#include "DiskFile.h"
#include <memory.h>
const int c_nBufferSize = 1024 * 32; // 32k cache

CDiskFileReader::CDiskFileReader()
: m_pFile( NULL )
, m_pBuffer( NULL )
, m_uiBufferAllocSize( 0 )
, m_uiBufferReadSize( 0 )
, m_uiBufferBeginPos( 0 )
, m_uiFilePos( 0 )
, m_bGood( false )
, m_nFileSize( 0 )
, m_nFileBeginPos( 0 )
{
	m_pBuffer = new BYTE[c_nBufferSize];
	m_uiBufferAllocSize = c_nBufferSize;
}

CDiskFileReader::~CDiskFileReader()
{
	if ( m_pBuffer )
	{
		delete [] m_pBuffer;
		m_pBuffer = NULL;
	}
}

void CDiskFileReader::SetFileInfo( FILE* pFile, unsigned int nFileSize, unsigned int nFileBeginPos )
{
	if ( m_pFile != pFile )
	{
		m_uiBufferReadSize = 0;
		m_uiFilePos = 0;
		m_uiBufferBeginPos = 0;
	}
	m_nFileSize = nFileSize;
	m_nFileBeginPos = nFileBeginPos;
	m_pFile = pFile;
	m_bGood = m_pFile != NULL;
}

void CDiskFileReader::Seek( int iOffset, int iWhence)
{
    if (m_bGood)
    {   
        unsigned int uiNewPos = 0;
		
		switch ( iWhence )
		{
		case SEEK_CUR:
			uiNewPos = (int)m_uiFilePos + iOffset;
			break;
		case SEEK_SET:
			uiNewPos = iOffset;
			break;
		case SEEK_END:
			uiNewPos = (int)m_nFileBeginPos + (int)m_nFileSize - iOffset;
			break;
		}
		if ( uiNewPos < m_uiBufferBeginPos || uiNewPos > m_uiBufferBeginPos + m_uiBufferReadSize )
		{
	        Flush();
		}
		m_uiFilePos = uiNewPos;
    }
}

void CDiskFileReader::Seek( int iOffset )
{
	Seek( iOffset, SEEK_CUR );
}

unsigned int CDiskFileReader::Read( void* pBuffer, unsigned int uiBytes )
{
    if (m_bGood)
    {
		unsigned int uiRead = 0;
        //uiAvailBufferBytes = m_uiBufferReadSize - m_uiPos;
		int nAvailBufferBytes = (int)m_uiBufferBeginPos + (int)m_uiBufferReadSize - (int)m_uiFilePos;
		if ( nAvailBufferBytes < 0 )
			nAvailBufferBytes = 0;
		if ( nAvailBufferBytes > (int)m_uiBufferReadSize )
		{
			nAvailBufferBytes = 0;
		}
		int nPos = m_uiFilePos - m_uiBufferBeginPos;
		if ( nPos < 0 )
		{
			return 0;
		}

        if (uiBytes > (unsigned int )nAvailBufferBytes)
        {
            if (nAvailBufferBytes > 0)
            {
                memcpy_s(pBuffer, uiBytes, &m_pBuffer[nPos], nAvailBufferBytes);
                pBuffer = &(((char *) pBuffer)[nAvailBufferBytes]);
                uiBytes -= nAvailBufferBytes;
                uiRead = nAvailBufferBytes;
				m_uiFilePos += uiRead;
            }
            Flush();
			nPos = 0;
            if (uiBytes > m_uiBufferAllocSize)
            {
                return uiRead + DiskRead(pBuffer, uiBytes);
            }
            else
            {
                m_uiBufferReadSize = DiskRead(m_pBuffer, m_uiBufferAllocSize);
                if (m_uiBufferReadSize < uiBytes)
                {
                    uiBytes = m_uiBufferReadSize;
                }
            }
        }
		if ( uiBytes > 0 )
		{
			memcpy_s( pBuffer, uiBytes, m_pBuffer + nPos, uiBytes );
		}
        m_uiFilePos += uiBytes;
        return uiRead + uiBytes;
    }
    else
    {
        return 0;
    }
}

void CDiskFileReader::Flush()
{
	m_uiBufferBeginPos = 0;
	m_uiBufferReadSize = 0;
}

unsigned int CDiskFileReader::DiskRead(void* pBuffer, unsigned int uiBytes)
{
	if ( fseek( m_pFile, m_uiFilePos, SEEK_SET ) != 0 )
	{
		m_bGood = false;
		return 0;
	}
	m_uiBufferBeginPos = m_uiFilePos;
	return (unsigned int)fread(pBuffer, 1, uiBytes, m_pFile);
}