/*
 * Copyright (C) 2014 Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
 *               2016 Freie Universität Berlin
 *
 * This file is subject to the terms and conditions of the GNU Lesser
 * General Public License v2.1. See the file LICENSE in the top level
 * directory for more details.
 */

/**
 * @ingroup     native_cpu
 * @defgroup    native_rng
 * @{
 *
 * @file
 * @brief       HWRNG interface implementation
 *
 * @author      Ludwig Knüpfer <ludwig.knuepfer@fu-berlin.de>
 */

#include <string.h>
#include <stdlib.h>
#include <err.h>
#include <sys/stat.h>
#include <fcntl.h>

#include "cpu_conf.h"
#include "native_internal.h"

#include "periph/hwrng.h"

#define ENABLE_DEBUG (0)
#include "debug.h"

static int initialized = 0;
static int dev_random = -1;

/**********************************************************************
 * internal API declaration
 **********************************************************************/

/**
 * seed host random module with @ref _native_rng_seed
 */
void _native_rng_init_det(void);
void _native_rng_init_hq(void);
unsigned _native_rng_read_det(uint8_t *buf, unsigned num);
unsigned _native_rng_read_hq(uint8_t *buf, unsigned num);

/**********************************************************************
 * public API implementation
 **********************************************************************/

void hwrng_init(void)
{
    DEBUG("hwrng_init: initializing\n");
    switch (_native_rng_mode) {
        case 0:
            _native_rng_init_hq();
            break;
        case 1:
            _native_rng_init_det();
            break;
        default:
            err(EXIT_FAILURE, "hwrng_init: _native_rng_mode is in invalid state %i\n",
                   _native_rng_mode);
            break;
    }

    initialized = 1;
}

void hwrng_read(uint8_t *buf, unsigned int num)
{
    if (!initialized) {
        warnx("hwrng_read: random device not initialized, failing\n");
        return;
    }

    DEBUG("hwrng_read: writing %u bytes\n", num);
    switch (_native_rng_mode) {
        case 0:
            _native_rng_read_hq(buf, num);
            break;
        case 1:
            _native_rng_read_det(buf, num);
            break;
        default:
            err(EXIT_FAILURE, "hwrng_read: _native_rng_mode is in invalid state %i\n",
                   _native_rng_mode);
            break;
    }
}

/**********************************************************************
 * internal API implementation
 **********************************************************************/

void _native_rng_init_det(void)
{
    DEBUG("_native_rng_init_det\n");
    _native_syscall_enter();
    real_srandom(_native_rng_seed);
    _native_syscall_leave();
}

void _native_rng_init_hq(void)
{
    DEBUG("_native_rng_init_hq\n");
    _native_syscall_enter();
    dev_random = real_open("/dev/urandom", O_RDONLY | O_CLOEXEC);
    if (dev_random == -1) {
        dev_random = real_open("/dev/random", O_RDONLY | O_CLOEXEC);
        if (dev_random == -1) {
            err(EXIT_FAILURE, "_native_rng_init_hq: open(/dev/urandom|/dev/random)");
        }
    }
    _native_syscall_leave();
}

unsigned _native_rng_read_det(uint8_t *buf, unsigned num)
{
    DEBUG("_native_rng_read_det\n");
    for (unsigned i = 0; i < num; i++) {
        _native_syscall_enter();
        buf[i] = (uint8_t)real_random();
        _native_syscall_leave();
    }

    return num;
}

unsigned _native_rng_read_hq(uint8_t *buf, unsigned num)
{
    DEBUG("_native_rng_read_hq\n");
    unsigned offset = 0;

    while (num > 0) {
        _native_syscall_enter();
        int r = real_read(dev_random, (buf + offset), num);
        _native_syscall_leave();

        if (r == -1) {
            err(EXIT_FAILURE, "_native_rng_read_hq: read");
        }

        num -= r;
        offset += r;
    }

    return offset;
}

/**
 * @}
 */