#!/bin/bash

# usage
prog="${0##*/}"
usage="Usage: $prog <recipients> <command>

    Run <command> and, if the command fails, email its output (both
    stdout and stderr) to one or more comma-delimited <recipients>.

    Log the command's output to a file regardless. The path to the log
    file is determined as follows, with \$cmd equal to the basename of
    <command>'s executable.

        * If the \$LOGFILE environment variable is set, log to that file.
        * If the effective user id is root, log to /var/local/$prog/\$cmd.log
        * Otherwise, log to ~/log/\$cmd.log

    By default, the email's subject is \"Failure report for \`<command>\`\",
    and its sender is \`whoami\`@\`hostname -f\`. Use the \$SUBJECT
    and/or \$MAILFROM environment variables to override this behavior.
"

# parse args
mailto="$1"
shift

# check args
if [[ $# == 0 || "$mailto" != *@* || "$mailto $*" == *'--help'* ]]; then
	echo "$usage" >&2
	exit 1
fi

# create temp file
trap 'rm -f "$tmpfile"' EXIT
tmpfile="$(mktemp --tmpdir "$prog.XXXXXXXXXX")"

# prep log file
if [[ -n "$LOGFILE" ]]; then
	logfile="$LOGFILE"
elif (( EUID == 0 )); then
	logfile="/var/local/$prog/${1##/*}.log"
else
	logfile="$HOME/log/${1##/*}.log"
fi
mkdir -p -m 700 "$(dirname "$logfile")"

# print timestamps, run the command we were passed,
# capture its output in a temp file,
# and log its output in a log file
set -o pipefail
(
	date +"%F %T %:z $prog: Started running \`$*\`"
	"$@"
	retval=$?
	date +"%F %T %:z $prog: Finished running \`$*\`: Exit status $retval"
	exit $retval
) 2>&1 | tee "$tmpfile" &>> "$logfile"
retval=$?
set +o pipefail

# check if the command failed
if (( $retval != 0 )); then
	# it failed, so send an email notification
	sendmail -t <<-EOF
		Subject: ${SUBJECT-"Failure report for \`$*\`"}
		To: $mailto
		From: ${MAILFROM-$(whoami)@$(hostname -f)}

		$(< "$tmpfile" )
	EOF
fi