg")
      if [ -d "$d" ]; then
        echo "Valid:   $d"
      else
        echo "Invalid: $d"
      fi
    done
  fi
}

#######################################
# Main routine: Parse subcommand and arguments, normalize PATH,
# and dispatch to the appropriate functionality.
#######################################
if [ "$#" -lt 1 ]; then
  echo "Usage: $0 <command> <directory1> [<directory2> ...]"
  echo "Commands:"
  echo "  append (or a)   - Append directories to PATH"
  echo "  prepend (or p)  - Prepend directories to PATH"
  echo "  remove          - Remove directories from PATH"
  echo "  check           - Check validity of directories (or all in PATH if none given)"
  exit 1
fi

cmd="$1"
shift

# Normalize the current PATH variable.
normalize_path_var

case "$cmd" in
  append | a)
    [ "$#" -ge 1 ] || {
      echo "Usage: $0 append <directory1> [<directory2> ...]"
      exit 1
    }
    do_append "$@"
    ;;
  prepend | p)
    [ "$#" -ge 1 ] || {
      echo "Usage: $0 prepend <directory1> [<directory2> ...]"
      exit 1
    }
    do_prepend "$@"
    ;;
  remove)
    [ "$#" -ge 1 ] || {
      echo "Usage: $0 remove <directory1> [<directory2> ...]"
      exit 1
    }
    do_remove "$@"
    ;;
  check)
    # If no directories are provided, check all directories in PATH.
    do_check "$@"
    ;;
  *)
    echo "Unknown command: $cmd"
    echo "Usage: $0 <command> <directory1> [<directory2> ...]"
    exit 1
    ;;
esac