snotify

#!/bin/sh -e

help() {
	cat - >&2 <<EOF
snotify - a simple notification system

snotify [-ndr]

snotify is a simple notification system designed for use with status
bars et al. and based around keeping notifications in a single file
located at ~/.snotify (snotify manages this file, don't modify it
manually).

The default behavior when supplied no arguments is to display the most
recent notification.

The following options are recognized:

-n msg...
	Add notification msg. Multiple arguments to this option will be
	joined by the first character of the IFS (usually whitespace).

-d
	Delete the most recent notification

-r
	Delete all notifications

-
	Concatenate stdin onto the end of the notification file
EOF
}

case "$1" in --help|-h) help; exit 0;; esac

: "${SNOTIFY_FILE:="$HOME"/.snotify}"
case "$SNOTIFY_FILE" in -*) SNOTIFY_FILE=./"$SNOTIFY_FILE" ;; esac

LOCK=$SNOTIFY_FILE.lock

if command -v flock > /dev/null 2>&1; then
	has_flock=1
else
	unset -v has_flock
fi

lock() {
	# tries a good lock implementation, falls back to something dirtier
	if [ "$has_flock" ]; then
		exec 9> "$LOCK"
		flock 9
	else
		while ! mkdir "$LOCK"; do
			sleep 0.1
		done
	fi
}

unlock() {
	if [ "$has_flock" ]; then
		flock -u 9
	else
		rmdir "$LOCK"
	fi
}

if [ ! "$has_flock" ]; then
	trap 'trap - EXIT QUIT HUP INT TERM ABRT; rmdir "$LOCK"' EXIT QUIT HUP INT TERM ABRT
fi

if [ "$*" ]; then
	case "$1" in
		-n)
			lock
			shift 1
			# avoid recording duplicate messages
			if ! grep -Fxqe "$*" "$SNOTIFY_FILE"; then
				printf '%s\n' "$*" >> "$SNOTIFY_FILE"
			fi
			;;
		-d)
			lock
			new=$(head -n -1 "$SNOTIFY_FILE")
			cat > "$SNOTIFY_FILE" <<-EOF
				$new
			EOF
			;;
		-r)
			rm "$SNOTIFY_FILE" "$LOCK"
			;;
		-)
			while read -r line; do
				lock
				# avoid recording duplicate messages
				if grep -Fxqe "$line" "$SNOTIFY_FILE"; then
					continue
				fi
				printf '%s\n' "$line" >> "$SNOTIFY_FILE"
				unlock
			done
			;;
		*)
			help
			exit 1
			;;
	esac
else
	# shouldn't be necessary to lock here
	: >> "$SNOTIFY_FILE"
	tail -n 1 "$SNOTIFY_FILE"
fi