/*
 * crc
 *  Checks CRC values for resource files
 *
 * v. 1.00 (24 August 1993)
 *
 * © 1993-1998 Straylight
 */

/*----- Licensing note ----------------------------------------------------*
 *
 * This file is part of Straylight's Steel library.
 *
 * Steel 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, or (at your option)
 * any later version.
 *
 * Steel 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 Steel.  If not, write to the Free Software Foundation,
 * 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 */

#include "crc.h"
#include "crc32.h"
#include "os.h"
#include "res.h"
#include "msgs.h"
#include "werr.h"
#include "wimpt.h"
#include <stdio.h>
#include <stdlib.h>

/*
 * long crc__doCRC(char *filename,int offset)
 *
 * Use
 *  Returns the CRC value for a file starting from a certain offset.
 *
 * Parameters
 *  char *filename == the resource filename to use
 *  int offset == the offset to start from
 *
 * Returns
 *  A 4-byte CRC value.
 */ 

static long crc__doCRC(char *filename,int offset)
{
  FILE *fp;
  char buffer[1024];
  int read;
  long c=0;
  fp=res_openfile(filename,"rb");
  if (!fp)
  {
    werr(FALSE,msgs_lookup("crcFNF:Couldn't open file '%s'."),filename);
    exit(0);
  }
  fseek(fp,offset,SEEK_SET);
  do
  {
    read=fread(buffer,1,1024,fp);
    c=crc32(c,buffer,read,1);
  }
  while (read==1024);
  fclose(fp);
  return (c);
}

/*
 * long crc(char *filename)
 *
 * Use
 *  Calculates the CRC value for the file specified.  Uses the same method
 *  as WindowEd etc.
 *
 * Parameters
 *  char *filename == the filename of the file to check (leaf only - it's
 *    passed through res_findname()).  Note that CRC-checking the
 *    '!RunImage' file is rather silly.
 *
 * Returns
 *  A 4-byte CRC value
 */

long crc(char *filename)
{
  return (crc__doCRC(filename,0));
}

/*
 * void crc_check(char *filename,int check)
 *
 * Use
 *  Checks a CRC value for a file and reports a fatal error if the check
 *  fails.
 *
 * Parameters
 *  char *filename == the leafname of the file
 *  long check == the CRC number to check with
 */

void crc_check(char *filename,long check)
{
  if (check==-1)
    return;
  if (crc__doCRC(filename,0)!=check)
  {
    werr
    (
      FALSE,
      msgs_lookup("crcFC:%s resource file '%s' has been corrupted.  "
                  "Please restore this file from the distribution disk."),
      wimpt_programname(),
      filename
    );
    exit(0);
  }
}

/*
 * void crc_checkRunImage(void)
 *
 * Use
 *  Corruption-checks the main !RunImage file.  It must have been passed
 *  through CodeScr first, to install the CRC into the code.
 */

void crc_checkRunImage(void)
{
  FILE *fp=res_openfile("!RunImage","r");
  long c;
  if (!fp)
    werr(TRUE,msgs_lookup("crcFNF:Couldn't open file '%s'."),"!RunImage");
  fseek(fp,8,SEEK_SET);
  fread(&c,4,1,fp);
  fclose(fp);
  if (c!=crc__doCRC("!RunImage",12))
  {
    werr
    (
      FALSE,
      msgs_lookup("crcFC:%s resource file '%s' has been corrupted.  "
                  "Please restore this file from the distribution disk."),
      wimpt_programname(),
      "!RunImage"
    );
    exit(0);
  }
}