#!/bin/sh
# AUTOSHART: autostart *.desktop files
# Copyright (C) 2022 Case Duckworth <acdw@acdw.net>
# Licensed under the Fair license.  See COPYING for details.
#
# Commentary:
#
# An autostart script.  Called "autoshart" because I literally sharted it out,
# and have /not/ tested it at all. So, caveat emptor, I guess.
#
# Freedesktop autostart specification:
# https://specifications.freedesktop.org/autostart-spec/latest/
# Freedesktop desktop entry specification:
# https://specifications.freedesktop.org/desktop-entry-spec/latest/
#
# Prior art:
# - dex -- https://github.com/jceb/dex
#
# Code:

usage() {
	cat <<EOF
AUTOSHART: autostart without the shit
USAGE:	autoshart -h
	autoshart [-k] [-n] [-q]

FLAGS:
 -h	Show this help and exit.
 -k	Kill all processes started by autoshart and exit.
 -n	Only print what would happen; don't execute anything.
 -q	Don't print any output.
EOF
}

main() {
	PID_FILE="${AUTOSHART_PID_FILE:-/tmp/autoshart.pid}"
	FOUND_FILE="${AUTOSHART_FOUND_FILE:-/tmp/autoshart.found}"
	RUN=true
	QUIET=false
	while getopts hknq opt; do
		case "$opt" in
		h) usage ;;
		k) auto_kill ;;
		n) RUN=false ;;
		q) QUIET=true ;;
		esac
	done
	shift "$((OPTIND - 1))"
	auto_search
}

## Library functions

auto_kill() {
	cat "$PID_FILE" | xargs kill
}

auto_start() { ## auto_start FILE
	eprint "$1"
	# When the .desktop file has the Hidden key set to true, the .desktop
	# file MUST be ignored. When multiple .desktop files with the same name
	# exists in multiple directories then only the Hidden key in the most
	# important .desktop file must be considered: If it is set to true all
	# .desktop files with the same name in the other directories MUST be
	# ignored as well.
	hidden="$(get Hidden "$1")"
	test "$hidden" = true && return "$(die 1 "Stopped: Hidden: $1")"
	# This specification defines 3 types of desktop entries: Application
	# (type 1), Link (type 2) and Directory (type 3). To allow the addition
	# of new types in the future, implementations should ignore desktop
	# entries with an unknown type. (REQUIRED)
	type="$(get Type "$1")"
	test "$type" = Application || return "$(die 2 "Error: Bad desktop type: ${type:-[none]}")"
	# Specific name of the application, for example "Mozilla".  (REQUIRED)
	name="$(get Name "$1" | head -n1)"
	test -n "$name" || return "$(die 3 "Error: No application name")"
	# Program to execute, possibly with arguments. See the Exec key for
	# details on how this key works. The Exec key is required if
	# DBusActivatable is not set to true. Even if DBusActivatable is true,
	# Exec should be specified for compatibility with implementations that
	# do not understand DBusActivatable. (Makes no sense to be omitted in an
	# autostart context --- acdw)
	exec="$(get Exec "$1")"
	test -n "$exec" || return "$(die 4 "Error: No Exec key: $1")"
	# The OnlyShowIn entry may contain a list of strings identifying
	# the desktop environments that MUST autostart this application, all
	# other desktop environments MUST NOT autostart this application.  The
	# NotShowIn entry may contain a list of strings identifying the desktop
	# environments that MUST NOT autostart this application, all other
	# desktop environments MUST autostart this application.  Only one of
	# these keys, either OnlyShowIn or NotShowIn, may appear in a single
	# .desktop file.
	#
	### The OnlyShowIn, NotShowIn keys are specified thus:
	#
	# A list of strings identifying the desktop environments that should
	# display/not display a given desktop entry.
	#
	# By default, a desktop file should be shown, unless an OnlyShowIn key
	# is present, in which case, the default is for the file not to be
	# shown.
	#
	# If $XDG_CURRENT_DESKTOP is set then it contains a colon-separated list
	# of strings. In order, each string is considered. If a matching entry
	# is found in OnlyShowIn then the desktop file is shown. If an entry is
	# found in NotShowIn then the desktop file is not shown. If none of the
	# strings match then the default action is taken (as above).
	#
	# $XDG_CURRENT_DESKTOP should have been set by the login manager,
	# according to the value of the DesktopNames found in the session
	# file. The entry in the session file has multiple values separated in
	# the usual way: with a semicolon.
	#
	# The same desktop name may not appear in both OnlyShowIn and NotShowIn
	# of a group.
	#
	### I think this "functionality" is dubious at best and pretty
	### ... silly.  --- acdw
	onlyshowin="$(get OnlyShowIn "$1")"
	notshowin="$(get NotShowIn "$1")"
	if test -n "$onlyshowin" && test -n "$notshowin"; then
		return "$(die 5 "Error: Incompatible keys: OnlyShowIn, NotShowIn: $1")"
	elif test -n "$onlyshowin"; then
		start=false
	else
		start=true
	fi

	# This is so cursed
	quit="$(
		echo "$XDG_CURRENT_DESKTOP" | tr : \\n |
			while read desktop; do
				case "$onlyshowin;$notshowin" in
				*$desktop*)
					if test -n "$onlyshowin"; then
						break
					elif test -n "$notshowin"; then
						echo true
						die 6 "Stopped: NotShowIn=$notshowin"
					fi
					;;
				*)
					if ! $start; then
						echo true
						die 6 "Stopped: OnlyShowIn=$onlyshowin"
					fi
					;;
				esac
			done
		echo false
	)"
	if $quit; then
		return 6
	fi

	# A .desktop file with a non-empty TryExec field MUST NOT be autostarted
	# if the value of the TryExec key does NOT match with an installed
	# executable program. The value of the TryExec field may either be an
	# absolute path or the name of an executable without any path
	# components. If the name of an executable is specified without any path
	# components then the $PATH environment is searched to find a matching
	# executable program.
	tryexec="$(get TryExec "$1")"
	if test -n "$tryexec"; then
		command -v "$tryexec" | grep -v ^alias | grep -q / ||
			return "$(die 7 "Error: TryExec command not found: $tryexec")"
	fi
	# If all these tests pass, we're ready to go
	# XXX: probably won't do quoting properly
	eprint "> $exec"
	if $RUN; then
		$exec &
		print $! >>"$PID_FILE"
	fi
	:
}

auto_search() { ## auto_search
	#  The Autostart Directories are $XDG_CONFIG_DIRS/autostart as defined
	#  in accordance with the "Referencing this specification" section in
	#  the "desktop base directory specification".
	#
	# If the same filename is located under multiple Autostart Directories
	# only the file under the most important directory should be used.
	#
	# Example: If $XDG_CONFIG_HOME is not set the Autostart Directory in the
	# user's home directory is ~/.config/autostart/
	#
	# Example: If $XDG_CONFIG_DIRS is not set the system wide Autostart
	# Directory is /etc/xdg/autostart/
	#
	# Example: If $XDG_CONFIG_HOME and $XDG_CONFIG_DIRS are not set and the
	# two files /etc/xdg/autostart/foo.desktop and
	# ~/.config/autostart/foo.desktop exist then only the file
	# ~/.config/autostart/foo.desktop will be used because
	# ~/.config/autostart/ is more important than /etc/xdg/autostart/
	echo "${XDG_CONFIG_HOME:-$HOME/.config}:${XDG_CONFIG_DIRS:-/etc/xdg}" | tr : \\n |
		sed 's,$,/autostart,' |
		while read dir; do
			if test -d "$dir"; then
				for desktop in "$dir"/*.desktop; do
					if ! grep -q "$desktop" "$FOUND_FILE"; then
						auto_start "$desktop" &&
							# `echo' here is
							# important; it /needs/
							# to be output to the
							# $FOUND_FILE
							echo "$desktop" >>"$FOUND_FILE"
					else
						eprint "Already executed: $desktop"
					fi
				done
			fi
		done
}

## Convenience functions

get() { # get KEY FILE
	grep "^$1" "${2:-}" 2>/dev/null | cut -d= -f2-
}

print() {
	$QUIET || printf '%s\n' "$*"
}

eprint() {
	print "$@" >&2
}

die() {
	errcode="$1"
	shift
	eprint "! $@"
	echo $errcode
	exit $errcode
}

## Entry point

test "$DEBUG" && set -x
main "$@"