#!/bin/sh
#
# xzize.sh, Copyright © 2010, 2019 Matteo Cypriani
#
# This program is free software. It comes without any warranty, to
# the extent permitted by applicable law. You can redistribute it
# and/or modify it under the terms of the Do What The Fuck You Want
# To Public License, Version 2, as published by Sam Hocevar. See
# http://sam.zoy.org/wtfpl/COPYING for more details.
#
# This script recompresses to XZ one or several GZip (.gz, .tgz), BZip2 (.bz2,
# .tbz, .tb2), LZMA (.lzma, .tlz), or Lempel-Ziv (.Z, .taz) compressed file(s).
# The original files are kept.
#
# If a file extension does not correspond to a known compression format, that
# file is compressed to XZ. In that case, the original file is removed.
#
# If the file is already XZ-compressed (.xz, .txz), nothing is done.

#set -x
set -u

# Destination file suffix when source file name suffix is a
# 3-letter compressed tar suffix:
readonly TAR_XZ_EXT=txz

# Default compression level:
COMPRESSION_LEVEL=

test_extension()
{
    FILE="$1"
    EXTENSION="$2"
    NEWEXTENSION=xz
    if [ $# -eq 3 ] ; then
        NEWEXTENSION="$3"
    fi

    BASE="$(echo "$FILE" | sed "s/\.${EXTENSION}//")"
    if [ "$BASE" != "$FILE" ] ; then
        DEST="$BASE".$NEWEXTENSION
        return 0
    fi

    DEST="$FILE"
    return 1
}


do_recompress()
{
    if [ -e "$DEST" ] ; then
        echo "Skipping source file « $SOURCE »: destination file « $DEST » already exists!" >&2
        return 0
    fi
    echo "Recompressing « $SOURCE » to  « $DEST »…"
    $ACTION -c "$SOURCE" | xz $COMPRESSION_LEVEL >"$DEST"
    return $?
}


## Verify number of arguments ##

if [ $# -lt 1 ] ; then
    echo "$0 requires at least one argument!" >&2
    exit 2
fi


## Process files ##

for SOURCE in "$@" ; do
    # Does source file exist?
    if [ ! -e "$SOURCE" ] ; then
        echo "Skipping source file « $SOURCE »: does not exist!" >&2
        continue
    fi

    # Is source file regular?
    if [ ! -f "$SOURCE" ] ; then
        echo "Skipping source file « $SOURCE »: is not a regular file!" >&2
        continue
    fi

    # GZip
    if test_extension "$SOURCE" gz ; then
        ACTION="gunzip"
        do_recompress
        continue
    fi

    # GZipped Tar (.tgz)
    if test_extension "$SOURCE" tgz $TAR_XZ_EXT ; then
        ACTION="gunzip"
        do_recompress
        continue
    fi

    # BZip2
    if test_extension "$SOURCE" bz2 ; then
        ACTION="bunzip2"
        do_recompress
        continue
    fi

    # BZipped Tar (.tbz)
    if test_extension "$SOURCE" tbz $TAR_XZ_EXT ; then
        ACTION="bunzip2"
        do_recompress
        continue
    fi

    # BZipped Tar (.tb2)
    if test_extension "$SOURCE" tb2 $TAR_XZ_EXT ; then
        ACTION="bunzip2"
        do_recompress
        continue
    fi

    # LZMA
    if test_extension "$SOURCE" lzma ; then
        ACTION="unlzma"
        do_recompress
        continue
    fi

    # LZMA compressed Tar (.tlz)
    if test_extension "$SOURCE" tlz $TAR_XZ_EXT ; then
        ACTION="unlzma"
        do_recompress
        continue
    fi

    # Compress
    if test_extension "$SOURCE" Z ; then
        ACTION="uncompress"
        do_recompress
        continue
    fi

    # Compressed Tar (.taz)
    if test_extension "$SOURCE" taz $TAR_XZ_EXT ; then
        ACTION="uncompress"
        do_recompress
        continue
    fi

    # XZ
    if test_extension "$SOURCE" xz ; then
        echo "Skipping source file « $DEST »: has already .xz suffix!" >&2
        continue
    fi

    # XZipped Tar (.txz)
    if test_extension "$SOURCE" txz $TAR_XZ_EXT ; then
        echo "Skipping source file « $DEST »: seems to be a XZipped Tar archive (.txz suffix)!" >&2
        continue
    fi

    # Uncompressed file: fall back to simple compression
    echo "Compressing « $SOURCE » to xz…"
    xz $COMPRESSION_LEVEL "$SOURCE"

done

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