/*
** This is the implementation of generic hash-tables
** used in eDb.
*/
#include "eDbInit.h"

/* Turn bulk memory into a hash table object by initializing the
** fields of the Hash structure.
**
** "new" is a pointer to the hash table that is to be initialized.
** keyClass is one of the constants eDb_HASH_INT, eDb_HASH_POINTER,
** eDb_HASH_BINARY, or eDb_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.  CopyKey only makes
** sense for eDb_HASH_STRING and eDb_HASH_BINARY and is ignored
** for other key classes.
*/
void eDbHashInit(Hash *pHash, int keyClass, int copyKey){
	assert( pHash!=0 );
	assert( keyClass>=eDb_HASH_INT && keyClass<=eDb_HASH_BINARY );
	pHash->keyClass = keyClass;
	pHash->copyKey = copyKey &&
				(keyClass==eDb_HASH_STRING || keyClass==eDb_HASH_BINARY);
	pHash->first = 0;
	pHash->count = 0;
	pHash->htsize = 0;
	pHash->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 eDbHashClear(Hash *pH){
	HashElem *elem;         /* For looping over all elements of the table */
	assert( pH!=0 );
	elem = pH->first;
	pH->first = 0;
	if( pH->ht ) eDbFree(pH->ht);
	pH->ht = 0;
	pH->htsize = 0;
	while( elem ){
		HashElem *next_elem = elem->next;
		if( pH->copyKey && elem->pKey ){
			eDbFree(elem->pKey);
		}
		eDbFree(elem);
		elem = next_elem;
	}
	pH->count = 0;
}

/*
** Hash and comparison functions when the mode is eDb_HASH_INT
*/
static int intHash(const void *pKey, int nKey){
	return nKey ^ (nKey<<8) ^ (nKey>>8);
}
static int intCompare(const void *pKey1, int n1, const void *pKey2, int n2){
	return n2 - n1;
}

#if 0 /* NOT USED */
/*
** Hash and comparison functions when the mode is eDb_HASH_POINTER
*/
static int ptrHash(const void *pKey, int nKey){
	uptr x = Addr(pKey);
	return x ^ (x<<8) ^ (x>>8);
}
static int ptrCompare(const void *pKey1, int n1, const void *pKey2, int n2){
	if( pKey1==pKey2 ) return 0;
	if( pKey1<pKey2 ) return -1;
	return 1;
}
#endif

/*
** Hash and comparison functions when the mode is eDb_HASH_STRING
*/
static int strHash(const void *pKey, int nKey){
	return eDbHashNoCase((const char*)pKey, nKey); 
}
static int strCompare(const void *pKey1, int n1, const void *pKey2, int n2){
	if( n1!=n2 ) return n2-n1;
	return eDbStrNICmp((const char*)pKey1,(const char*)pKey2,n1);
}

/*
** Hash and comparison functions when the mode is eDb_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 n2-n1;
	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){
	switch( keyClass ){
		case eDb_HASH_INT:     return &intHash;
		/* case eDb_HASH_POINTER: return &ptrHash; // NOT USED */
		case eDb_HASH_STRING:  return &strHash;
		case eDb_HASH_BINARY:  return &binHash;;
		default: break;
	}
	return 0;
}

/*
** 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){
	switch( keyClass ){
		case eDb_HASH_INT:     return &intCompare;
		/* case eDb_HASH_POINTER: return &ptrCompare; // NOT USED */
		case eDb_HASH_STRING:  return &strCompare;
		case eDb_HASH_BINARY:  return &binCompare;
		default: break;
	}
	return 0;
}


/* 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 eDbMalloc() fails.
*/
static void rehash(Hash *pH, int new_size){
	struct _ht *new_ht;            /* The new hash table */
	HashElem *elem, *next_elem;    /* For looping over existing elements */
	HashElem *x;                   /* Element being copied to new hash table */
	int (*xHash)(const void*,int); /* The hash function */

	assert( (new_size & (new_size-1))==0 );
	new_ht = (struct _ht *)eDbMalloc( new_size*sizeof(struct _ht) );
	if( new_ht==0 ) return;
	if( pH->ht ) eDbFree(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;
		x = new_ht[h].chain;
		if( x ){
			elem->next = x;
			elem->prev = x->prev;
			if( x->prev ) x->prev->next = elem;
			else          pH->first = elem;
			x->prev = elem;
		}else{
			elem->next = pH->first;
			if( pH->first ) pH->first->prev = elem;
			elem->prev = 0;
			pH->first = elem;
		}
		new_ht[h].chain = elem;
		new_ht[h].count++;
	}
}

/* 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 HashElem *findElementGivenHash(
	const Hash *pH,     /* The pH to be searched */
	const void *pKey,   /* The key we are searching for */
	int nKey,
	int h               /* The hash for this key. */
){
	HashElem *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 ){
		elem = pH->ht[h].chain;
		count = pH->ht[h].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(
	Hash *pH,         /* The pH containing "elem" */
	HashElem* elem,   /* The element to be removed from the pH */
	int h             /* Hash value for the element */
){
	if( elem->prev ){
		elem->prev->next = elem->next; 
	}else{
		pH->first = elem->next;
	}
	if( elem->next ){
		elem->next->prev = elem->prev;
	}
	if( pH->ht[h].chain==elem ){
		pH->ht[h].chain = elem->next;
	}
	pH->ht[h].count--;
	if( pH->ht[h].count<=0 ){
		pH->ht[h].chain = 0;
	}
	if( pH->copyKey && elem->pKey ){
		eDbFree(elem->pKey);
	}
	eDbFree( elem );
	pH->count--;
}

/* 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 *eDbHashFind(const Hash *pH, const void *pKey, int nKey){
	int h;             /* A hash on key */
	HashElem *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 *eDbHashInsert(Hash *pH, const void *pKey, int nKey, void *data){
	int hraw;             /* Raw hash value of the key */
	int h;                /* the hash of the key modulo hash table size */
	HashElem *elem;       /* Used to loop thru the element list */
	HashElem *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 = (HashElem*)eDbMalloc( sizeof(HashElem) );
	if( new_elem==0 ) return data;
	if( pH->copyKey && pKey!=0 ){
		new_elem->pKey = eDbMallocRaw( nKey );
		if( new_elem->pKey==0 ){
			eDbFree(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;
		eDbFree(new_elem);
		return data;
	}
	if( pH->count > pH->htsize ){
		rehash(pH,pH->htsize*2);
	}
	assert( (pH->htsize & (pH->htsize-1))==0 );
	h = hraw & (pH->htsize-1);
	elem = pH->ht[h].chain;
	if( elem ){
		new_elem->next = elem;
		new_elem->prev = elem->prev;
		if( elem->prev ){
			elem->prev->next = new_elem;
		}else{
			pH->first = new_elem;
		}
		elem->prev = new_elem;
	}else{
		new_elem->next = pH->first;
		new_elem->prev = 0;
		if( pH->first ){
			pH->first->prev = new_elem;
		}
		pH->first = new_elem;
	}
	pH->ht[h].count++;
	pH->ht[h].chain = new_elem;
	new_elem->data = data;
	return 0;
}