#!/bin/bash

# GPIO.sh

# Copyright © 2016 František Kučera (frantovo.cz)

#

# This program is free software: you can redistribute it and/or modify

# it under the terms of the GNU General Public License as published by

# the Free Software Foundation, version 3 of the License.

#

# This program is distributed in the hope that it will be useful,

# but WITHOUT ANY WARRANTY; without even the implied warranty of

# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the

# GNU General Public License for more details.

#

# You should have received a copy of the GNU General Public License

# along with this program. If not, see <http://www.gnu.org/licenses/>.

# GPIO.sh is a set of functions for controlling GPIO pins of Raspberry Pi or similar computer

_gpio_valid_port() {

	case $1 in 0|1|4|7|8|9|10|11|14|15|17|18|21|22|23|24|25)

		return 0;;

	*)

		return 1;;

	esac

}

# export -f _gpio_valid_port

# seq 0 30 | xargs -n1 bash -c 'printf "%4s" "$0: "; _gpio_valid_port $0 ; if [ $? -eq 0 ]; then echo "valid port number"; else echo; fi'

_gpio_log_error() {

	# TODO: $(date --rfc-3339=seconds) or ● ?

	echo -e "\e[1;31m$1\e[0m"; > /dev/stderr;

}

_gpio_log_warning() {

	echo -e "\e[2;33m$1 \e[0m"; > /dev/stderr;

}

# open (export) the port and set its direction

# parameters:

#	port number

#	direction: in/out

gpio_open() {

	local port="$1";

	local direction="$2";

	if [ $# -ne 2 ] || [[ "$direction" != @("in"|"out") ]]; then _gpio_log_error "usage: ${FUNCNAME[0]} <port> <in|out>"; return 1; fi

	if ! _gpio_valid_port "$port";                          then _gpio_log_error "invalid port number: $port";            return 1; fi;

	if [ -d  "/sys/class/gpio/gpio$port" ]; then 

		_gpio_log_warning "port $port is already exported → will just set direction: $direction";

	else

		echo "$port" > "/sys/class/gpio/export" || return 1;

	fi;

	echo "$direction" > "/sys/class/gpio/gpio$1/direction";

}

# close (unexport) the port and set its direction

# parameters:

#	port number

gpio_close() {

	local port="$1";

	if [ $# -ne 1 ];               then _gpio_log_error "usage: ${FUNCNAME[0]} <port>"; return 1; fi

	if ! _gpio_valid_port "$port"; then _gpio_log_error "invalid port number: $port";   return 1; fi;

	if [ -d  "/sys/class/gpio/gpio$port" ]; then 

		echo "$port" > "/sys/class/gpio/unexport";

	else

		_gpio_log_error "port $port is not open";

		return 1;

	fi;

}

# reads value of given port

# parameters:

#	port number

gpio_read() {

	local port="$1";

	if [ $# -ne 1 ];               then _gpio_log_error "usage: ${FUNCNAME[0]} <port>"; return 1; fi

	if ! _gpio_valid_port "$port"; then _gpio_log_error "invalid port number: $port";   return 1; fi;

	if ! cat "/sys/class/gpio/gpio$port/value"; then

		_gpio_log_error "unable to read value of port $port";

		return 1;

	fi

}

# writes the value to given port

# parameters:

#	port number

#	value: 0/1

gpio_write() {

	local port="$1";

	local value="$2";

	if [ $# -ne 2 ] || [[ "$value" != @("0"|"1") ]]; then _gpio_log_error "usage: ${FUNCNAME[0]} <port> <0|1>"; return 1; fi

	if ! _gpio_valid_port "$port";                   then _gpio_log_error "invalid port number: $port";         return 1; fi;

	if ! echo "$value" > "/sys/class/gpio/gpio$port/value"; then

		_gpio_log_error "unable to write value $value to port $port";

		return 1;

	fi

}