/*-------------------------------------------------------------------------
 *
 * like_match.c
 *	  LIKE pattern matching internal code.
 *
 * This file is included by like.c four times, to provide matching code for
 * (1) single-byte encodings, (2) UTF8, (3) other multi-byte encodings,
 * and (4) case insensitive matches in single byte encodings.
 * (UTF8 is a special case because we can use a much more efficient version
 * of NextChar than can be used for general multi-byte encodings.)
 *
 * Before the inclusion, we need to define the following macros:
 *
 * NextChar
 * MatchText - to name of function wanted
 * do_like_escape - name of function if wanted - needs CHAREQ and CopyAdvChar
 * MATCH_LOWER - define for case (4), using to_lower on single-byte chars
 *
 * Copyright (c) 1996-2009, PostgreSQL Global Development Group
 *
 * IDENTIFICATION
 *	$PostgreSQL: pgsql/src/backend/utils/adt/like_match.c,v 1.26.2.1 2010/05/28 17:35:30 tgl Exp $
 *
 *-------------------------------------------------------------------------
 */

/*
 *	Originally written by Rich $alz, mirror!rs, Wed Nov 26 19:03:17 EST 1986.
 *	Rich $alz is now <rsalz@bbn.com>.
 *	Special thanks to Lars Mathiesen <thorinn@diku.dk> for the LABORT code.
 *
 *	This code was shamelessly stolen from the "pql" code by myself and
 *	slightly modified :)
 *
 *	All references to the word "star" were replaced by "percent"
 *	All references to the word "wild" were replaced by "like"
 *
 *	All the nice shell RE matching stuff was replaced by just "_" and "%"
 *
 *	As I don't have a copy of the SQL standard handy I wasn't sure whether
 *	to leave in the '\' escape character handling.
 *
 *	Keith Parks. <keith@mtcc.demon.co.uk>
 *
 *	SQL92 lets you specify the escape character by saying
 *	LIKE <pattern> ESCAPE <escape character>. We are a small operation
 *	so we force you to use '\'. - ay 7/95
 *
 *	Now we have the like_escape() function that converts patterns with
 *	any specified escape character (or none at all) to the internal
 *	default escape character, which is still '\'. - tgl 9/2000
 *
 * The code is rewritten to avoid requiring null-terminated strings,
 * which in turn allows us to leave out some memcpy() operations.
 * This code should be faster and take less memory, but no promises...
 * - thomas 2000-08-06
 */


/*--------------------
 *	Match text and pattern, return LIKE_TRUE, LIKE_FALSE, or LIKE_ABORT.
 *
 *	LIKE_TRUE: they match
 *	LIKE_FALSE: they don't match
 *	LIKE_ABORT: not only don't they match, but the text is too short.
 *
 * If LIKE_ABORT is returned, then no suffix of the text can match the
 * pattern either, so an upper-level % scan can stop scanning now.
 *--------------------
 */

#ifdef MATCH_LOWER
#define GETCHAR(t) ((char) tolower((unsigned char) (t)))
#else
#define GETCHAR(t) (t)
#endif

static int
MatchText(char *t, int tlen, char *p, int plen)
{
	/* Fast path for match-everything pattern */
	if (plen == 1 && *p == '%')
		return LIKE_TRUE;

	/* Since this function recurses, it could be driven to stack overflow */
	check_stack_depth();

	/*
	 * In this loop, we advance by char when matching wildcards (and thus on
	 * recursive entry to this function we are properly char-synced). On other
	 * occasions it is safe to advance by byte, as the text and pattern will
	 * be in lockstep. This allows us to perform all comparisons between the
	 * text and pattern on a byte by byte basis, even for multi-byte
	 * encodings.
	 */
	while (tlen > 0 && plen > 0)
	{
		if (*p == '\\')
		{
			/* Next pattern byte must match literally, whatever it is */
			NextByte(p, plen);
			/* ... and there had better be one, per SQL standard */
			if (plen <= 0)
				ereport(ERROR,
						(errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
				 errmsg("LIKE pattern must not end with escape character")));
			if (GETCHAR(*p) != GETCHAR(*t))
				return LIKE_FALSE;
		}
		else if (*p == '%')
		{
			char		firstpat;

			/*
			 * % processing is essentially a search for a text position at
			 * which the remainder of the text matches the remainder of the
			 * pattern, using a recursive call to check each potential match.
			 *
			 * If there are wildcards immediately following the %, we can skip
			 * over them first, using the idea that any sequence of N _'s and
			 * one or more %'s is equivalent to N _'s and one % (ie, it will
			 * match any sequence of at least N text characters).  In this
			 * way we will always run the recursive search loop using a
			 * pattern fragment that begins with a literal character-to-match,
			 * thereby not recursing more than we have to.
			 */
			NextByte(p, plen);

			while (plen > 0)
			{
				if (*p == '%')
					NextByte(p, plen);
				else if (*p == '_')
				{
					/* If not enough text left to match the pattern, ABORT */
					if (tlen <= 0)
						return LIKE_ABORT;
					NextChar(t, tlen);
					NextByte(p, plen);
				}
				else
					break;		/* Reached a non-wildcard pattern char */
			}

			/*
			 * If we're at end of pattern, match: we have a trailing % which
			 * matches any remaining text string.
			 */
			if (plen <= 0)
				return LIKE_TRUE;

			/*
			 * Otherwise, scan for a text position at which we can match the
			 * rest of the pattern.  The first remaining pattern char is known
			 * to be a regular or escaped literal character, so we can compare
			 * the first pattern byte to each text byte to avoid recursing
			 * more than we have to.  This fact also guarantees that we don't
			 * have to consider a match to the zero-length substring at the
			 * end of the text.
			 */
			if (*p == '\\')
			{
				if (plen < 2)
					return LIKE_FALSE; /* XXX should throw error */
				firstpat = GETCHAR(p[1]);
			}
			else
				firstpat = GETCHAR(*p);

			while (tlen > 0)
			{
				if (GETCHAR(*t) == firstpat)
				{
					int			matched = MatchText(t, tlen, p, plen);

					if (matched != LIKE_FALSE)
						return matched;		/* TRUE or ABORT */
				}

				NextChar(t, tlen);
			}

			/*
			 * End of text with no match, so no point in trying later places
			 * to start matching this pattern.
			 */
			return LIKE_ABORT;
		}
		else if (*p == '_')
		{
			/* _ matches any single character, and we know there is one */
			NextChar(t, tlen);
			NextByte(p, plen);
			continue;
		}
		else if (GETCHAR(*p) != GETCHAR(*t))
		{
			/* non-wildcard pattern char fails to match text char */
			return LIKE_FALSE;
		}

		/*
		 * Pattern and text match, so advance.
		 *
		 * It is safe to use NextByte instead of NextChar here, even for
		 * multi-byte character sets, because we are not following immediately
		 * after a wildcard character. If we are in the middle of a multibyte
		 * character, we must already have matched at least one byte of the
		 * character from both text and pattern; so we cannot get out-of-sync
		 * on character boundaries.  And we know that no backend-legal
		 * encoding allows ASCII characters such as '%' to appear as non-first
		 * bytes of characters, so we won't mistakenly detect a new wildcard.
		 */
		NextByte(t, tlen);
		NextByte(p, plen);
	}

	if (tlen > 0)
		return LIKE_FALSE;		/* end of pattern, but not of text */

	/*
	 * End of text, but perhaps not of pattern.  Match iff the remaining
	 * pattern can match a zero-length string, ie, it's zero or more %'s.
	 */
	while (plen > 0 && *p == '%')
		NextByte(p, plen);
	if (plen <= 0)
		return LIKE_TRUE;

	/*
	 * End of text with no match, so no point in trying later places to start
	 * matching this pattern.
	 */
	return LIKE_ABORT;
}	/* MatchText() */

/*
 * like_escape() --- given a pattern and an ESCAPE string,
 * convert the pattern to use Postgres' standard backslash escape convention.
 */
#ifdef do_like_escape

static text *
do_like_escape(text *pat, text *esc)
{
	text	   *result;
	char	   *p,
			   *e,
			   *r;
	int			plen,
				elen;
	bool		afterescape;

	p = VARDATA_ANY(pat);
	plen = VARSIZE_ANY_EXHDR(pat);
	e = VARDATA_ANY(esc);
	elen = VARSIZE_ANY_EXHDR(esc);

	/*
	 * Worst-case pattern growth is 2x --- unlikely, but it's hardly worth
	 * trying to calculate the size more accurately than that.
	 */
	result = (text *) palloc(plen * 2 + VARHDRSZ);
	r = VARDATA(result);

	if (elen == 0)
	{
		/*
		 * No escape character is wanted.  Double any backslashes in the
		 * pattern to make them act like ordinary characters.
		 */
		while (plen > 0)
		{
			if (*p == '\\')
				*r++ = '\\';
			CopyAdvChar(r, p, plen);
		}
	}
	else
	{
		/*
		 * The specified escape must be only a single character.
		 */
		NextChar(e, elen);
		if (elen != 0)
			ereport(ERROR,
					(errcode(ERRCODE_INVALID_ESCAPE_SEQUENCE),
					 errmsg("invalid escape string"),
				  errhint("Escape string must be empty or one character.")));

		e = VARDATA_ANY(esc);

		/*
		 * If specified escape is '\', just copy the pattern as-is.
		 */
		if (*e == '\\')
		{
			memcpy(result, pat, VARSIZE_ANY(pat));
			return result;
		}

		/*
		 * Otherwise, convert occurrences of the specified escape character to
		 * '\', and double occurrences of '\' --- unless they immediately
		 * follow an escape character!
		 */
		afterescape = false;
		while (plen > 0)
		{
			if (CHAREQ(p, e) && !afterescape)
			{
				*r++ = '\\';
				NextChar(p, plen);
				afterescape = true;
			}
			else if (*p == '\\')
			{
				*r++ = '\\';
				if (!afterescape)
					*r++ = '\\';
				NextChar(p, plen);
				afterescape = false;
			}
			else
			{
				CopyAdvChar(r, p, plen);
				afterescape = false;
			}
		}
	}

	SET_VARSIZE(result, r - ((char *) result));

	return result;
}
#endif   /* do_like_escape */

#ifdef CHAREQ
#undef CHAREQ
#endif

#undef NextChar
#undef CopyAdvChar
#undef MatchText

#ifdef do_like_escape
#undef do_like_escape
#endif

#undef GETCHAR

#ifdef MATCH_LOWER
#undef MATCH_LOWER

#endif
