##! Functions for creating and working with patterns.

module GLOBAL;

## Given a pattern as a string with two tildes (~~) contained in it, it will
## return a pattern with string set's elements OR'd together where the
## double-tilde was given.  Examples:
##
##   .. code-block:: zeek
##
##     global r1 = set_to_regex(set("a", "b", "c"), "~~");
##     # r1 = /^?(a|b|c)$?/
##     global r2 = set_to_regex(set("a.com", "b.com", "c.com"), "\\.(~~)");
##     # r2 = /^?(\.(a\.com|b\.com|c\.com))$?/
##
## ss: a set of strings to OR together.
##
## pat: the pattern containing a "~~"  in it.  If a literal backslash is
##      included, it needs to be escaped with another backslash due to Zeek's
##      string parsing reducing it to a single backslash upon rendering.
##
## Returns: the input pattern with "~~" replaced by OR'd elements of input set.
function set_to_regex(ss: set[string], pat: string): pattern
	{
	local i: count = 0;
	local return_pat = "";
	for ( s in ss )
		{
		local tmp_pattern = convert_for_pattern(s);
		return_pat = ( i == 0 ) ?
			 tmp_pattern : cat(tmp_pattern, "|", return_pat);
		++i;
		}
	return string_to_pattern(sub(pat, /~~/, return_pat), F);
	}

type PatternMatchResult: record {
	## T if a match was found, F otherwise.
	matched: bool;
	## Portion of string that first matched.
	str: string;
	## 1-based offset where match starts.
	off: count;
};

## Matches the given pattern against the given string, returning
## a :zeek:type:`PatternMatchResult` record.
## For example: ``match_pattern("foobar", /o*[a-k]/)`` returns
## ``[matched=T, str=f, off=1]``,  because the *first* match is for
## zero o's followed by an [a-k], but ``match_pattern("foobar", /o+[a-k]/)``
## returns ``[matched=T, str=oob, off=2]``.
##
## s: a string to match against.
##
## p: a pattern to match.
##
## Returns: a record indicating the match status.
function match_pattern(s: string, p: pattern): PatternMatchResult
	{
	local a = split_string_n(s, p, T, 1);

	if ( |a| == 1 )
		# no match
		return PatternMatchResult($matched = F, $str = "", $off = 0);
	else
		return PatternMatchResult($matched = T, $str = a[1], $off = |a[0]| + 1);
	}
