/* $Id$
 *
 * Keep a cache of name/id mappings
 *
 * Copyright (C) 1989-1998 by the Massachusetts Institute of Technology
 * For copying and distribution information, please see the file
 * <mit-copyright.h>.
 */

#include <mit-copyright.h>
#include "mr_server.h"
#include "query.h"

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

EXEC SQL INCLUDE sqlca;

RCSID("$Header$");

EXEC SQL WHENEVER SQLERROR DO dbmserr();

extern char *whoami;

/* Cache parameters: */
#define CACHESIZE 101		/* number of cache slots */

struct item {
  char name[MAX_FIELD_WIDTH];
  enum tables type;
  int nhash;
  int id;
  struct item *next;
  struct item *prev;
  struct item *trans;		/* keep track of transactions */
};

static struct item cachehead;
static int cachesize;

/* statistics counters */
int cachehits = 0, cachemisses = 0;

int hashname(char *name, enum tables type);

/* Name hash function. */

int hashname(char *name, enum tables type)
{
  int val = type;

  while (*name)
    val = (val << 5) - val + *name++ - '`';
  return val;
}


/* Initialize the cache, flushing any old data, and report the statistics
 * if the cache was previously in use.
 */

void flush_cache(void)
{
  struct item *i;

  if (cachehits + cachemisses != 0)
    {
      com_err(whoami, 0, "Flushing cache; %d hits, %d misses, %d%% hit rate",
	      cachehits, cachemisses,
	      (100 * cachehits) / (cachehits + cachemisses));
    }
  else
    cachehead.next = cachehead.prev = &cachehead;
  cachehits = cachemisses = cachesize = 0;
  for (i = cachehead.next; i != &cachehead; i = i->next)
    {
      if (i->prev != &cachehead)
	free(i->prev);
    }
  if (cachehead.prev != &cachehead)
    free(cachehead.prev);
  cachehead.next = cachehead.prev = &cachehead;
  cachehead.trans = NULL;
}


/* Do a name to ID translation.  id will be updated with the answer if
 * it is available, and as a side effect the cache is updated.
 */

int name_to_id(char *name, enum tables type, int *id)
{
  struct item *i, *t;
  EXEC SQL BEGIN DECLARE SECTION;
  char *iname;
  int j, h;
  EXEC SQL END DECLARE SECTION;

  h = hashname(name, type);
  for (i = cachehead.next; i != &cachehead; i = i->next)
    {
      if (i->nhash != h || strcmp(name, i->name) || type != i->type)
	continue;
      *id = i->id;
      cachehits++;
      i->next->prev = i->prev;
      i->prev->next = i->next;
      i->next = cachehead.next;
      i->prev = &cachehead;
      cachehead.next->prev = i;
      cachehead.next = i;
      return MR_SUCCESS;
    }

  cachemisses++;
  iname = name;

  switch (type)
    {
    case USERS_TABLE:
      if (strchr(iname, '@') || (strlen(iname) > 8))
	{
	  sqlca.sqlcode = SQL_NO_MATCH;
	  break;
	}
      EXEC SQL SELECT users_id INTO :j FROM users WHERE login = :iname;
      break;
    case LIST_TABLE:
      EXEC SQL SELECT list_id INTO :j FROM list WHERE name = :iname;
      break;
    case MACHINE_TABLE:
      EXEC SQL SELECT mach_id INTO :j FROM machine WHERE name = UPPER(:iname);
      break;
    case SUBNET_TABLE:
      EXEC SQL SELECT snet_id INTO :j FROM subnet WHERE name = UPPER(:iname);
      break;
    case CLUSTERS_TABLE:
      EXEC SQL SELECT clu_id INTO :j FROM clusters WHERE name = :iname;
      break;
    case FILESYS_TABLE:
      EXEC SQL SELECT filsys_id INTO :j FROM filesys WHERE label = :iname;
      break;
    case STRINGS_TABLE:
      if (!iname[0])	/* special-case empty string */
	{
	  *id = 0;
	  return MR_SUCCESS;
	}
      EXEC SQL SELECT string_id INTO :j FROM strings WHERE string = :iname;
      break;
    default:
      return MR_INTERNAL;
    }
  if (sqlca.sqlcode == SQL_NO_MATCH)
    return MR_NO_MATCH;
  if (sqlca.sqlerrd[2] > 1)
    return MR_NOT_UNIQUE;
  if (sqlca.sqlcode)
    return MR_DBMS_ERR;
  *id = j;
  if (name[0] == '#' && type != USERS_TABLE)
    return MR_SUCCESS;
  if (cachesize < CACHESIZE)
    {
      i = malloc(sizeof(struct item));
      if (!i)
	return MR_SUCCESS;
      cachesize++;
    }
  else
    {
      i = cachehead.prev;
      cachehead.prev = i->prev;
      i->prev->next = &cachehead;
    }
  strcpy(i->name, name);
  i->type = type;
  i->nhash = h;
  i->id = j;
  i->next = cachehead.next;
  i->prev = &cachehead;
  i->trans = NULL;
  cachehead.next->prev = i;
  cachehead.next = i;
  /* find the end of the transaction chain & add this item */
  for (t = &cachehead; t->trans && t != i; t = t->trans)
    ;
  if (t != i)
    t->trans = i;
  return MR_SUCCESS;
}


/* Perform an ID to name mapping.  name should be a pointer to a pointer to
 * malloc'ed data.  The buffer it refers to will be freed, and a new buffer
 * allocated with the answer.
 */

int id_to_name(int id, enum tables type, char **name)
{
  struct item *i, *t;
  EXEC SQL BEGIN DECLARE SECTION;
  char iname[MAX_FIELD_WIDTH];
  int j;
  EXEC SQL END DECLARE SECTION;

  for (i = cachehead.next; i != &cachehead; i = i->next)
    {
      if (i->id != id || type != i->type)
	continue;
      free(*name);
      *name = xstrdup(i->name);
      cachehits++;
      i->next->prev = i->prev;
      i->prev->next = i->next;
      i->next = cachehead.next;
      i->prev = &cachehead;
      cachehead.next->prev = i;
      cachehead.next = i;
      return MR_SUCCESS;
    }

  cachemisses++;
  j = id;

  switch (type)
    {
    case USERS_TABLE:
      EXEC SQL SELECT login INTO :iname FROM users WHERE users_id = :j;
      break;
    case LIST_TABLE:
      EXEC SQL SELECT name INTO :iname FROM list WHERE list_id = :j;
      break;
    case MACHINE_TABLE:
      EXEC SQL SELECT name INTO :iname FROM machine WHERE mach_id = :j;
      break;
    case SUBNET_TABLE:
      EXEC SQL SELECT name INTO :iname FROM subnet WHERE snet_id = :j;
      break;
    case CLUSTERS_TABLE:
      EXEC SQL SELECT name INTO :iname FROM clusters WHERE clu_id = :j;
      break;
    case FILESYS_TABLE:
      EXEC SQL SELECT label INTO :iname FROM filesys WHERE filsys_id = :j;
      break;
    case STRINGS_TABLE:
      EXEC SQL SELECT string INTO :iname FROM strings WHERE string_id = :j;
      break;
    default:
      return MR_INTERNAL;
    }
  if (sqlca.sqlcode == SQL_NO_MATCH)
    {
      free(*name);
      sprintf(iname, "#%d", j);
      *name = xstrdup(iname);
      return MR_NO_MATCH;
    }
  if (sqlca.sqlerrd[2] > 1)
    return MR_INTERNAL;
  if (sqlca.sqlcode)
    return MR_DBMS_ERR;
  free(*name);
  *name = xstrdup(strtrim(iname));
  if (**name == '#' && type != USERS_TABLE)
    return MR_SUCCESS;
  if (cachesize < CACHESIZE)
    {
      i = malloc(sizeof(struct item));
      if (!i)
	return MR_SUCCESS;
      cachesize++;
    }
  else
    {
      i = cachehead.prev;
      cachehead.prev = i->prev;
      i->prev->next = &cachehead;
    }
  strcpy(i->name, *name);
  i->type = type;
  i->nhash = hashname(*name, type);
  i->id = id;
  i->next = cachehead.next;
  i->prev = &cachehead;
  i->trans = NULL;
  cachehead.next->prev = i;
  cachehead.next = i;
  /* find the end of the transaction chain & add this item */
  for (t = &cachehead; t->trans && t != i; t = t->trans)
    ;
  if (t != i)
    t->trans = i;
  return MR_SUCCESS;
}


/* Explicitly add something to the cache without doing a lookup in the
 * database.
 */

int cache_entry(char *name, enum tables type, int id)
{
  struct item *i, *t;

  for (i = cachehead.next; i != &cachehead; i = i->next)
    {
      if (i->id == id && i->type == type)
	{
	  if (strcmp(i->name, name))
	    {
	      strcpy(i->name, name);
	      i->nhash = hashname(name, type);
	    }
	  return MR_SUCCESS;
	}
    }
  if (cachesize < CACHESIZE)
    {
      i = malloc(sizeof(struct item));
      if (!i)
	return MR_SUCCESS;
      cachesize++;
    }
  else
    {
      i = cachehead.prev;
      cachehead.prev = i->prev;
      i->prev->next = &cachehead;
    }
  strcpy(i->name, name);
  i->type = type;
  i->nhash = hashname(name, type);
  i->id = id;
  i->next = cachehead.next;
  i->prev = &cachehead;
  i->trans = NULL;
  cachehead.next->prev = i;
  cachehead.next = i;
  /* find the end of the transaction chain & add this item */
  for (t = &cachehead; t->trans && t != i; t = t->trans)
    ;
  if (t != i)
    t->trans = i;
  return MR_SUCCESS;
}


/* Flush something that may or may not already be in the cache. */

void flush_name(char *name, enum tables type)
{
  struct item *i;

  /* first clear it out of the transaction chain */
  for (i = &cachehead; i && i->trans; i = i->trans)
    {
      if (!strcmp(name, i->trans->name) && type == i->trans->type)
	i->trans = i->trans->trans;
    }

  /* now remove it */
  for (i = cachehead.next; i != &cachehead; i = i->next)
    {
      if (!strcmp(name, i->name) && type == i->type)
	{
	  cachesize--;
	  i->next->prev = i->prev;
	  i->prev->next = i->next;
	  free(i);
	  break;
	}
    }
}


/* Called when a transaction is committed to also commit any cache changes.
 * Just throws away the list of cache changes for this transaction.
 */

void cache_commit(void)
{
  cachehead.trans = NULL;
}


/* Called whan a transaction is aborted to throw away any cache changes
 * from that transaction.
 */

void cache_abort(void)
{
  struct item *i, *t;

  for (i = cachehead.trans; i; i = t)
    {
      t = i->trans;
      flush_name(i->name, i->type);
    }
  cachehead.trans = NULL;
}