#!/bin/bash
{# nocheck: shell-template  grandfathered, values only: the mail envelope, charset and timeout #}
set -u
# Reverse systemd escaping for human-readable mail subject/body
friendly="$(systemd-escape --unescape "$1")"

sendmail_bin="$(command -v sendmail 2>/dev/null || true)"
if [ -z "$sendmail_bin" ] && [ -x /usr/sbin/sendmail ]; then
  sendmail_bin="/usr/sbin/sendmail"
fi
if [ -z "$sendmail_bin" ] && [ -x /usr/bin/sendmail ]; then
  sendmail_bin="/usr/bin/sendmail"
fi
if [ -z "$sendmail_bin" ]; then
  echo "ERROR: sendmail binary not found" >&2
  exit 1
fi

STATUS_OUT="$(systemctl status --full "$1" 2>/dev/null | head -n 30)"
if [ -z "$STATUS_OUT" ]; then
  esc="$(systemd-escape "$1")"
  STATUS_OUT="$(systemctl status --full "$esc" 2>/dev/null | head -n 30)"
fi

mail_tmp="$(mktemp)"
trap 'rm -f "$mail_tmp"' EXIT

{% set email = lookup('email') %}
cat > "$mail_tmp" <<ERRMAIL
To: {{ lookup('users', 'administrator').email }}
From: systemd <{{ email['from'] }}>
Subject: ${friendly}
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset={{ HOST_CS }}

A problem with the service ${friendly} occurred:

$STATUS_OUT

ERRMAIL

attempts=3
delay=10

for attempt in $(seq 1 "${attempts}"); do
  send_err="$(timeout "{{ email.timeout }}s" "$sendmail_bin" -t < "$mail_tmp" 2>&1 1>/dev/null)"
  rc=$?
  [ "$rc" -eq 0 ] && exit 0

  case "$rc" in
    69 | 75 | 124 | 137) ;;
    76)
      case "$send_err" in
        *"the server sent an empty reply"*) ;;
        *) break ;;
      esac
      ;;
    77)
      case "$send_err" in
        *"server message: 4"* | *"Temporary authentication failure"*) ;;
        *) break ;;
      esac
      ;;
    *) break ;;
  esac

  if [ "$attempt" -lt "$attempts" ]; then
    echo "sendmail transient failure (rc=${rc}), attempt ${attempt}/${attempts}; retrying in ${delay}s" >&2
    sleep "$delay"
  fi
done

[ -n "$send_err" ] && echo "$send_err" >&2

if [ "$rc" -eq 124 ] || [ "$rc" -eq 137 ]; then
  echo "ERROR: sendmail timed out after {{ email.timeout }}s" >&2
  exit 1
fi

exit "$rc"