subcommander

#!/bin/sh
set -eu

export APPLICATION="${APPLICATION:-$0}"
export SUBCOMMANDS="${SUBCOMMANDS:-./subcommands}"
export DESCRIPTION="${DESCRIPTION:-$APPLICATION}"
export HELP_COLUMN_WIDTH="${HELP_COLUMN_WIDTH:-15}"
export HOOK="${HOOK:-}"
export VERSION="${VERSION:-unknown}"

subcommander() {
	scope="$1"
	subcmd="${2:-}"
	newscope="$scope/$subcmd"
	code=0
	shift

	if [ -n "$subcmd" ] &&  [ -d "$newscope" ]; then # if the subcmd is a directory
		shift && subcommander "$newscope" "$@" # recurse into it
	fi

	if [ -n "$subcmd" ] && [ -f "$newscope" ]; then # if given a subcmd is a file
		if is_help "${2:-}"; then # if the subcmd is an indication for help info
			script_to_help "$newscope" # display help info
		elif is_version "${2:-}"; then # if the subcmd is an indication for version info
			display_version # display version info
		else # otherwise execute the file
			shift && "$newscope" "$@" # pass along the rest of a params
		fi
		exit $? # exit with the status of one of the above blocks
	fi

	is_version "$subcmd" && display_version
	if ! is_help "$subcmd"; then
		[ -z "$subcmd" ] || warn "Unknown subcommand: $(scope_to_subcommand "$newscope")"
		code=1
	fi

	usage "$scope/"
	exit "$code"
}

warn() {
	>&2 printf '\e[1;33m%s\e[0m\n' "$*"
}

subcmd_row() {
	echo "$1\`\`$2"
}

usage() {
	draw_row() {
		printf "%-${HELP_COLUMN_WIDTH}s │ %-${HELP_COLUMN_WIDTH}s │ %s\n" "$@"
	}

	suffix=''
	[ -n "$1" ] || suffix=' '

	echo 'Usage:'
	echo "	$APPLICATION $(scope_to_subcommand "$1")$suffix<SUBCOMMAND> [<ARGUMENT>...]"
	echo
	echo "$DESCRIPTION"
	echo
	draw_row SUBCOMMAND ALIASES DESCRIPTION
	IFS=$'\n'
	subcommands_help "$1" | sort -s -k 1,1 | while read -r line; do
		[ -n "$line" ] || continue
		draw_row \
			"$(echo "$line" | cut -d'`' -f1)" \
			"$(echo "$line" | cut -d'`' -f2)" \
			"$(echo "$line" | cut -d'`' -f3)"
	done
}

# Takes a usage string (eg. '<SERVICE_NAME>') and a description string
print_usage() {
	printf 'Usage:\n\t%s\n\n%s\n' "$1" "$2"
}

script_to_usage() {
	suffix=''
	[ -z "$1" ] || suffix=' '
	echo "$APPLICATION $(scope_to_subcommand "$1")$suffix$(extract_from_script 'Usage' "$1")"
}

script_to_help() {
	print_usage "$(script_to_usage "$1")" "$(extract_from_script 'Description' "$1")"
}

subcommands_help() {
	scope="$1"
	out=""
	addToOutput() {
		name="$1"
		aliases="$2"
		description="$3"
		out="$out
$name\`$aliases\`$description"
	}
	addAliasToOutput() {
		name="$1"
		newAlias="$2"
		description="$3"
		if echo "$out" | grep -E "^$name\`" >/dev/null 2>&1; then
			out="$(echo "$out" | sed "s/^$name\`/$name\`$newAlias /")"
		else
			addToOutput "$@"
		fi
	}
	wrapped_readlink() {
		if [ "$(uname)" == 'Darwin' ]; then
			readlink "$@"
		else
			readlink -f "$@"
		fi
	}

	set +f
	linkednsd="$(mktemp -d)"
	for subcmd in "$scope"/*; do
		[ "$(basename "$subcmd")" = 'version' ] && custom_version=true
		[ "$(basename "$subcmd")" = 'help' ] && custom_help=true
		if [ -L "$subcmd" ]; then
			real="$(wrapped_readlink "$subcmd")"
			realsubcmd="$(basename "$real")"
			desc="$(dir_to_usage "$realsubcmd" | cut -d'`' -f 3)"
			[ -d "$real" ] || desc="$(extract_from_script 'Description' "$subcmd")"
			touch "$linkednsd/$realsubcmd"
			addAliasToOutput "$realsubcmd" \
				"$(basename "$subcmd")" \
				"$desc"

		elif [ -f "$subcmd" ] && ! echo "$out" | grep -E "^$(basename "$subcmd")\`" >/dev/null 2>&1; then
			addToOutput "$(basename "$subcmd")" "" "$(extract_from_script 'Description' "$subcmd")"
		elif [ -d "$subcmd" ] && [ ! -f "$linkednsd/$(basename "$subcmd")" ] ; then
			touch "$linkednsd/$(basename "$subcmd")"
			dir_to_usage "$subcmd"
		fi
	done
	set -f
	echo "$out"

	"${custom_help:-false}" || subcmd_row help 'You are looking at it'
	"${custom_version:-false}" || subcmd_row version 'Display version information'
}

extract_from_script() {
	grep -E "^(#|//) $1" "$2" | cut -d":" -f2 | sed 's/^[[:space:]]*//' || true
}

scope_to_subcommand() {
	echo "$1" | sed -e "s@$SUBCOMMANDS/@@" -e 's@/@ @g' -e 's@/$@@'
}

dir_to_usage() {
	subcmd_row "$(basename "$1")" 'Nested subcommand, try giving it --help'
}

is_help() {
	case "${1:-}" in
	'-h' | '--help' | 'help')
		return 0
		;;
	*)
		return 1
		;;
	esac
}

display_version() {
	echo "$VERSION"
	exit 0
}

is_version() {
	case "${1:-}" in
	'-v' | '--version' | 'version')
		return 0
		;;
	*)
		return 1
		;;
	esac
}

maybe_call_hook() {
	# shellcheck disable=SC1090
	[ -z "$HOOK" ] || . "$HOOK" "$@"
}

maybe_call_hook "$@"
subcommander "$SUBCOMMANDS" "$@"