#!/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

 }