/*

** 2001 September 22

**

** The author disclaims copyright to this source code.  In place of

** a legal notice, here is a blessing:

**

**    May you do good and not evil.

**    May you find forgiveness for yourself and forgive others.

**    May you share freely, never taking more than you give.

**

*************************************************************************

** This is the implementation of generic hash-tables used in SQLite.

** We've modified it slightly to serve as a standalone hash table

** implementation for the full-text indexing module.

*/

/*

** The code in this file is only compiled if:

**

**     * The FTS2 module is being built as an extension

**       (in which case SQLITE_CORE is not defined), or

**

**     * The FTS2 module is being built into the core of

**       SQLite (in which case SQLITE_ENABLE_FTS2 is defined).

*/

#if !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2)

#include <assert.h>

#include <stdlib.h>

#include <string.h>

#include "sqlite3.h"

#include "fts2_hash.h"

/*

** Malloc and Free functions

*/

static void *fts2HashMalloc(int n){

  void *p = sqlite3_malloc(n);

  if( p ){

    memset(p, 0, n);

  }

  return p;

}

static void fts2HashFree(void *p){

  sqlite3_free(p);

}

/* Turn bulk memory into a hash table object by initializing the

** fields of the Hash structure.

**

** "pNew" is a pointer to the hash table that is to be initialized.

** keyClass is one of the constants 

** FTS2_HASH_BINARY or FTS2_HASH_STRING.  The value of keyClass 

** determines what kind of key the hash table will use.  "copyKey" is

** true if the hash table should make its own private copy of keys and

** false if it should just use the supplied pointer.

*/

void sqlite3Fts2HashInit(fts2Hash *pNew, int keyClass, int copyKey){

  assert( pNew!=0 );

  assert( keyClass>=FTS2_HASH_STRING && keyClass<=FTS2_HASH_BINARY );

  pNew->keyClass = keyClass;

  pNew->copyKey = copyKey;

  pNew->first = 0;

  pNew->count = 0;

  pNew->htsize = 0;

  pNew->ht = 0;

}

/* Remove all entries from a hash table.  Reclaim all memory.

** Call this routine to delete a hash table or to reset a hash table

** to the empty state.

*/

void sqlite3Fts2HashClear(fts2Hash *pH){

  fts2HashElem *elem;         /* For looping over all elements of the table */

  assert( pH!=0 );

  elem = pH->first;

  pH->first = 0;

  fts2HashFree(pH->ht);

  pH->ht = 0;

  pH->htsize = 0;

  while( elem ){

    fts2HashElem *next_elem = elem->next;

    if( pH->copyKey && elem->pKey ){

      fts2HashFree(elem->pKey);

    }

    fts2HashFree(elem);

    elem = next_elem;

  }

  pH->count = 0;

}

/*

** Hash and comparison functions when the mode is FTS2_HASH_STRING

*/

static int strHash(const void *pKey, int nKey){

  const char *z = (const char *)pKey;

  int h = 0;

  if( nKey<=0 ) nKey = (int) strlen(z);

  while( nKey > 0  ){

    h = (h<<3) ^ h ^ *z++;

    nKey--;

  }

  return h & 0x7fffffff;

}

static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){

  if( n1!=n2 ) return 1;

  return strncmp((const char*)pKey1,(const char*)pKey2,n1);

}

/*

** Hash and comparison functions when the mode is FTS2_HASH_BINARY

*/

static int binHash(const void *pKey, int nKey){

  int h = 0;

  const char *z = (const char *)pKey;

  while( nKey-- > 0 ){

    h = (h<<3) ^ h ^ *(z++);

  }

  return h & 0x7fffffff;

}

static int binCompare(const void *pKey1, int n1, const void *pKey2, int n2){

  if( n1!=n2 ) return 1;

  return memcmp(pKey1,pKey2,n1);

}

/*

** Return a pointer to the appropriate hash function given the key class.

**

** The C syntax in this function definition may be unfamilar to some 

** programmers, so we provide the following additional explanation:

**

** The name of the function is "hashFunction".  The function takes a

** single parameter "keyClass".  The return value of hashFunction()

** is a pointer to another function.  Specifically, the return value

** of hashFunction() is a pointer to a function that takes two parameters

** with types "const void*" and "int" and returns an "int".

*/

static int (*hashFunction(int keyClass))(const void*,int){

  if( keyClass==FTS2_HASH_STRING ){

    return &strHash;

  }else{

    assert( keyClass==FTS2_HASH_BINARY );

    return &binHash;

  }

}

/*

** Return a pointer to the appropriate hash function given the key class.

**

** For help in interpreted the obscure C code in the function definition,

** see the header comment on the previous function.

*/

static int (*compareFunction(int keyClass))(const void*,int,const void*,int){

  if( keyClass==FTS2_HASH_STRING ){

    return &strCompare;

  }else{

    assert( keyClass==FTS2_HASH_BINARY );

    return &binCompare;

  }

}

/* Link an element into the hash table

*/

static void insertElement(

  fts2Hash *pH,            /* The complete hash table */

  struct _fts2ht *pEntry,  /* The entry into which pNew is inserted */

  fts2HashElem *pNew       /* The element to be inserted */

){

  fts2HashElem *pHead;     /* First element already in pEntry */

  pHead = pEntry->chain;

  if( pHead ){

    pNew->next = pHead;

    pNew->prev = pHead->prev;

    if( pHead->prev ){ pHead->prev->next = pNew; }

    else             { pH->first = pNew; }

    pHead->prev = pNew;

  }else{

    pNew->next = pH->first;

    if( pH->first ){ pH->first->prev = pNew; }

    pNew->prev = 0;

    pH->first = pNew;

  }

  pEntry->count++;

  pEntry->chain = pNew;

}

/* Resize the hash table so that it cantains "new_size" buckets.

** "new_size" must be a power of 2.  The hash table might fail 

** to resize if sqliteMalloc() fails.

*/

static void rehash(fts2Hash *pH, int new_size){

  struct _fts2ht *new_ht;          /* The new hash table */

  fts2HashElem *elem, *next_elem;  /* For looping over existing elements */

  int (*xHash)(const void*,int);   /* The hash function */

  assert( (new_size & (new_size-1))==0 );

  new_ht = (struct _fts2ht *)fts2HashMalloc( new_size*sizeof(struct _fts2ht) );

  if( new_ht==0 ) return;

  fts2HashFree(pH->ht);

  pH->ht = new_ht;

  pH->htsize = new_size;

  xHash = hashFunction(pH->keyClass);

  for(elem=pH->first, pH->first=0; elem; elem = next_elem){

    int h = (*xHash)(elem->pKey, elem->nKey) & (new_size-1);

    next_elem = elem->next;

    insertElement(pH, &new_ht[h], elem);

  }

}

/* This function (for internal use only) locates an element in an

** hash table that matches the given key.  The hash for this key has

** already been computed and is passed as the 4th parameter.

*/

static fts2HashElem *findElementGivenHash(

  const fts2Hash *pH, /* The pH to be searched */

  const void *pKey,   /* The key we are searching for */

  int nKey,

  int h               /* The hash for this key. */

){

  fts2HashElem *elem;            /* Used to loop thru the element list */

  int count;                     /* Number of elements left to test */

  int (*xCompare)(const void*,int,const void*,int);  /* comparison function */

  if( pH->ht ){

    struct _fts2ht *pEntry = &pH->ht[h];

    elem = pEntry->chain;

    count = pEntry->count;

    xCompare = compareFunction(pH->keyClass);

    while( count-- && elem ){

      if( (*xCompare)(elem->pKey,elem->nKey,pKey,nKey)==0 ){ 

        return elem;

      }

      elem = elem->next;

    }

  }

  return 0;

}

/* Remove a single entry from the hash table given a pointer to that

** element and a hash on the element's key.

*/

static void removeElementGivenHash(

  fts2Hash *pH,         /* The pH containing "elem" */

  fts2HashElem* elem,   /* The element to be removed from the pH */

  int h                 /* Hash value for the element */

){

  struct _fts2ht *pEntry;

  if( elem->prev ){

    elem->prev->next = elem->next; 

  }else{

    pH->first = elem->next;

  }

  if( elem->next ){

    elem->next->prev = elem->prev;

  }

  pEntry = &pH->ht[h];

  if( pEntry->chain==elem ){

    pEntry->chain = elem->next;

  }

  pEntry->count--;

  if( pEntry->count<=0 ){

    pEntry->chain = 0;

  }

  if( pH->copyKey && elem->pKey ){

    fts2HashFree(elem->pKey);

  }

  fts2HashFree( elem );

  pH->count--;

  if( pH->count<=0 ){

    assert( pH->first==0 );

    assert( pH->count==0 );

    fts2HashClear(pH);

  }

}

/* Attempt to locate an element of the hash table pH with a key

** that matches pKey,nKey.  Return the data for this element if it is

** found, or NULL if there is no match.

*/

void *sqlite3Fts2HashFind(const fts2Hash *pH, const void *pKey, int nKey){

  int h;                 /* A hash on key */

  fts2HashElem *elem;    /* The element that matches key */

  int (*xHash)(const void*,int);  /* The hash function */

  if( pH==0 || pH->ht==0 ) return 0;

  xHash = hashFunction(pH->keyClass);

  assert( xHash!=0 );

  h = (*xHash)(pKey,nKey);

  assert( (pH->htsize & (pH->htsize-1))==0 );

  elem = findElementGivenHash(pH,pKey,nKey, h & (pH->htsize-1));

  return elem ? elem->data : 0;

}

/* Insert an element into the hash table pH.  The key is pKey,nKey

** and the data is "data".

**

** If no element exists with a matching key, then a new

** element is created.  A copy of the key is made if the copyKey

** flag is set.  NULL is returned.

**

** If another element already exists with the same key, then the

** new data replaces the old data and the old data is returned.

** The key is not copied in this instance.  If a malloc fails, then

** the new data is returned and the hash table is unchanged.

**

** If the "data" parameter to this function is NULL, then the

** element corresponding to "key" is removed from the hash table.

*/

void *sqlite3Fts2HashInsert(

  fts2Hash *pH,        /* The hash table to insert into */

  const void *pKey,    /* The key */

  int nKey,            /* Number of bytes in the key */

  void *data           /* The data */

){

  int hraw;                 /* Raw hash value of the key */

  int h;                    /* the hash of the key modulo hash table size */

  fts2HashElem *elem;       /* Used to loop thru the element list */

  fts2HashElem *new_elem;   /* New element added to the pH */

  int (*xHash)(const void*,int);  /* The hash function */

  assert( pH!=0 );

  xHash = hashFunction(pH->keyClass);

  assert( xHash!=0 );

  hraw = (*xHash)(pKey, nKey);

  assert( (pH->htsize & (pH->htsize-1))==0 );

  h = hraw & (pH->htsize-1);

  elem = findElementGivenHash(pH,pKey,nKey,h);

  if( elem ){

    void *old_data = elem->data;

    if( data==0 ){

      removeElementGivenHash(pH,elem,h);

    }else{

      elem->data = data;

    }

    return old_data;

  }

  if( data==0 ) return 0;

  new_elem = (fts2HashElem*)fts2HashMalloc( sizeof(fts2HashElem) );

  if( new_elem==0 ) return data;

  if( pH->copyKey && pKey!=0 ){

    new_elem->pKey = fts2HashMalloc( nKey );

    if( new_elem->pKey==0 ){

      fts2HashFree(new_elem);

      return data;

    }

    memcpy((void*)new_elem->pKey, pKey, nKey);

  }else{

    new_elem->pKey = (void*)pKey;

  }

  new_elem->nKey = nKey;

  pH->count++;

  if( pH->htsize==0 ){

    rehash(pH,8);

    if( pH->htsize==0 ){

      pH->count = 0;

      fts2HashFree(new_elem);

      return data;

    }

  }

  if( pH->count > pH->htsize ){

    rehash(pH,pH->htsize*2);

  }

  assert( pH->htsize>0 );

  assert( (pH->htsize & (pH->htsize-1))==0 );

  h = hraw & (pH->htsize-1);

  insertElement(pH, &pH->ht[h], new_elem);

  new_elem->data = data;

  return 0;

}

#endif /* !defined(SQLITE_CORE) || defined(SQLITE_ENABLE_FTS2) */