filesystem: Move pre-compiler checks to interface

[bwrsandman]

This allows for more interfaces to use custom read functions than android.
Such a usecase would be single ISO reads.

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[FalseIlyu]

Tested on a windows computer :
Normally launching the game works without problem, i tried setting the default filesystem preferedBuffer to true and it seems to cause no issue too and everything seems right to me.

However i wonder if we could not have a way to forgo the check and change this

if (Locator::filesystem::value().PreferBuffer())
{
	lnd.Open(Locator::filesystem::value().ReadAll(path));
}
else
{
	lnd.Open(path);
}

Into and just hide the whether the file is read from a buffer or from the filesystem.

lnd.Open(path);

It seems like it should be feasible without too much hassle but if i'm wrong having the asset read from the iso should be the priority preference in expression be damned.

[bwrsandman]

I had the same thought to reduce duplicate code but couldn't find a satisfying implementation.

The issue is that a static lib like lnd would not have details of custom filesystem read implementations if they took charge of reading.

And since I want components to be independent of each other, I don't want to have some monster reader common class.

[FalseIlyu]

Wouldn't going the other way around and having things written as

lnd.Open(Locator::filesystem::value().ReadAll(path));

Maybe not exactly like this something of the effect of the filesystem is in charge of getting the data to the reader and then reader do its job.

[bwrsandman]

So just always reading the whole file and using the buffer implementation.
I wonder if there are performance implications to consider such as the cost of allocation or read time.
That being said SSDs are fast nowadays.

It's worth considering and would be a non trivial change in the way we interact with our files.

[FalseIlyu]

void PackFile::Open(const std::filesystem::path& file)
{
	_filename = file;

	std::ifstream stream(_filename, std::ios::binary);

	if (!stream.is_open())
	{
		Fail("Could not open file.");
	}

	ReadFile(stream);
}

void PackFile::Open(const std::vector<uint8_t>& buffer)
{
	assert(!_isLoaded);

	imemstream stream(reinterpret_cast<const char*>(buffer.data()), buffer.size() * sizeof(buffer[0]));

	// File name set to "buffer" when file is load from a buffer
	// Impact code using L3DFile::GetFilename method
	_filename = std::filesystem::path("buffer");

	ReadFile(stream);
}

Seeing as the Open method of many file reader is mostly setting up a stream for ReadFile couldn't we just make ReadFile accessible to LND and charge FileSystem with the job of setting up the stream?
Something like

lnd.Open(Locator::filesystem::value().GetData(path));

Where GetData would return an istream, wouldn't something like 73c4fe6 i did here do ? (The android Filesystem compiles but is blindcoded so i do not guarantee it runs)

[bwrsandman]

Superseded by #706