/* bytes to hex implementation */

#include "Python.h"

#include "pystrhex.h"

static PyObject *_Py_strhex_impl(const char* argbuf, const Py_ssize_t arglen,
                                 const PyObject* sep, int bytes_per_sep_group,
                                 const int return_bytes)
{
    assert(arglen >= 0);

    Py_UCS1 sep_char = 0;
    if (sep) {
        Py_ssize_t seplen = PyObject_Length((PyObject*)sep);
        if (seplen < 0) {
            return NULL;
        }
        if (seplen != 1) {
            PyErr_SetString(PyExc_ValueError, "sep must be length 1.");
            return NULL;
        }
        if (PyUnicode_Check(sep)) {
            if (PyUnicode_READY(sep))
                return NULL;
            if (PyUnicode_KIND(sep) != PyUnicode_1BYTE_KIND) {
                PyErr_SetString(PyExc_ValueError, "sep must be ASCII.");
                return NULL;
            }
            sep_char = PyUnicode_READ_CHAR(sep, 0);
        }
        else if (PyBytes_Check(sep)) {
            sep_char = PyBytes_AS_STRING(sep)[0];
        }
        else {
            PyErr_SetString(PyExc_TypeError, "sep must be str or bytes.");
            return NULL;
        }
        if (sep_char > 127 && !return_bytes) {
            PyErr_SetString(PyExc_ValueError, "sep must be ASCII.");
            return NULL;
        }
    }
    else {
        bytes_per_sep_group = 0;
    }

    unsigned int abs_bytes_per_sep = abs(bytes_per_sep_group);
    Py_ssize_t resultlen = 0;
    if (bytes_per_sep_group && arglen > 0) {
        /* How many sep characters we'll be inserting. */
        resultlen = (arglen - 1) / abs_bytes_per_sep;
    }
    /* Bounds checking for our Py_ssize_t indices. */
    if (arglen >= PY_SSIZE_T_MAX / 2 - resultlen) {
        return PyErr_NoMemory();
    }
    resultlen += arglen * 2;

    if ((size_t)abs_bytes_per_sep >= (size_t)arglen) {
        bytes_per_sep_group = 0;
        abs_bytes_per_sep = 0;
    }

    PyObject *retval;
    Py_UCS1 *retbuf;
    if (return_bytes) {
        /* If _PyBytes_FromSize() were public we could avoid malloc+copy. */
        retval = PyBytes_FromStringAndSize(NULL, resultlen);
        if (!retval) {
            return NULL;
        }
        retbuf = (Py_UCS1 *)PyBytes_AS_STRING(retval);
    }
    else {
        retval = PyUnicode_New(resultlen, 127);
        if (!retval) {
            return NULL;
        }
        retbuf = PyUnicode_1BYTE_DATA(retval);
    }

    /* Hexlify */
    Py_ssize_t i, j;
    for (i=j=0; i < arglen; ++i) {
        assert((j + 1) < resultlen);
        unsigned char c;
        c = (argbuf[i] >> 4) & 0x0f;
        retbuf[j++] = Py_hexdigits[c];
        c = argbuf[i] & 0x0f;
        retbuf[j++] = Py_hexdigits[c];
        if (bytes_per_sep_group && i < arglen - 1) {
            Py_ssize_t anchor;
            anchor = (bytes_per_sep_group > 0) ? (arglen - 1 - i) : (i + 1);
            if (anchor % abs_bytes_per_sep == 0) {
                retbuf[j++] = sep_char;
            }
        }
    }
    assert(j == resultlen);

#ifdef Py_DEBUG
    if (!return_bytes) {
        assert(_PyUnicode_CheckConsistency(retval, 1));
    }
#endif

    return retval;
}

PyObject * _Py_strhex(const char* argbuf, const Py_ssize_t arglen)
{
    return _Py_strhex_impl(argbuf, arglen, NULL, 0, 0);
}

/* Same as above but returns a bytes() instead of str() to avoid the
 * need to decode the str() when bytes are needed. */
PyObject * _Py_strhex_bytes(const char* argbuf, const Py_ssize_t arglen)
{
    return _Py_strhex_impl(argbuf, arglen, NULL, 0, 1);
}

/* These variants include support for a separator between every N bytes: */

PyObject * _Py_strhex_with_sep(const char* argbuf, const Py_ssize_t arglen, const PyObject* sep, const int bytes_per_group)
{
    return _Py_strhex_impl(argbuf, arglen, sep, bytes_per_group, 0);
}

/* Same as above but returns a bytes() instead of str() to avoid the
 * need to decode the str() when bytes are needed. */
PyObject * _Py_strhex_bytes_with_sep(const char* argbuf, const Py_ssize_t arglen, const PyObject* sep, const int bytes_per_group)
{
    return _Py_strhex_impl(argbuf, arglen, sep, bytes_per_group, 1);
}