/* See LICENSE file for copyright and license details. */
#include <libsimple-arg.h>
#include <libsimple.h>
#include <regex.h>

USAGE("[-b block-size] [-h] ([-i | +i | -n | +n] ... (-r basic-regex | -e extended-regex | -x text)) ... "
      "file [first-block [last-block]]");


/*
 * TODO on SIGINT stop and print last completed block
 * TODO use madvise, posix_advise or readahead
 * TODO allocate addition blocks to reduce memory copying
 * TODO show progress
 * TODO make program that extracts (binary) or displays (hex + text) the blocks
 * TODO add support for NUL support in regex
 */


struct memstring {
	const char *text;
	size_t len;
	int icase;
};


static struct memstring *texts = NULL;
static size_t ntexts = 0;
static regex_t *automata = NULL;
static size_t nautomata = 0;
static int analyse_holes = 0;
static off_t position;


static void
analyse(char *block, size_t blksize, size_t available) /* TODO */
{
}


static size_t
encountered_data(char *block, size_t blksize, size_t available)
{
	if (available < blksize * 2u)
		return available;

	analyse(block, blksize, available);

	memcpy(&block[0], &block[blksize], blksize);
	position += (off_t)blksize;
	return blksize;

}


static size_t
encountered_hole(char *block, size_t blksize, size_t available, off_t size)
{
	off_t q = size / (off_t)blksize;
	off_t r = size % (off_t)blksize;
	size_t n;

	if (q) {
		q--;
		r += (off_t)blksize;
	}

	while (r || q) {
		n = blksize * 2u - available;
		n = MIN(n, (size_t)r);
		memset(&block[available], 0, n);
		available += n;
		r -= (off_t)n;

		available = encountered_data(block, blksize, available);
		if (q) {
			q--;
			memset(&block[available], 0, blksize);
			available = encountered_data(block, blksize, available);
		}
		if (q) {
			q--;
			memset(&block[available], 0, blksize);
			available = encountered_data(block, blksize, available);
		}
		if (analyse_holes) {
			for (; q; q--)
				available = encountered_data(block, blksize, available);
		}
	}

	return available;
}


static void
encountered_eof(char *block, size_t blksize, size_t available)
{
	analyse(block, blksize, available);
}


static void
eregcomp(regex_t *restrict preg, const char *restrict regex, int cflags)
{
	int e = regcomp(preg, regex, cflags);
	if (e) {
		char buf_static[512];
		char *buf_dynamic = NULL;
		char *buf = buf_static;
		size_t buf_size = sizeof(buf_static);
		size_t r;
	regerror_again:
		r = regerror(e, preg, buf, buf_size);
		if (r > buf_size) {
			buf = buf_dynamic = erealloc(buf_dynamic, buf_size *= 2);
			goto regerror_again;
		}
		eprintf("regcomp %s: %s", regex, buf);
		free(buf_dynamic);
	}
}


int
main(int argc, char *argv[])
{
	const char *path;
	char *block;
	size_t available = 0u;
	int regex_flags = REG_NOSUB;
	int have_unused_flags = 0;
	size_t blksize = 4ul << 10;
	off_t first_block = 0;
	off_t last_block = -1;
	off_t data, hole;
	int skip_holes = 1;
	int fd;
	struct stat st;

	ARGBEGIN {
	case 'r':
	case 'e':
		have_unused_flags = 0;
		automata = ereallocarray(automata, nautomata + 1u, sizeof(*automata));
		eregcomp(&automata[nautomata++], ARG(), regex_flags | (FLAG() == 'e' ? REG_EXTENDED : 0));
		break;

	case 'x':
		have_unused_flags = 0;
		texts = ereallocarray(texts, ntexts + 1u, sizeof(*texts));
		texts[ntexts].text = ARG();
		texts[ntexts].len = strlen(texts[ntexts].text);
		texts[ntexts].icase = !!(regex_flags & REG_ICASE);
		ntexts++;
		break;

	case 'h':
		analyse_holes = 1;
		break;

	case 'b':
		/* TODO set `blksize` */
		break;

	case 'i': regex_flags |= REG_ICASE;    have_unused_flags = 1; break;
	case 'n': regex_flags |= REG_NEWLINE;  have_unused_flags = 1; break;
	default:
		usage();
	} ARGALT('+') {
	case 'i': regex_flags &= ~REG_ICASE;    have_unused_flags = 1; break;
	case 'n': regex_flags &= ~REG_NEWLINE;  have_unused_flags = 1; break;
	default:
		usage();
	} ARGEND;

	if (argc < 1 || argc > 3 || have_unused_flags || !nautomata)
		usage();

	path = argv[0];

	if (argc >= 2)
		; /* TODO set first_block */

	if (argc >= 3) {
		; /* TODO set last_block */
		if (last_block < first_block)
			usage();
	}

	block = emalloc(blksize * 2u);
	first_block *= (off_t)blksize;
	if (last_block >= 0) {
		last_block += 1;
		last_block *= (off_t)blksize;
	}

	/* Open file to analyse */
	fd = open(path, O_RDONLY);
	if (fd < 0)
		eprintf("open %s O_RDONLY", path);

	/* Can skip holes? */
	if (fstat(fd, &st))
		eprintf("fstat %s:", path);
	if (!S_ISREG(st.st_mode))
		skip_holes = 0;

	/* Skip to first block to analyse */
	if (first_block && lseek(fd, first_block, SEEK_SET) == (off_t)-1) {
		off_t remaining = first_block;
		while (remaining) {
			uintmax_t n = MIN((uintmax_t)remaining, (uintmax_t)(blksize * 2u));
			ssize_t r = read(fd, block, (size_t)n);
			if (r <= 0) {
				if (!r)
					goto out;
				if (errno == EINTR)
					continue;
				eprintf("read %s:", path);
			}
			position += (off_t)r;
		}
	}
	position = first_block;

	/* Analyse to last block (to end of file if last_block < 0) */
	for (; last_block < 0 || first_block < last_block; first_block = data) {
		/* Seek to data to find end of hole, and analyse the hole */
		if (skip_holes) {
			data = lseek(fd, first_block, SEEK_DATA);
			if (data == (off_t)-1) {
				data = first_block;
				if (errno != EBADF)
					skip_holes = 0;
				else
					eprintf("lseek %s %ji SEEK_DATA", path, (intmax_t)first_block);
			} else {
				available = encountered_hole(block, blksize, available, data - first_block);
			}
		} else {
			data = first_block;
		}

		/* Seek to hole to find end of data */
		if (skip_holes) {
			hole = lseek(fd, data, SEEK_HOLE);
			if (hole == (off_t)-1) {
				if (errno != EBADF)
					skip_holes = 0;
				else
					eprintf("lseek %s %ji SEEK_HOLE", path, (intmax_t)data);
			} else {
				if (lseek(fd, data, SEEK_SET) == (off_t)-1)
					eprintf("lseek %s %ji SEEK_SET", path, (intmax_t)data);
			}
		} else {
			hole = (off_t)-1;
		}
		if (hole > last_block)
			hole = last_block;

		/* Analyse the data */
		while (data < hole) {
			off_t n_off = hole - data;
			size_t n_size = blksize * 2u - available;
			size_t n = (uintmax_t)n_off > (uintmax_t)SSIZE_MAX ? n_size : MIN((size_t)n_off, n_size);
			ssize_t r = read(fd, &block[available], n);
			if (r <= 0) {
				if (!r)
					goto eof;
				if (errno == EINTR)
					continue;
				eprintf("read %s:", path);
			}
			available += (size_t)r;
			if (available == blksize * 2u)
				available = encountered_data(block, blksize, available);
		}
	}
eof:
	/* Analyse end of file */
	available = encountered_data(block, blksize, available);
	if (skip_holes && first_block < st.st_size)
		available = encountered_hole(block, blksize, available, st.st_size - first_block);
	encountered_eof(block, blksize, available);

out:
	close(fd);

	while (nautomata)
		regfree(&automata[--nautomata]);
	free(automata);
	free(texts);
	free(block);
	return 0;
}