/*
 * This file is part of the MicroPython project, http://micropython.org/
 *
 * The MIT License (MIT)
 *
 * Copyright (c) 2021 Scott Shawcroft for Adafruit Industries
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */

#include "genhdr/mpversion.h"
#include "py/mpconfig.h"
#include "py/objstr.h"
#include "py/objtuple.h"
#include "py/qstr.h"

#include "shared-bindings/os/__init__.h"

#include "lib/crypto-algorithms/sha256.h"

#include "hardware/structs/rosc.h"

#include <string.h>

STATIC const qstr os_uname_info_fields[] = {
    MP_QSTR_sysname, MP_QSTR_nodename,
    MP_QSTR_release, MP_QSTR_version, MP_QSTR_machine
};
STATIC const MP_DEFINE_STR_OBJ(os_uname_info_sysname_obj, "rp2040");
STATIC const MP_DEFINE_STR_OBJ(os_uname_info_nodename_obj, "rp2040");
STATIC const MP_DEFINE_STR_OBJ(os_uname_info_release_obj, MICROPY_VERSION_STRING);
STATIC const MP_DEFINE_STR_OBJ(os_uname_info_version_obj, MICROPY_GIT_TAG " on " MICROPY_BUILD_DATE);
STATIC const MP_DEFINE_STR_OBJ(os_uname_info_machine_obj, MICROPY_HW_BOARD_NAME " with " MICROPY_HW_MCU_NAME);


STATIC MP_DEFINE_ATTRTUPLE(
    os_uname_info_obj,
    os_uname_info_fields,
    5,
    (mp_obj_t)&os_uname_info_sysname_obj,
    (mp_obj_t)&os_uname_info_nodename_obj,
    (mp_obj_t)&os_uname_info_release_obj,
    (mp_obj_t)&os_uname_info_version_obj,
    (mp_obj_t)&os_uname_info_machine_obj
    );

mp_obj_t common_hal_os_uname(void) {
    return (mp_obj_t)&os_uname_info_obj;
}

// NIST Special Publication 800-90B (draft) recommends several extractors,
// including the SHA hash family and states that if the amount of entropy input
// is twice the number of bits output from them, that output can be considered
// essentially fully random.  If every RANDOM_SAFETY_MARGIN bits from
// `rosc_hw->randombit` have at least 1 bit of entropy, then this criterion is met.
//
// This works by seeding the `random_state` with plenty of random bits (SHA256
// as entropy harvesting function), then using that state it as a counter input
// (SHA256 as a CSPRNG), re-seeding at least every 256 blocks (8kB).
//
// In practice, `PractRand` doesn't detect any gross problems with the output
// random numbers on samples of 1 to 8 megabytes, no matter the setting of
// RANDOM_SAFETY_MARGIN.  (it does detect "unusual" results from time to time,
// as it will with any RNG)
#define RANDOM_SAFETY_MARGIN (4)

static BYTE random_state[SHA256_BLOCK_SIZE];
static void seed_random_bits(BYTE out[SHA256_BLOCK_SIZE]) {
    CRYAL_SHA256_CTX context;
    sha256_init(&context);
    for (int i = 0; i < 2 * RANDOM_SAFETY_MARGIN; i++) {
        for (int j = 0; j < SHA256_BLOCK_SIZE; j++) {
            out[j] = rosc_hw->randombit & 1;
            for (int k = 0; k < 8; k++) {
                out[j] = (out[j] << 1) ^ (rosc_hw->randombit & 1);
            }
        }
        sha256_update(&context, out, SHA256_BLOCK_SIZE);
    }
    sha256_final(&context, out);
}

static void get_random_bits(BYTE out[SHA256_BLOCK_SIZE]) {
    if (!random_state[0]++) {
        seed_random_bits(random_state);
    }
    CRYAL_SHA256_CTX context;
    sha256_init(&context);
    sha256_update(&context, random_state, SHA256_BLOCK_SIZE);
    sha256_final(&context, out);
}

bool common_hal_os_urandom(uint8_t *buffer, mp_uint_t length) {
#define ROSC_POWER_SAVE (1) // assume ROSC is not necessarily active all the time
    #if ROSC_POWER_SAVE
    uint32_t old_rosc_ctrl = rosc_hw->ctrl;
    rosc_hw->ctrl = (old_rosc_ctrl & ~ROSC_CTRL_ENABLE_BITS) | (ROSC_CTRL_ENABLE_VALUE_ENABLE << 12);
    #endif
    while (length) {
        size_t n = MIN(length, SHA256_BLOCK_SIZE);
        BYTE sha_buf[SHA256_BLOCK_SIZE];
        get_random_bits(sha_buf);
        memcpy(buffer, sha_buf, n);
        buffer += n;
        length -= n;
    }
    #if ROSC_POWER_SAVE
    rosc_hw->ctrl = old_rosc_ctrl;
    #endif
    return true;
}
