/* auth:faster */
#include <stdio.h>
#include <stdlib.h>

#define D2CHARSAVE_VERSION_OFFSET 0x04
#define D2CHARSAVE_CHECKSUM_OFFSET 0x0C
#define D2CHARSAVE_STATUS_OFFSET_109 0x24
#define D2CHARINFO_STATUS_FLAG_LADDER 0x40

#define tf(a) ((a)?1:0)

#define charstatus_set_ladder(status) ( status |= (D2CHARINFO_STATUS_FLAG_LADDER))
#define charstatus_switch_ladder(status) ( status ^= (D2CHARINFO_STATUS_FLAG_LADDER))
#define charstatus_get_ladder(status) tf( status & D2CHARINFO_STATUS_FLAG_LADDER)


static int d2charsave_checksum(unsigned char const *data, unsigned int len, unsigned int offset)
{
int checksum;
unsigned int i;
unsigned int ch;

if (!data) return 0;
checksum=0;
for (i=0; i<len; i++) {
ch=data[i];
if (i>=offset && i<offset+sizeof(int)) ch=0;
ch+=(checksum<0);
checksum=2*checksum+ch;
}
return checksum;
}


static unsigned char buf[65536];

int main(int argc, char **argv)
{
FILE *fp;
unsigned int checksum;
unsigned int size;
unsigned char status;

if (argc!=2) {
printf("%s <charsave>\n", argv[0]);
return 0;
}
fp = fopen(argv[1], "rb+");
if (!fp) {
printf("failed open file\n");
return -1;
}
size = fread(buf, 1, sizeof(buf), fp);
if (!feof(fp)) {
printf("error reading file\n");
fclose(fp);
return -2;
}
if (buf[D2CHARSAVE_VERSION_OFFSET]<0x5c) {
printf("wrong version number\n");
fclose(fp);
return -3;
}
status = buf[D2CHARSAVE_STATUS_OFFSET_109];
charstatus_switch_ladder(status);
buf[D2CHARSAVE_STATUS_OFFSET_109] = status;
checksum = d2charsave_checksum(buf, size, D2CHARSAVE_CHECKSUM_OFFSET);
*((unsigned int*)(buf+D2CHARSAVE_CHECKSUM_OFFSET)) = checksum;
fseek(fp, 0, SEEK_SET);
if (fwrite(buf, 1, size, fp)!=size) {
printf("error writing save file\n");
fclose(fp);
return -4;
}
fclose(fp);
if (charstatus_get_ladder(status))
printf("set to LADDER char.\n");
else
printf("set to none-LADDER char.\n");
return 0;
}