/* Accumulator struct implementation */

#include "Python.h"
#include "accu.h"

static PyObject *
join_list_unicode(PyObject *lst)
{
 /* return ''.join(lst) */
 PyObject *sep, *ret;
 sep = PyUnicode_FromStringAndSize("", 0);
 ret = PyUnicode_Join(sep, lst);
 Py_DECREF(sep);
 return ret;
}

int
_PyAccu_Init(_PyAccu *acc)
{
 /* Lazily allocated */
 acc->large = NULL;
 acc->small = PyList_New(0);
 if (acc->small == NULL)
 return -1;
 return 0;
}

static int
flush_accumulator(_PyAccu *acc)
{
 Py_ssize_t nsmall = PyList_GET_SIZE(acc->small);
 if (nsmall) {
 int ret;
 PyObject *joined;
 if (acc->large == NULL) {
 acc->large = PyList_New(0);
 if (acc->large == NULL)
 return -1;
 }
 joined = join_list_unicode(acc->small);
 if (joined == NULL)
 return -1;
 if (PyList_SetSlice(acc->small, 0, nsmall, NULL)) {
 Py_DECREF(joined);
 return -1;
 }
 ret = PyList_Append(acc->large, joined);
 Py_DECREF(joined);
 return ret;
 }
 return 0;
}

int
_PyAccu_Accumulate(_PyAccu *acc, PyObject *unicode)
{
 Py_ssize_t nsmall;
 assert(PyUnicode_Check(unicode));

 if (PyList_Append(acc->small, unicode))
 return -1;
 nsmall = PyList_GET_SIZE(acc->small);
 /* Each item in a list of unicode objects has an overhead (in 64-bit
 * builds) of:
 * - 8 bytes for the list slot
 * - 56 bytes for the header of the unicode object
 * that is, 64 bytes. 100000 such objects waste more than 6 MiB
 * compared to a single concatenated string.
 */
 if (nsmall < 100000)
 return 0;
 return flush_accumulator(acc);
}

PyObject *
_PyAccu_FinishAsList(_PyAccu *acc)
{
 int ret;
 PyObject *res;

 ret = flush_accumulator(acc);
 Py_CLEAR(acc->small);
 if (ret) {
 Py_CLEAR(acc->large);
 return NULL;
 }
 res = acc->large;
 acc->large = NULL;
 return res;
}

PyObject *
_PyAccu_Finish(_PyAccu *acc)
{
 PyObject *list, *res;
 if (acc->large == NULL) {
 list = acc->small;
 acc->small = NULL;
 }
 else {
 list = _PyAccu_FinishAsList(acc);
 if (!list)
 return NULL;
 }
 res = join_list_unicode(list);
 Py_DECREF(list);
 return res;
}

void
_PyAccu_Destroy(_PyAccu *acc)
{
 Py_CLEAR(acc->small);
 Py_CLEAR(acc->large);
}