#!/bin/bash
# Copyright (C) 2014 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

isdiff() {
    local help="Usage: isdiff [--help|-h] [-v] [-x] FILE1 FILE2
Test if FILE1 and FILE2 have the same contents

Returns 0 for same, 1 for diff, 2 for error.

-v   verbose
-r   use most reliable checksum available, ie. sha instead of md5"

    local v x y reliable
    while true; do
        if [[ $1 == --help ]]  || [[ $1 == -[^-]* && $1 == *h* ]]; then
            echo "$help"
            return
        elif [[ $1 == -[^-]* && $1 == *v* ]]; then
            v=true
            shift
        elif [[ $1 == -[^-]* && $1 == *r* ]]; then
            reliable=true
            shift
        else
            break
        fi
    done

    x=($(type -p sha512sum) $(type -p sha256sum) $(type -p sha1sum) $(type -p md5sum))
    if [[ $reliable ]]; then
        sumbinary=$x
    else
        sumbinary=${x[${#x[@]}-1]}
    fi

    [[ $sumbinary ]] || {
	echo "Need 1 of sha512sum sha256sum sha1sum or md5sum for sum() function"
	return 1
    }
    if [[ $# != 2 ]]; then
	[[ $v ]] && echo Error: need 2 arguments.
	return 2
    fi
    if [[ $v ]]; then
	x=$($sumbinary < "$1" ) || return 2
	y=$($sumbinary < "$2" ) || return 2
    else
	{ x=$($sumbinary < "$1" ) ;} 2>/dev/null || return 2
	{ y=$($sumbinary < "$2" ) ;} 2>/dev/null || return 2
    fi
    if [[  $x == "$y" ]]; then
	return 1 # same
    else
	[[ $v ]] && echo "$1" "$2" different.
	return 0
    fi
}
isdiff "$@"