VariableListDeltaTracker.h

/*
 *  Copyright (c) 2014, Oculus VR, Inc.
 *  All rights reserved.
 *
 *  This source code is licensed under the BSD-style license found in the
 *  LICENSE file in the root directory of this source tree. An additional grant 
 *  of patent rights can be found in the PATENTS file in the same directory.
 *
 */

#include "NativeTypes.h"
#include "DS_List.h"
#include "RakMemoryOverride.h"
#include "BitStream.h"

#ifndef __VARIABLE_LIST_DELTA_TRACKER
#define __VARIABLE_LIST_DELTA_TRACKER

namespace RakNet
{
/// Class to write a series of variables, copy the contents to memory, and return if the newly written value is different than what was last written
/// Can also encode the reads, writes, and results directly to/from a bitstream
class VariableListDeltaTracker
{
public:
	VariableListDeltaTracker();
	~VariableListDeltaTracker();

	// Call before using a series of WriteVar
	void StartWrite(void);

	bool IsPastEndOfList(void) const {return nextWriteIndex>=variableList.Size();}

	/// Records the passed value of the variable to memory, and returns true if the value is different from the write before that (or if it is the first write)
	/// \pre Call StartWrite() before doing the first of a series of calls to WriteVar or other functions that call WriteVar
	/// \note Variables must be of the same type, written in the same order, each time
	template <class VarType>
	bool WriteVar(const VarType &varData)
	{
		RakNet::BitStream temp;
		temp.Write(varData);
		if (nextWriteIndex>=variableList.Size())
		{
			variableList.Push(VariableLastValueNode(temp.GetData(),temp.GetNumberOfBytesUsed()),_FILE_AND_LINE_);
			nextWriteIndex++;
			return true; // Different because it's new
		}

		if (temp.GetNumberOfBytesUsed()!=variableList[nextWriteIndex].byteLength)
		{
			variableList[nextWriteIndex].lastData=(char*) rakRealloc_Ex(variableList[nextWriteIndex].lastData, temp.GetNumberOfBytesUsed(),_FILE_AND_LINE_);
			variableList[nextWriteIndex].byteLength=temp.GetNumberOfBytesUsed();
			memcpy(variableList[nextWriteIndex].lastData,temp.GetData(),temp.GetNumberOfBytesUsed());
			nextWriteIndex++;
			variableList[nextWriteIndex].isDirty=false;
			return true; // Different because the serialized size is different
		}
		if (variableList[nextWriteIndex].isDirty==false && memcmp(temp.GetData(),variableList[nextWriteIndex].lastData, variableList[nextWriteIndex].byteLength)==0)
		{
			nextWriteIndex++;
			return false; // Same because not dirty and memcmp is the same
		}

		variableList[nextWriteIndex].isDirty=false;
		memcpy(variableList[nextWriteIndex].lastData,temp.GetData(),temp.GetNumberOfBytesUsed());
		nextWriteIndex++;
		return true; // Different because dirty or memcmp was different
	}
	/// Calls WriteVar. If the variable has changed, writes true, and writes the variable. Otherwise writes false.
	template <class VarType>
	bool WriteVarToBitstream(const VarType &varData, RakNet::BitStream *bitStream)
	{
		bool wasDifferent = WriteVar(varData);
		bitStream->Write(wasDifferent);
		if (wasDifferent)
		{
			bitStream->Write(varData);
			return true;
		}
		return false;
	}
	/// Calls WriteVarToBitstream(). Additionally, adds the boolean result of WriteVar() to boolean bit array
	template <class VarType>
	bool WriteVarToBitstream(const VarType &varData, RakNet::BitStream *bitStream, unsigned char *bArray, unsigned short writeOffset)
	{
		if (WriteVarToBitstream(varData,bitStream)==true)
		{
			BitSize_t numberOfBitsMod8 = writeOffset & 7;

			if ( numberOfBitsMod8 == 0 )
				bArray[ writeOffset >> 3 ] = 0x80;
			else
				bArray[ writeOffset >> 3 ] |= 0x80 >> ( numberOfBitsMod8 ); // Set the bit to 1

			return true;
		}
		else
		{
			if ( ( writeOffset & 7 ) == 0 )
				bArray[ writeOffset >> 3 ] = 0;

			return false;
		}
	}

	/// Paired with a call to WriteVarToBitstream(), will read a variable if it had changed. Otherwise the values remains the same.
	template <class VarType>
	static bool ReadVarFromBitstream(VarType &varData, RakNet::BitStream *bitStream)
	{
		bool wasWritten;
		if (bitStream->Read(wasWritten)==false)
			return false;
		if (wasWritten)
		{
			if (bitStream->Read(varData)==false)
				return false;
		}
		return wasWritten;
	}

	/// Variables flagged dirty will cause WriteVar() to return true, even if the variable had not otherwise changed
	/// This updates all the variables in the list, where in each index \a varsWritten is true, so will the variable at the corresponding index be flagged dirty
	void FlagDirtyFromBitArray(unsigned char *bArray);

	/// \internal
	struct VariableLastValueNode
	{
		VariableLastValueNode();
		VariableLastValueNode(const unsigned char *data, int _byteLength);
		~VariableLastValueNode();
		char *lastData;
		unsigned int byteLength;
		bool isDirty;
	};

protected:
	/// \internal
	DataStructures::List<VariableLastValueNode> variableList;
	/// \internal
	unsigned int nextWriteIndex;
};


}

#endif