/* _PyUnicode_InsertThousandsGrouping() helper functions */

typedef struct {
 const char *grouping;
 char previous;
 Py_ssize_t i; /* Where we're currently pointing in grouping. */
} GroupGenerator;


static void
GroupGenerator_init(GroupGenerator *self, const char *grouping)
{
 self->grouping = grouping;
 self->i = 0;
 self->previous = 0;
}


/* Returns the next grouping, or 0 to signify end. */
static Py_ssize_t
GroupGenerator_next(GroupGenerator *self)
{
 /* Note that we don't really do much error checking here. If a
 grouping string contains just CHAR_MAX, for example, then just
 terminate the generator. That shouldn't happen, but at least we
 fail gracefully. */
 switch (self->grouping[self->i]) {
 case 0:
 return self->previous;
 case CHAR_MAX:
 /* Stop the generator. */
 return 0;
 default: {
 char ch = self->grouping[self->i];
 self->previous = ch;
 self->i++;
 return (Py_ssize_t)ch;
 }
 }
}


/* Fill in some digits, leading zeros, and thousands separator. All
 are optional, depending on when we're called. */
static void
InsertThousandsGrouping_fill(_PyUnicodeWriter *writer, Py_ssize_t *buffer_pos,
 PyObject *digits, Py_ssize_t *digits_pos,
 Py_ssize_t n_chars, Py_ssize_t n_zeros,
 PyObject *thousands_sep, Py_ssize_t thousands_sep_len,
 Py_UCS4 *maxchar)
{
 if (!writer) {
 /* if maxchar > 127, maxchar is already set */
 if (*maxchar == 127 && thousands_sep) {
 Py_UCS4 maxchar2 = PyUnicode_MAX_CHAR_VALUE(thousands_sep);
 *maxchar = Py_MAX(*maxchar, maxchar2);
 }
 return;
 }

 if (thousands_sep) {
 *buffer_pos -= thousands_sep_len;

 /* Copy the thousands_sep chars into the buffer. */
 _PyUnicode_FastCopyCharacters(writer->buffer, *buffer_pos,
 thousands_sep, 0,
 thousands_sep_len);
 }

 *buffer_pos -= n_chars;
 *digits_pos -= n_chars;
 _PyUnicode_FastCopyCharacters(writer->buffer, *buffer_pos,
 digits, *digits_pos,
 n_chars);

 if (n_zeros) {
 *buffer_pos -= n_zeros;
 enum PyUnicode_Kind kind = PyUnicode_KIND(writer->buffer);
 void *data = PyUnicode_DATA(writer->buffer);
 unicode_fill(kind, data, '0', *buffer_pos, n_zeros);
 }
}