#include <stdio.h>
#include <string.h>
#include <openssl/evp.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <stdint.h>
#include <stdbool.h>

#define BUF_SIZE 4096

void print_usage (void) {
	dprintf(STDERR_FILENO, "Usage:\n"
"\n"
"  hash-pipe ALGORITHM FILENAME LOGFILE\n"
"\n"
"where\n"
"  ALGORITHM is an openssl Digest name, e.g. sha512\n"
"  FILENAME is the name to display within the logfile\n"
"  LOGFILE is a text file into which sha*sum-compatible hashes are to be appended\n");
}

int main (int argc, char **argv) {
	if (argc != 4) {
		print_usage();
		exit(1);
	}
	
	const char *algo_name = argv[1];
	const char *file_name = argv[2];
	const char *log_name = argv[3];
	
	/*
	 * determine the algorithm
	 */
	const EVP_MD *md = EVP_get_digestbyname(algo_name);
	if (md == NULL) {
		dprintf(STDERR_FILENO, "Unknown algorithm: %s\n", algo_name);
		exit(1);
	}
	
	/*
	 * open the file for appending, create if necessary
	 */
	int fd = open(log_name, O_WRONLY | O_APPEND | O_CREAT, 0644);
	if (fd == -1) {
		dprintf(STDERR_FILENO, "Unable to open file for writing: %s\n", log_name);
	}
	
	EVP_MD_CTX *mdctx = EVP_MD_CTX_new();
	EVP_DigestInit_ex(mdctx, md, NULL);
	
	uint8_t buf[BUF_SIZE];
	ssize_t s;
	
	while (true) {
		s = read(STDIN_FILENO, buf, BUF_SIZE);
		
		if (s == -1) {
			dprintf(STDERR_FILENO, "Unknown error.\n");
			exit(1);
		} else if (s == 0) {
			break;
		}
		
		/*
		 * add the chunk to the digest and transparently pass
		 * it to stdout
		 */
		EVP_DigestUpdate(mdctx, buf, s);
		write(STDOUT_FILENO, buf, s);
	}
	
	/*
	 * convert to an ascii representation
	 */
	unsigned char md_value[EVP_MAX_MD_SIZE];
	unsigned int md_len;
	EVP_DigestFinal_ex(mdctx, md_value, &md_len);
	EVP_MD_CTX_free(mdctx);
	
	for (int i = 0; i < md_len; i++) {
		dprintf(fd, "%02x", md_value[i]);
	}
	
	dprintf(fd, "  %s\n", file_name);
	
	close(fd);
	
	return 0;
}