#!/bin/bash -eu
# usb-charger.sh: Enable USB charging for devices on Linux.

function usage {
	# show usage
	echo "usb-charger.sh: Enable USB charging for devices on Linux."
	echo "Usage: $0 [bus port [on|auto]]"
	echo
	echo "If no arguments are given, the script will detect your device and ask you to confirm."
	echo "If you specify bus and port, the script will set the control to 'on' for that port."
	echo "If you specify 'on' or 'auto' as the third argument, the script will set the control to that value."
}

function set_usb_power {
	# set control to on or auto for the given bus and port
	local bus=$1
	local port=$2
	local control=${3:-on}
	echo "Setting control to '$control' for port $bus-$port."
	echo "$control" | sudo tee "/sys/bus/usb/devices/$bus-$port/power/control"
}

function list_usb_power {
	# list the current control setting for all ports
	cd /sys/bus/usb/devices || exit
	for dir in [0-9]*-[0-9]*; do
		if [[ $dir == *:* ]]; then
			continue
		fi
		if [ -d "$dir" ]; then
			echo -n "Port $dir: "
			cat "$dir/power/control"
		fi
	done
}

function usbinfo {
	# list the current USB topology
	lsusb -t | perl -ne '
		$bus = 0+$1 if m{^/:  Bus (\d+)\.};
		if (/Port (\d+)/) {
			print "bus=$bus port=$1\n";
		}
	'
}

function detect_usb_port {
	# detect the port your device is plugged into
	local tmpfile1=$(mktemp)
	local tmpfile2=$(mktemp)

	read -p "Please ensure your device is unplugged and press Enter."
	
	usbinfo > $tmpfile1
	
	read -p "Please plug in your device and press Enter."
	
	usbinfo > $tmpfile2
	
	local controller_and_port=$(diff $tmpfile1 $tmpfile2 | sed -n '/^> / { s/^> //; p; q; }')
	
	if [ -z "$controller_and_port" ]; then
		echo "Could not detect your device. Please run the script again."
		exit 1
	fi

	echo "$controller_and_port"
}

function confirm_change {
	# confirm the change with the user, and do it
	local bus=$1
	local port=$2
	read -p "Detected your device on port $bus-$port. Set control to 'on' for this port? (y/n) " answer
	
	if [ "$answer" != "${answer#[Yy]}" ]; then
		echo on | sudo tee "$bus-$port/power/control"
		echo "Done. Your device should continue charging now."
	else
		echo "Okay, no changes made."
	fi
}

function usb_charger {
	# main function
	if [ "${1:-}" = "-h" -o "${1:-}" = "--help" ]; then
		usage
		exit 0
	fi

	local bus=${1:-}
	local port=${2:-}
	local control=${3:-auto}

	# if $# > 3 or bus or port not numeric, or if provided, not both provided, or control if provided not "on" or "auto", error out
	if [[ "$#" -gt 3 || -n "${bus//[0-9]/}" || -n "${port//[0-9]/}" ||
		( -n "$bus" && -z "$port" ) || ( -z "$bus" && -n "$port" ) ||
		( -n "$control" && "$control" != "on" && "$control" != "auto" ) ]]; then
		usage >&2
		exit 1
	fi

	if [ -n "$bus" -a -n "$port" ]; then
		set_usb_power $bus $port $control
	else
		list_usb_power
		controller_and_port=$(detect_usb_port)
		eval $controller_and_port
		confirm_change $bus $port
	fi

}

# if script is being run directly, run the main function
# otherwise, this could be sourced and used as a library
if [ "$0" = "$BASH_SOURCE" ]; then
	usb_charger "$@"
fi