#!/usr/bin/env sh

# printc(args, description)
#   Helper function to properly format text
printc() {
    args="$1"
    cmd="$2"
    printf '    %s' "$1"
    yes '' | head -n "$((20-${#args}))" | tr \\n ' '
    printf '%s' "$cmd"
    echo
}

# usage()
#   Display usage information
usage() {
    echo   "usage: tartar [-0..9] [--level N] [--format F] DIR"
    echo   "Creates a compressed tape archive of every subdirectory in a given directory"
    echo
    echo   "positional arguments:"
    printc "DIR" "the directory to archive"
    echo
    echo   "parameters:"
    printc "-f, --format" "the compression format to use. default: xz"
    printf '%44s %s\n' "options: gzip, xz"
    printc "-0..-9, --level" "the level of compression to use: default 6"
    echo
    echo   "environment variables:"
    printc "ARCHIVE_DIR" "same as positional argument DIR"
    printc "COMPRESSION_FORMAT" "same as --format"
    printc "COMPRESSION_LEVEL" "same as --level"
}

includes() {
    test="$1"
    shift
    for x in "$@"; do
        if test "$test" = "$x"; then
            return 0
        fi
    done
    return 1
}

FORMATS="gzip xz"
LEVELS="0 1 2 3 4 5 6 7 8 9"

COMPRESSION_FORMAT="xz"
COMPRESSION_LEVEL="-6"

set_format() {
    if includes "$1" "$FORMATS"; then
        COMPRESSION_FORMAT="$1"
    fi
}

set_level() {
    if includes "$1" "$LEVELS"; then
        COMPRESSION_LEVEL="-$1"
    fi
}

parse_args() {
    POSITIONAL_ARGS=""

    # parse args
    while [ $# -gt 0 ]; do
      case $1 in
        -f|--format)
            set_format "$2"
            shift
            shift
            ;;
        --level)
            set_level "$2"
            shift
            shift
            ;;
        -0|-1|-2|-3|-4|-5|-6|-7|-8|-9)
            COMPRESSION_LEVEL="$1"
            shift
            ;;
        -h|--help)
          usage
          exit 0
          ;;
        *)
          POSITIONAL_ARGS="$POSITIONAL_ARGS $1"
          shift # past argument
          ;;
      esac
    done

    # drop the first space
    POSITIONAL_ARGS=$( echo "$POSITIONAL_ARGS" | tail -c +2 )
}

can_archive() {
    if test ! -f "${1}/backup.done"; then
        echo "skipping $1; it is either incomplete or corrupted"
        return 1
    fi

    if test ! -f "${1}/compression.done" || \
        test ! -f "${1}.tar.xz" || \
        ! sha1sum -sc "${1}/compression.done"; then
        return 0
    else
        return 1
    fi
}

parse_args "$@"

# get the first positional argument, trim whitespace
dir=$( echo "$POSITIONAL_ARGS" | cut -d' ' -f1 | xargs )
dir=${dir:-"$ARCHIVE_DIR"}


cd "$dir" || exit 1

for dir in ./*/; do
    dir="${dir%*/}"
    if can_archive "$dir"; then
        fname="$(basename $dir).tar.xz"
        tar cv --exclude='*.done' "$dir" | "$COMPRESSION_FORMAT" "$COMPRESSION_LEVEL" > "$fname"
        sha1sum "$fname" > "${dir}/compression.done"
    fi
done