/* clear the 'embedding' bit in a TrueType font */

#include <windows.h>
#include <io.h>
#include <fcntl.h>
#include <stdio.h>

int GetD(unsigned char* buffer, int offset)
{
    union {
	unsigned char c[4];
	int x;
    } u;

    buffer += offset;
    for (int i = 0; i < 4; i++)
	u.c[i] = buffer[3 - i];

    return u.x;
}


void SetD(unsigned char* buffer, int offset, int value)
{
    *(int *)&buffer[offset] = GetD((unsigned char *)&value, 0);
}


int Get(unsigned char* buffer, int offset)
{
    union {
	unsigned char c[2];
	unsigned short x;
    } u;

    buffer += offset;
    u.c[0] = buffer[1];
    u.c[1] = buffer[0];

    return (int)u.x;
}


int CalcTableChecksum(unsigned char* table, int length)
{
    int sum = 0;

    long* barrier = (long *)&table[length];
    long gap = *barrier;
    *barrier = 0;

    int len = length;
    while (len > 0) {
	sum += GetD(table, 0);
	table += 4;
	len -= 4;
    }

    *barrier = gap;
    return sum;
}


int main(int argc, char* argv[])
{
    char *filename = argv[1];

    HANDLE ttfFile = CreateFile(filename, GENERIC_READ,
				FILE_SHARE_READ, NULL, OPEN_EXISTING,
				0, NULL);

    if (ttfFile == INVALID_HANDLE_VALUE)
	return -4;

    DWORD length = GetFileSize(ttfFile, NULL);

    if (length <= 0)
	return -4;

    unsigned char* buffer = new unsigned char [length];
    DWORD got = 0;

    ReadFile(ttfFile, (void *)buffer, length, &got, NULL);

    if (got <= 0)
	return -4;

    CloseHandle(ttfFile);

    int CheckVersion     = GetD(buffer, 0);
    int numTables        = Get(buffer, 4);

    if (CheckVersion != 0x10000)
	return -4;

    for (int id = 0; id < numTables; id++) {
	int ResourceName = 12 + 16 * id;

	// unsigned char c = buffer[ResourceName + 4]; buffer[ResourceName + 4] = 0;
	// printf("%s\n", &buffer[ResourceName]);
	// buffer[ResourceName + 4] = c;

	if (strncmp((char *)&buffer[ResourceName], "OS/2", 4) == 0) {
	    int tableChecksum = GetD(buffer, ResourceName + 4);
	    int tableOffset = GetD(buffer, ResourceName + 8);
	    int tableLength = GetD(buffer, ResourceName + 12);

	    int actualSum = CalcTableChecksum(&buffer[tableOffset], tableLength);

	    if (actualSum != tableChecksum)
		printf("warning: bad checksum\n");
	    
	    int version = Get(buffer, tableOffset);
	    int fsType  = Get(buffer, tableOffset + 8);

	    if (fsType != 0) {
		printf("%s: fsType = %x - setting to zero\n", filename, fsType);
		*(short *)&buffer[tableOffset + 8] = 0; /* set fsType = 0 */
		SetD(buffer, ResourceName + 4, CalcTableChecksum(&buffer[tableOffset], tableLength));
	    }

	    int _f = _open(filename, O_RDWR|O_CREAT|O_BINARY|O_TRUNC, 0666);
	    _write(_f, buffer, length);
	    _close(_f);
	    break;
	}
    }


    return 0;
}
/* end */