/******************************************************************************/
/* SlunkCrypt, by LoRd_MuldeR <MuldeR2@GMX.de>                                */
/* This work has been released under the CC0 1.0 Universal license!           */
/******************************************************************************/

/* Internal */
#include "../include/slunkcrypt.h"

/* CRT */
#include <string.h>
#include <fcntl.h>
#include <limits.h>

/* Platform compatibility */
#ifdef _WIN32
#	define WIN32_LEAN_AND_MEAN 1
#	include <Windows.h>
#else
#	include <unistd.h>
#	include <pthread.h>
#endif

/* Compiler compatibility */
#if defined(__GNUC__) || defined(__clang__)
#	define HAVE_DESTRUCTOR 1
#else
#	define HAVE_DESTRUCTOR 0
#endif

// ==========================================================================
// Call once support
// ==========================================================================

#ifdef _WIN32
#	define CALL_ONCE win32_call_once
#	define CALL_ONCE_TYPE volatile LONG
#	define CALL_ONCE_INIT 0L
#else
#	define CALL_ONCE pthread_once
#	define CALL_ONCE_TYPE pthread_once_t
#	define CALL_ONCE_INIT PTHREAD_ONCE_INIT
#endif

#ifdef _WIN32
static void win32_call_once(CALL_ONCE_TYPE *const control, void (*init_routine)(void))
{
	LONG status;
	while ((status = InterlockedCompareExchange(control, -1L, 0L)) != 0L)
	{
		if(status > 0L)
		{
			return; /*already initialized*/
		}
		SwitchToThread();
	}
	init_routine();
	InterlockedExchange(control, 1L);
}
#endif

// ==========================================================================
// Random bytes
// ==========================================================================

#ifdef _WIN32
#	define HAVE_GETRANDOM 0
#else
#	if defined(__GLIBC__) && (__GLIBC__ >= 2) && (__GLIBC_MINOR__ >= 25)
#		define HAVE_GETRANDOM 1
#	elif defined(__FreeBSD__) && (__FreeBSD__ >= 12)
#		define HAVE_GETRANDOM 1
#	else
#		define HAVE_GETRANDOM 0
#	endif
#endif
#if HAVE_GETRANDOM
#	include <sys/random.h>
#endif

/* Global state */
static CALL_ONCE_TYPE s_random_is_initialized = CALL_ONCE_INIT;
#if defined(_WIN32)
typedef BOOLEAN(WINAPI *rtl_genrandom_t)(void *buffer, ULONG buff_size);
static HMODULE s_dll_advapi32 = NULL;
static rtl_genrandom_t s_rtl_genrandom = NULL;
#elif !HAVE_GETRANDOM
static const char *const DEV_RANDOM[] = { "/dev/urandom", "/dev/arandom", "/dev/random", NULL };
static int s_random_fd = -1;
#endif

/* De-initialize CSRNG */
static void exit_random_source(void)
{
#if defined(_WIN32)
	s_rtl_genrandom = NULL;
	if (s_dll_advapi32)
	{
		FreeLibrary(s_dll_advapi32);
		s_dll_advapi32 = NULL;
	}
#elif !HAVE_GETRANDOM
	if (s_random_fd >= 0)
	{
		close(s_random_fd);
		s_random_fd = -1;
	}
#endif
}

/* Initialize CSRNG */
static void init_random_source(void)
{
#if defined(_WIN32)
	if ((s_dll_advapi32 = LoadLibraryW(L"advapi32.dll")))
	{
		s_rtl_genrandom = (rtl_genrandom_t)GetProcAddress(s_dll_advapi32, "SystemFunction036");
	}
#elif !HAVE_GETRANDOM
	for (size_t i = 0U; DEV_RANDOM[i]; ++i)
	{
		if ((s_random_fd = open(DEV_RANDOM[i], O_RDONLY)) >= 0)
		{
			break; /*success*/
		}
	}
#endif
#if !HAVE_DESTRUCTOR
	atexit(exit_random_source);
#endif
}

/* Generate random bytes */
size_t slunkcrypt_random_bytes(uint8_t* const buffer, const size_t length)
{
	CALL_ONCE(&s_random_is_initialized, init_random_source);
#if defined(_WIN32)
	if (s_rtl_genrandom)
	{
		const ULONG buff_size = (ULONG)length;
		return s_rtl_genrandom(buffer, buff_size) ? buff_size : 0U;
	}
#elif HAVE_GETRANDOM
	const ssize_t result = getrandom(buffer, length, 0U);
	return (result < 0) ? 0U : ((size_t)result);
#else
	if (s_random_fd >= 0)
	{
		const ssize_t result = read(s_random_fd, buffer, length);
		return (result < 0) ? 0U : ((size_t)result);
	}
#endif
	return 0U;
}

// ==========================================================================
// Zero memory
// ==========================================================================

#ifdef _WIN32
#	ifdef SecureZeroMemory
#		define HAVE_EXPLICIT_BZERO 1
#		define explicit_bzero SecureZeroMemory
#	else
#		define HAVE_EXPLICIT_BZERO 0
#	endif
#else
#	if defined(__GLIBC__) && (__GLIBC__ >= 2) && (__GLIBC_MINOR__ >= 25)
#		define HAVE_EXPLICIT_BZERO 1
#	elif defined(__FreeBSD__) && (__FreeBSD__ >= 11)
#		define HAVE_EXPLICIT_BZERO 1
#	else
#		define HAVE_EXPLICIT_BZERO 0
#	endif
#endif

void slunkcrypt_bzero(void* const buffer, const size_t length)
{
	if ((buffer) && (length > 0U))
	{
#if HAVE_EXPLICIT_BZERO
		explicit_bzero(buffer, length);
#else
		volatile uint8_t* ptr = (volatile uint8_t*) buffer;
		for (size_t i = 0U; i < length; ++i)
		{
			ptr[i] = 0U;
		}
#endif
	}
}

// ==========================================================================
// Destructor
// ==========================================================================

#if HAVE_DESTRUCTOR
__attribute__((destructor)) void slunkcrypt_destructor()
{
	exit_random_source();
}
#endif