#!/bin/sh

# calcpath return a path which is $1/$2/$3 when $2 is relative and $2/$3 if absolute.

# Copyright (C) 2021-2023 Free Software Foundation, Inc.
# Contributed by Gaius Mulley <gaius.mulley@southwales.ac.uk>.
#
# This file is part of GNU Modula-2.
#
# GNU Modula-2 is free software; you can redistribute it and/or modify it under
# the terms of the GNU General Public License as published by the Free
# Software Foundation; either version 3, or (at your option) any later
# version.
#
# GNU Modula-2 is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or
# FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
# for more details.
#
# You should have received a copy of the GNU General Public License along
# with gm2; see the file COPYING.  If not, write to the Free Software
# Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. *)


Usage () {
   cat<<EOF
Usage: $0 pathcomponent1 pathcomponent2 subdir
  if pathcomponent2 is relative then pathcomponent1/pathcompinent2/subdir is returned
  otherwise pathcomponent2/subdir is returned
  the path is checked for legality in subdir.
EOF
}

die () {
   printf "calcpath: error: %s\n" "$1" >&2
   exit 1
}

if [ $# -eq 3 ]; then
   case "$2" in
      /*) the_path="$2/$3" ;;
      *) the_path="$1/$2/$3" ;;
   esac
   cd "$3" || die "could not access $3"
   if ( cd "$the_path" ); then
      printf '%s\n' "${the_path}"
   else
      die "${the_path} is not a valid path in subdirectory $3"
   fi
else
   Usage
   exit 1
fi