#if 0
exec cc -Wall -Wextra -pedantic $@ -o $(dirname $0)/xx $0
#endif

#include <ctype.h>
#include <err.h>
#include <stdbool.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <sysexits.h>
#include <unistd.h>

static bool allZero(const uint8_t *buf, size_t len) {
    for (size_t i = 0; i < len; ++i)
        if (buf[i]) return false;
    return true;
}

enum {
    FLAG_ASCII = 1,
    FLAG_OFFSET = 2,
    FLAG_SKIP = 4,
};

int main(int argc, char *argv[]) {
    size_t cols = 16;
    size_t group = 8;
    uint8_t flags = FLAG_ASCII | FLAG_OFFSET;
    char *path = NULL;

    int opt;
    while ((opt = getopt(argc, argv, "ac:fg:hk")) > 0) {
        switch (opt) {
            case 'a': flags ^= FLAG_ASCII; break;
            case 'f': flags ^= FLAG_OFFSET; break;
            case 'k': flags ^= FLAG_SKIP; break;
            case 'c': cols = strtoul(optarg, NULL, 10); break;
            case 'g': group = strtoul(optarg, NULL, 10); break;
            default:
                fprintf(stderr, "usage: xx [-afk] [-c cols] [-g group] [file]\n");
                return (opt == 'h') ? EX_OK : EX_USAGE;
        }
    }
    if (!cols) return EX_USAGE;
    if (argc > optind)
        path = argv[optind];

    FILE *file = path ? fopen(path, "r") : stdin;
    if (!file) err(EX_NOINPUT, "%s", path);

    uint8_t buf[cols];
    size_t offset = 0, len = 0;
    for (;;) {
        offset += len;
        len = fread(buf, 1, sizeof(buf), file);
        if (!len) break;

        if ((flags & FLAG_SKIP) && len == sizeof(buf)) {
            static bool skip;
            if (allZero(buf, len)) {
                if (!skip) printf("*\n");
                skip = true;
                continue;
            }
            skip = false;
        }

        if (flags & FLAG_OFFSET)
            printf("%08zx:  ", offset);

        for (size_t i = 0; i < len; ++i) {
            if (group && i && !(i % group)) printf(" ");
            printf("%02x ", buf[i]);
        }

        if (flags & FLAG_ASCII) {
            for (size_t i = len; i < cols; ++i)
                printf((group && !(i % group)) ? "    " : "   ");
            printf(" ");
            for (size_t i = 0; i < len; ++i)
                printf("%c", isprint(buf[i]) ? buf[i] : '.');
        }

        printf("\n");
        if (len < sizeof(buf)) break;
    }

    if (ferror(file)) err(EX_IOERR, "%s", path);
    return EX_OK;
}