#####################################################################
# Utilities for adding and subtracting paths from PATH, MANPATH etc #
#####################################################################

# Usage:
# -p == priority == append to the front of the path.
# -r == realpath, e.g. "pathadd ." adds $PWD to the path
# -n <name> == modify <name> instead of PATH
#
# Note: pathadd dedupes new paths against existing ones.
#       Duplicate entries in the path just slow down lookups.


function pathadd
{
  [ -n "$(which sed)" ] || \
  {
    echo "ERROR:  Pathadd needs sed.  Please install sed.  Quitting." >&2
    return 1
  }

  local priority=0
  local realpath=0
  local name=PATH

  while [ "x-" = "x${1:0:1}" ]
  do
      # check this isn't an end of flags - or --
      [ "x-"  = "x$1" ] && break
      [ "x--" = "x$1" ] && break

      # Read the flag
      argv1="${1:1}"
      shift 1
      while (( ${#argv1} > 0 ))
      do
      case "${argv1:0:1}" in
          n)   name="$1"
               [[ "$name" == +([abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_])*([abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_1234567890]) ]] ||\
               { echo "The given \"$name\" is not a valid variable name"
                 return 1
               }
               shift 1
               ;;
          p)   priority=1
               ;;
          r)   realpath=1
               ;;
          *)   echo "Don't recognise flag \"$1\" remainder \"$argv1\"" >&2
               return 1
               ;;
      esac
      argv1="${argv1:1}"
      done
  done

  local path
  local path_supplement
  local priority_path_supplement
  local trailing_path_supplement

  eval path=\"\$${name}\"

  while (( $# > 0 ))
  do
      if (( realpath == 1 ))
      then path_supplement="$(realpath $1)"
      else path_supplement="$1"
      fi
      shift 1

      if (( priority == 1 ))
      then priority_path_supplement="$path_supplement"
           trailing_path_supplement=""
      else trailing_path_supplement="$path_supplement"
           priority_path_supplement=""
      fi

      path=":${path}:"
      path="$(echo "$path" | sed "s?:${path_supplement}:?:?g")"
      path="${priority_path_supplement}:${path}:${trailing_path_supplement}"
      path="$(echo "$path" | sed 's/^:*//g;s/:*$//g;s/::*/:/g')"
  done
  export $name="$path"
}

function pathsubtract
{
  [ -n "$(which sed)" ] || \
  {
    echo "ERROR:  Pathadd needs sed.  Please install sed.  Quitting." >&2
    return 1
  }

  local name=PATH
  local realpath=0

  while [ "x-" = "x${1:0:1}" ]
  do
      # check this isn't an end of flags - or --
      [ "x-"  = "x$1" ] && break
      [ "x--" = "x$1" ] && break

      # Read the flag
      argv1="${1:1}"
      shift 1
      while (( ${#argv1} > 0 ))
      do
      case "${argv1:0:1}" in
          n)   name="$1"
               [[ "$name" == +([abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_])*([abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_1234567890]) ]] ||\
               { echo "The given \"$name\" is not a valid variable name"
                 return 1
               }
               shift 1
               ;;
          r)   realpath=1
               ;;
          *)   echo "Don't recognise flag \"$1\" remainder \"$argv1\"" >&2
               return 1
               ;;
      esac
      argv1="${argv1:1}"
      done
  done


  local path
  local path_supplement

  eval path=\"\$${name}\"

  while (( $# > 0 ))
  do
      if (( realpath == 1 ))
      then path_supplement="$(realpath $1)"
      else path_supplement="$1"
      fi
      shift 1

      path=":${path}:"
      path="$(echo "$path" | sed "s?:${path_supplement}:?:?g")"
      path="$(echo "$path" | sed 's/^:*//g;s/:*$//g;s/::*/:/g')"
  done
  export $name="$path"
}

pathrm()
{
  pathsubtract "$@"
}