#include <stdio.h>
#include <openssl/evp.h>
#include <openssl/err.h>

#define CHUNK_SIZE 8 * 1024

int main(int argc, char *argv[]) {
    if (argc == 0) {
        fprintf(stderr, "Usage: streamhash <algorithm>\n");
        return 1;
    }
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <algorithm>\n", argv[0]);
        return 1;
    }
    const EVP_MD *type = EVP_get_digestbyname(argv[1]);
    if (!type) {
        fprintf(stderr, "Invalid algorithm: %s\n", argv[1]);
        return 1;
    }
    EVP_MD_CTX *ctx = EVP_MD_CTX_new();
    if (EVP_DigestInit(ctx, type) != 1) {
        ERR_print_errors_fp(stderr);
        return 1;
    }
    char chunk[CHUNK_SIZE];
    char loop = 1;
    while (loop) {
        size_t size = fread(chunk, 1, CHUNK_SIZE, stdin);
        if (size != CHUNK_SIZE) {
            if (feof(stdin))
                loop = 0;
            else {
                EVP_MD_CTX_free(ctx);
                perror("fread");
                return 1;
            }
        }
        if (fwrite(chunk, 1, size, stdout) != size) {
            EVP_MD_CTX_free(ctx);
            perror("fwrite");
            return 1;
        }
        if (EVP_DigestUpdate(ctx, chunk, size) != 1) {
            EVP_MD_CTX_free(ctx);
            ERR_print_errors_fp(stderr);
            return 1;
        }
    }
    unsigned char md[EVP_MAX_MD_SIZE];
    unsigned int size;
    if (EVP_DigestFinal(ctx, md, &size) != 1) {
        ERR_print_errors_fp(stderr);
        EVP_MD_CTX_free(ctx);
        return 1;
    }
    for (unsigned int i=0; i < size; i++)
        fprintf(stderr, "%02x", md[i]);
    fprintf(stderr, "\n");
    return 0;
}