#include <string.h>
#include <unistd.h>
#include <stdint.h>
#include <fcntl.h>
#include <openssl/sha.h>
#include <openssl/evp.h>

#define RAND_FILE		"/dev/random"
#define SHA_STR			"{SHA256}"

/* string length */
#define LEN_PASSWD_MIN		8
#define LEN_PASSWD_MAX		64
#define LEN_RAND_STR            16
#define LEN_BUFFER		LEN_PASSWD_MAX + LEN_RAND_STR + \
						SHA256_DIGEST_LENGTH
#define LEN_ENC64		64
#define	LEN_SHA_STR		8
#define LEN_FINAL_PASSWD	LEN_ENC64 + LEN_SHA_STR


uint8_t check_passwd(const char *p, size_t len)
{
	return ((len > LEN_PASSWD_MIN) || (len < LEN_PASSWD_MAX)) ? 1 : 0;
}

char* get_crypt_sha256(const char *p)
{
	int rand_fd;
	ssize_t size;
	size_t len = strlen(p);
	char rand_str[LEN_RAND_STR];
	char passwd_buff[LEN_BUFFER];
	char sha_pwd[SHA256_DIGEST_LENGTH];
	char enc64_pwd[LEN_ENC64];
	char *final_pwd;

	rand_fd = open(RAND_FILE, O_RDONLY);
	if (rand_fd < 0) {
		fprintf(stderr, "impossible to open " RAND_FILE "\n");
		exit(EXIT_FAILURE);
	}

	size = read(rand_fd, rand_str, LEN_RAND_STR);
	close(rand_fd);
	if (size != LEN_RAND_STR) {
		fprintf(stderr, "failed to read from " RAND_FILE "\n");
		exit(EXIT_FAILURE);
	}

	memcpy(passwd_buff + SHA256_DIGEST_LENGTH, p, len);
	memcpy(passwd_buff + SHA256_DIGEST_LENGTH + len,
						rand_str, LEN_RAND_STR);

	SHA256((unsigned char*) passwd_buff + SHA256_DIGEST_LENGTH,
			len + LEN_RAND_STR, (unsigned char*) sha_pwd);

	memcpy(passwd_buff, sha_pwd, SHA256_DIGEST_LENGTH);

	EVP_EncodeBlock((unsigned char*) enc64_pwd, (unsigned char*) sha_pwd,
				SHA256_DIGEST_LENGTH + len + LEN_RAND_STR);


	final_pwd = (char*) malloc (LEN_FINAL_PASSWD + 1);
	memcpy(final_pwd, SHA_STR, LEN_SHA_STR);
	memcpy(final_pwd+8, enc64_pwd, LEN_ENC64);
	final_pwd[LEN_FINAL_PASSWD] = '\0';

	return final_pwd;
}