/* kwset.c - search for any of a set of keywords.
   Copyright 1989 Free Software Foundation
		  Written August 1989 by Mike Haertel.

   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 1, or (at your option)
   any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.

   The author may be reached (Email) at the address mike@ai.mit.edu,
   or (US mail) as Mike Haertel c/o Free Software Foundation. */

/* MS-DOS port (c) 1990 by Thorsten Ohl, ohl@gnu.ai.mit.edu
   This port is also distributed under the terms of the
   GNU General Public License as published by the
   Free Software Foundation.

   Please note that this file is not identical to the
   original GNU release, you should have received this
   code as patch to the official release.

   $Header: e:/gnu/fgrep/RCS/kwset.c 1.1.0.3 90/09/24 00:37:52 tho Exp $
 */

#include "std.h"

/* The algorithm implemented by these routines bears a startling resemblence
   to one discovered by Beate Commentz-Walter, although it is not identical.
   See "A String Matching Algorithm Fast on the Average," Technical Report,
   IBM-Germany, Scientific Center Heidelberg, Tiergartenstrasse 15, D-6900
   Heidelberg, Germany.  See also Aho, A.V., and M. Corasick, "Efficient
   String Matching:  An Aid to Bibliographic Search," CACM June 1975,
   Vol. 18, No. 6, which describes the failure function used below. */

#include "kwset.h"

#ifdef MSDOS

#ifdef USE_OBSTACKS
#if defined(M_I86CM) || defined(M_I86LM)
#error The GNU `obstack' macros don't work with far pointers yet!
#else /* M_I86SM or M_I86MM */
#include "obstack.h"
#endif /* M_I86SM or M_I86MM */
#else /* not USE_OBSTACKS */
#undef obstack_alloc
#undef obstack_free
#undef obstack_init
#define obstack_alloc(dummy, size)	xmalloc (size)
#define obstack_free(dummy1, dummy2)
#define obstack_init(dummy)
#endif /* not USE_OBSTACKS */

#else /* not MSDOS */

#include "obstack.h"

#endif /* not MSDOS */


#define NCHAR (UCHAR_MAX + 1)
#ifdef MSDOS			/* walk on the save side */
#define obstack_chunk_alloc xmalloc
#else
#define obstack_chunk_alloc malloc
#endif
#define obstack_chunk_free free

/* Balanced tree of edges and labels leaving a given trie node. */
struct tree
{
  struct tree *llink;		/* Left link; MUST be first field. */
  struct tree *rlink;		/* Right link (to larger labels). */
  struct trie *trie;		/* Trie node pointed to by this edge. */
  unsigned char label;		/* Label on this edge. */
  char balance;			/* Difference in depths of subtrees. */
};

/* Node of a trie representing a set of reversed keywords. */
struct trie
{
  unsigned int accepting;	/* Word index of accepted word, or zero. */
  struct tree *links;		/* Tree of edges leaving this node. */
  struct trie *parent;		/* Parent of this node. */
  struct trie *next;		/* List of all trie nodes in level order. */
  struct trie *fail;		/* Aho-Corasick failure function. */
  int depth;			/* Depth of this node from the root. */
  int shift;			/* Shift function for search failures. */
  int maxshift;			/* Max shift of self and descendents. */
};

/* Structure returned opaquely to the caller, containing everything. */
struct kwset
{
#if !defined (MSDOS) || defined (USE_OBSTACKS)
  struct obstack obstack;	/* Obstack for node allocation. */
#endif
  int words;			/* Number of words in the trie. */
  struct trie *trie;		/* The trie itself. */
  int mind;			/* Minimum depth of an accepting node. */
  int maxd;			/* Maximum depth of any node. */
  int delta[NCHAR];		/* Delta table for rapid search. */
  struct trie *next[NCHAR];	/* Table of children of the root. */
  const char *trans;		/* Character translation table. */
};

/* Allocate and initialize a keyword set object, returning an opaque
   pointer to it.  Return NULL if memory is not available. */
kwset_t
DEFUN(kwsalloc, (trans), const char *trans)
{
  struct kwset *kwset;

  kwset = (struct kwset *) malloc(sizeof (struct kwset));
  if (!kwset)
    return NULL;

  obstack_init(&kwset->obstack);
  kwset->words = 0;
  kwset->trie
    = (struct trie *) obstack_alloc(&kwset->obstack, sizeof (struct trie));
  if (!kwset->trie)
    {
      kwsfree((kwset_t) kwset);
      return NULL;
    }
  kwset->trie->accepting = 0;
  kwset->trie->links = NULL;
  kwset->trie->parent = NULL;
  kwset->trie->next = NULL;
  kwset->trie->fail = NULL;
  kwset->trie->depth = 0;
  kwset->trie->shift = 0;
  kwset->mind = INT_MAX;
  kwset->maxd = -1;
  kwset->trans = trans;

  return (kwset_t) kwset;
}

/* Add the given string to the contents of the keyword set.  Return NULL
   for success, an error message otherwise. */
const char *
DEFUN(kwsincr, (kws, text, len),
      kwset_t kws AND const char *text AND size_t len)
{
  struct kwset *kwset;
  register struct trie *trie;
  register unsigned char label;
  register struct tree *link;
  register int depth;
  struct tree *links[12];
  enum { L, R } dirs[12];
  struct tree *t, *r, *l, *rl, *lr;

  kwset = (struct kwset *) kws;
  trie = kwset->trie;
  text += len;

  /* Descend the trie (built of reversed keywords) character-by-character,
     installing new nodes when necessary. */
  while (len--)
    {
      label = kwset->trans ? kwset->trans[(unsigned char) *--text] : *--text;

      /* Descend the tree of outgoing links for this trie node,
	 looking for the current character and keeping track
	 of the path followed. */
      link = trie->links;
      links[0] = (struct tree *) &trie->links;
      dirs[0] = L;
      depth = 1;

      while (link && label != link->label)
	{
	  links[depth] = link;
	  if (label < link->label)
	    dirs[depth++] = L, link = link->llink;
	  else
	    dirs[depth++] = R, link = link->rlink;
	}

      /* The current character doesn't have an outgoing link at
	 this trie node, so build a new trie node and install
	 a link in the current trie node's tree. */
      if (!link)
	{
	  link = (struct tree *) obstack_alloc(&kwset->obstack,
					       sizeof (struct tree));
	  if (!link)
	    return "memory exhausted";
	  link->llink = NULL;
	  link->rlink = NULL;
	  link->trie = (struct trie *) obstack_alloc(&kwset->obstack,
						     sizeof (struct trie));
	  if (!link->trie)
	    return "memory exhausted";
	  link->trie->accepting = 0;
	  link->trie->links = NULL;
	  link->trie->parent = trie;
	  link->trie->next = NULL;
	  link->trie->fail = NULL;
	  link->trie->depth = trie->depth + 1;
	  link->trie->shift = 0;
	  link->label = label;
	  link->balance = 0;

	  /* Install the new tree node in its parent. */
	  if (dirs[--depth] == L)
	    links[depth]->llink = link;
	  else
	    links[depth]->rlink = link;

	  /* Back up the tree fixing the balance flags. */
	  while (depth && !links[depth]->balance)
	    {
	      if (dirs[depth] == L)
		--links[depth]->balance;
	      else
		++links[depth]->balance;
	      --depth;
	    }

	  /* Rebalance the tree by pointer rotations if necessary. */
	  if (depth && (dirs[depth] == L && --links[depth]->balance
			|| dirs[depth] == R && ++links[depth]->balance))
	    {
	      switch (links[depth]->balance)
		{
		case (char) -2:
		  switch (dirs[depth + 1])
		    {
		    case L:
		      r = links[depth], t = r->llink, rl = t->rlink;
		      t->rlink = r, r->llink = rl;
		      t->balance = r->balance = 0;
		      break;
		    case R:
		      r = links[depth], l = r->llink, t = l->rlink;
		      rl = t->rlink, lr = t->llink;
		      t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
#ifdef MSDOS
		      l->balance = (char) (t->balance != 1 ? 0 : -1);
		      r->balance = (char) (t->balance != (char) -1 ? 0 : 1);
#else
		      l->balance = t->balance != 1 ? 0 : -1;
		      r->balance = t->balance != (char) -1 ? 0 : 1;
#endif
		      t->balance = 0;
		      break;
		    }
		  break;
		case 2:
		  switch (dirs[depth + 1])
		    {
		    case R:
		      l = links[depth], t = l->rlink, lr = t->llink;
		      t->llink = l, l->rlink = lr;
		      t->balance = l->balance = 0;
		      break;
		    case L:
		      l = links[depth], r = l->rlink, t = r->llink;
		      lr = t->llink, rl = t->rlink;
		      t->llink = l, l->rlink = lr, t->rlink = r, r->llink = rl;
#ifdef MSDOS
		      l->balance = (char) (t->balance != 1 ? 0 : -1);
		      r->balance = (char) (t->balance != (char) -1 ? 0 : 1);
#else
		      l->balance = t->balance != 1 ? 0 : -1;
		      r->balance = t->balance != (char) -1 ? 0 : 1;
#endif
		      t->balance = 0;
		      break;
		    }
		  break;
		}

	      if (dirs[depth - 1] == L)
		links[depth - 1]->llink = t;
	      else
		links[depth - 1]->rlink = t;
	    }
	}

      trie = link->trie;
    }

  /* Mark the node we finally reached as accepting, encoding the
     index number of this word in the keyword set so far. */
  if (!trie->accepting)
    trie->accepting = 1 + 2 * kwset->words;
  ++kwset->words;

  /* Keep track of the longest and shortest string of the keyword set. */
  if (trie->depth < kwset->mind)
    kwset->mind = trie->depth;
  if (trie->depth > kwset->maxd)
    kwset->maxd = trie->depth;

  return NULL;
}

/* Enqueue the trie nodes referenced from the given tree in the
   given queue. */
static void
DEFUN(enqueue, (tree, last), struct tree *tree AND struct trie **last)
{
  if (!tree)
    return;
  enqueue(tree->llink, last);
  enqueue(tree->rlink, last);
  (*last) = (*last)->next = tree->trie;
}

/* Compute the Aho-Corasick failure function for the trie nodes referenced
   from the given tree, given the failure function for their parent as
   well as a last resort failure node. */
static void
DEFUN(treefails, (tree, fail, recourse),
      register struct tree *tree
      AND struct trie *fail AND struct trie *recourse)
{
  register struct tree *link;

  if (!tree)
    return;

  treefails(tree->llink, fail, recourse);
  treefails(tree->rlink, fail, recourse);

  /* Find, in the chain of fails going back to the root, the first
     node that has a descendent on the current label. */
  while (fail)
    {
      link = fail->links;
      while (link && tree->label != link->label)
	if (tree->label < link->label)
	  link = link->llink;
	else
	  link = link->rlink;
      if (link)
	{
	  tree->trie->fail = link->trie;
	  return;
	}
      fail = fail->fail;
    }

  tree->trie->fail = recourse;
}

/* Set delta entries for the links of the given tree such that
   the preexisting delta value is larger than the current depth. */
static void
DEFUN(treedelta, (tree, depth, delta),
      register struct tree *tree AND register int depth AND int delta[])
{
  if (!tree)
    return;
  treedelta(tree->llink, depth, delta);
  treedelta(tree->rlink, depth, delta);
  if (depth < delta[tree->label])
    delta[tree->label] = depth;
}

/* Return true if A has every label in B. */
static int
DEFUN(hasevery, (a, b), register struct tree *a AND register struct tree *b)
{
  if (!b)
    return 1;
  if (!hasevery(a, b->llink))
    return 0;
  if (!hasevery(a, b->rlink))
    return 0;
  while (a && b->label != a->label)
    if (b->label < a->label)
      a = a->llink;
    else
      a = a->rlink;
  return !!a;
}

/* Compute a vector, indexed by character code, of the trie nodes
   referenced from the given tree. */
static void
DEFUN(treenext, (tree, next), struct tree *tree AND struct trie *next[])
{
  if (!tree)
    return;
  treenext(tree->llink, next);
  treenext(tree->rlink, next);
  next[tree->label] = tree->trie;
}

/* Compute the shift for each trie node, as well as the delta
   table and next cache for the given keyword set. */
const char *
DEFUN(kwsprep, (kws), kwset_t kws)
{
  register struct kwset *kwset;
  register int i;
  register struct trie *curr, *fail;
  register const char *trans;
  int delta[NCHAR];
  struct trie *last, *next[NCHAR];

  kwset = (struct kwset *) kws;

  /* Initial values for the delta table; will be changed later.  The
     delta entry for a given character is the smallest depth of any
     node at which an outgoing edge is labeled by that character. */
  for (i = 0; i < NCHAR; ++i)
    delta[i] = kwset->mind;

  /* Traverse the nodes of the trie in level order, simultaneously
     computing the delta table, failure function, and shift function. */
  for (curr = last = kwset->trie; curr; curr = curr->next)
    {
      /* Enqueue the immediate descendents in the level order queue. */
      enqueue(curr->links, &last);

      curr->shift = kwset->mind;
      curr->maxshift = kwset->mind;

      /* Update the delta table for the descendents of this node. */
      treedelta(curr->links, curr->depth, delta);

      /* Compute the failure function for the decendents of this node. */
      treefails(curr->links, curr->fail, kwset->trie);

      /* Update the shifts at each node in the current node's chain
	 of fails back to the root. */
      for (fail = curr->fail; fail; fail = fail->fail)
	{
	  /* If the current node has some outgoing edge that the fail
	     doesn't, then the shift at the fail should be no larger
	     than the difference of their depths. */
	  if (!hasevery(fail->links, curr->links))
	    if (curr->depth - fail->depth < fail->shift)
	      fail->shift = curr->depth - fail->depth;

	  /* If the current node is accepting then the shift at the
	     fail and its descendents should be no larger than the
	     difference of their depths. */
	  if (curr->accepting && fail->maxshift > curr->depth - fail->depth)
	    fail->maxshift = curr->depth - fail->depth;
	}
    }

  /* Traverse the trie in level order again, fixing up all nodes whose
     shift exceeds their inherited maxshift. */
  for (curr = kwset->trie->next; curr; curr = curr->next)
    {
      if (curr->maxshift > curr->parent->maxshift)
	curr->maxshift = curr->parent->maxshift;
      if (curr->shift > curr->maxshift)
	curr->shift = curr->maxshift;
    }

  /* Create a vector, indexed by character code, of the outgoing links
     from the root node. */
  for (i = 0; i < NCHAR; ++i)
    next[i] = NULL;
  treenext(kwset->trie->links, next);

  /* Fix things up for any translation table. */
  if (trans = kwset->trans)
    for (i = 0; i < NCHAR; ++i)
      {
	kwset->delta[i] = delta[(unsigned char) trans[i]];
	kwset->next[i] = next[(unsigned char) trans[i]];
      }
  else
    for (i = 0; i < NCHAR; ++i)
      {
	kwset->delta[i] = delta[i];
	kwset->next[i] = next[i];
      }

  return NULL;
}

/* Search through the given text for a match of any member of the
   given keyword set.  Return a pointer to the first character of
   the matching substring, or NULL if no match is found.  If FOUNDLEN
   is non-NULL store in the referenced location the length of the
   matching substring.  Similarly, if FOUNDIDX is non-NULL, store
   in the referenced location the index number of the particular
   keyword matched. */
char *
DEFUN(kwsexec, (kws, text, len, kwsmatch),
      kwset_t kws AND char *text AND size_t len AND struct kwsmatch *kwsmatch)
{
  struct kwset *kwset;
  struct trie **next, *trie, *accept;
  char *beg, *lim, *mch, *lmch;
  register unsigned char c;
  register int *delta, d;
  register char *end, *qlim;
  register struct tree *tree;
  register const char *trans;

  /* Initialize register copies and look for easy ways out. */
  kwset = (struct kwset *) kws;
  if (len < kwset->mind)
    return NULL;
  next = kwset->next;
  delta = kwset->delta;
  trans = kwset->trans;
  lim = text + len;
  end = text;
  if (d = kwset->mind)
    mch = NULL;
  else
    {
      mch = text, accept = kwset->trie;
      goto match;
    }

  if (len >= 4 * kwset->mind)
    qlim = lim - 4 * kwset->mind;
  else
    qlim = NULL;

  while (lim - end >= d)
    {
      if (qlim && end <= qlim)
	{
	  end += d - 1;
	  while ((d = delta[c = *end]) && end < qlim)
	    {
	      end += d;
	      end += delta[(unsigned char) *end];
	      end += delta[(unsigned char) *end];
	    }
	  ++end;
	}
      else
	d = delta[c = (end += d)[-1]];
      if (d)
	continue;
      beg = end - 1;
      trie = next[c];
      if (trie->accepting)
	{
	  mch = beg;
	  accept = trie;
	}
      d = trie->shift;
      while (beg > text)
	{
	  c = trans ? trans[(unsigned char) *--beg] : *--beg;
	  tree = trie->links;
	  while (tree && c != tree->label)
	    if (c < tree->label)
	      tree = tree->llink;
	    else
	      tree = tree->rlink;
	  if (tree)
	    {
	      trie = tree->trie;
	      if (trie->accepting)
		{
		  mch = beg;
		  accept = trie;
		}
	    }
	  else
	    break;
	  d = trie->shift;
	}
      if (mch)
	goto match;
    }
  return NULL;

 match:
  /* Given a known match, find the longest possible match anchored
     at or before its starting point.  This is nearly a verbatim
     copy of the preceding main search loops. */
  if (lim - mch > kwset->maxd)
    lim = mch + kwset->maxd;
  lmch = NULL;
  d = 1;
  while (lim - end >= d)
    {
      if (d = delta[c = (end += d)[-1]])
	continue;
      beg = end - 1;
      if (!(trie = next[c]))
	{
	  d = 1;
	  continue;
	}
      if (trie->accepting && beg <= mch)
	{
	  lmch = beg;
	  accept = trie;
	}
      d = trie->shift;
      while (beg > text)
	{
	  c = trans ? trans[(unsigned char) *--beg] : *--beg;
	  tree = trie->links;
	  while (tree && c != tree->label)
	    if (c < tree->label)
	      tree = tree->llink;
	    else
	      tree = tree->rlink;
	  if (tree)
	    {
	      trie = tree->trie;
	      if (trie->accepting && beg <= mch)
		{
		  lmch = beg;
		  accept = trie;
		}
	    }
	  else
	    break;
	  d = trie->shift;
	}
      if (lmch)
	{
	  mch = lmch;
	  goto match;
	}
      if (!d)
	d = 1;
    }

  if (kwsmatch)
    {
      kwsmatch->index = accept->accepting / 2;
      kwsmatch->beg[0] = mch;
      kwsmatch->size[0] = accept->depth;
    }
  return mch;
}
  
/* Free the components of the given keyword set. */
void
DEFUN(kwsfree, (kws), kwset_t kws)
{
  struct kwset *kwset;

  kwset = (struct kwset *) kws;
  obstack_free(&kwset->obstack, (PTR) NULL);
  free((PTR) kws);
}
