#!/usr/bin/env bash

_VERSION="0.2.0"

function help() {
	I="  "
	cat <<USAGE
fsw - run a command when a file is modified

Usage:
${I}fsw <command> [filter] [dirs...]

${I}command - the specified bash command to eval
${I}filter  - an optional filename filter
${I}dirs    - the directories to watch (defaults to current directory)

Advanced:
${I}Command Variables:
${I}${I}Your commands have runtime access to some variables associated with the
${I}${I}${I}inotifywait event enabling further extensibility:
${I}${I}+ FSW_FILENAME    - the name of the file
${I}${I}+ FSW_DIR         - the directory containing the file
${I}${I}+ FSW_PATH        - the full relative path of the file
${I}${I}+ FSW_FILE_EVENTS - a comma-separated list of the inotify events
${I}Environment:
${I}${I}Some customization options exist using environment variables
${I}${I}${I}due to their uncommon usage.
${I}${I}+ FSW_EVENTS - the list of events to have inotifywait observe

References:
${I}+ Filter works with grep -P
${I}+ See inotifywait(1) for FSW_EVENTS options.

Examples:
${I}fsw 'make' '\.c$'
${I}fsw 'bash \$filename' '\.bash$'
${I}fsw 'mix test --failed' '.exs?$' lib test
${I}FSW_EVENTS=open,access fsw 'espeak "Intruder Alert!"' \\
${I}${I}${I}'.*' /etc/secrets \$HOME/.secrets
USAGE
}

dbg() {
	if [[ ! -z ${FSW_DEBUG+x} ]]; then
		echo -e "[debug] fsw: $@"
	fi
}

if [[ $1 = '-h' ]] || [[ $1 = '--help' ]] || [[ -z $1 ]]; then
	help
	exit 0
fi

FSW_EVENTS="${FSW_EVENTS:-close_write}"
dbg "Events: $FSW_EVENTS"
SHELL_COMMAND="${1}"; shift
dbg "Command: $SHELL_COMMAND"
FILTER="${1}"; shift
dbg "Filter: $FILTER"
dbg "Directory: ${1}"
DIRS=("${1:-.}"); shift
if [[ -e $FILTER ]]; then
	# TODO: this is a sad hack/workaround
	echo "It looks like your filter is an actual file. I'll just watch that for you."
	DIRS=("${FILTER}")
fi
while [[ ! -z $1 ]] && $(realpath $1) &> /dev/null; do
	dbg "Directory: ${1}"
	DIRS+=("$1"); shift
done
inotifywait -m -e "${FSW_EVENTS}" -r "${DIRS[@]}" 2>&1 \
	| grep --line-buffered -v '  Beware: since -r was given, this may take a while!' \
	| while read -r dir events filename; do
	if [[ "$dir $events" = "Watches established." ]]; then
		echo "Ready."
		dbg "Directory: ${DIRS[@]}"
	else
		export FSW_FILENAME="$filename"
		export FSW_DIR="$dir"
		export FSW_PATH="$dir$filename"
		export FSW_FILE_EVENTS="$events"
		export FSW_EVENT="$events $dir$filename"
		dbg "Event:\n  $(date)\n  $FSW_PATH\n  $FILTER\n  $FSW_EVENT\n  $dir $events $filename\n  ${SHELL_COMMAND}"
		dbg "Filtered Event: $(<<< "$FSW_PATH" grep -P "$FILTER")"
		<<< "$FSW_PATH" grep -P "$FILTER" > /dev/null 2>&1 && eval "${SHELL_COMMAND}" &> /dev/null
	fi
done