#!/bin/sh
# https://mg.pov.lt/blog/sysadmin-diary.html is the closest this thing has to
# documentation.  Other than the man page, that is.
version=1.2.0
changelog=/root/Changelog
editor=vim

if [ x"$1" = x-h ] || [ x"$1" = x--help ]; then
    echo "Usage: $0 [filename] [-a] [message]"
    echo "Usage: $0 [filename] [-e]"
    echo "Usage: $0 [--] [message]"
    echo
    echo "Opens an admin change log file (default: $changelog) in $editor"
    echo "or appends a timestamped message to the end and prints it."
    echo
    echo "Options:"
    echo "  -h, --help   this help message"
    echo "  --version    print version number and exit"
    echo "  -a           append to the last message without adding a timestamped header"
    echo "  -e           edit the changelog without adding a timestamped header"
    echo "  --           treat the next argument as part of the message"
    echo "               even if it looks like a filename"
    exit
fi

if [ x"$1" = x--version ]; then
    echo "new-changelog-entry version $version"
    echo "Written by Marius Gedminas <marius@gedmin.as>"
    exit
fi

if test -n "$1" && test -f "$1" || test "$1" = "$changelog"; then
    changelog=$1
    shift

    case "$changelog" in
        *[Cc]hangelog*)
            ;;
        *)
            echo "Cowardly refusing to edit $changelog since it doesn't mention Changelog in the filename" 1>&2
            exit 1
            ;;
    esac
fi

swapfile="$(dirname "$changelog")/.$(basename "$changelog").swp"

if [ -f "$swapfile" ]; then
    echo "Someone is currently editing $changelog ($swapfile exists)" 1>&2
    exit 1
fi

if ! [ -w "$changelog" ] && [ "$(id -u)" -ne 0 ]; then
    exec sudo "$0" "$changelog" "$@"
fi

header=1
append=1
if [ x"$1" = x-a ]; then
    header=0
    shift
elif [ x"$1" = x-e ]; then
    header=0
    append=0
    shift $#
elif [ x"$1" = x-- ]; then
    shift
fi

msg="$*"

if [ $header -eq 1 ]; then
    if [ -f "$changelog" ]; then
        # append an empty line if it is not there
        test -n "$(tail -n 1 "$changelog")" && echo >> "$changelog"
    fi

    # append a header
    cat >> "$changelog" <<END
$(date +'%Y-%m-%d %H:%M %z'): ${SUDO_USER:-$USER}
  $msg
END
elif [ $append -eq 1 ]; then
    printf "  %s\n" "$msg" >> "$changelog"
fi

# shellcheck disable=SC2015
test -z "$msg" \
  && exec "$editor" "$changelog" +$ \
  || tail "$changelog"