using System;
using System.Diagnostics;
using System.Text;

using u8 = System.Byte;
using u32 = System.UInt32;

namespace CS_SQLite3
{
  public partial class CSSQLite
  {
    /*
    ** 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.
    **
    ** $Id: hash.c,v 1.38 2009/05/09 23:29:12 drh Exp
    **
    *************************************************************************
    **  Included in SQLite3 port to C#-SQLite;  2008 Noah B Hart
    **  C#-SQLite is an independent reimplementation of the SQLite software library
    **
    **  $Header$
    *************************************************************************
    */
    //#include "sqliteInt.h"
    //#include <assert.h>

    /* 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.
    */
    static void sqlite3HashInit( Hash pNew )
    {
      Debug.Assert( pNew != null );
      pNew.first = null;
      pNew.count = 0;
      pNew.htsize = 0;
      pNew.ht = null;
    }

    /* 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.
    */
    static void sqlite3HashClear( Hash pH )
    {
      HashElem elem;         /* For looping over all elements of the table */

      Debug.Assert( pH != null );
      elem = pH.first;
      pH.first = null;
      //sqlite3_free( ref  pH.ht );
      pH.ht = null;
      pH.htsize = 0;
      while ( elem != null )
      {
        HashElem next_elem = elem.next;
        ////sqlite3_free(ref  elem );
        elem = next_elem;
      }
      pH.count = 0;
    }

    /*
    ** The hashing function.
    */
    static u32 strHash( string z, int nKey )
    {
      int h = 0;
      Debug.Assert( nKey >= 0 );
      int _z = 0;
      while ( nKey > 0 )
      {
        h = ( h << 3 ) ^ h ^ ( ( _z < z.Length ) ? (int)sqlite3UpperToLower[(byte)z[_z++]] : 0 );
        nKey--;
      }
      return (u32)h;
    }

    /* Link pNew element into the hash table pH.  If pEntry!=0 then also
    ** insert pNew into the pEntry hash bucket.
    */
    static void insertElement(
    Hash pH,              /* The complete hash table */
    _ht pEntry,           /* The entry into which pNew is inserted */
    HashElem pNew         /* The element to be inserted */
    )
    {
      HashElem pHead;       /* First element already in pEntry */
      if ( pEntry != null )
      {
        pHead = pEntry.count != 0 ? pEntry.chain : null;
        pEntry.count++;
        pEntry.chain = pNew;
      }
      else
      {
        pHead = null;
      }
      if ( pHead != null )
      {
        pNew.next = pHead;
        pNew.prev = pHead.prev;
        if ( pHead.prev != null ) { pHead.prev.next = pNew; }
        else { pH.first = pNew; }
        pHead.prev = pNew;
      }
      else
      {
        pNew.next = pH.first;
        if ( pH.first != null ) { pH.first.prev = pNew; }
        pNew.prev = null;
        pH.first = pNew;
      }
    }

    /* Resize the hash table so that it cantains "new_size" buckets.
    **
    ** The hash table might fail to resize if sqlite3_malloc() fails or
    ** if the new size is the same as the prior size.
    ** Return TRUE if the resize occurs and false if not.
    */
    static bool rehash( ref Hash pH, u32 new_size )
    {
      _ht[] new_ht;            /* The new hash table */
      HashElem elem;
      HashElem next_elem;    /* For looping over existing elements */

#if SQLITE_MALLOC_SOFT_LIMIT
if( new_size*sizeof(struct _ht)>SQLITE_MALLOC_SOFT_LIMIT ){
new_size = SQLITE_MALLOC_SOFT_LIMIT/sizeof(struct _ht);
}
if( new_size==pH->htsize ) return false;
#endif

      /* There is a call to sqlite3Malloc() inside rehash(). If there is
** already an allocation at pH.ht, then if this malloc() fails it
** is benign (since failing to resize a hash table is a performance
** hit only, not a fatal error).
*/
      sqlite3BeginBenignMalloc();
      new_ht = new _ht[new_size]; //(struct _ht *)sqlite3Malloc( new_size*sizeof(struct _ht) );
      for ( int i = 0 ; i < new_size ; i++ ) new_ht[i] = new _ht();
      sqlite3EndBenignMalloc();

      if ( new_ht == null ) return false;
      //sqlite3_free( ref  pH.ht );
      pH.ht = new_ht;
      // pH.htsize = new_size = sqlite3MallocSize(new_ht)/sizeof(struct _ht);
      //memset(new_ht, 0, new_size*sizeof(struct _ht));
      pH.htsize = new_size;

      for ( elem = pH.first, pH.first = null ; elem != null ; elem = next_elem )
      {
        u32 h = strHash( elem.pKey, elem.nKey ) % new_size;
        next_elem = elem.next;
        insertElement( pH, new_ht[h], elem );
      }
      return true;
    }

    /* 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(
    Hash pH,       /* The pH to be searched */
    string pKey,   /* The key we are searching for */
    int nKey,      /* Bytes in key (not counting zero terminator) */
    u32 h         /* The hash for this key. */
    )
    {
      HashElem elem;                /* Used to loop thru the element list */
      int count;                    /* Number of elements left to test */

      if ( pH.ht != null && pH.ht[h] != null )
      {
        _ht pEntry = pH.ht[h];
        elem = pEntry.chain;
        count = (int)pEntry.count;
      }
      else
      {
        elem = pH.first;
        count = (int)pH.count;
      }
      while ( count-- > 0 && ALWAYS( elem ) )
      {
        if ( elem.nKey == nKey && sqlite3StrNICmp( elem.pKey, pKey, nKey ) == 0 )
        {
          return elem;
        }
        elem = elem.next;
      }
      return null;
    }

    /* 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" */
    ref HashElem elem,  /* The element to be removed from the pH */
    u32 h               /* Hash value for the element */
    )
    {
      _ht pEntry;
      if ( elem.prev != null )
      {
        elem.prev.next = elem.next;
      }
      else
      {
        pH.first = elem.next;
      }
      if ( elem.next != null )
      {
        elem.next.prev = elem.prev;
      }
      if ( pH.ht != null && pH.ht[h] != null )
      {
        pEntry = pH.ht[h];
        if ( pEntry.chain == elem )
        {
          pEntry.chain = elem.next;
        }
        pEntry.count--;
        Debug.Assert( pEntry.count >= 0 );
      }
      //sqlite3_free( ref  elem );
      pH.count--;
      if ( pH.count <= 0 )
      {
        Debug.Assert( pH.first == null );
        Debug.Assert( pH.count == 0 );
        sqlite3HashClear( 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.
    */
    static object sqlite3HashFind( Hash pH, string pKey, int nKey )
    {
      HashElem elem;  /* The element that matches key */
      u32 h;          /* A hash on key */

      Debug.Assert( pH != null );
      Debug.Assert( pKey != null );
      Debug.Assert( nKey >= 0 );
      if ( pH.ht != null )
      {
        h = strHash( pKey, nKey ) % pH.htsize;
      }
      else
      {
        h = 0;
      }
      elem = findElementGivenHash( pH, pKey, nKey, h );
      return elem != null ? elem.data : null;
    }

    /* 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 and 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.
    */
    static object sqlite3HashInsert( ref Hash pH, string pKey, int nKey, object data )
    {
      u32 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 */

      Debug.Assert( pH != null );
      Debug.Assert( pKey != null );
      Debug.Assert( nKey >= 0 );

      if ( pH.htsize != 0 )
      {
        h = strHash( pKey, nKey ) % pH.htsize;
      }
      else
      {
        h = 0;
      }
      elem = findElementGivenHash( pH, pKey, nKey, h );
      if ( elem != null )
      {
        object old_data = elem.data;
        if ( data == null )
        {
          removeElementGivenHash( pH, ref elem, h );
        }
        else
        {
          elem.data = data;
          elem.pKey = pKey;
          Debug.Assert( nKey == elem.nKey );
        }
        return old_data;
      }
      if ( data == null ) return null;
      new_elem = new HashElem();//(HashElem*)sqlite3Malloc( sizeof(HashElem) );
      if ( new_elem == null ) return data;
      new_elem.pKey = pKey;
      new_elem.nKey = nKey;
      new_elem.data = data;
      pH.count++;
      if ( pH.count >= 10 && pH.count > 2 * pH.htsize )
      {
        if ( rehash( ref  pH, pH.count * 2 ) )
        {
          Debug.Assert( pH.htsize > 0 );
          h = strHash( pKey, nKey ) % pH.htsize;
        }
      }
      if ( pH.ht != null )
      {
        insertElement( pH, pH.ht[h], new_elem );

      }
      else
      {
        insertElement( pH, null, new_elem );
      }
      return null;
    }

  }
}
