/* Provide access to the collection of available transformation modules.
   Copyright (C) 1997 Free Software Foundation, Inc.
   This file is part of the GNU C Library.
   Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.

   The GNU C Library is free software; you can redistribute it and/or
   modify it under the terms of the GNU Library General Public License as
   published by the Free Software Foundation; either version 2 of the
   License, or (at your option) any later version.

   The GNU C Library 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
   Library General Public License for more details.

   You should have received a copy of the GNU Library General Public
   License along with the GNU C Library; see the file COPYING.LIB.  If not,
   write to the Free Software Foundation, Inc., 59 Temple Place - Suite 330,
   Boston, MA 02111-1307, USA.  */

#include <gconv.h>
#include <search.h>
#include <stdlib.h>
#include <string.h>
#include <bits/libc-lock.h>


/* Simple data structure for alias mapping.  We have two names, `from'
   and `to'.  */
void *__gconv_alias_db;

/* Array with available modules.  */
size_t __gconv_nmodules;
struct gconv_module **__gconv_modules_db;


/* Function for searching alias.  */
int
__gconv_alias_compare (const void *p1, const void *p2)
{
  struct gconv_alias *s1 = (struct gconv_alias *) p1;
  struct gconv_alias *s2 = (struct gconv_alias *) p2;
  return __strcasecmp (s1->fromname, s2->fromname);
}


/* To search for a derivation we create a list of intermediate steps.
   Each element contains a pointer to the element which precedes it
   in the derivation order.  */
struct derivation_step
{
  const char *result_set;
  struct gconv_module *code;
  struct derivation_step *last;
  struct derivation_step *next;
};

#define NEW_STEP(result, module, last_mod) \
  ({ struct derivation_step *newp = alloca (sizeof (struct derivation_step)); \
     newp->result_set = result;						      \
     newp->code = module;						      \
     newp->last = last_mod;						      \
     newp->next = NULL;							      \
     newp; })


/* If a specific transformation is used more than once we should not need
   to start looking for it again.  Instead cache each successful result.  */
struct known_derivation
{
  const char *from;
  const char *to;
  struct gconv_step *steps;
  size_t nsteps;
};

/* Compare function for database of found derivations.  */
static int
derivation_compare (const void *p1, const void *p2)
{
  struct known_derivation *s1 = (struct known_derivation *) p1;
  struct known_derivation *s2 = (struct known_derivation *) p2;
  int result;

  result = strcmp (s1->from, s2->from);
  if (result == 0)
    result = strcmp (s1->to, s2->to);
  return result;
}

/* The search tree for known derivations.  */
static void *known_derivations;

/* Look up whether given transformation was already requested before.  */
static int
derivation_lookup (const char *fromset, const char *toset,
		   struct gconv_step **handle, size_t *nsteps)
{
  struct known_derivation key = { fromset, toset, NULL, 0 };
  struct known_derivation *result;

  result = __tfind (&key, &known_derivations, derivation_compare);

  if (result == NULL)
    return GCONV_NOCONV;

  *handle = result->steps;
  *nsteps = result->nsteps;

  /* Please note that we return GCONV_OK even if the last search for
     this transformation was unsuccessful.  */
  return GCONV_OK;
}

/* Add new derivation to list of known ones.  */
static void
add_derivation (const char *fromset, const char *toset,
		struct gconv_step *handle, size_t nsteps)
{
  struct known_derivation *new_deriv;
  size_t fromset_len = strlen (fromset) + 1;
  size_t toset_len = strlen (toset) + 1;

  new_deriv = (struct known_derivation *)
    malloc (sizeof (struct known_derivation) + fromset_len + toset_len);
  if (new_deriv != NULL)
    {
      new_deriv->from = memcpy ((char *) new_deriv
				+ sizeof (struct known_derivation),
				fromset, fromset_len);
      new_deriv->to = memcpy ((char *) new_deriv->from + fromset_len,
			      toset, toset_len);

      new_deriv->steps = handle;
      new_deriv->nsteps = nsteps;

      __tsearch (new_deriv, &known_derivations, derivation_compare);
    }
  /* Please note that we don't complain if the allocation failed.  This
     is not tragically but in case we use the memory debugging facilities
     not all memory will be freed.  */
}

static void
free_derivation (void *p)
{
  struct known_derivation *deriv = (struct known_derivation *) p;

  free ((struct gconv_step *) deriv->steps);
  free (deriv);
}


static int
internal_function
gen_steps (struct derivation_step *best, const char *toset,
	   const char *fromset, struct gconv_step **handle, size_t *nsteps)
{
  size_t step_cnt = 0;
  struct gconv_step *result;
  struct derivation_step *current;
  int status = GCONV_NOMEM;

  /* First determine number of steps.  */
  for (current = best; current->last != NULL; current = current->last)
    ++step_cnt;

  result = (struct gconv_step *) malloc (sizeof (struct gconv_step)
					 * step_cnt);
  if (result != NULL)
    {
      int failed = 0;

      *nsteps = step_cnt;
      current = best;
      while (step_cnt-- > 0)
	{
	  result[step_cnt].from_name = (step_cnt == 0
					? __strdup (fromset)
					: current->last->result_set);
	  result[step_cnt].to_name = (step_cnt + 1 == *nsteps
				      ? __strdup (current->result_set)
				      : result[step_cnt + 1].from_name);

	  if (current->code->module_name[0] == '/')
	    {
	      /* Load the module, return handle for it.  */
	      void *shlib_handle =
		__gconv_find_shlib (current->code->module_name);

	      if (shlib_handle == NULL)
		{
		  failed = 1;
		  break;
		}

	      result[step_cnt].shlib_handle = shlib_handle;

	      result[step_cnt].fct = __gconv_find_func (shlib_handle, "gconv");
	      if (result[step_cnt].fct == NULL)
		{
		  /* Argh, no conversion function.  There is something
		     wrong here.  */
		  __gconv_release_shlib (result[step_cnt].shlib_handle);
		  failed = 1;
		  break;
		}

	      result[step_cnt].init_fct = __gconv_find_func (shlib_handle,
							     "gconv_init");
	      result[step_cnt].end_fct = __gconv_find_func (shlib_handle,
							    "gconv_end");
	    }
	  else
	    /* It's a builtin transformation.  */
	    __gconv_get_builtin_trans (current->code->module_name,
				       &result[step_cnt]);

	  current = current->last;
	}

      if (failed != 0)
	{
	  /* Something went wrong while initializing the modules.  */
	  while (++step_cnt < *nsteps)
	    __gconv_release_shlib (result[step_cnt].shlib_handle);
	  free (result);
	  *nsteps = 0;
	  status = GCONV_NOCONV;
	}
      else
	{
	  *handle = result;
	  status = GCONV_OK;
	}
    }

  return status;
}


/* The main function: find a possible derivation from the `fromset' (either
   the given name or the alias) to the `toset' (again with alias).  */
static int
internal_function
find_derivation (const char *toset, const char *toset_expand,
		 const char *fromset, const char *fromset_expand,
		 struct gconv_step **handle, size_t *nsteps)
{
  __libc_lock_define_initialized (static, lock)
  struct derivation_step *first, *current, **lastp, *best = NULL;
  int best_cost = 0;
  int result;

  result = derivation_lookup (fromset_expand ?: fromset, toset_expand ?: toset,
			      handle, nsteps);
  if (result == GCONV_OK)
    return result;

  __libc_lock_lock (lock);

  /* There is a small chance that this derivation is meanwhile found.  This
     can happen if in `find_derivation' we look for this derivation, didn't
     find it but at the same time another thread looked for this derivation. */
  result = derivation_lookup (fromset_expand ?: fromset, toset_expand ?: toset,
			      handle, nsteps);
  if (result == GCONV_OK)
    return result;

  /* ### TODO
     For now we use a simple algorithm with quadratic runtime behaviour.
     The task is to match the `toset' with any of the available.  */
  if (fromset_expand != NULL)
    {
      first = NEW_STEP (fromset_expand, NULL, NULL);
      first->next = NEW_STEP (fromset, NULL, NULL);
      lastp = &first->next->next;
    }
  else
    {
      first = NEW_STEP (fromset, NULL, NULL);
      lastp = &first->next;
    }

  current = first;
  while (current != NULL)
    {
      /* Now match all the available module specifications against the
         current charset name.  If any of them matches check whether
         we already have a derivation for this charset.  If yes, use the
         one with the lower costs.  Otherwise add the new charset at the
         end.  */
      size_t cnt;

      for (cnt = 0; cnt < __gconv_nmodules; ++cnt)
        {
	  const char *result_set = NULL;

	  if (__gconv_modules_db[cnt]->from_pattern == NULL)
	    {
	      if (__strcasecmp (current->result_set,
				__gconv_modules_db[cnt]->from_constpfx) == 0)
		{
		  if (strcmp (__gconv_modules_db[cnt]->to_string, "-") == 0)
		    result_set = toset_expand ?: toset;
		  else
		    result_set = __gconv_modules_db[cnt]->to_string;
		}
	    }
	  else
	    /* We have a regular expression.  First see if the prefix
	       matches.  */
	    if (__strncasecmp (current->result_set,
			       __gconv_modules_db[cnt]->from_constpfx,
			       __gconv_modules_db[cnt]->from_constpfx_len)
		== 0)
	      {
		/* First compile the regex if not already done.  */
		if (__gconv_modules_db[cnt]->from_regex == NULL)
		  {
		    regex_t *newp = (regex_t *) malloc (sizeof (regex_t));

		    if (regcomp (newp, __gconv_modules_db[cnt]->from_pattern,
				 REG_EXTENDED | REG_ICASE) != 0)
		      {
			/* Something is wrong.  Remember this.  */
			free (newp);
			__gconv_modules_db[cnt]->from_regex = (regex_t *) -1L;
		      }
		    else
		      __gconv_modules_db[cnt]->from_regex = newp;
		  }

		if (__gconv_modules_db[cnt]->from_regex != (regex_t *) -1L)
		  {
		    /* Try to match the from name.  */
		    regmatch_t match[4];

		    if (regexec (__gconv_modules_db[cnt]->from_regex,
				 current->result_set, 4, match, 0) == 0
			&& match[0].rm_so == 0
			&& current->result_set[match[0].rm_eo] == '\0')
		      {
			/* At least the whole <from> string is matched.
			   We must now match sed-like possible
			   subexpressions from the match to the
			   toset expression.  */
#define ENSURE_LEN(LEN) \
  if (wp + (LEN) >= constr + len - 1)					      \
    {									      \
      char *newp = alloca (len += 128);					      \
      memcpy (newp, constr, wp - constr);				      \
      wp = newp + (wp - constr);					      \
      constr = newp;							      \
    }
			size_t len = 128;
			char *constr = alloca (len);
			char *wp = constr;
			const char *cp = __gconv_modules_db[cnt]->to_string;

			while (*cp != '\0')
			  {
			    if (*cp != '\\')
			      {
				ENSURE_LEN (1);
				*wp++ = *cp++;
			      }
			    else if (cp[1] == '\0')
			      /* Backslash at end of string.  */
			      break;
			    else
			      {
				++cp;
				if (*cp == '\\')
				  {
				    *wp++ = *cp++;
				    ENSURE_LEN (1);
				  }
				else if (*cp < '1' || *cp > '3')
				  break;
				else
				  {
				    int idx = *cp - '0';
				    if (match[idx].rm_so == -1)
				      /* No match.  */
				      break;

				    ENSURE_LEN (match[idx].rm_eo
						- match[idx].rm_so);
				    wp = __mempcpy (wp,
						    &current->result_set[match[idx].rm_so],
						    match[idx].rm_eo
						    - match[idx].rm_so);
				    ++cp;
				  }
			      }
			  }
			if (*cp == '\0' && wp != constr)
			  {
                                /* Terminate the constructed string.  */
			    *wp = '\0';
			    result_set = constr;
			  }
		      }
		  }
	      }

	  if (result_set != NULL)
	    {
	      /* We managed to find a derivation.  First see whether
		 this is what we are looking for.  */
	      if (__strcasecmp (result_set, toset) == 0
		  || (toset_expand != NULL
		      && __strcasecmp (result_set, toset_expand) == 0))
		{
		  /* Determine the costs.  If they are lower than the
		     previous solution (or this is the first solution)
		     remember this solution.  */
		  int cost = __gconv_modules_db[cnt]->cost;
		  struct derivation_step *runp = current;
		  while (runp->code != NULL)
		    {
		      cost += runp->code->cost;
		      runp = runp->last;
		    }
		  if (best == NULL || cost < best_cost)
		    {
		      best = NEW_STEP (result_set, __gconv_modules_db[cnt],
				       current);
		      best_cost = cost;
		    }
		}
	      else
		{
		  /* Append at the end if there is no entry with this name.  */
		  struct derivation_step *runp = first;

		  while (runp != NULL)
		    {
		      if (__strcasecmp (result_set, runp->result_set) == 0)
			break;
		      runp = runp->next;
		    }

		  if (runp == NULL)
		    {
		      *lastp = NEW_STEP (result_set, __gconv_modules_db[cnt],
					 current);
		      lastp = &(*lastp)->next;
		    }
                }
	    }
	}

      /* Go on with the next entry.  */
      current = current->next;
    }

  if (best != NULL)
    /* We really found a way to do the transformation.  Now build a data
       structure describing the transformation steps.*/
    result = gen_steps (best, toset_expand ?: toset, fromset_expand ?: fromset,
			handle, nsteps);
  else
    {
      /* We haven't found a transformation.  Clear the result values.  */
      *handle = NULL;
      *nsteps = 0;
    }

  /* Add result in any case to list of known derivations.  */
  add_derivation (fromset_expand ?: fromset, toset_expand ?: toset,
		  *handle, *nsteps);

  __libc_lock_unlock (lock);

  return result;
}


int
__gconv_find_transform (const char *toset, const char *fromset,
			struct gconv_step **handle, size_t *nsteps)
{
  __libc_once_define (static, once);
  const char *fromset_expand = NULL;
  const char *toset_expand = NULL;
  int result;

  /* Ensure that the configuration data is read.  */
  __libc_once (once, __gconv_read_conf);

  /* If we don't have a module database return with an error.  */
  if (__gconv_modules_db == NULL)
    return GCONV_NOCONV;

  /* See whether the names are aliases.  */
  if (__gconv_alias_db != NULL)
    {
      struct gconv_alias key;
      struct gconv_alias **found;

      key.fromname = fromset;
      found = __tfind (&key, &__gconv_alias_db, __gconv_alias_compare);
      fromset_expand = found != NULL ? (*found)->toname : NULL;

      key.fromname = toset;
      found = __tfind (&key, &__gconv_alias_db, __gconv_alias_compare);
      toset_expand = found != NULL ? (*found)->toname : NULL;
    }

  result = find_derivation (toset, toset_expand, fromset, fromset_expand,
			    handle, nsteps);

  /* The following code is necessary since `find_derivation' will return
     GCONV_OK even when no derivation was found but the same request
     was processed before.  I.e., negative results will also be cached.  */
  return (result == GCONV_OK
	  ? (*handle == NULL ? GCONV_NOCONV : GCONV_OK)
	  : result);
}


/* Release the entries of the modules list.  */
int
__gconv_close_transform (struct gconv_step *steps, size_t nsteps)
{
  int result = GCONV_OK;

  while (nsteps-- > 0)
    if (steps[nsteps].shlib_handle != NULL)
      {
	result = __gconv_release_shlib (steps[nsteps].shlib_handle);
	if (result != GCONV_OK)
	  break;
      }

  return result;
}


/* Free all resources if necessary.  */
static void __attribute__ ((unused))
free_mem (void)
{
  size_t cnt;

  if (__gconv_alias_db != NULL)
    __tdestroy (__gconv_alias_db, free);

  for (cnt = 0; cnt < __gconv_nmodules; ++cnt)
    {
      if (__gconv_modules_db[cnt]->from_regex != NULL)
	regfree ((regex_t *) __gconv_modules_db[cnt]->from_regex);

      /* Modules which names do not start with a slash are builtin
	 transformations and the memory is not allocated dynamically.  */
      if (__gconv_modules_db[cnt]->module_name[0] == '/')
	free (__gconv_modules_db[cnt]);
    }

  if (known_derivations != NULL)
    __tdestroy (known_derivations, free_derivation);
}

text_set_element (__libc_subfreeres, free_mem);