/* SPDX-License-Identifier: GPL-3.0-or-later
   Origin: coreutils-9.7/lib/filevercmp.c
   Copyright (C) 1995 Ian Jackson <iwj10@cus.cam.ac.uk>
   Copyright (C) 2001 Anthony Towns <aj@azure.humbug.org.au>
   Copyright (C) 2008-2025 Free Software Foundation, Inc.
*/

#ifndef _GNU_SOURCE
#define _GNU_SOURCE
#endif

#include <cctype>
#include <climits>
#include <cstddef>
#include <cstdlib>

#include "coreutils-sort.hh"

/* Return the length of a prefix of S that corresponds to the suffix
   defined by this extended regular expression in the C locale:
     (\.[A-Za-z~][A-Za-z0-9~]*)*$
   Use the longest suffix matching this regular expression,
   except do not use all of S as a suffix if S is nonempty.
   If *LEN is -1, S is a string; set *LEN to S's length.
   Otherwise, *LEN should be nonnegative, S is a char array,
   and *LEN does not change. */
static
ptrdiff_t file_prefixlen(char const * s, ptrdiff_t * len)
{
	size_t n = *len; /* SIZE_MAX if N == -1. */
	ptrdiff_t prefixlen = 0;

	for (ptrdiff_t i = 0; ; ) {
		if ((*len < 0) ? !s[i] : (i == n)) {
			*len = i;
			return prefixlen;
		}

		i++;
		prefixlen = i;
		while ((i + 1 < n) && (s[i] == '.') && (isalpha(s[i + 1]) || (s[i + 1] == '~'))) {
			for (i += 2; (i < n) && (isalnum(s[i]) || (s[i] == '~')); i++) {
				continue;
			}
		}
	}
}

/* Return a version sort comparison value for S's byte at position POS.
   S has length LEN. If POS == LEN, sort before all non-'~' bytes. */
static
int order(char const * s, ptrdiff_t pos, ptrdiff_t len)
{
	if (pos == len) return -1;

	unsigned char c = s[pos];
	if (isdigit(c)) return 0;
	else if (isalpha(c)) return c;
	else if (c == '~') return -2;
	else
	{
		static_assert (UCHAR_MAX <= (INT_MAX - 1 - 2) / 2);
		return c + UCHAR_MAX + 1;
	}
}

/* slightly modified verrevcmp function from dpkg
   S1, S2 - compared char array
   S1_LEN, S2_LEN - length of arrays to be scanned

   This implements the algorithm for comparison of version strings
   specified by Debian and now widely adopted. The detailed
   specification can be found in the Debian Policy Manual in the
   section on the 'Version' control field. This version of the code
   implements that from s5.6.12 of Debian Policy v3.8.0.1
   https://www.debian.org/doc/debian-policy/ch-controlfields.html#s-f-Version */
static
int verrevcmp(const char * s1, ptrdiff_t s1_len, const char * s2, ptrdiff_t s2_len)
{
	ptrdiff_t s1_pos = 0;
	ptrdiff_t s2_pos = 0;

	while (s1_pos < s1_len || s2_pos < s2_len) {
		int first_diff = 0;
		while (((s1_pos < s1_len) && !isdigit(s1[s1_pos])) || ((s2_pos < s2_len) && !isdigit(s2[s2_pos]))) {
			int s1_c = order(s1, s1_pos, s1_len);
			int s2_c = order(s2, s2_pos, s2_len);
			if (s1_c != s2_c) return s1_c - s2_c;
			s1_pos++;
			s2_pos++;
		}

		while ((s1_pos < s1_len) && (s1[s1_pos] == '0')) {
			s1_pos++;
		}
		while ((s2_pos < s2_len) && (s2[s2_pos] == '0')) {
			s2_pos++;
		}
		while ((s1_pos < s1_len) && (s2_pos < s2_len) && isdigit(s1[s1_pos]) && isdigit(s2[s2_pos])) {
			if (!first_diff) first_diff = s1[s1_pos] - s2[s2_pos];
			s1_pos++;
			s2_pos++;
		}

		if ((s1_pos < s1_len) && isdigit(s1[s1_pos])) return 1;
		if ((s2_pos < s2_len) && isdigit(s2[s2_pos])) return -1;
		if (first_diff) return first_diff;
	}
	return 0;
}

static
int filenvercmp (char const * a, ptrdiff_t alen, char const * b, ptrdiff_t blen)
{
	/* Special case for empty versions. */
	bool aempty = (alen < 0) ? !a[0] : !alen;
	bool bempty = (blen < 0) ? !b[0] : !blen;
	if (aempty) return -!bempty;
	if (bempty) return 1;

	/* Special cases for leading ".": "." sorts first, then "..", then
	   other names with leading ".", then other names. */
	if (a[0] == '.') {
		if (b[0] != '.') return -1;

		bool adot = alen < 0 ? !a[1] : alen == 1;
		bool bdot = blen < 0 ? !b[1] : blen == 1;
		if (adot) return -!bdot;
		if (bdot) return 1;

		bool adotdot = (a[1] == '.') && ((alen < 0) ? !a[2] : (alen == 2));
		bool bdotdot = (b[1] == '.') && ((blen < 0) ? !b[2] : (blen == 2));
		if (adotdot) return -!bdotdot;
		if (bdotdot) return 1;
	}
	else if (b[0] == '.') {
		return 1;
	}

	/* Cut file suffixes. */
	ptrdiff_t aprefixlen = file_prefixlen(a, &alen);
	ptrdiff_t bprefixlen = file_prefixlen(b, &blen);

	/* If both suffixes are empty, a second pass would return the same thing. */
	bool one_pass_only = (aprefixlen == alen) && (bprefixlen == blen);

	int result = verrevcmp(a, aprefixlen, b, bprefixlen);

	/* Return the initial result if nonzero, or if no second pass is needed.
	   Otherwise, restore the suffixes and try again. */
	return (result || one_pass_only) ? result : verrevcmp(a, alen, b, blen);
}

static inline
int filevercmp(const char * s1, const char * s2)
{
	return filenvercmp(s1, -1, s2, -1);
}

int coreutils_version_sort(char const * a, char const * b)
{
	return filevercmp(a, b);
}