tmux/fuzzy.c

/* $OpenBSD: fuzzy.c,v 1.1 2026/06/26 14:40:30 nicm Exp $ */

/*
 * Copyright (c) 2026 Nicholas Marriott <nicholas.marriott@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF MIND, USE, DATA OR PROFITS, WHETHER
 * IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING
 * OUT OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */

#include <sys/types.h>

#include <ctype.h>
#include <stdlib.h>
#include <string.h>

#include "tmux.h"

/*
 * Fuzzy matching in the style of fzf. The pattern is split into groups by |
 * and each group is split on spaces into terms. A row matches if any group
 * matches; within a group all positive terms must match and all inverse terms
 * must not match.
 *
 * Plain positive terms are fuzzy subsequences. A leading ' makes a term an
 * exact substring match, ^ anchors a term at the start and $ anchors it at
 * the end. A leading ! inverts the term. Plain inverse terms are exact
 * substring matches rather than inverse fuzzy matches, like fzf.
 *
 * Both the pattern and the text are UTF-8. The text may contain tmux style
 * directives (#[...]); these and their contents are invisible to matching and
 * occupy no columns, but align= styles do move the surrounding text and are
 * accounted for exactly as format_draw lays it out (the no-list layout, see
 * format_draw_none). Matching is smart-case: case is ignored unless the pattern
 * contains an uppercase character (ASCII case folding only; other characters
 * are compared exactly by their UTF-8 data).
 *
 * On a match a bitstr_t of the requested display width is returned with a bit
 * set for every column occupied by a matched character, so the caller can
 * highlight them; NULL is returned if there is no match. A cheap fzf-style
 * score (matches at the start, after word boundaries and in contiguous runs
 * score higher) is also produced so callers can rank best-match-first.
 */

#define FUZZY_BONUS_EXACT 1000
#define FUZZY_BONUS_PREFIX 200
#define FUZZY_BONUS_SUFFIX 100
#define FUZZY_BONUS_START 12
#define FUZZY_BONUS_BOUNDARY 8
#define FUZZY_BONUS_CONSECUTIVE 6
#define FUZZY_PENALTY_LEADING 1
#define FUZZY_PENALTY_LEADING_MAX 10
#define FUZZY_PENALTY_GAP 1

/* A single visible character of the text. */
struct fuzzy_char {
	enum style_align	 align;
	struct utf8_data	 ud;		/* original UTF-8 data */
	u_int			 width;		/* display width */
	u_int			 offset;	/* within its alignment */
};

/* One parsed query term. */
struct fuzzy_term {
	int			 inverse;
	int			 exact;
	int			 prefix;
	int			 suffix;
	const char		*text;
	size_t			 len;
};

/* Is this character a word boundary, so a match after it scores higher? */
static int
fuzzy_is_boundary(const struct utf8_data *ud)
{
	static const char	*boundary = " -_/.:";

	if (ud->size != 1)
		return (0);
	return (strchr(boundary, ud->data[0]) != NULL);
}

/*
 * Compare two characters, folding ASCII case if wanted. UTF-8 is compared
 * directly without case folding.
 */
static int
fuzzy_char_equal(const struct utf8_data *a, const struct utf8_data *b, int fold)
{
	if (fold &&
	    a->size == 1 &&
	    b->size == 1 &&
	    a->data[0] < 0x80 &&
	    b->data[0] < 0x80)
		return (tolower(a->data[0]) == tolower(b->data[0]));
	return (a->size == b->size && memcmp(a->data, b->data, a->size) == 0);
}

/* Map a style alignment onto one of the four layout columns. */
static enum style_align
fuzzy_align(enum style_align align)
{
	if (align == STYLE_ALIGN_DEFAULT)
		return (STYLE_ALIGN_LEFT);
	return (align);
}

/* Add a visible character to the array, updating the alignment width. */
static void
fuzzy_add(struct fuzzy_char **cs, u_int *ncs, u_int *alloc, enum style_align a,
    const struct utf8_data *ud, u_int *widths)
{
	struct fuzzy_char	*fc;

	if (*ncs == *alloc) {
		*alloc = (*alloc == 0) ? 64 : *alloc * 2;
		*cs = xreallocarray(*cs, *alloc, sizeof **cs);
	}
	fc = &(*cs)[(*ncs)++];
	fc->align = a;
	memcpy(&fc->ud, ud, sizeof fc->ud);
	fc->width = ud->width;
	fc->offset = widths[a];
	widths[a] += ud->width;
}

/* Decode a character as UTF-8. */
static const char *
fuzzy_decode_one(const char *cp, const char *end, struct utf8_data *ud)
{
	enum utf8_state	 more;
	const char	*start = cp;

	if ((more = utf8_open(ud, (u_char)*cp)) == UTF8_MORE) {
		while (++cp != end && more == UTF8_MORE)
			more = utf8_append(ud, (u_char)*cp);
		if (more == UTF8_DONE)
			return (cp);
		cp = start;
	}
	utf8_set(ud, (u_char)*cp);
	return (cp + 1);
}

/*
 * Scan the text into an array of visible characters, skipping styles and
 * recording the alignment and intra-alignment offset of each. Returns the
 * array and its length and fills in the per-alignment widths.
 */
static struct fuzzy_char *
fuzzy_scan(const char *text, u_int *ncs, u_int *widths)
{
	struct fuzzy_char	*cs = NULL;
	u_int			 alloc = 0, n, leading, i;
	enum style_align	 current = STYLE_ALIGN_LEFT;
	struct style		 sy;
	const char		*cp = text, *textend = text + strlen(text);
	const char		*end;
	struct utf8_data	 ud, hash, bracket;
	char			*tmp;

	*ncs = 0;
	memset(widths, 0, sizeof *widths * (STYLE_ALIGN_ABSOLUTE_CENTRE + 1));
	style_set(&sy, &grid_default_cell);
	utf8_set(&hash, '#');
	utf8_set(&bracket, '[');

	while (*cp != '\0') {
		/* Handle a run of #s, which may introduce a style. */
		if (*cp == '#') {
			for (n = 0; cp[n] == '#'; n++)
				/* nothing */;
			if (cp[n] != '[') {
				/* Escaped #s: ##->#, so half (rounded up). */
				leading = (n % 2 == 0) ? n / 2 : n / 2 + 1;
				for (i = 0; i < leading; i++) {
					fuzzy_add(&cs, ncs, &alloc, current,
					    &hash, widths);
				}
				cp += n;
				continue;
			}

			/* Even count: all #s escaped, the [ is literal. */
			for (i = 0; i < n / 2; i++)
				fuzzy_add(&cs, ncs, &alloc, current, &hash,
				    widths);
			if (n % 2 == 0) {
				fuzzy_add(&cs, ncs, &alloc, current, &bracket,
				    widths);
				cp += n + 1;
				continue;
			}

			/* Odd count: this is a style, find and parse it. */
			end = format_skip(cp + n + 1, "]");
			if (end == NULL)
				break;
			tmp = xstrndup(cp + n + 1, end - (cp + n + 1));
			if (style_parse(&sy, &grid_default_cell, tmp) == 0)
				current = fuzzy_align(sy.align);
			free(tmp);
			cp = end + 1;
			continue;
		}

		/* Decode one character, multibyte or single byte. */
		cp = fuzzy_decode_one(cp, textend, &ud);

		/*
		 * Skip non-printable single bytes (control characters and raw
		 * bytes left over from a failed decode); keep printable ASCII
		 * and any decoded UTF-8.
		 */
		if (ud.size == 1 && (ud.data[0] <= 0x1f || ud.data[0] >= 0x7f))
			continue;
		fuzzy_add(&cs, ncs, &alloc, current, &ud, widths);
	}
	return (cs);
}

/*
 * Work out the display column of a visible character given the trimmed widths
 * and start columns of each alignment. Returns 0 and sets the column if the
 * character is visible, otherwise returns -1.
 */
static int
fuzzy_column(const struct fuzzy_char *fc, const u_int *start, const u_int *src,
    const u_int *vis, u_int *column)
{
	enum style_align	a = fc->align;

	if (fc->offset < src[a] || fc->offset >= src[a] + vis[a])
		return (-1);
	*column = start[a] + (fc->offset - src[a]);
	return (0);
}

/* Decode a UTF-8 term into an array of characters. */
static u_int
fuzzy_decode(const char *tok, size_t len, struct utf8_data *out)
{
	const char	*cp = tok, *end = tok + len;
	u_int		 n = 0;

	while (cp != end)
		cp = fuzzy_decode_one(cp, end, &out[n++]);
	return (n);
}

/* Add the score for a fuzzy token matched at the given positions. */
static int
fuzzy_score_positions(const u_int *pos, u_int npos, const struct fuzzy_char *cs)
{
	u_int	i, gap, span;
	int	score = 0;

	if (npos == 0)
		return (0);
	if (pos[0] == 0)
		score += FUZZY_BONUS_START;
	else {
		if (fuzzy_is_boundary(&cs[pos[0] - 1].ud))
			score += FUZZY_BONUS_BOUNDARY;
		if (pos[0] < FUZZY_PENALTY_LEADING_MAX)
			score -= pos[0] * FUZZY_PENALTY_LEADING;
		else {
			score -= FUZZY_PENALTY_LEADING_MAX *
			    FUZZY_PENALTY_LEADING;
		}
	}
	for (i = 1; i < npos; i++) {
		if (pos[i] == pos[i - 1] + 1)
			score += FUZZY_BONUS_CONSECUTIVE;
		else if (fuzzy_is_boundary(&cs[pos[i] - 1].ud))
			score += FUZZY_BONUS_BOUNDARY;
	}
	span = pos[npos - 1] - pos[0] + 1;
	gap = span - npos;
	score -= gap * FUZZY_PENALTY_GAP;
	return (score);
}

/*
 * Match a token as a subsequence of the visible characters. Returns if the
 * token matches.
 */
static int
fuzzy_match_fuzzy(const struct utf8_data *tok, u_int toklen,
    struct fuzzy_char *cs, u_int ncs, int fold, int *score, char *matched)
{
	u_int	pi, ci, *pos;
	int	found, value;

	if (toklen == 0 || ncs == 0)
		return (0);
	pos = xcalloc(toklen, sizeof *pos);

	/* First find a subsequence from the start. */
	ci = 0;
	for (pi = 0; pi < toklen; pi++) {
		while (ci != ncs &&
		    !fuzzy_char_equal(&tok[pi], &cs[ci].ud, fold))
			ci++;
		if (ci == ncs) {
			free(pos);
			return (0);
		}
		pos[pi] = ci++;
	}

	/* Then compact it backwards to prefer a shorter span. */
	ci = pos[toklen - 1];
	for (pi = toklen; pi > 0; pi--) {
		found = 0;
		for (;;) {
			if (fuzzy_char_equal(&tok[pi - 1], &cs[ci].ud, fold)) {
				pos[pi - 1] = ci;
				found = 1;
				break;
			}
			if (ci == 0)
				break;
			ci--;
		}
		if (!found) {
			free(pos);
			return (0);
		}
		if (pi != 1)
			ci--;
	}

	value = fuzzy_score_positions(pos, toklen, cs);
	*score += value;
	for (pi = 0; pi < toklen; pi++)
		matched[pos[pi]] = 1;
	free(pos);
	return (1);
}

/* Score an exact, prefix or suffix match. */
static int
fuzzy_score_exact(u_int start, u_int toklen, u_int ncs,
    const struct fuzzy_char *cs, int prefix, int suffix)
{
	int	score;

	score = FUZZY_BONUS_EXACT + toklen * FUZZY_BONUS_CONSECUTIVE;
	if (prefix)
		score += FUZZY_BONUS_PREFIX;
	if (suffix)
		score += FUZZY_BONUS_SUFFIX;
	if (start == 0)
		score += FUZZY_BONUS_START;
	else if (fuzzy_is_boundary(&cs[start - 1].ud))
		score += FUZZY_BONUS_BOUNDARY;
	if (start < FUZZY_PENALTY_LEADING_MAX)
		score -= start * FUZZY_PENALTY_LEADING;
	else
		score -= FUZZY_PENALTY_LEADING_MAX * FUZZY_PENALTY_LEADING;
	if (!prefix && !suffix)
		score -= ncs - (start + toklen);
	return (score);
}

/* Match an exact, prefix or suffix term against the visible characters. */
static int
fuzzy_match_exact(const struct utf8_data *tok, u_int toklen,
    struct fuzzy_char *cs, u_int ncs, int fold, int prefix, int suffix,
    int *score, char *matched)
{
	u_int	start, end, i, j, best = 0;
	int	ok, found = 0, value, bestscore = 0;

	if (toklen == 0 || toklen > ncs)
		return (0);

	if (prefix && suffix) {
		if (toklen != ncs)
			return (0);
		start = 0;
		end = 1;
	} else if (prefix) {
		start = 0;
		end = 1;
	} else if (suffix) {
		start = ncs - toklen;
		end = start + 1;
	} else {
		start = 0;
		end = ncs - toklen + 1;
	}

	for (i = start; i < end; i++) {
		ok = 1;
		for (j = 0; j < toklen; j++) {
			if (!fuzzy_char_equal(&tok[j], &cs[i + j].ud, fold)) {
				ok = 0;
				break;
			}
		}
		if (!ok)
			continue;
		value = fuzzy_score_exact(i, toklen, ncs, cs, prefix, suffix);
		if (!found || value > bestscore) {
			found = 1;
			best = i;
			bestscore = value;
		}
	}
	if (!found)
		return (0);
	*score += bestscore;
	if (matched != NULL) {
		for (i = 0; i < toklen; i++)
			matched[best + i] = 1;
	}
	return (1);
}

/* Parse one term. */
static int
fuzzy_parse_term(const char *start, const char *end, struct fuzzy_term *term)
{
	memset(term, 0, sizeof *term);
	if (start == end)
		return (0);
	if (*start == '!') {
		term->inverse = 1;
		start++;
	}
	if (start == end)
		return (0);
	if (*start == '\'') {
		term->exact = 1;
		start++;
	} else if (*start == '^') {
		term->exact = 1;
		term->prefix = 1;
		start++;
	}
	if (start == end)
		return (0);
	if (end[-1] == '$') {
		term->exact = 1;
		term->suffix = 1;
		end--;
	}
	if (start == end)
		return (0);

	if (term->inverse)
		term->exact = 1;
	term->text = start;
	term->len = end - start;
	return (1);
}

/* Match one parsed term. */
static int
fuzzy_match_term(const struct fuzzy_term *term, struct utf8_data *tok,
    struct fuzzy_char *cs, u_int ncs, int fold, int *score, char *matched)
{
	u_int	toklen;
	int	value = 0, matched_term;

	toklen = fuzzy_decode(term->text, term->len, tok);
	if (term->exact) {
		matched_term = fuzzy_match_exact(tok, toklen, cs, ncs, fold,
		    term->prefix, term->suffix, &value,
		    term->inverse ? NULL : matched);
	} else {
		matched_term = fuzzy_match_fuzzy(tok, toklen, cs, ncs, fold,
		    &value, term->inverse ? NULL : matched);
	}

	if (term->inverse)
		return (!matched_term);
	if (!matched_term)
		return (0);
	*score += value;
	return (1);
}

/* Match one AND group of terms. */
static int
fuzzy_match_group(const char *start, const char *end, struct utf8_data *tok,
    struct fuzzy_char *cs, u_int ncs, int fold, int *score, char *matched)
{
	const char		*cp = start, *sp;
	struct fuzzy_term	 term;
	int			 any = 0;

	*score = 0;
	while (cp != end) {
		while (cp != end && *cp == ' ')
			cp++;
		if (cp == end)
			break;
		sp = cp;
		while (cp != end && *cp != ' ')
			cp++;
		if (!fuzzy_parse_term(sp, cp, &term))
			return (0);
		any = 1;
		if (!fuzzy_match_term(&term, tok, cs, ncs, fold, score,
		    matched))
			return (0);
	}
	return (any);
}

/*
 * Fuzzy match pattern against text, which is drawn into a region of the given
 * display width. Returns a bitstr_t of width bits with a bit set for each
 * column occupied by a matched character, or NULL if there is no match. A
 * higher returned score is better.
 */
bitstr_t *
fuzzy_match(const char *pattern, const char *text, u_int width, u_int *score)
{
	struct fuzzy_char	*cs;
	char			*matched = NULL, *best = NULL, *groupmatched;
	struct utf8_data	*tok;
	bitstr_t		*mask;
	u_int			 ncs, i, j, column;
	u_int			 widths[STYLE_ALIGN_ABSOLUTE_CENTRE + 1];
	u_int			 start[STYLE_ALIGN_ABSOLUTE_CENTRE + 1];
	u_int			 src[STYLE_ALIGN_ABSOLUTE_CENTRE + 1];
	u_int			 vis[STYLE_ALIGN_ABSOLUTE_CENTRE + 1];
	u_int			 wl, wc, wr, wa;
	const char		*cp, *sp;
	int			 bestscore = 0, groupscore, found = 0, fold;

	if (width == 0)
		return (NULL);

	/* An empty query matches everything, with nothing highlighted. */
	for (cp = pattern; *cp == ' ' || *cp == '|'; cp++)
		/* nothing */;
	if (*cp == '\0') {
		if (score != NULL)
			*score = 0;
		return (bit_alloc(width));
	}

	/* Smart-case: fold unless the pattern has an uppercase character. */
	fold = 1;
	for (cp = pattern; *cp != '\0'; cp++) {
		if (*cp >= 'A' && *cp <= 'Z') {
			fold = 0;
			break;
		}
	}

	/* Scan the text into visible characters. */
	cs = fuzzy_scan(text, &ncs, widths);
	matched = xcalloc(ncs == 0 ? 1 : ncs, sizeof *matched);
	best = xcalloc(ncs == 0 ? 1 : ncs, sizeof *best);
	tok = xreallocarray(NULL, strlen(pattern) + 1, sizeof *tok);

	/* Match each |-separated group and keep the best-scoring one. */
	cp = pattern;
	while (*cp != '\0') {
		while (*cp == ' ' || *cp == '|')
			cp++;
		if (*cp == '\0')
			break;
		sp = cp;
		while (*cp != '\0' && *cp != '|')
			cp++;
		memset(matched, 0, ncs == 0 ? 1 : ncs);
		groupmatched = matched;
		if (fuzzy_match_group(sp, cp, tok, cs, ncs, fold,
		    &groupscore, groupmatched)) {
			if (!found || groupscore > bestscore) {
				found = 1;
				bestscore = groupscore;
				memcpy(best, matched, ncs == 0 ? 1 : ncs);
			}
		}
	}
	free(tok);
	if (!found) {
		free(best);
		free(matched);
		free(cs);
		return (NULL);
	}

	/*
	 * Work out the trimmed widths and start columns of each alignment,
	 * mirroring format_draw_none.
	 */
	wl = widths[STYLE_ALIGN_LEFT];
	wc = widths[STYLE_ALIGN_CENTRE];
	wr = widths[STYLE_ALIGN_RIGHT];
	wa = widths[STYLE_ALIGN_ABSOLUTE_CENTRE];
	while (wl + wc + wr > width) {
		if (wc > 0)
			wc--;
		else if (wr > 0)
			wr--;
		else
			wl--;
	}
	if (wa > width)
		wa = width;

	start[STYLE_ALIGN_LEFT] = 0;
	src[STYLE_ALIGN_LEFT] = 0;
	vis[STYLE_ALIGN_LEFT] = wl;

	start[STYLE_ALIGN_RIGHT] = width - wr;
	src[STYLE_ALIGN_RIGHT] = widths[STYLE_ALIGN_RIGHT] - wr;
	vis[STYLE_ALIGN_RIGHT] = wr;

	start[STYLE_ALIGN_CENTRE] =
	    wl + ((width - wr) - wl) / 2 - wc / 2;
	src[STYLE_ALIGN_CENTRE] = widths[STYLE_ALIGN_CENTRE] / 2 - wc / 2;
	vis[STYLE_ALIGN_CENTRE] = wc;

	start[STYLE_ALIGN_ABSOLUTE_CENTRE] = (width - wa) / 2;
	src[STYLE_ALIGN_ABSOLUTE_CENTRE] = 0;
	vis[STYLE_ALIGN_ABSOLUTE_CENTRE] = wa;

	/* Set a bit for each column of each matched character. */
	mask = bit_alloc(width);
	for (i = 0; i < ncs; i++) {
		if (!best[i])
			continue;
		if (fuzzy_column(&cs[i], start, src, vis, &column) != 0)
			continue;
		for (j = 0; j < cs[i].width && column + j < width; j++)
			bit_set(mask, column + j);
	}

	free(best);
	free(matched);
	free(cs);

	if (score != NULL)
		*score = (bestscore < 0) ? 0 : (u_int)bestscore;
	return (mask);
}