lua-patterns 0.1.0

#include <stdio.h>
#include <string.h>
#include <stddef.h>
#include <ctype.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdint.h>
#include <stdarg.h>
#include <setjmp.h>

typedef struct LuaMatch {
  int start;
  int end;
} LuaMatch;


/* macro to `unsign' a character */
#define uchar(c)	((unsigned char)(c))


/*
** {======================================================
** PATTERN MATCHING
** =======================================================
*/

#define LUA_MAXCAPTURES		32

/* maximum recursion depth for 'match' */
#define MAXCCALLS	200

#define CAP_UNFINISHED	(-1)
#define CAP_POSITION	(-2)

typedef struct MatchState {
  int matchdepth;  /* control for recursive depth (to avoid C stack overflow) */
  const char *src_init;  /* init of source string */
  const char *src_end;  /* end ('\0') of source string */
  const char *p_end;  /* end ('\0') of pattern */
  int level;  /* total number of captures (finished or unfinished) */
  struct {
    const char *init;
    ptrdiff_t len;
  } capture[LUA_MAXCAPTURES];
  jmp_buf jump_buf;
  char msg_buff[256];  
} MatchState;

/* recursive function */
static const char *match (MatchState *ms, const char *s, const char *p);

#define L_ESC		'%'
#define SPECIALS	"^$*+?.([%-"

static int throw_error(MatchState *ms, const char *fmt,...) {
    va_list ap;
    va_start(ap,fmt);
    vsnprintf(ms->msg_buff,sizeof(ms->msg_buff),fmt,ap);
    va_end(ap);
    longjmp(ms->jump_buf,1);
    return 0;
}

static int check_capture (MatchState *ms, int l) {
  l -= '1';
  if (l < 0 || l >= ms->level || ms->capture[l].len == CAP_UNFINISHED)
    return throw_error(ms,"invalid capture index %%%d", l + 1);
  return l;
}

static int capture_to_close (MatchState *ms) {
  int level = ms->level;
  for (level--; level>=0; level--)
    if (ms->capture[level].len == CAP_UNFINISHED) return level;
  return throw_error(ms,"invalid pattern capture");
}


static const char *classend (MatchState *ms, const char *p) {

  switch (*p++) {
    case L_ESC: {
      if (p == ms->p_end)
        throw_error(ms,"malformed pattern (ends with '%')");
      return p+1;
    }
    case '[': {
      if (*p == '^') p++;
      do {  /* look for a `]' */
        if (p == ms->p_end)
          throw_error(ms,"malformed pattern (missing ']')");
        if (*(p++) == L_ESC && p < ms->p_end)
          p++;  /* skip escapes (e.g. `%]') */
      } while (*p != ']');
      return p+1;
    }
    default: {
      return p;
    }
  }
}


static int match_class (int c, int cl) {
  int res;
  switch (tolower(cl)) {
    case 'a' : res = isalpha(c); break;
    case 'c' : res = iscntrl(c); break;
    case 'd' : res = isdigit(c); break;
    case 'g' : res = isgraph(c); break;
    case 'l' : res = islower(c); break;
    case 'p' : res = ispunct(c); break;
    case 's' : res = isspace(c); break;
    case 'u' : res = isupper(c); break;
    case 'w' : res = isalnum(c); break;
    case 'x' : res = isxdigit(c); break;
    case 'z' : res = (c == 0); break;  /* deprecated option */
    default: return (cl == c);
  }
  return (islower(cl) ? res : !res);
}


static int matchbracketclass (int c, const char *p, const char *ec) {
  int sig = 1;
  if (*(p+1) == '^') {
    sig = 0;
    p++;  /* skip the `^' */
  }
  while (++p < ec) {
    if (*p == L_ESC) {
      p++;
      if (match_class(c, uchar(*p)))
        return sig;
    }
    else if ((*(p+1) == '-') && (p+2 < ec)) {
      p+=2;
      if (uchar(*(p-2)) <= c && c <= uchar(*p))
        return sig;
    }
    else if (uchar(*p) == c) return sig;
  }
  return !sig;
}


static int singlematch (MatchState *ms, const char *s, const char *p,
                        const char *ep) {
  if (s >= ms->src_end)
    return 0;
  else {
    int c = uchar(*s);
    switch (*p) {
      case '.': return 1;  /* matches any char */
      case L_ESC: return match_class(c, uchar(*(p+1)));
      case '[': return matchbracketclass(c, p, ep-1);
      default:  return (uchar(*p) == c);
    }
  }
}


static const char *matchbalance (MatchState *ms, const char *s,
                                   const char *p) {
  if (p >= ms->p_end - 1)
    throw_error(ms,"malformed pattern "
                      "(missing arguments to  '%b')");
  if (*s != *p) return NULL;
  else {
    int b = *p;
    int e = *(p+1);
    int cont = 1;
    while (++s < ms->src_end) {
      if (*s == e) {
        if (--cont == 0) return s+1;
      }
      else if (*s == b) cont++;
    }
  }
  return NULL;  /* string ends out of balance */
}


static const char *max_expand (MatchState *ms, const char *s,
                                 const char *p, const char *ep) {
  ptrdiff_t i = 0;  /* counts maximum expand for item */
  while (singlematch(ms, s + i, p, ep))
    i++;
  /* keeps trying to match with the maximum repetitions */
  while (i>=0) {
    const char *res = match(ms, (s+i), ep+1);
    if (res) return res;
    i--;  /* else didn't match; reduce 1 repetition to try again */
  }
  return NULL;
}


static const char *min_expand (MatchState *ms, const char *s,
                                 const char *p, const char *ep) {
  for (;;) {
    const char *res = match(ms, s, ep+1);
    if (res != NULL)
      return res;
    else if (singlematch(ms, s, p, ep))
      s++;  /* try with one more repetition */
    else return NULL;
  }
}


static const char *start_capture (MatchState *ms, const char *s,
                                    const char *p, int what) {
  const char *res;
  int level = ms->level;
  if (level >= LUA_MAXCAPTURES) throw_error(ms,"too many captures");
  ms->capture[level].init = s;
  ms->capture[level].len = what;
  ms->level = level+1;
  if ((res=match(ms, s, p)) == NULL)  /* match failed? */
    ms->level--;  /* undo capture */
  return res;
}


static const char *end_capture (MatchState *ms, const char *s,
                                  const char *p) {
  int l = capture_to_close(ms);
  const char *res;
  ms->capture[l].len = s - ms->capture[l].init;  /* close capture */
  if ((res = match(ms, s, p)) == NULL)  /* match failed? */
    ms->capture[l].len = CAP_UNFINISHED;  /* undo capture */
  return res;
}


static const char *match_capture (MatchState *ms, const char *s, int l) {
  size_t len;
  l = check_capture(ms, l);
  len = ms->capture[l].len;
  if ((size_t)(ms->src_end-s) >= len &&
      memcmp(ms->capture[l].init, s, len) == 0)
    return s+len;
  else return NULL;
}

static const char *match (MatchState *ms, const char *s, const char *p) {
  if (ms->matchdepth-- == 0)
    throw_error(ms,"pattern too complex");
  init: /* using goto's to optimize tail recursion */
  if (p != ms->p_end) {  /* end of pattern? */
    switch (*p) {
      case '(': {  /* start capture */
        if (*(p + 1) == ')')  /* position capture? */
          s = start_capture(ms, s, p + 2, CAP_POSITION);
        else
          s = start_capture(ms, s, p + 1, CAP_UNFINISHED);
        break;
      }
      case ')': {  /* end capture */
        s = end_capture(ms, s, p + 1);
        break;
      }
      case '$': {
        if ((p + 1) != ms->p_end)  /* is the `$' the last char in pattern? */
          goto dflt;  /* no; go to default */
        s = (s == ms->src_end) ? s : NULL;  /* check end of string */
        break;
      }
      case L_ESC: {  /* escaped sequences not in the format class[*+?-]? */
        switch (*(p + 1)) {
          case 'b': {  /* balanced string? */
            s = matchbalance(ms, s, p + 2);
            if (s != NULL) {
              p += 4; goto init;  /* return match(ms, s, p + 4); */
            }  /* else fail (s == NULL) */
            break;
          }
          case 'f': {  /* frontier? */
            const char *ep; char previous;
            p += 2;
            if (*p != '[')
              throw_error(ms,"missing '[' after '%f' in pattern");
            ep = classend(ms, p);  /* points to what is next */
            previous = (s == ms->src_init) ? '\0' : *(s - 1);
            if (!matchbracketclass(uchar(previous), p, ep - 1) &&
               matchbracketclass(uchar(*s), p, ep - 1)) {
              p = ep; goto init;  /* return match(ms, s, ep); */
            }
            s = NULL;  /* match failed */
            break;
          }
          case '0': case '1': case '2': case '3':
          case '4': case '5': case '6': case '7':
          case '8': case '9': {  /* capture results (%0-%9)? */
            s = match_capture(ms, s, uchar(*(p + 1)));
            if (s != NULL) {
              p += 2; goto init;  /* return match(ms, s, p + 2) */
            }
            break;
          }
          default: goto dflt;
        }
        break;
      }
      default: dflt: {  /* pattern class plus optional suffix */
        const char *ep = classend(ms, p);  /* points to optional suffix */
        /* does not match at least once? */
        if (!singlematch(ms, s, p, ep)) {
          if (*ep == '*' || *ep == '?' || *ep == '-') {  /* accept empty? */
            p = ep + 1; goto init;  /* return match(ms, s, ep + 1); */
          }
          else  /* '+' or no suffix */
            s = NULL;  /* fail */
        }
        else {  /* matched once */
          switch (*ep) {  /* handle optional suffix */
            case '?': {  /* optional */
              const char *res;
              if ((res = match(ms, s + 1, ep + 1)) != NULL)
                s = res;
              else {
                p = ep + 1; goto init;  /* else return match(ms, s, ep + 1); */
              }
              break;
            }
            case '+':  /* 1 or more repetitions */
              s++;  /* 1 match already done */
              /* go through */
            case '*':  /* 0 or more repetitions */
              s = max_expand(ms, s, p, ep);
              break;
            case '-':  /* 0 or more repetitions (minimum) */
              s = min_expand(ms, s, p, ep);
              break;
            default:  /* no suffix */
              s++; p = ep; goto init;  /* return match(ms, s + 1, ep); */
          }
        }
        break;
      }
    }
  }
  ms->matchdepth++;
  return s;
}



static void push_onecapture (MatchState *ms, int i, const char *s,
                                                    const char *e, LuaMatch *mm) {
  if (i >= ms->level) {
    if (i == 0)  { /* ms->level == 0, too */
      mm->start = 0;
      mm->end = e - s;
    } else
      throw_error(ms,"invalid capture index");
  }
  else {
    ptrdiff_t l = ms->capture[i].len;
    if (l == CAP_UNFINISHED) throw_error(ms,"unfinished capture");
    if (l == CAP_POSITION) {
      mm[i].start = ms->capture[i].init - ms->src_init + 1;
      mm[i].end = mm[i].start;
    } else {
      mm[i].start = ms->capture[i].init - ms->src_init;
      mm[i].end = mm[i].start + l;
    }
  }
}


static int push_captures (MatchState *ms, const char *s, const char *e, LuaMatch *mm) {
  int i;
  int nlevels = (ms->level == 0 && s) ? 1 : ms->level;
  for (i = 0; i < nlevels; i++)
    push_onecapture(ms, i, s, e, mm);
  return nlevels;  /* number of strings pushed */
}

int str_match (const char *s, unsigned int ls, const char *p, unsigned int lp, char **err_msg, LuaMatch *mm) {
  const char *s1 = s;
  MatchState ms;
  int anchor = (*p == '^');
  if (anchor) {
    p++; lp--;  /* skip anchor character */
  }
  
  memset(ms.msg_buff,0,sizeof(ms.msg_buff));

  if (setjmp(ms.jump_buf) != 0) {
    if (err_msg != NULL) {
        *err_msg = strdup(ms.msg_buff);
    }
    return 0;
  }

  ms.matchdepth = MAXCCALLS;
  ms.src_init = s;
  ms.src_end = s + ls;
  ms.p_end = p + lp;
  do {
    const char *res;
    ms.level = 0;
    if ((res=match(&ms, s1, p)) != NULL) {
        mm[0].start = s1 - s;  /* start */
        mm[0].end = res - s;   /* end */
        return push_captures(&ms, NULL, 0, mm+1) + 1;
    }
  } while (s1++ < ms.src_end && !anchor);

  return 0;
}