#!/bin/bash
#
# Usage: untar tarball [-]destdir [specific-files-or-directories-to-be-untarred]
#
# Does: tar xf tarball -C destdir --strip-components=1
#
# For example, given the RAPS17.tgz -tarball
# * with conventional command "tar xf RAPS17.tgz" it would create RAPS17
# * we want to be able to strip the leading RAPS17/ component out and untar into (say) gnu.dp/ directory 
# * the command is thus: "untar RAPS17.tgz gnu.dp" would create RAPS17 for (presumably) GNU double precision builds
#

errcnt=0

if [[ $# -ge 2 ]] ; then
    tarball=$1
    destdir=$2
    shift 2
    enforce=0

    if [[ "$(echo $destdir | cut -c1)" = "-" ]] ; then
	enforce=1
	destdir=$(echo $destdir | cut -c2-)
    fi

    if [[ ! -f $tarball ]] ; then
	echo "Error: tarball $tarball does not exist" >&2
	((errcnt += 1))
    fi

    if [[ $enforce -eq 0 ]] && [[ -d $destdir ]] ; then
	echo "Error: destdir $destdir already exists -- use -$destdir syntax for destdir" >&2
	((errcnt += 1))
    elif [[ -f $destdir ]] ; then
	echo "Error: destdir $destdir already exists but is a file" >&2
	((errcnt += 1))
    fi

    if [[ $errcnt -eq 0 ]] ; then
	mkdir -p $destdir || :
	common="$tarball -C $destdir --strip-components=1 ${*:-}"
	is_gz=0
	echo $tarball | egrep -q 'gz$' || is_gz=$?
	if [[ $is_gz -eq 0 ]] ; then # tarball is gzipped -- trying to get speedup with parallel gunzip -- unpigz
	    unpigz=$(which unpigz 2>/dev/null || echo "unpigz")
	    if [[ -x "$unpigz" ]] ; then # multithreaded gzip
		cmd="tar -I $unpigz -xf $common"
	    else
		cmd="tar -zxf $common"
	    fi
	else
	    cmd="tar -xf $common"
	fi
	echo "Executing $cmd" >&2
	$cmd || errcnt=$?
    fi
else
    echo "Usage: $0 tarball [-]destdir [extra-files-or-directories-to-untar]" >&2
    ((errcnt += 1))
fi

exit $errcnt