#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <semaphore.h>
#include <fcntl.h> 

int main(int argc, char** argv) {
	if(argc != 3) {
		fprintf(stderr, "usage: %s name [balance]\n", argv[0]);
		return EXIT_FAILURE;
	}

	char*  name = argv[1];
	float  balance = 0;
	sem_t* sem = sem_open(name, O_CREAT, S_IRWXU, 1);

	sem_wait(sem);

	FILE* f = fopen(name, "r");

	if(f) {
		fread(&balance, sizeof(float), 1, f);
		fclose(f);
	}

	balance += atof(argv[2]);

	printf("%s has %f euros\n", name, balance);
	
	f = fopen(name, "w");
	fwrite(&balance, sizeof(float), 1, f);

	fclose(f);

	sem_post(sem);

	return EXIT_SUCCESS;
}