nostalgia/deps/ox/ox-docs.md

# Ox Docs

## Project Structure

All components have a platform indicator next to them:

    (OB) - OS, Bare Metal
    (-B) - Bare Metal
    (O-) - OS

* Ox - Library of things useful for portable bare metal and userland code. Not really that external...
    * clargs - Command Line Args processing (OB)
    * claw - Reads and writes Metal or Organic Claw with header to indicate which
    * event - Qt-like signal system (OB)
    * fs - file system (OB)
        * logconn - connects logging to Bullock (O-)
    * mc - Metal Claw serialization, builds on model (OB)
    * oc - Organic Claw serialization (wrapper around JsonCpp), builds on model (O-)
    * model - Data structure modelling (OB)
        * preloader - library for handling preloading of data (OB)
    * std - Standard-ish Library with a lot missing and some things added (OB)

## Systems

### Error Handling

Ox provides ```ox::Error``` to report errors.
```ox::Error``` is a struct that has overloaded operators to behave like an
integer error code, plus some extra fields to enhance debuggability.
If instantiated through the ```OxError(x)``` macro, it will also include the
file and line of the error.
The ```OxError(x)``` macro should only be used for the initial instantiation of
an ```ox::Error```.

In addition to ```ox::Error``` there is also the template ```ox::Result<T>```.
```ox::Result``` simply wraps the type T value in a struct that also includes
error information, which allows the returning of a value and an error without
resorting to output parameters.

If a function returns an ```ox::Error``` or ```ox::Result``` it should be
declared as ```noexcept``` and all exceptions should be translated to an
```ox::Error```.

```ox::Result``` can be used as follows:

```cpp
ox::Result<int> foo(int i) noexcept {
	if (i < 10) {
		return i + 1; // implicitly calls ox::Result<T>::Result(T)
	}
	return OxError(1); // implicitly calls ox::Result<T>::Result(ox::Error)
}

int caller1() {
	auto v = foo(argc);
	if (v.error) {
		return 1;
	}
	std::cout << v.value << '\n';
	return 0;
}

int caller2() {
	// it is also possible to capture the value and error in their own variables
	auto [val, err] = foo(argc);
	if (err) {
		return 1;
	}
	std::cout << val << '\n';
	return 0;
}

ox::Error caller3(int &i) {
    return foo(i).moveTo(i);
}

ox::Error caller4(int &i) {
    return foo(i).copyTo(i);
}

int caller5(int i) {
    return foo(i).unwrap(); // unwrap will kill the program if there is an error
}

int caller6(int i) {
    return foo(i).unwrapThrow(); // unwrap will throw if there is an error
}

int caller7(int i) {
    return foo(i).or_value(0); // will return 0 if foo returned an error
}

ox::Result<uint64_t> caller8(int i) {
    return foo(i).to<uint64_t>(); // will convert the result of foo to uint64_t
}
```

Lastly, there are a few macros available to help in passing ```ox::Error```s
back up the call stack, ```oxReturnError```, ```oxThrowError```, and
```oxRequire```.

```oxReturnError``` is by far the more helpful of the two.
```oxReturnError``` will return an ```ox::Error``` if it is not 0 and
```oxThrowError``` will throw an ```ox::Error``` if it is not 0.

Since ```ox::Error``` is always nodiscard, you must do something with them.
In rare cases, you may not have anything you can do with them or you may know
the code will never fail in that particular instance.
This should be used sparingly.


```cpp
void studioCode() {
	auto [val, err] = foo(1);
	oxThrowError(err);
	doStuff(val);
}

ox::Error engineCode() noexcept {
	auto [val, err] = foo(1);
	oxReturnError(err);
	doStuff(val);
	return {};
}

void anyCode() {
    auto [val, err] = foo(1);
    std::ignore = err;
    doStuff(val);
}
```

Both macros will also take the ```ox::Result``` directly:

```cpp
void studioCode() {
	auto valerr = foo(1);
	oxThrowError(valerr);
	doStuff(valerr.value);
}

ox::Error engineCode() noexcept {
	auto valerr = foo(1);
	oxReturnError(valerr);
	doStuff(valerr.value);
	return {};
}
```

Ox also has the ```oxRequire``` macro, which will initialize a value if there is no error, and return if there is.
It aims to somewhat emulate the ```?``` operator in Rust and Swift.

Rust ```?``` operator:
```rust
fn f() -> Result<i32, i32> {
  // do stuff
}

fn f2() -> Result<i32, i32> {
  let i = f()?;
  Ok(i + 4)
}
```

```oxRequire```:
```cpp
ox::Result<int> f() noexcept {
	// do stuff
}

ox::Result<int> f2() noexcept {
	oxRequire(i, f()); // const auto [out, oxConcat(oxRequire_err_, __LINE__)] = x; oxReturnError(oxConcat(oxRequire_err_, __LINE__))
	return i + 4;
}
```
```oxRequire``` is not quite as versatile, but it should still cleanup a lot of otherwise less ideal code.

```oxRequire``` by default creates a const, but there is also an ```oxRequireM``` (oxRequire Mutable)
variant for creating a non-const value.

* ```oxRequireM``` - oxRequire Mutable

### Logging and Output

Ox provides for logging and debug prints via the ```oxTrace```, ```oxDebug```, and ```oxError``` macros.
Each of these also provides a format variation.

Ox also provide ```oxOut``` and ```oxErr``` for printing to stdout and stderr.
These are intended for permanent messages and always go to stdout and stderr.

Tracing functions do not go to stdout unless the OXTRACE environment variable is set.
They also print with the channel that they are on, along with file and line.

Debug statements go to stdout and go to the logger on the "debug" channel.
Where trace statements are intended to be written with thoughtfulness,
debug statements are intended to be quick and temporary insertions.
Debug statements trigger compilation failures if OX_NODEBUG is enabled when CMake is run,
as it is on Jenkins builds, so ```oxDebug``` statements should never be checked in.
This makes ```oxDebug``` preferable to other forms of logging, as temporary prints should
never be checked in.

```oxError``` always prints.
It includes file and line, and is prefixed with a red "ERROR:".
It should generally be used conservatively.
It should be used only when there is an error that is not technically fatal, but
the user almost certainly wants to know about it.

```oxTrace``` and ```oxTracef```:
```cpp
void f(int x, int y) { // x = 9, y = 4
	oxTrace("nostalgia.core.sdl.gfx") << "f:" << x << y; // Output: "f: 9 4"
	oxTracef("nostalgia.core.sdl.gfx", "f: {}, {}", x, y); // Output: "f: 9, 4"
}
```

```oxDebug``` and ```oxDebugf```:
```cpp
void f(int x, int y) { // x = 9, y = 4
	oxDebug() << "f:" << x << y; // Output: "f: 9 4"
	oxDebugf("f: {}, {}", x, y); // Output: "f: 9, 4"
}
```

```oxError``` and ```oxErrorf```:
```cpp
void f(int x, int y) { // x = 9, y = 4
	oxError() << "f:" << x << y; // Output: "ERROR: (<file>:<line>): f: 9 4"
	oxErrorf("f: {}, {}", x, y); // Output: "ERROR: (<file>:<line>): f: 9, 4"
}
```

### Model System

Ox has a model system that provides a sort of manual reflection mechanism.

Models require a model function for the type that you want to model.
It is also good to provide a type name and type version number, though that is not required.

The model function takes an instance of the type it is modelling and a template
parameter type.
The template parameter type must implement the API used in the models, but it
can do anything with the data provided to it.

Here is an example from the Nostalgia/Core package:

```cpp
struct NostalgiaPalette {
	static constexpr auto TypeName = "net.drinkingtea.nostalgia.core.NostalgiaPalette";
	static constexpr auto TypeVersion = 1;
	ox::Vector<Color16> colors;
};

struct NostalgiaGraphic {
	static constexpr auto TypeName = "net.drinkingtea.nostalgia.core.NostalgiaGraphic";
	static constexpr auto TypeVersion = 1;
	int8_t bpp = 0;
	// rows and columns are really only used by TileSheetEditor
	int rows = 1;
	int columns = 1;
	ox::FileAddress defaultPalette;
	NostalgiaPalette pal;
	ox::Vector<uint8_t> pixels;
};

template<typename T>
constexpr ox::Error model(T *h, ox::CommonPtrWith<NostalgiaPalette> auto *pal) noexcept {
	h->template setTypeInfo<NostalgiaPalette>();
	// it is also possible to provide the type name and type version as function arguments
	//h->setTypeInfo("net.drinkingtea.nostalgia.core.NostalgiaPalette", 1);
	oxReturnError(h->field("colors", &pal->colors));
	return {};
}

template<typename T>
constexpr ox::Error model(T *h, ox::CommonPtrWith<NostalgiaGraphic> auto *ng) noexcept {
	h->template setTypeInfo<NostalgiaGraphic>();
	oxReturnError(h->field("bpp", &ng->bpp));
	oxReturnError(h->field("rows", &ng->rows));
	oxReturnError(h->field("columns", &ng->columns));
	oxReturnError(h->field("defaultPalette", &ng->defaultPalette));
	oxReturnError(h->field("pal", &ng->pal));
	oxReturnError(h->field("pixels", &ng->pixels));
	return {};
}
```

The model system also provides for unions:

```cpp

#include <ox/model/types.hpp>

class FileAddress {

	template<typename T>
	friend constexpr Error model(T*, ox::CommonPtrWith<FileAddress> auto*) noexcept;

	public:
		static constexpr auto TypeName = "net.drinkingtea.ox.FileAddress";

		union Data {
			static constexpr auto TypeName = "net.drinkingtea.ox.FileAddress.Data";
			char *path;
			const char *constPath;
			uint64_t inode;
		};

	protected:
		FileAddressType m_type = FileAddressType::None;
		Data m_data;

};

template<typename T>
constexpr Error model(T *h, ox::CommonPtrWith<FileAddress::Data> auto *obj) noexcept {
	h->template setTypeInfo<FileAddress::Data>();
	oxReturnError(h->fieldCString("path", &obj->path));
	oxReturnError(h->fieldCString("constPath", &obj->path));
	oxReturnError(h->field("inode", &obj->inode));
	return {};
}

template<typename T>
constexpr Error model(T *io, ox::CommonPtrWith<FileAddress> auto *fa) noexcept {
	io->template setTypeInfo<FileAddress>();
	// cannot read from object in Reflect operation
	if constexpr(ox_strcmp(T::opType(), OpType::Reflect) == 0) {
		int8_t type = 0;
		oxReturnError(io->field("type", &type));
		oxReturnError(io->field("data", UnionView(&fa->m_data, 0)));
	} else {
		auto type = static_cast<int8_t>(fa->m_type);
		oxReturnError(io->field("type", &type));
		fa->m_type = static_cast<FileAddressType>(type);
		oxReturnError(io->field("data", UnionView(&fa->m_data, static_cast<int>(fa->m_type))));
	}
	return {};
}

```

There are also macros in ```<ox/model/def.hpp>``` for simplifying the declaration of models:

```cpp
oxModelBegin(NostalgiaGraphic)
	oxModelField(bpp)
	oxModelField(rows)
	oxModelField(columns)
	oxModelField(defaultPalette)
	oxModelField(pal)
	oxModelField(pixels)
oxModelEnd()
```

### Serialization

Using the model system, Ox provides for serialization.
Ox has MetalClaw and OrganicClaw as its serialization format options.
MetalClaw is a custom binary format designed for minimal size.
OrganicClaw is a wrapper around JsonCpp, chosen because it technically
implements a superset of JSON.
OrganicClaw requires support for 64 bit integers, whereas normal JSON
technically does not.

These formats do not currently support floats.

There is also a wrapper format called Claw that provides a header at the
beginning of the file and can dynamically switch between the two depending on
what the header says is present.
The Claw header also includes information about the type and type version of
the data.

Claw header: ```M1;net.drinkingtea.nostalgia.core.NostalgiaPalette;1;```

That reads:

* Format is Metal Claw, version 1
* Type ID is net.drinkingtea.nostalgia.core.NostalgiaPalette
* Type version is 1

#### Metal Claw Example

##### Read

```cpp
#include <ox/mc/read.hpp>

ox::Result<NostalgiaPalette> loadPalette1(ox::BufferView const&buff) noexcept {
	return ox::readMC<NostalgiaPalette>(buff);
}

ox::Result<NostalgiaPalette> loadPalette2(ox::BufferView const&buff) noexcept {
	NostalgiaPalette pal;
	oxReturnError(ox::readMC(buff, pal));
	return pal;
}
```

##### Write

```cpp
#include <ox/mc/write.hpp>

ox::Result<ox::Buffer> writeSpritePalette1(NostalgiaPalette const&pal) noexcept {
	ox::Buffer buffer(ox::units::MB);
	std::size_t sz = 0;
	oxReturnError(ox::writeMC(buffer.data(), buffer.size(), pal, &sz));
	buffer.resize(sz);
	return buffer;
}

ox::Result<ox::Buffer> writeSpritePalette2(NostalgiaPalette const&pal) noexcept {
	return ox::writeMC(pal);
}
```

#### Organic Claw Example

##### Read

```cpp
#include <ox/oc/read.hpp>

ox::Result<NostalgiaPalette> loadPalette1(ox::BufferView const&buff) noexcept {
	return ox::readOC<NostalgiaPalette>(buff);
}

ox::Result<NostalgiaPalette> loadPalette2(ox::BufferView const&buff) noexcept {
	NostalgiaPalette pal;
	oxReturnError(ox::readOC(buff, &pal));
	return pal;
}
```

##### Write

```cpp
#include <ox/oc/write.hpp>

ox::Result<ox::Buffer> writeSpritePalette1(NostalgiaPalette const&pal) noexcept {
	ox::Buffer buffer(ox::units::MB);
	oxReturnError(ox::writeOC(buffer.data(), buffer.size(), pal));
	return buffer;
}

ox::Result<ox::Buffer> writeSpritePalette2(NostalgiaPalette const&pal) noexcept {
	return ox::writeOC(pal);
}
```

#### Claw Example

##### Read

```cpp
#include <ox/claw/read.hpp>

ox::Result<NostalgiaPalette> loadPalette1(ox::BufferView const&buff) noexcept {
	return ox::readClaw<NostalgiaPalette>(buff);
}

ox::Result<NostalgiaPalette> loadPalette2(ox::BufferView const&buff) noexcept {
	NostalgiaPalette pal;
	oxReturnError(ox::readClaw(buff, pal));
	return pal;
}
```

##### Write

```cpp
#include <ox/claw/write.hpp>

ox::Result<ox::Buffer> writeSpritePalette(NostalgiaPalette const&pal) noexcept {
	return ox::writeClaw(pal);
}
```