/*

   3dsspec - Nintendo 3DS Sinclair Spectrum 48K emulator.

   Copyright (C) 2021  Ian Cowburn
   
   This program is free software; you can redistribute it and/or
   modify it under the terms of the GNU General Public License
   as published by the Free Software Foundation; either version 2
   of the License, or (at your option) any later version.
   
   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.
   
   You should have received a copy of the GNU General Public License
   along with this program; if not, write to the Free Software
   Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA  02111-1307, USA.
  
   $Id: snap.c 4 2006-09-15 00:30:18Z ianc $

*/
#include "snap.h"

/* ---------------------------------------- MACROS
*/
#ifndef TRUE
#define TRUE 1
#endif

#ifndef FALSE
#define FALSE 0
#endif

#define ROMLEN 0x4000


/* ---------------------------------------- PRIVATE DATA
*/
static Z80Byte	*tap_file;
static int	tap_len;
static int	tap_ptr;


/* ---------------------------------------- PRIVATE FUNCTIONS
*/
static Z80Byte GetByte(void)
{
    Z80Byte ret=0;

    if (tap_len)
    {
	ret=tap_file[tap_ptr];
	tap_ptr=(tap_ptr+1)%tap_len;
    }

    return ret;
}


static Z80Word GetLSBWord(void)
{
    int c1,c2;

    c1=GetByte();
    c2=GetByte();

    return c1+(c2<<8);
}


/* ---------------------------------------- INTERFACES
*/
void TAPSetTape(Z80Byte *tape, int len)
{
    tap_file = tape;
    tap_len = len;
    tap_ptr = 0;
}


int TAPLoad(Z80Byte id, Z80Word *addr, Z80Word *len, SNAP_Poke poke)
{
    Z80Word blen;
    Z80Byte type,b,csum,tape_csum;

    if (!tap_file)
    {
    	return FALSE;
    }

    b=0;

    blen=GetLSBWord();
    type=GetByte();
    csum=id;

    /* Have we found the requested block?
    */
    if (id==type)
    {
    	/* Knock of block type
	*/
	blen--;

	while(blen && *len)
	{
	    b=GetByte();
	    csum^=b;

	    poke(*addr,b);

	    (*addr)++;
	    (*len)--;
	    blen--;
	}

	/* Get the checksum
	*/
	if (blen)
	{
	    tape_csum=GetByte();
	    blen--;
	}
	else
	    tape_csum=b;

	/* In case we've been request less bytes than the block size
	*/
	while(blen--)
	    GetByte();

	/* Check the checksum
	*/
	return csum==tape_csum;
    }
    else
    {
    	/* If it's the wrong type, skip it
	*/
	while(blen--)
	    GetByte();

	return FALSE;
    }
}


/* END OF FILE */