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

#define LONGMIN 0x8000000000000000
#define RED "\x1b[91m"
#define GRN "\x1b[92m"
#define RST "\x1b[0m"

/* segfaults if x = 0x8000000000000000 */
char* tobin(long int x) {
	size_t i = 0, j = 0;
	char buffer[64];
	char *ret;
	char sgn = x < 0;

	x *= ((x > 0) << 1) - 1;			/* Negate the number without if statement */
	for (; x; x >>= 1) buffer[i++] = '0' + (x & 1); /* Write the bits to the buffer */
	ret = calloc(i + 1 + sgn, sizeof *ret);		/* Allocate an arary for the number */
	ret[0] = '-';					/* Always write minus as the first sign*/
	j += sgn;					/* If sign is negative, increment j so that '-' is not overwritten */
	while (i) ret[j++] = buffer[--i];		/* reverse copy buffer into ret */

	return ret;
}

void handle_main_arg(int argc, char *argv[]) {
	long number;
	char *bin;
	int i;
	
	/* Iterate over every argument and print conversions to stdout */
	for (i = 1; i < argc; ++i) {
		number = atol(argv[i]);

		/* Since I am negating a number using the branchless trick,
		 * Multiplying this number by -1 still gives you a negative number because of the overflow 
		 * Unfortunately this has to be handled separately */
		if (number == LONGMIN) {
			fprintf(stderr, RED "Error: " RST "The number %li does not fit in 64 bits\n", number);
			continue;
		}

		bin = tobin(number);
		printf("Binary for %-20li: %s\n", number, bin);
		free(bin);
	}
}

int handle_main_noarg(char *filename) {
	FILE *f;
	long num, pos, max;
	char *buf;

	f = fopen(filename, "r+");
	if (!f) {
		fprintf(stderr, RED "Error: could not open file %s" RST " (errno %i: %s)\n", filename, errno, strerror(errno));
		return EXIT_FAILURE;
	}
	fseek(f, 0, SEEK_END);
	max = ftell(f);
	fseek(f, 0, SEEK_SET);
	while (fscanf(f, "%li", &num) == 1) {
		if (num == LONGMIN) {
			fprintf(stderr, RED "Error: " RST "The number %li does not fit in 64 bits\n", num);
			continue;
		}
		pos = ftell(f);			/* Remember position in file */
		if (pos >= max) break;
		fseek(f, 0, SEEK_END);		/* Go to end of file */
		buf = tobin(num);		/* Perform conversion */
		fprintf(f, "%s\n", buf);	/* Write the conversion there */
		fseek(f, pos, SEEK_SET);	/* Restore file position*/
		free(buf);
	}
	fclose(f);
	return EXIT_SUCCESS;
}

int main(int argc, char* argv[]) {
	char * filename;
	if (argc < 2) {
		fprintf(stderr, RED "Error: Invalid arguments.\n" RST "Usage: " GRN "%s filename" RST " or " GRN "%s num1 num2 num3...\n" RST, *argv, *argv);
		return EXIT_FAILURE;
	}
	if (argc == 2) return handle_main_noarg(argv[1]);
	handle_main_arg(argc, argv);
	return EXIT_SUCCESS;
}