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

#define LINE_LEN 16

int main(int argc, char **argv)
{
    int readfd = 0;
    if (argc == 2)
    {
        readfd = open(argv[1], O_RDONLY, 0666);
        if (readfd < 0)
        {
            fprintf(stderr, "open: %s\n", strerror(errno));
            return 1;
        }
    }
    else if (argc > 2)
    {
        printf("usage: hd [file]\n");
        return 1;
    }

    char lastbuf[LINE_LEN];
    char curbuf[LINE_LEN];
    int off = 0;
    int lastrep = 0;
    int bytes;

    int i;
    while ((bytes = read(readfd, curbuf, LINE_LEN)) > 0)
    {
        if (off > 0 && !memcmp(lastbuf, curbuf, LINE_LEN))
        {
            if (!lastrep)
            {
                printf("*\n");
                lastrep = 1;
            }
            off += bytes;
            continue;
        }
        lastrep = 0;
        printf("%08x  ", off);
        off += bytes;
        /* print bytes */
        for (i = 0; i < LINE_LEN; ++i)
        {
            if (i < bytes)
            {
                printf("%02x ", (unsigned char)curbuf[i]);
            }
            else
            {
                printf("   ");
            }
            if (i == 7)
            {
                printf(" ");
            }
        }
        /* show printable characters */
        printf("|");
        for (i = 0; i < bytes; ++i)
        {
            char c = curbuf[i];
            if (c < 32 || c > 126)
            {
                printf(".");
            }
            else
            {
                printf("%c", c);
            }
        }
        printf("|\n");
        memcpy(lastbuf, curbuf, LINE_LEN);
    }
    printf("%08x\n", off);

    if (readfd > 0)
    {
        close(readfd);
    }
    return 0;
}