#define PY_SSIZE_T_CLEAN
#include <Python.h>
#include <structmember.h>

#include <stdint.h>
#include <stdlib.h>

// htons for win and mac
#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__) || defined(__NT__)
    #pragma comment(lib, "Ws2_32.lib")
    #include "Winsock2.h"
#else
    #include <arpa/inet.h>
#endif

static PyObject *disarm_block_fast(PyObject *self, PyObject *args);
static PyObject *apply_checksum(PyObject *self, PyObject *args);

static PyMethodDef fd_top_level[] = {
    {"disarm_block_fast", disarm_block_fast, METH_VARARGS, "Decrypt the data within a buffer object."},
    {"checksum_block_fast", apply_checksum, METH_VARARGS, "Compute and append the checksum."},
    {NULL, NULL, 0, NULL}
};

static PyModuleDef modinfo = {
    PyModuleDef_HEAD_INIT,
    .m_name = "_acb_speedup",
    .m_doc = "Speedups for disarm_actual",
    .m_size = -1,
    .m_methods = fd_top_level,
};

////////////////////////////////////////////////////////

static uint16_t CHECKSUM_TABLE[] = {
    0x0000, 0x8005, 0x800F, 0x000A, 0x801B, 0x001E, 0x0014, 0x8011,
    0x8033, 0x0036, 0x003C, 0x8039, 0x0028, 0x802D, 0x8027, 0x0022,
    0x8063, 0x0066, 0x006C, 0x8069, 0x0078, 0x807D, 0x8077, 0x0072,
    0x0050, 0x8055, 0x805F, 0x005A, 0x804B, 0x004E, 0x0044, 0x8041,
    0x80C3, 0x00C6, 0x00CC, 0x80C9, 0x00D8, 0x80DD, 0x80D7, 0x00D2,
    0x00F0, 0x80F5, 0x80FF, 0x00FA, 0x80EB, 0x00EE, 0x00E4, 0x80E1,
    0x00A0, 0x80A5, 0x80AF, 0x00AA, 0x80BB, 0x00BE, 0x00B4, 0x80B1,
    0x8093, 0x0096, 0x009C, 0x8099, 0x0088, 0x808D, 0x8087, 0x0082,
    0x8183, 0x0186, 0x018C, 0x8189, 0x0198, 0x819D, 0x8197, 0x0192,
    0x01B0, 0x81B5, 0x81BF, 0x01BA, 0x81AB, 0x01AE, 0x01A4, 0x81A1,
    0x01E0, 0x81E5, 0x81EF, 0x01EA, 0x81FB, 0x01FE, 0x01F4, 0x81F1,
    0x81D3, 0x01D6, 0x01DC, 0x81D9, 0x01C8, 0x81CD, 0x81C7, 0x01C2,
    0x0140, 0x8145, 0x814F, 0x014A, 0x815B, 0x015E, 0x0154, 0x8151,
    0x8173, 0x0176, 0x017C, 0x8179, 0x0168, 0x816D, 0x8167, 0x0162,
    0x8123, 0x0126, 0x012C, 0x8129, 0x0138, 0x813D, 0x8137, 0x0132,
    0x0110, 0x8115, 0x811F, 0x011A, 0x810B, 0x010E, 0x0104, 0x8101,
    0x8303, 0x0306, 0x030C, 0x8309, 0x0318, 0x831D, 0x8317, 0x0312,
    0x0330, 0x8335, 0x833F, 0x033A, 0x832B, 0x032E, 0x0324, 0x8321,
    0x0360, 0x8365, 0x836F, 0x036A, 0x837B, 0x037E, 0x0374, 0x8371,
    0x8353, 0x0356, 0x035C, 0x8359, 0x0348, 0x834D, 0x8347, 0x0342,
    0x03C0, 0x83C5, 0x83CF, 0x03CA, 0x83DB, 0x03DE, 0x03D4, 0x83D1,
    0x83F3, 0x03F6, 0x03FC, 0x83F9, 0x03E8, 0x83ED, 0x83E7, 0x03E2,
    0x83A3, 0x03A6, 0x03AC, 0x83A9, 0x03B8, 0x83BD, 0x83B7, 0x03B2,
    0x0390, 0x8395, 0x839F, 0x039A, 0x838B, 0x038E, 0x0384, 0x8381,
    0x0280, 0x8285, 0x828F, 0x028A, 0x829B, 0x029E, 0x0294, 0x8291,
    0x82B3, 0x02B6, 0x02BC, 0x82B9, 0x02A8, 0x82AD, 0x82A7, 0x02A2,
    0x82E3, 0x02E6, 0x02EC, 0x82E9, 0x02F8, 0x82FD, 0x82F7, 0x02F2,
    0x02D0, 0x82D5, 0x82DF, 0x02DA, 0x82CB, 0x02CE, 0x02C4, 0x82C1,
    0x8243, 0x0246, 0x024C, 0x8249, 0x0258, 0x825D, 0x8257, 0x0252,
    0x0270, 0x8275, 0x827F, 0x027A, 0x826B, 0x026E, 0x0264, 0x8261,
    0x0220, 0x8225, 0x822F, 0x022A, 0x823B, 0x023E, 0x0234, 0x8231,
    0x8213, 0x0216, 0x021C, 0x8219, 0x0208, 0x820D, 0x8207, 0x0202
};

static void checksum(uint8_t *block, size_t len) {
    uint16_t sum = 0;
    for (size_t i = len; i < len - 2; ++i) {
        sum = ((sum << 8) ^ CHECKSUM_TABLE[(sum >> 8) ^ block[i]]);
    }

    uint16_t *target = (uint16_t *)(block + len - 2);
    *target = htons(sum);
}

static PyObject *apply_checksum(PyObject *self, PyObject *args) {
    Py_buffer block;

    if (!PyArg_ParseTuple(args, "w*", &block)) {
        return NULL;
    }

    if (block.len < 2) {
        PyErr_SetString(PyExc_ValueError, "invalid size");
        PyBuffer_Release(&block);
        return NULL;
    }

    checksum(block.buf, block.len);

    PyBuffer_Release(&block);
    Py_RETURN_NONE;
}

static PyObject *disarm_block_fast(PyObject *self, PyObject *args) {
    Py_buffer edata;
    Py_buffer keytab;

    if (!PyArg_ParseTuple(args, "w*y*", &edata, &keytab)) {
        return NULL;
    }

    if (edata.len < 2) {
        PyErr_SetString(PyExc_ValueError, "invalid size");
        PyBuffer_Release(&edata);
        PyBuffer_Release(&keytab);
        return NULL;
    }

    if (keytab.len != 256) {
        PyErr_SetString(PyExc_ValueError, "invalid substitution table");
        PyBuffer_Release(&edata);
        PyBuffer_Release(&keytab);
        return NULL;
    }

    uint8_t *t = (uint8_t *)keytab.buf;
    uint8_t *e = (uint8_t *)edata.buf;
    uint16_t sum = 0;
    for (int i = 0; i < edata.len - 2; ++i) {
        e[i] = t[e[i]];
        sum = ((sum << 8) ^ CHECKSUM_TABLE[(sum >> 8) ^ e[i]]);
    }

    uint16_t *target = (uint16_t *)(e + edata.len - 2);
    *target = htons(sum);

    PyBuffer_Release(&edata);
    PyBuffer_Release(&keytab);
    Py_RETURN_NONE;
}

PyMODINIT_FUNC PyInit__acb_speedup(void) {
    PyObject *m;

    m = PyModule_Create(&modinfo);
    if (m == NULL)
        return NULL;

    return m;
}