#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/md5.h>

int main() {
	size_t PUZZLE_SIZE = 8;		//puzzle input is 8 characters with no ending newline character

	//load input string
	FILE *file = fopen("input", "r");
	if (file == NULL) {
		perror("main: error opening file.");
		return -1;
	}
	char input[256];
	while (fgets(input, sizeof(input), file));
	if (strlen(input) != PUZZLE_SIZE) {		
		perror("main: error reading file.");
		return -1;
	}
	printf("puzzle input: %s\n", input);
	
	//initialize MD5 context
	//note: ignore gcc's warnings that MD5 is depreciated
	MD5_CTX md5_context;
	uint8_t md5_hash[MD5_DIGEST_LENGTH];
	char md5_string[MD5_DIGEST_LENGTH * 2 + 1];	//32 hexadecimal digits
												//each byte needs two characters in hex, plus one for '\0'
	char *md5_string_ptr = md5_string;
	
	int32_t chars_written;
	int32_t available_space;
	int32_t count = -1;		//initialize count at -1 so that the first count++ sets it to 0
 	
	while (strncmp(md5_string, "00000", 5) != 0) {
		count++;
		chars_written = snprintf(input + PUZZLE_SIZE, sizeof(input) - strlen(input), "%i", count);
        available_space = sizeof(input) - strlen(input);
		if (chars_written >= available_space) {
			perror("main: buffer overflow.");
			return -1;
		}
   	
		//initialize MD5 context
		MD5_Init(&md5_context);
        
		//update context with input (+ count) data
		MD5_Update(&md5_context, input, strlen(input));

		//finalize MD5 hash
		MD5_Final(md5_hash, &md5_context);

	    for (int i = 0; i < MD5_DIGEST_LENGTH; i++) {
			md5_string_ptr += sprintf(md5_string_ptr, "%02x", md5_hash[i]);
		}
		md5_string_ptr = md5_string;	//reset pointer
	}
	
	printf("count %i: %s\n", count, md5_string);
	return 0;
}