/*

* Copyright (c) 2004-2009 Nokia Corporation and/or its subsidiary(-ies).

* All rights reserved.

* This component and the accompanying materials are made available

* under the terms of "Eclipse Public License v1.0"

* which accompanies this distribution, and is available

* at the URL "http://www.eclipse.org/legal/epl-v10.html".

*

* Initial Contributors:

* Nokia Corporation - initial contribution.

*

* Contributors:

*

* Description: 

*

*/

#ifndef __T_RNDUTILS_H__

#define __T_RNDUTILS_H__

#include "t_utils.h"

#include "t_utils2.h"

const TInt KDigramNumberOfNonLetters =  3;	// space, -, null

const TInt KDigramNumberOfLetters =  26 ;

const TInt KDigramNumberOfChars =  KDigramNumberOfLetters*2+ KDigramNumberOfNonLetters;

/** Used to create randomly generated words using n-grams found in the specified data file.

	Using n-grams lead to much more realistic words and thus makes it obvious a descriptor

	is data and not noise.

	This implementation only supports digrams */

class CWordNgrams : public CBase, public MRandomWordGenerator

	{

	public:

		HBufC* WordLC();

	protected: 

		TBool AddLetter(TDes& aWord);

		void ConstructL(const TDesC& aFilename, TInt aNgramSize = 2, TBool aUseNarrowChar = ETrue);

		virtual TChar NextLetter(const TDesC& aWord) = 0;

		virtual void SetNgram(const TDesC8& aNgram, TUint aNumber) = 0;

		virtual void SetNgram(const TDesC16& aNgram, TUint aNumber) = 0;

	};

/** Implementation of CWordNgrams which uses digram frequencies (letter pairs)

	to generate random words */

class CWordDigrams : public CWordNgrams

	{

	public:

		static CWordDigrams* NewLC(const TDesC& aFilename, TInt64& aRandSeed );

		virtual ~CWordDigrams();

	protected: 

		void ConstructL(const TDesC& aFilename);

		void SetNgram(const TDesC8& aNgram, TUint aNumber);

		void SetNgram(const TDesC16& aNgram, TUint aNumber); // empty function

		TChar NextLetter(const TDesC& aWord);

	private:

		CWordDigrams(TInt64& aRandSeed);

		static TInt Index(const TChar c);

		static TChar Char(TInt i);

	private:

		TInt64& iRandSeed;

		TUint8 iDigrams[KDigramNumberOfChars][KDigramNumberOfChars];

		TUint16 iSizes[KDigramNumberOfChars];

	};

#endif