banan-os/BAN/include/BAN/Errors.h

#pragma once

#include <BAN/Formatter.h>

#include <string.h>

#if defined(__is_kernel)
	#include <kernel/panic.h>
	#define MUST(error)	({ auto e = error; if (e.IsError()) Kernel::panic("{}", e.GetError()); e.Value(); })
#else
	#error "NOT IMPLEMENTED"
#endif

#define TRY(error) ({ auto e = error; if (e.IsError()) return e; e.Value(); })


class Error
{
public:
	static Error FromString(const char* message)
	{
		Error result;
		strncpy(result.m_message, message, sizeof(m_message));
		result.m_message[sizeof(result.m_message) - 1] = '\0';
		result.m_error_code = 0xFF;
		return result;
	}

	uint8_t GetErrorCode() const { return m_error_code; }
	const char* GetMessage() const { return m_message; }

private:
	char m_message[128];
	uint8_t m_error_code;
};

template<typename T>
class ErrorOr
{
public:
	ErrorOr(const T& value)		: m_has_error(false)	{ m_data = (void*)new T(value); }
	ErrorOr(const Error& error) : m_has_error(true)		{ m_data = (void*)new Error(error); }
	template<typename S> ErrorOr(const ErrorOr<S>& other) : ErrorOr(other.GetError()) {}
	~ErrorOr()											{ IsError() ? (delete reinterpret_cast<Error*>(m_data)) : (delete reinterpret_cast<T*>(m_data)); }

	bool IsError() const			{ return m_has_error; }
	const Error& GetError() const	{ return *reinterpret_cast<Error*>(m_data); }
	T& Value()						{ return *reinterpret_cast<T*>(m_data); }

private:
	bool	m_has_error;
	void*	m_data;
};

template<>
class ErrorOr<void>
{
public:
	ErrorOr() : m_error(nullptr)	{ }
	ErrorOr(const Error& error)		{ m_error = new Error(error); }
	~ErrorOr()						{ delete m_error; }

	bool IsError() const			{ return m_error; }
	const Error& GetError() const	{ return *m_error; }
	void Value()					{ }

private:
	Error*	m_error;
};


namespace BAN::Formatter
{
	template<void(*PUTC_LIKE)(char)>
	void print_argument_impl(const Error& error, const ValueFormat&)
	{
		if (error.GetErrorCode() == 0xFF)
			print<PUTC_LIKE>(error.GetMessage());
		else
			print<PUTC_LIKE>("{} ({})", error.GetMessage(), error.GetErrorCode());
	}
}