#!/bin/sh

set -u #abort when undefined vars are used

# Frobnicator
#
# Copyright (C) 2016 Assaf Gordon <assafgordon@gmail.com>
#
# This program 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 of the License, or
# (at your option) any later version.
#
# This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.

die()
{
    BASE=$(basename "$0")
    echo "$BASE: error: $*" >&2
    exit 1
}

show_help_and_exit()
{
    BASE=$(basename "$0")
    echo \
"Frobnicator - fronbnicates files

Usage: $BASE [OPTIONS] FILE

Mandatory arguments to long options are mandatory for short options too.

Options:
    -h, --help        = This help screen.
    -v, --verbose     = Be verbose.
    -n, --number=N    = example option with value

"
    exit
}



parse_cmdline_options()
{
    verbose=
    number=
    input=
    while test $# != 0 ; do
        case "$1" in
            -h|--h|--he|--hel|--help)
                show_help_and_exit
                ;;

            -v|--v|--ve|--ver|--verb|--verbo|--verbos|--verbose)
                verbose=1
                ;;

            # The user has specied the value as a separate
            # parameter, e.g.:
            #  ./script --number 4
            # so fetch the next param
            -n|--n|--nu|--num|--numb|--numbe|--number)
                shift
                test $# != 0 || die "missing value for -n/--number parameter"
                number="$1"
                ;;

            # The user specified a single-letter option with
            # the value immediately following it, e.g.:
            #  ./script -n4
            # So remove the "-n" prefix and keep the value
            -n*)
                number=${1#-n}
                ;;

            # The user specified a long option with
            # the value immediately following it, e.g.:
            #  ./script --number=4
            # So remove the prefix and keep the value
            --n=*|--nu=*|--num=*|--numb=*|--numbe=*|--number=*)
                number=${1#*=}
                ;;

            --)
                shift
                break;;

            -*)
                die "Unknown option '$1'. See --help for help."
                ;;

            *) break;;
        esac
        shift
    done

    # Parameters input validation
    if test "$number" ; then
        expr match "$number" '^[0-9][0-9]*$' >/dev/null \
            || die "invalid --number value '$number'"
    fi


    test $# -eq 0 \
        && die "missing input file. See --help for more information."
    test $# -ge 2 \
        && die "extra operand ($2). See --help for help."

    # first parameter - filename
    input="$1"

    # optional input validation
    #test -e "$input" \
    #    || die "input file '$input' not found"
}



##
## Program starts here
##
parse_cmdline_options "$@"

if test "$verbose" ; then
    echo "Processing file '$input'"

    test "$number" \
        && echo "optional number = $number" \
        || echo "optional number not set"

fi