#!/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 [[ $2 = "reset" ]]; then
	if [[ ! "$3" -gt "0" ]]; then echo "Parameter 3: Needs to be a number"; exit;fi
	rm -f $1
	[[ -d "$1_lockdir" ]] && rmdir $1_lockdir
	echo $3 > $1
	exit 0
fi
if [[ ! -f $1 ]]; then echo "Parameter 1: File Does not exist"; exit; fi
if [[ $2 != "lock" ]] && [[ $2 != "release" ]] && [[ $2 != "reset" ]]; then echo "Parameter 2: must be lock, release or reset"; 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"
                        else
                                sleep 1; wait
                        fi
                else
                        sleep 0.5;
                fi
        done
        rmdir $1_lockdir
else
        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
        done
        rmdir $1_lockdir
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