/* $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);

}