/*
  * return the next sequence number.  if the value returned is negative then
  * an error occured while trying to obtain the next sequence number.
  */

LONG __saveds __asm GetSequenceNumber(register __a0 PagerHandle_t * ph, register __d0 UWORD increment)
{
	BPTR fh;
	BPTR lock;
	LONG seq;
	ULONG seqTemp;
	UBYTE buffer[20];
	STRPTR sequenceFileName;

	seq = -1;

	if (sequenceFileName = NameInSpool(ph, "sequence")) {
		if (LockFile(ph, sequenceFileName)) {

			/*
			 * we need to determine if the sequence file exists.
			 * we do this in the following manner:  initialize
			 * buffer to be a null string.  then try and Lock()
			 * the sequence file.  if it locks, UnLock() it and
			 * continue on.  If it does not lock, see if IoErr()
			 * is telling us that the file doesn't exist.  If it
			 * doesn't exist, put an ASCII "1" into buffer.
			 * otherwise leave buffer as a null string.  then we
			 * try opening the sequence file in READWRITE mode.
			 * this should create the file for us if it doesn't
			 * exist.  if the lock failed and it wasn't because
			 * the file didn't exist then the Open() will most
			 * likely fail and the user will get the error
			 * message that we couldn't open the sequence file.
			 * after we open the sequence file, we check to see
			 * if buffer is still a null string.  if it is null,
			 * try reading the old value from the sequence file,
			 * reporting an error if we fail to read the file
			 * properly.  if buffer is not null (has the "1" we
			 * copied into it when the file doesn't exist) then
			 * we don't try to read from the file, but rather
			 * fall through to writing the updated sequence
			 * number to the file.
			 */

			buffer[0] = '\0';

			if (lock = Lock(sequenceFileName, ACCESS_READ))
				UnLock(lock);
			else if (IoErr() == ERROR_OBJECT_NOT_FOUND)
				strcpy(buffer, "1");

			if (fh = Open(sequenceFileName, MODE_READWRITE)) {
				if (buffer[0] || FGets(fh, buffer, sizeof(buffer) - 1)) {
					seqTemp = atol(buffer) + increment;

					if (seqTemp > 0x3FFFFFFF)
						seqTemp = increment;

					if (Seek(fh, 0, OFFSET_BEGINNING) != -1) {
						if (FPrintf(fh, "%ld\n", seqTemp) == -1)
							ULog(ph, -1, "Error writing new sequence value.");
						else
							seq = seqTemp - increment;
					}
					else
						ULog(ph, -1, "Error writing new sequence value.");

				}
				else
					ULog(ph, -1, "Error reading old sequence value.");

				Close(fh);
			}
			else
				ULog(ph, -1, "Couldn't open sequence file.");

			UnLockFile(ph, sequenceFileName);
		}
		else
			ULog(ph, -1, "Couldn't open sequence file.");

		FreeNameInSpool(sequenceFileName);
	}

	return seq;
}

 /*
  * convert a sequence number in a numeric/character combination.  Names are
  * unique and case in-sensitive.  Each position in the 6 character name will
  * be 0-9 a-z, or base 36. The input buffer must be at least 7 bytes in
  * length.  a pointer to this buffer is returned on exit.
  */

STRPTR __saveds __asm SequenceToName(register __a0 STRPTR buffer, register __d0 LONG sequenceNumber)
{
	int i, j;

	sequenceNumber &= 0x3FFFFFFF;

	for (i = 5; i != -1; i--) {
		j = sequenceNumber % 36;

		if (j < 10)
			buffer[i] = j + '0';
		else
			buffer[i] = j + 'a' - 10;

		sequenceNumber /= 36;
	}

	buffer[6] = 0;

	return buffer;
}