#!/usr/bin/env bash
#
# mail-wrapper -- Report results of a command by email
# Copyright (c)2017 Alexander Barton (alex@barton.de)
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#

NAME=$(basename "$0")

# Include "ax-common.sh":
ax_common_sourced=
for dir in "$HOME/lib" "$HOME/.ax" /usr/local /opt/ax /usr; do
	[ -z "$ax_common_sourced" ] || break
	ax_common="${dir}/lib/ax/ax-common.sh"
	# shellcheck source=/usr/local/lib/ax/ax-common.sh
	[ -r "$ax_common" ] && . "$ax_common"
done
if [ -z "$ax_common_sourced" ]; then
	echo "Error ($(basename "$0")): \"ax-common.sh\" not found, aborting!"
	echo "Please install 'ax-unix', \"Alex' UNIX Tools & Scripts\", and try again."
	exit 99
fi
unset dir ax_common ax_common_sourced

usage() {
	{
		echo
		echo "Usage:"
		echo "  $NAME [--help|--usage]"
		echo "  $NAME {parameters} [<command> [<arg> [<…>]]]"
		echo
		echo "  -C                      Use the \"C\" locale, no localized (error) messages."
		echo "  --errors|-e             Generate email on errors only."
		echo "  --from|-f               Email address of the sender of the email."
		echo "  --subject|-s <subject>  Subject for the email."
		echo "  --to|-t <address>       Email address to send the email to."
		echo
		echo "When no <command> is given, $NAME reads from standard input."
		echo
	} >&2
	exit "${1:-0}"
}

syntax_error() {
	ax_error -l "Syntax error!"
	usage 2
}

# Initialize internal state.
unset is_error
host=$(hostname -f 2>/dev/null || hostname)

# Some defaults (can be adjusted by command line parameters).
unset do_errors_only
unset subject
from="${LOGNAME:-root} <${LOGNAME:-root}@$host>"
to="$from"

# Parse the command line ...
while [[ $# -gt 0 ]]; do
	case "$1" in
		"-C")
			unset LANG
			export LC_ALL="C"
			;;
		"--debug"|"-D")
			export DEBUG=1
			;;
		"--errors"|"-e")
			do_errors_only=1
			;;
		"--from"|"-f")
			shift
			[[ $# -gt 0 ]] || syntax_error
			from="$1"
			;;
		"--help"|"--usage")
			usage
			;;
		"--subject"|"-s")
			shift
			[[ $# -gt 0 ]] || syntax_error
			subject="$1"
			;;
		"--to"|"-t")
			shift
			[[ $# -gt 0 ]] || syntax_error
			to="$1"
			;;
		"-"*)
			syntax_error
			;;
		*)
			# Command to execute follows in command line.
			break
			;;
	esac
	shift
done

# Initialize the "buffer file" on file handle #3. This file will store all
# output, stdout and stderr combined. The file is immediately unliked so that
# we can't leak stale files. Afterwards this script accesses the "buffer file"
# by its file descriptor only.
buffer_file=$(mktemp) \
	|| ax_abort -l "Failed to create buffer file: \"$buffer_file\"!"
ax_debug "buffer_file=\"$buffer_file\""
exec 3>"$buffer_file" \
	|| ax_abort -l "Failed to redirect FD #3 to buffer file!"
rm "$buffer_file" \
	|| ax_error -l "Failed to delete buffer file: \"$buffer_file\"!"
buffer_file="/dev/fd/3"

if [[ $# -gt 0 ]]; then
	# Execute command and save output in buffer file.
	# Use a sub-shell to not pollute our name space!
	error_file=$(mktemp) \
		|| ax_abort -l "Failed to create error buffer file: \"$error_file\"!"
	ax_debug "error_file=\"$error_file\""
	exec 4>"$error_file" \
		|| ax_abort -l "Failed to redirect FD #4 to error file!"
	rm "$error_file" \
		|| ax_error -l "Failed to delete error buffer file: \"$error_file\"!"
	error_file="/dev/fd/4"

	job=$(basename "$1")

	ax_debug "Running command \"$*\" ..."
	exit_code=$(
		"$@" 2>&1 1>&3 | tee "$error_file" >&3
		echo "${PIPESTATUS[0]}"
	)
else
	# Read from stdin and save it to the buffer file.
	error_file="/dev/null"
	job="Job"

	ax_debug "Reading from stdin ..."
	while read -r line; do
		echo "$line" >&3 \
			|| ax_abort -l "Failed to write to buffer file!"
	done
	exit_code=0
fi

ax_debug "exit_code=$exit_code"

count_all=$(wc -l <"$buffer_file" || ax_abort -l "Failed to count buffer file!")
count_err=$(wc -l <"$error_file" || ax_abort -l "Failed to count error file!")

# Error or no error -- that's the question! An error is assumed when either the
# exit code of the command was non-zero or there was output to stderr.
[[ $count_err -gt 0 || $exit_code -ne 0 ]] && is_error=1

# Construct email subject ...
[[ -z "$subject" ]] && subject="$host: $job report"
[[ -n "$is_error" ]] && subject="$subject - ERROR!" || subject="$subject - success"

ax_debug "from=\"$from\""
ax_debug "to=\"$to\""
ax_debug "subject=$subject"

if [[ -n "$DEBUG" ]]; then
	echo "--- stdout+stderr ---"
	cat "$buffer_file"
	echo "--- stderr ---"
	cat "$error_file"
	echo "---"
fi

ax_debug "count_all=$count_all"
ax_debug "count_err=$count_err"
ax_debug "is_error=$is_error"

# No errors detected (exit code & stderr), and email should be sent on errors
# only: so exit early!
[[ -z "$is_error" && -n "$do_errors_only" ]] && exit $exit_code

# No error detected and no output at all: skip email, exit early:
[[ -z "$is_error" && $count_all -eq 0 ]] && exit $exit_code

# Build the report mail.
# Make sure to ignore all mail(1) configuration files, system wide /etc/mailrc
# (by using the "-n" option) as well as ~/.mailrc (by setting the MAILRC
# environment varialbe).
export MAILRC=/dev/null
(
	echo "$job report:"
	echo
	echo " - Host: $host"
	echo " - User: $(id -un)"
	echo " - Exit code: $exit_code"
	echo
	if [[ $# -gt 0 ]]; then
		# A command name is known (not stdin), show it!
		echo "Command:"
		echo "$@"
		echo
	fi
	if [[ $count_err -gt 0 ]]; then
		# Prefix mail with all error messages.
		echo "Error summary:"
		echo "-----------------------------------------------------------------------------"
		cat "$error_file" \
			|| ax_abort -l "Failed to dump error file!"
		echo "-----------------------------------------------------------------------------"
		echo
	fi
	if [[ $count_all -ne $count_err ]]; then
		# Show full output when different to "error output" only.
		cat "$buffer_file" \
			|| ax_abort -l "Failed to dump buffer file!"
	fi
) | mail -n -a "From: $from" -s "$subject" "$to" \
	|| ax_abort -l "Failed to send email to \"$to\"!"

exit $exit_code