extents-difference

#!/bin/bash

# SPDX-FileCopyrightText: 2016-2020 Graham R. Cobb
# SPDX-License-Identifier: GPL-3.0-or-later
#
# Copyright (C) 2016 Graham R. Cobb
# Released under GPL V3.0 -- see LICENSE
#
# extents-difference [-s] <filename>...
#
#
# Output the extents contained in the first named file, with the extents from the other files removed
# I.e. <file1> - ( Union of file2..fileN )
#
# Note: uses file descriptors 7 and 8
#

# Make sure errors are passed back
set -o pipefail

if [ "$1" = "-s" ]
then
    shift
    $0 "$@" | extents-size
    exit $?
fi

if [ $# -lt 2 ]
then
    echo "Usage: $0 <filename> <filename>..." >&2
    exit 1
fi

copy_remainder() {
    cat <&${IN1}-
}

diff2() {
    # File descriptors
    IN1=7
    IN2=8
    exec 7<$1 8<$2

    read -u $IN1 start1 end1 restofline || return 0
    if [ -z "$start1" -o -z "$end1" ] ; then return 0 ; fi
    
    if ! read -u $IN2 start2 end2 restofline ; then copy_remainder ; return $? ; fi
    if [ -z "$start2" -o -z "$end2" ] ; then copy_remainder ; return $? ; fi

    while true
    do
#	echo "Outer loop: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	
	while [ $start1 -gt $end2 ]
	do
	    if ! read -u $IN2 start2 end2 restofline ; then copy_remainder ; return $?; fi
	    if [ -z "$start2" -o -z "$end2" ] ; then copy_remainder ; return $? ; fi
	done

	# Output any extents before extent2
#	echo "Overlap?: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	if [ $start1 -lt $start2 ]
	then
	    if [ $end1 -lt $start2 ] ; then let end=end1 ; else let end=start2-1 ; fi
	    let length=end-start1+1
	    echo $start1 $end $length || return $?
	fi

	# Skip extents contained in extent2
	let start1=end2+1

	if [ $start1 -gt $end1 ]
	then
#	    echo "Before read1: S1=$start1 E1=$end1 S2=$start2 E2=$end2"
	    read -u $IN1 start1 end1 restofline || return 0
	    if [ -z "$start1" -o -z "$end1" ] ; then return 0 ; fi
	fi
    done
}

if [ $# -eq 2 ]
then diff2 "$@"
else
    file1=$1
    file2=$2
    shift 2
    outfile="$(mktemp)" || exit $?

    diff2 $file1 $file2 >$outfile
    status=$?
    if [ $status != 0 ] ; then rm $outfile ; exit $status ; fi

    $0 $outfile "$@"
    status=$?
    rm $outfile
    exit $status
fi