#!/bin/bash
# I, Ian Kelling, follow the GNU license recommendations at
# https://www.gnu.org/licenses/license-recommendations.en.html. They
# recommend that small programs, < 300 lines, be licensed under the
# Apache License 2.0. This file contains or is part of one or more small
# programs. If a small program grows beyond 300 lines, I plan to switch
# its license to GPL.

# Copyright 2024 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
tmp=(~)
cbase="${tmp[0]}/sysd-mail-once-state"
to=root
dryrun=false
print_all=false
while [[ $1 == -* ]]; do
  case "$1" in
    -h|--help)
      cat <<EOF
Usage: sysd-mail-once [-t TO_ADDRESS] [-ERRORS] SERVICE COMMAND [COMMAND_ARGS...]

For use with systemd timers, to email (with exim) 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.

-a              Email the logs of all errors intead of just the last one.
-t TO_ADDRESS   Address to email about errors
-n              Dry run. Execute command but only print out what we would do in response.
EOF
      exit 0
      ;;
    -[0-9]*)
      errors=${1#-}
      ;;
    -a)
      print_all=true
      ;;
    -t)
      to="$2"
      shift
      ;;
    -n)
      dryrun=true
      ;;
    *)
      echo "error: unexpected arg: $1"
      exit 1
      ;;
  esac
  shift
done

if (( $# < 2 )); then
  echo "error: expected at least 2 args after options. args:"
  exit 1
fi

service="$1"
shift


# maybe run, depending on $dryrun
m() {
  if $dryrun; then
    printf "%s\n" "$*"
  else
    "$@"
  fi
}
# maybe run, with stdin
mi() {
  if $dryrun; then
    printf "%s <<'EOF'\n" "$*"
    cat
    echo EOF
  else
    "$@"
  fi
}
e() {
  if $dryrun; then
    printf "dryrun: %s\n" "$*"
  fi
}

c=$cbase/$service # c for command file path base

e "c=$c"

glob="${c}[0-9]*"
arr=($glob); file="${arr[0]}"; [[ $glob != "$file" ]] || file=
if [[ $file ]]; then
  e "file=$file"
fi

if ! [[ -d $cbase ]]; then
  mkdir -p $cbase
fi


code=0
"$@" || code=$?
if (( code )); then
  send_mail=false
  cursor=$(journalctl --show-cursor -qn0|sed 's/^\s*--\scursor:\s*//')
  if [[ $file ]]; then
    i=${file#"$c"}
    if (( i < errors )); then
      new_file=$c$((i+1))
      m mv $file $new_file
      file=$new_file
      if [[ $file == $c$errors ]]; then
        send_mail=true
      else
        if $dryrun; then
          printf "dryrun: appending to file $file: %s\n" "$cursor"
        else
          printf "%s\n" "$cursor" >>$file
        fi
      fi
    fi
  else
    file=${c}1
    if $dryrun; then
      printf "dryrun: creating $file, contents: %s\n" "$cursor"
    else
      printf "%s\n" "$cursor" >$file
    fi
    if (( errors == 1 )); then
      send_mail=true
    fi
  fi
  if $send_mail; then
    if $print_all; then
      cursor=$(head -n1 $file)
    else
      cursor=$(tail -n1 $file)
    fi
    echo "sysd-mail-once: emailing on $errors errors. exit code: $code"
    mi exim -odf -t <<EOF
To: $to
From: $(id -u -n)@$(hostname -f)
Subject: $HOSTNAME: $service exit code: $code

$(journalctl -u $service.service --after-cursor="$cursor")
EOF
  fi
else
  if [[ $file ]]; then
    m rm -f $file
    if [[ $file == $c$errors ]]; then
      echo "sysd-mail-once: emailing success after >= $errors errors."
      mi exim -odf -t <<EOF
To: $to
From: $(id -u -n)@$(hostname -f)
Subject: $HOSTNAME: $service success

EOF
    fi
  fi
fi