#!/usr/bin/env bash

# A generic counting semaphore in bash
# Parameter is the lockfile and operation
# Setup:
# rm /tmp/test
# echo $num > /tmp/test

set -e
if [[ ! -f $1 ]]; then echo "Parameter 1: File Does not exist"; exit; fi
if [[ $2 != "lock" ]] && [[ $2 != "release" ]]; then echo "Parameter 2: must be lock or release"; exit; fi
if [[ $2 = "lock" ]]; then
	SEM=''
	while [[ -z $SEM ]]; do
		if (( $(cat $1 ) == 0 )); then sleep 1; wait; continue; fi
		if mkdir $1_lockdir > /dev/null 2>&1 ; then
			VAL=$(cat $1)
			if (( $VAL > 0 ))
			then
				SEM=$(sed -i "s@$VAL@$(( $VAL - 1))@w /dev/stdout" $1)
				echo "Take $VAL -> $SEM"
				rmdir $1_lockdir
			else
				rmdir $1_lockdir
				sleep 1; wait
			fi
		else
			sleep 0.5;
		fi
	done
else
	echo "Attempt unlock"
	SEM=''
	while [[ -z $SEM ]]; do
		if mkdir $1_lockdir > /dev/null 2>&1 ; then
			VAL=$(cat $1)
			SEM=$(sed -i "s@$VAL@$(( $VAL + 1))@w /dev/stdout" $1)
			echo "Give $VAL -> $(( $VAL + 1 ))"
		else
			sleep 0.1;
		fi
		rmdir $1_lockdir
	done
fi

#SEM=''; while [[ -z SEM ]]; do VAL=$(cat /tmp/test); if (( $VAL > 0 )); then SEM=$(sed -i "s@$VAL@$(( $VAL - 1))@w /dev/stdout" /tmp/test); else sleep 1; wait; fi; done