#include <assert.h>
#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>

/*

       -A, --show-all
              equivalent to -vET

       -b, --number-nonblank
              number nonempty output lines, overrides -n

       -e     equivalent to -vE

       -E, --show-ends
              display $ at end of each line

       -n, --number
              number all output lines

       -s, --squeeze-blank
              suppress repeated empty output lines

       -t     equivalent to -vT

       -T, --show-tabs
              display TAB characters as ^I

       -u     (ignored)

       -v, --show-nonprinting
              use ^ and M- notation, except for LFD and TAB

   */

static unsigned long long delay_nsecs = 0;
static unsigned chunk_size = 4096;

static void
calc_timespec(struct timespec *ts, unsigned long long nsecs)
{
	ts->tv_sec = nsecs / 1000000000;
	ts->tv_nsec = nsecs % 1000000000;
}

static void
do_it(int fd, const char *fn, unsigned chunk_size)
{
	char inbuf[chunk_size];
	const size_t max = sizeof(inbuf);
	size_t len = 0;
	ssize_t n;
	int done = 0;

	while (!done) {

		// fill buffer
		assert(max > len);
		n = read(fd, inbuf + len, max - len);
		if (n < 0) {
			perror(fn);
			exit(EXIT_FAILURE);
		}
		if (!n) { // closed
			done = 1;
			continue;
		}
		len += n;

		// empty buffer
		size_t i = 0;
		while (i < len) {
			struct timespec ts;
			size_t n = len - i;
			calc_timespec(&ts, delay_nsecs * n);
			nanosleep(&ts, NULL);
			n = write(STDOUT_FILENO, inbuf + i, n);
			assert(n != 0);
			if (n < 0) {
				perror("slowcat");
				exit(EXIT_FAILURE);
			}
			i += n;
		}
		assert(len == i);
		len -= i;

	}
}

int
main(int argc, char *argv[])
{
	int i;
	int opt;

	while ((opt = getopt(argc, argv, "AbeEnstTuvd:c:")) != -1) {
		switch (opt) {
		case 'd':
			assert(optarg != NULL);
			delay_nsecs = strtoull(optarg, NULL, 0);
			break;
		case 'c':
			assert(optarg != NULL);
			chunk_size = strtoul(optarg, NULL, 0);
			break;
		default:
                   fprintf(stderr, "Usage: %s [-d delay_nsecs] [-c chunk_size] [files ... ]\n",
                           argv[0]);
                   exit(EXIT_FAILURE);
		}

	}

	if (optind >= argc) {
		do_it(STDIN_FILENO, "<stdin>", chunk_size);
	} else for (;optind < argc; optind++) {
		const char *fn = argv[optind];
		int fd = open(fn, O_RDONLY);
		if (fd < 0) {
			perror(fn);
			exit(EXIT_FAILURE);
		}
		do_it(fd, fn, chunk_size);
	}

	return 0;
}