#define PY_SSIZE_T_CLEAN

#include <Python.h>
#include <openssl/err.h>
#include <openssl/evp.h>

#define MODULE_NAME "aioquic._crypto"

#define AEAD_KEY_LENGTH_MAX 32
#define AEAD_NONCE_LENGTH 12
#define AEAD_TAG_LENGTH 16

#define PACKET_LENGTH_MAX 1500
#define PACKET_NUMBER_LENGTH_MAX 4
#define SAMPLE_LENGTH 16

#define CHECK_RESULT(expr) \
    if (!(expr)) { \
        ERR_clear_error(); \
        PyErr_SetString(CryptoError, "OpenSSL call failed"); \
        return NULL; \
    }

#define CHECK_RESULT_CTOR(expr) \
    if (!(expr)) { \
        ERR_clear_error(); \
        PyErr_SetString(CryptoError, "OpenSSL call failed"); \
        return -1; \
    }

static PyObject *CryptoError;

/* AEAD */

typedef struct {
    PyObject_HEAD
    EVP_CIPHER_CTX *decrypt_ctx;
    EVP_CIPHER_CTX *encrypt_ctx;
    unsigned char buffer[PACKET_LENGTH_MAX];
    unsigned char key[AEAD_KEY_LENGTH_MAX];
    unsigned char iv[AEAD_NONCE_LENGTH];
    unsigned char nonce[AEAD_NONCE_LENGTH];
} AEADObject;

static PyObject *AEADType;

static EVP_CIPHER_CTX *
create_ctx(const EVP_CIPHER *cipher, int key_length, int operation)
{
    EVP_CIPHER_CTX *ctx;
    int res;

    ctx = EVP_CIPHER_CTX_new();
    CHECK_RESULT(ctx != 0);

    res = EVP_CipherInit_ex(ctx, cipher, NULL, NULL, NULL, operation);
    CHECK_RESULT(res != 0);

    res = EVP_CIPHER_CTX_set_key_length(ctx, key_length);
    CHECK_RESULT(res != 0);

    res = EVP_CIPHER_CTX_ctrl(ctx, EVP_CTRL_CCM_SET_IVLEN, AEAD_NONCE_LENGTH, NULL);
    CHECK_RESULT(res != 0);

    return ctx;
}

static int
AEAD_init(AEADObject *self, PyObject *args, PyObject *kwargs)
{
    const char *cipher_name;
    const unsigned char *key, *iv;
    Py_ssize_t cipher_name_len, key_len, iv_len;

    if (!PyArg_ParseTuple(args, "y#y#y#", &cipher_name, &cipher_name_len, &key, &key_len, &iv, &iv_len))
        return -1;

    const EVP_CIPHER *evp_cipher = EVP_get_cipherbyname(cipher_name);
    if (evp_cipher == 0) {
        PyErr_Format(CryptoError, "Invalid cipher name: %s", cipher_name);
        return -1;
    }
    if (key_len > AEAD_KEY_LENGTH_MAX) {
        PyErr_SetString(CryptoError, "Invalid key length");
        return -1;
    }
    if (iv_len > AEAD_NONCE_LENGTH) {
        PyErr_SetString(CryptoError, "Invalid iv length");
        return -1;
    }

    memcpy(self->key, key, key_len);
    memcpy(self->iv, iv, iv_len);

    self->decrypt_ctx = create_ctx(evp_cipher, key_len, 0);
    CHECK_RESULT_CTOR(self->decrypt_ctx != 0);

    self->encrypt_ctx = create_ctx(evp_cipher, key_len, 1);
    CHECK_RESULT_CTOR(self->encrypt_ctx != 0);

    return 0;
}

static void
AEAD_dealloc(AEADObject *self)
{
    EVP_CIPHER_CTX_free(self->decrypt_ctx);
    EVP_CIPHER_CTX_free(self->encrypt_ctx);
    PyTypeObject *tp = Py_TYPE(self);
    freefunc free = PyType_GetSlot(tp, Py_tp_free);
    free(self);
    Py_DECREF(tp);
}

static PyObject*
AEAD_decrypt(AEADObject *self, PyObject *args)
{
    const unsigned char *data, *associated;
    Py_ssize_t data_len, associated_len;
    int outlen, outlen2, res;
    uint64_t pn;

    if (!PyArg_ParseTuple(args, "y#y#K", &data, &data_len, &associated, &associated_len, &pn))
        return NULL;

    if (data_len < AEAD_TAG_LENGTH || data_len > PACKET_LENGTH_MAX) {
        PyErr_SetString(CryptoError, "Invalid payload length");
        return NULL;
    }

    memcpy(self->nonce, self->iv, AEAD_NONCE_LENGTH);
    for (int i = 0; i < 8; ++i) {
        self->nonce[AEAD_NONCE_LENGTH - 1 - i] ^= (uint8_t)(pn >> 8 * i);
    }

    res = EVP_CIPHER_CTX_ctrl(self->decrypt_ctx, EVP_CTRL_CCM_SET_TAG, AEAD_TAG_LENGTH, (void*)(data + (data_len - AEAD_TAG_LENGTH)));
    CHECK_RESULT(res != 0);

    res = EVP_CipherInit_ex(self->decrypt_ctx, NULL, NULL, self->key, self->nonce, 0);
    CHECK_RESULT(res != 0);

    res = EVP_CipherUpdate(self->decrypt_ctx, NULL, &outlen, associated, associated_len);
    CHECK_RESULT(res != 0);

    res = EVP_CipherUpdate(self->decrypt_ctx, self->buffer, &outlen, data, data_len - AEAD_TAG_LENGTH);
    CHECK_RESULT(res != 0);

    res = EVP_CipherFinal_ex(self->decrypt_ctx, NULL, &outlen2);
    if (res == 0) {
        PyErr_SetString(CryptoError, "Payload decryption failed");
        return NULL;
    }

    return PyBytes_FromStringAndSize((const char*)self->buffer, outlen);
}

static PyObject*
AEAD_encrypt(AEADObject *self, PyObject *args)
{
    const unsigned char *data, *associated;
    Py_ssize_t data_len, associated_len;
    int outlen, outlen2, res;
    uint64_t pn;

    if (!PyArg_ParseTuple(args, "y#y#K", &data, &data_len, &associated, &associated_len, &pn))
        return NULL;

    if (data_len > PACKET_LENGTH_MAX) {
        PyErr_SetString(CryptoError, "Invalid payload length");
        return NULL;
    }

    memcpy(self->nonce, self->iv, AEAD_NONCE_LENGTH);
    for (int i = 0; i < 8; ++i) {
        self->nonce[AEAD_NONCE_LENGTH - 1 - i] ^= (uint8_t)(pn >> 8 * i);
    }

    res = EVP_CipherInit_ex(self->encrypt_ctx, NULL, NULL, self->key, self->nonce, 1);
    CHECK_RESULT(res != 0);

    res = EVP_CipherUpdate(self->encrypt_ctx, NULL, &outlen, associated, associated_len);
    CHECK_RESULT(res != 0);

    res = EVP_CipherUpdate(self->encrypt_ctx, self->buffer, &outlen, data, data_len);
    CHECK_RESULT(res != 0);

    res = EVP_CipherFinal_ex(self->encrypt_ctx, NULL, &outlen2);
    CHECK_RESULT(res != 0 && outlen2 == 0);

    res = EVP_CIPHER_CTX_ctrl(self->encrypt_ctx, EVP_CTRL_CCM_GET_TAG, AEAD_TAG_LENGTH, self->buffer + outlen);
    CHECK_RESULT(res != 0);

    return PyBytes_FromStringAndSize((const char*)self->buffer, outlen + AEAD_TAG_LENGTH);
}

static PyMethodDef AEAD_methods[] = {
    {"decrypt", (PyCFunction)AEAD_decrypt, METH_VARARGS, ""},
    {"encrypt", (PyCFunction)AEAD_encrypt, METH_VARARGS, ""},

    {NULL}
};

static PyType_Slot AEADType_slots[] = {
    {Py_tp_dealloc, AEAD_dealloc},
    {Py_tp_methods, AEAD_methods},
    {Py_tp_doc, "AEAD objects"},
    {Py_tp_init, AEAD_init},
    {0, 0},
};

static PyType_Spec AEADType_spec = {
    MODULE_NAME ".AEADType",
    sizeof(AEADObject),
    0,
    Py_TPFLAGS_DEFAULT,
    AEADType_slots
};

/* HeaderProtection */

typedef struct {
    PyObject_HEAD
    EVP_CIPHER_CTX *ctx;
    int is_chacha20;
    unsigned char buffer[PACKET_LENGTH_MAX];
    unsigned char mask[31];
    unsigned char zero[5];
} HeaderProtectionObject;

static PyObject *HeaderProtectionType;

static int
HeaderProtection_init(HeaderProtectionObject *self, PyObject *args, PyObject *kwargs)
{
    const char *cipher_name;
    const unsigned char *key;
    Py_ssize_t cipher_name_len, key_len;
    int res;

    if (!PyArg_ParseTuple(args, "y#y#", &cipher_name, &cipher_name_len, &key, &key_len))
        return -1;

    const EVP_CIPHER *evp_cipher = EVP_get_cipherbyname(cipher_name);
    if (evp_cipher == 0) {
        PyErr_Format(CryptoError, "Invalid cipher name: %s", cipher_name);
        return -1;
    }

    memset(self->mask, 0, sizeof(self->mask));
    memset(self->zero, 0, sizeof(self->zero));
    self->is_chacha20 = cipher_name_len == 8 && memcmp(cipher_name, "chacha20", 8) == 0;

    self->ctx = EVP_CIPHER_CTX_new();
    CHECK_RESULT_CTOR(self->ctx != 0);

    res = EVP_CipherInit_ex(self->ctx, evp_cipher, NULL, NULL, NULL, 1);
    CHECK_RESULT_CTOR(res != 0);

    res = EVP_CIPHER_CTX_set_key_length(self->ctx, key_len);
    CHECK_RESULT_CTOR(res != 0);

    res = EVP_CipherInit_ex(self->ctx, NULL, NULL, key, NULL, 1);
    CHECK_RESULT_CTOR(res != 0);

    return 0;
}

static void
HeaderProtection_dealloc(HeaderProtectionObject *self)
{
    EVP_CIPHER_CTX_free(self->ctx);
    PyTypeObject *tp = Py_TYPE(self);
    freefunc free = PyType_GetSlot(tp, Py_tp_free);
    free(self);
    Py_DECREF(tp);
}

static int HeaderProtection_mask(HeaderProtectionObject *self, const unsigned char* sample)
{
    int outlen;
    if (self->is_chacha20) {
        return EVP_CipherInit_ex(self->ctx, NULL, NULL, NULL, sample, 1) &&
               EVP_CipherUpdate(self->ctx, self->mask, &outlen, self->zero, sizeof(self->zero));
    } else {
        return EVP_CipherUpdate(self->ctx, self->mask, &outlen, sample, SAMPLE_LENGTH);
    }
}

static PyObject*
HeaderProtection_apply(HeaderProtectionObject *self, PyObject *args)
{
    const unsigned char *header, *payload;
    Py_ssize_t header_len, payload_len;
    int res;

    if (!PyArg_ParseTuple(args, "y#y#", &header, &header_len, &payload, &payload_len))
        return NULL;

    int pn_length = (header[0] & 0x03) + 1;
    int pn_offset = header_len - pn_length;

    res = HeaderProtection_mask(self, payload + PACKET_NUMBER_LENGTH_MAX - pn_length);
    CHECK_RESULT(res != 0);

    memcpy(self->buffer, header, header_len);
    memcpy(self->buffer + header_len, payload, payload_len);

    if (self->buffer[0] & 0x80) {
        self->buffer[0] ^= self->mask[0] & 0x0F;
    } else {
        self->buffer[0] ^= self->mask[0] & 0x1F;
    }

    for (int i = 0; i < pn_length; ++i) {
        self->buffer[pn_offset + i] ^= self->mask[1 + i];
    }

    return PyBytes_FromStringAndSize((const char*)self->buffer, header_len + payload_len);
}

static PyObject*
HeaderProtection_remove(HeaderProtectionObject *self, PyObject *args)
{
    const unsigned char *packet;
    Py_ssize_t packet_len;
    int pn_offset, res;

    if (!PyArg_ParseTuple(args, "y#I", &packet, &packet_len, &pn_offset))
        return NULL;

    res = HeaderProtection_mask(self, packet + pn_offset + PACKET_NUMBER_LENGTH_MAX);
    CHECK_RESULT(res != 0);

    memcpy(self->buffer, packet, pn_offset + PACKET_NUMBER_LENGTH_MAX);

    if (self->buffer[0] & 0x80) {
        self->buffer[0] ^= self->mask[0] & 0x0F;
    } else {
        self->buffer[0] ^= self->mask[0] & 0x1F;
    }

    int pn_length = (self->buffer[0] & 0x03) + 1;
    uint32_t pn_truncated = 0;
    for (int i = 0; i < pn_length; ++i) {
        self->buffer[pn_offset + i] ^= self->mask[1 + i];
        pn_truncated = self->buffer[pn_offset + i] | (pn_truncated << 8);
    }

    return Py_BuildValue("y#i", self->buffer, pn_offset + pn_length, pn_truncated);
}

static PyMethodDef HeaderProtection_methods[] = {
    {"apply", (PyCFunction)HeaderProtection_apply, METH_VARARGS, ""},
    {"remove", (PyCFunction)HeaderProtection_remove, METH_VARARGS, ""},
    {NULL}
};

static PyType_Slot HeaderProtectionType_slots[] = {
    {Py_tp_dealloc, HeaderProtection_dealloc},
    {Py_tp_methods, HeaderProtection_methods},
    {Py_tp_doc, "HeaderProtection objects"},
    {Py_tp_init, HeaderProtection_init},
    {0, 0},
};

static PyType_Spec HeaderProtectionType_spec = {
    MODULE_NAME ".HeaderProtectionType",
    sizeof(HeaderProtectionObject),
    0,
    Py_TPFLAGS_DEFAULT,
    HeaderProtectionType_slots
};

static struct PyModuleDef moduledef = {
    PyModuleDef_HEAD_INIT,
    MODULE_NAME,                        /* m_name */
    "Cryptography utilities.",          /* m_doc */
    -1,                                 /* m_size */
    NULL,                               /* m_methods */
    NULL,                               /* m_reload */
    NULL,                               /* m_traverse */
    NULL,                               /* m_clear */
    NULL,                               /* m_free */
};

PyMODINIT_FUNC
PyInit__crypto(void)
{
    PyObject* m;

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

    CryptoError = PyErr_NewException(MODULE_NAME ".CryptoError", PyExc_ValueError, NULL);
    Py_INCREF(CryptoError);
    PyModule_AddObject(m, "CryptoError", CryptoError);

    AEADType = PyType_FromSpec(&AEADType_spec);
    if (AEADType == NULL)
        return NULL;
    PyModule_AddObject(m, "AEAD", AEADType);

    HeaderProtectionType = PyType_FromSpec(&HeaderProtectionType_spec);
    if (HeaderProtectionType == NULL)
        return NULL;
    PyModule_AddObject(m, "HeaderProtection", HeaderProtectionType);

    // ensure required ciphers are initialised
    // LibreSSL loads all cipher by default, and doesn't support add_cipher
#ifndef LIBRESSL_VERSION_NUMBER
    EVP_add_cipher(EVP_aes_128_ecb());
    EVP_add_cipher(EVP_aes_128_gcm());
    EVP_add_cipher(EVP_aes_256_ecb());
    EVP_add_cipher(EVP_aes_256_gcm());
#endif

    return m;
}
