#!/bin/bash
# Copyright (C) 2016 Ian Kelling

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.


set -eE -o pipefail
trap 'echo "$0:$LINENO:error: \"$BASH_COMMAND\" returned $?" >&2' ERR

errors=3
cbase=$HOME/sysd-mail-once-state
case "$1" in
    -h|--help)
        cat <<EOF
Usage: sysd-log-once [-ERRORS] SERVICE COMMAND [ARGS...]
For systemd timers, email on repeated failure & success after failure.

In the service triggered by the timer, prepend this script to the ExecStart.
The email will contain the service's logs for the last ERRORS runs.


Stores error counts in $cbase

-ERRORS:  ERRORS is the number of failurs to accumulate before mailing the error.
          Default is 3.
EOF
        exit 0
        ;;
    -[0-9]*)
        errors=${1#-}
        shift
        ;;
esac
service=$1
shift

c=$cbase/$service

glob="$c[0-9]*"
arr=($glob); file="${arr[0]}"; [[ $glob != "$file" ]] || file=
u=${USER:-root}
[[ -d $cbase ]] || mkdir -p $cbase

if [[ ! $file ]]; then
    cursor=$(journalctl --show-cursor -qn0|sed 's/^\s*--\scursor:\s*//')
fi
if "$@"; then
    if [[ $file ]]; then
        rm -f $file
        if [[ $file == $c$errors ]]; then
            echo | mail -s "$HOSTNAME: $service success" $u@localhost
        fi
    fi
else # $@ failed
    if [[ $file ]]; then
        i=${file#$c}
        if (( i < errors )); then
            new_file=$c$((i+1))
            mv $file $new_file
            file=$new_file
            if [[ $file == $c$errors ]]; then
                journalctl -u $service.service --after-cursor=$(<$file) | \
                    mail -s "$HOSTNAME: $service failure" $u@localhost
            fi
        fi
    else
        file=${c}1
        printf "%s\n" "$cursor" >$file
    fi
fi