/*
* Copyright (c) 2024 Vaughn Nugent
*
* Package: noscrypt
* File: nc-util.h
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public License
* as published by the Free Software Foundation; either version 2.1
* of the License, or  (at your option) any later version.
*
* This library is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
* Lesser General Public License for more details.
*
* You should have received a copy of the GNU Lesser General Public License
* along with noscrypt. If not, see http://www.gnu.org/licenses/.
*/

#pragma once

#ifndef _NC_UTIL_H
#define _NC_UTIL_H

#include <platform.h>

/* NULL */
#ifndef NULL
	#define NULL ((void*)0)
#endif /*  !NULL */

#ifdef DEBUG
	/* Must include assert.h for assertions */
	#include <assert.h> 
	#define DEBUG_ASSERT(x) assert(x);
	#define DEBUG_ASSERT2(x, message) assert(x && message);	

	/*
	* Compiler enabled static assertion keywords are 
	* only available in C11 and later. Later versions 
	* have macros built-in from assert.h so we can use
	* the static_assert macro directly.
	* 
	* Static assertions are only used for testing such as 
	* sanity checks and this library targets the c89 standard
	* so static_assret very likely will not be available. 
	*/
	#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
		#define STATIC_ASSERT(x, m) static_assert(x, m);
	#elif !defined(STATIC_ASSERT)
		#define STATIC_ASSERT(x, m)
		#pragma message("Static assertions are not supported by this language version")
	#endif

#else
	#define DEBUG_ASSERT(x)
	#define DEBUG_ASSERT2(x, message)
	#define STATIC_ASSERT(x, m)
#endif

#include <stdint.h>

#if SIZE_MAX < UINT32_MAX
	#define _overflow_check(x) if(x > SIZE_MAX) return CSTATUS_FAIL;
#else
	#define _overflow_check(x)
#endif

#ifdef NC_EXTREME_COMPAT

	void _nc_memmove(void* dst, const void* src, uint32_t size)
	{
		uint32_t i;

		for (i = 0; i < size; i++)
		{
			((uint8_t*)dst)[i] = ((uint8_t*)src)[i];
		}
	}

	#define MEMMOV _nc_memmove

#else

	/* Include string for memmove */
	#include <string.h>
	#define MEMMOV(dst, src, size) memmove(dst, src, size)

#endif /* NC_EXTREME_COMPAT */

#ifndef EMPTY_SPANS
	#define EMPTY_SPANS 1
#endif

typedef struct memory_span_struct
{
	uint8_t* data;
	uint32_t size;
} span_t;

typedef struct read_only_memory_span_struct
{
	const uint8_t* data;
	uint32_t size;
} cspan_t;

static _nc_fn_inline int ncSpanIsValid(span_t span)
{
	return span.data != NULL;
}

static _nc_fn_inline int ncSpanIsValidC(cspan_t span)
{
	return span.data != NULL;
}

static _nc_fn_inline int ncSpanIsValidRange(span_t span, uint32_t offset, uint32_t size)
{
	return ncSpanIsValid(span) && offset + size <= span.size;
}

static _nc_fn_inline int ncSpanIsValidRangeC(cspan_t span, uint32_t offset, uint32_t size)
{
	return ncSpanIsValidC(span) && offset + size <= span.size;
}

static _nc_fn_inline void ncSpanInitC(cspan_t* span, const uint8_t* data, uint32_t size)
{
	span->data = data;
	span->size = size;
}

static _nc_fn_inline void ncSpanInit(span_t* span, uint8_t* data, uint32_t size)
{
	span->data = data;
	span->size = size;
}

static _nc_fn_inline const uint8_t* ncSpanGetOffsetC(cspan_t span, uint32_t offset)
{

#if EMPTY_SPANS
	
	/* 
	* Allow passing null pointers for empty spans, if enabled, 
	* otherwise debug guards will catch empty spans
	*/
	if (span.size == 0 && offset == 0)
	{
		return NULL;
	}

#endif /* !EMPTY_SPANS */

	DEBUG_ASSERT2(ncSpanIsValidC(span), "Expected span to be non-null");
	DEBUG_ASSERT2(offset < span.size,	"Expected offset to be less than span size");

	return span.data + offset;
}

static _nc_fn_inline uint8_t* ncSpanGetOffset(span_t span, uint32_t offset)
{
	cspan_t cspan;	
	ncSpanInitC(&cspan, span.data, span.size);
	return (uint8_t*)ncSpanGetOffsetC(cspan, offset);
}

static _nc_fn_inline uint32_t ncSpanGetSizeC(cspan_t span)
{
	return ncSpanIsValidC(span) 
		? span.size
		: 0;
}

static _nc_fn_inline uint32_t ncSpanGetSize(span_t span)
{
	return ncSpanIsValid(span)
		? span.size
		: 0;
}

static _nc_fn_inline void ncSpanWrite(span_t span, uint32_t offset, const uint8_t* data, uint32_t size)
{
	DEBUG_ASSERT2(ncSpanIsValid(span),	"Expected span to be non-null")
	DEBUG_ASSERT2(data != NULL,			"Expected data to be non-null")
	DEBUG_ASSERT2(offset + size <= span.size, "Expected offset + size to be less than span size")

	/* Copy data to span */
	MEMMOV(span.data + offset, data, size);
}

static _nc_fn_inline void ncSpanAppend(span_t span, uint32_t* offset, const uint8_t* data, uint32_t size)
{
	DEBUG_ASSERT2(offset != NULL,		"Expected offset to be non-null")

	/* Copy data to span (also performs argument assertions) */
	ncSpanWrite(span, *offset, data, size);

	/* Increment offset */
	*offset += size;
}

static _nc_fn_inline span_t ncSpanSlice(span_t span, uint32_t offset, uint32_t size)
{
	span_t slice;

	DEBUG_ASSERT2(ncSpanIsValid(span),	"Expected span to be non-null");
	DEBUG_ASSERT2(offset + size <= span.size, "Expected offset + size to be less than span size");

	/* If the size of the sliced span is 0 return an empty span */
	if (size == 0)
	{
		ncSpanInit(&slice, NULL, 0);
	}
	else
	{
		/* Initialize slice, offset input data by the specified offset */
		ncSpanInit(
			&slice,
			ncSpanGetOffset(span, offset),
			size
		);
	}

	return slice;
}

static _nc_fn_inline cspan_t ncSpanSliceC(cspan_t span, uint32_t offset, uint32_t size)
{
	cspan_t slice;

	DEBUG_ASSERT2(ncSpanIsValidC(span), "Expected span to be non-null");
	DEBUG_ASSERT2(offset + size <= span.size, "Expected offset + size to be less than span size")

	/* If the size of the sliced span is 0 return an empty span */
	if (size == 0)
	{
		ncSpanInitC(&slice, NULL, 0);
	}
	else
	{
		/* Initialize slice, offset input data by the specified offset */
		ncSpanInitC(
			&slice,
			ncSpanGetOffsetC(span, offset),
			size
		);
	}

	return slice;
}

static _nc_fn_inline void ncSpanCopyC(cspan_t src, span_t dest)
{
	DEBUG_ASSERT2(ncSpanIsValidC(src), "Expected span to be non-null");
	DEBUG_ASSERT2(ncSpanIsValid(dest), "Expected offset + size to be less than span size");
	DEBUG_ASSERT2(dest.size >= src.size, "Output buffer too small. Overrun detected");

	/* Copy data to span */
	MEMMOV(dest.data, src.data, src.size);
}

static _nc_fn_inline void ncSpanCopy(span_t src, span_t dest)
{
	cspan_t csrc;
	
	ncSpanInitC(&csrc, src.data, src.size);
	ncSpanCopyC(csrc, dest);
}

static _nc_fn_inline void ncSpanReadC(cspan_t src, uint8_t* dest, uint32_t size)
{
	span_t dsts;

	ncSpanInit(&dsts, dest, size);
	ncSpanCopyC(src, dsts);
}

static _nc_fn_inline void ncSpanRead(span_t src, uint8_t* dest, uint32_t size)
{
	cspan_t srcs;

	ncSpanInitC(&srcs, src.data, src.size);
	ncSpanReadC(srcs, dest, size);
}


#endif /* !_NC_UTIL_H */