#!/bin/bash
# A v. 2.0 Debian package is nothing but an ar(1) archive that contains
# three members:
# 1. A debian-binary file containing the string "2.0" and a newline,
# 2. A compressed tar archive with a name of control,
# 3. A compressed tar archive with a name of data.
# (See https://en.wikipedia.org/wiki/Deb_%28file_format%29.) Make one.
#
# There are other ways to do this, but they tend to be so complex and
# badly-documented that I found it easier to just roll my own.

# Name executed as
myname="${0##*/}"

# We must specify single directory name and an output file.
if [ $# -ne 2 ]
then
    1>&2 echo "$myname: expecting directory and output file"
    exit 2
fi

# Change to the directory, die if we can't
cd "$1" || exit 2

# Do some sanity checks.
for i in data control
do
    if [ ! -d "$i" ]
    then
        1>&2 echo "$myname: '$1/$i', no such directory"
        exit 2
    fi
done

# If there is no debian-binary file, make one.
dbin="debian-binary"
if [ ! -e "$dbin" ]
then
    1>&2 echo "$myname: warning - '$dbin' does not exist, creating it"
    echo "2.0" > "$dbin" || exit 1
fi

# Remember where we are, and bail on errors
set -e

# Process data
cd data
find * -type f -print0 | xargs -0 md5sum > ../control/md5sums
tar -c -z --owner=0 --group=0 -f ../data.tar.gz *

# Process control
cd ../control
tar -c -z --owner=0 --group=0 -f ../control.tar.gz *

# Finally, make deb file
cd ..
ar r "$2" "$dbin" control.tar.gz data.tar.gz