#include<stdio.h>
#include<unistd.h>
#include<fcntl.h>
#include<stdlib.h>
#include<string.h>
#include<sys/mman.h>

#define FILENAME ".charfreq"

int main(int argc, char ** argv){
	char filename[128];
	snprintf(filename, 128, "%s/%s", getenv("HOME"), FILENAME);
	int fd = open(filename, O_RDWR);
	unsigned int *counts;
	if(fd == -1 /* The file does not exist */ ){
		/* Create the file and initialize counts to 0 */
		printf("Initializing %s\n", filename);
		fd = open(filename, O_RDWR | O_CREAT, 0644);
		unsigned int zero = 0;
		for(unsigned int i = 0; i < 256; i++)
			write(fd, &zero, 4);
	}
	counts = mmap(0, 1024, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
	if(counts == MAP_FAILED){
		perror("mmap");
		return 1;
	}

	if(argc > 1 && !strcmp(argv[1], "-p")){
		for(unsigned int i = 0; i < 256; i++)
			printf("Character %u(%c): 	%u\n", i, i, counts[i]);	
		return 0;
	}
	/* Read from standard in and add to character array */
	unsigned char buffer[1024];
	ssize_t readlen;
	while(readlen = read(0, buffer, 1024)){
		/* Process readlen characters */
		for(int i = 0; i < readlen; i++){
			counts[buffer[i]]++;
		}
	}
	munmap(counts, 1024);


	return 0;

}