Luna/luna/include/luna/Result.h

#pragma once
#include <luna/Check.h>
#include <luna/Move.h>
#include <luna/Option.h>
#include <luna/PlacementNew.h>
#include <luna/SystemError.h>
#include <luna/Types.h>

struct Error
{
    Error(int err)
    {
        error = err;
    }

    int error;
};

template <typename T> class Result
{
  public:
    Result(const T& value) : m_value(value)
    {
        m_has_value = true;
        m_has_error = false;
    }

    Result(T&& value) : m_value(value)
    {
        m_has_value = true;
        m_has_error = false;
    }

    Result(const Result<T>& other) : m_value(other.m_value)
    {
        if (!other.m_has_error)
        {
            m_has_value = true;
            m_has_error = false;
        }
        else
        {
            m_has_error = true;
            m_has_value = false;
            m_error = other.m_error;
        }
    }

    Result(Result<T>&& other) : m_value(other.m_value)
    {
        if (!other.m_has_error)
        {
            m_has_value = true;
            m_has_error = false;
        }
        else
        {
            m_has_error = true;
            m_has_value = false;
            m_error = other.m_error;
        }
    }

    Result(const Error& err) : m_value()
    {
        m_error = err.error;
        m_has_error = true;
        m_has_value = false;
    }

    bool has_error()
    {
        return m_has_error;
    }

    bool has_value()
    {
        return m_has_value;
    }

    int error()
    {
        expect(has_error(), "Result::error() called on a Result that holds a value");
        return m_error;
    }

    Error release_error()
    {
        expect(has_error(), "Result::release_error() called on a Result that holds a value");
        return {m_error};
    }

    const char* error_string()
    {
        expect(has_error(), "Result::error_string() called on a Result that holds a value");
        return ::error_string(m_error);
    }

    T value()
    {
        expect(has_value(), "Result::value() called on a Result that holds an error");
        return m_value.value();
    }

    T expect_value(const char* reason)
    {
        expect(has_value(), reason);
        return move(m_value.release_value());
    }

    T value_or(const T& other)
    {
        return m_value.value_or(other);
    }

    bool try_set_value(T& ref)
    {
        return m_value.try_set_value(ref);
    }

    T release_value()
    {
        expect(has_value(), "Result::release_value() called on a Result that holds an error");
        return m_value.release_value();
    }

    T expect_release_value(const char* reason)
    {
        expect(has_value(), reason);
        return m_value.release_value();
    }

  private:
    Option<T> m_value;
    int m_error;
    bool m_has_error;
    bool m_has_value;
};

template <> class Result<void>
{
  public:
    Result()
    {
        m_has_error = false;
    }

    Result(const Result<void>& other)
    {
        m_has_error = other.m_has_error;
        m_error = other.m_error;
    }

    Result(Result<void>&& other)
    {
        m_has_error = other.m_has_error;
        m_error = other.m_error;
    }

    Result(const Error& err)
    {
        m_error = err.error;
        m_has_error = true;
    }

    bool has_error()
    {
        return m_has_error;
    }

    bool has_value()
    {
        return !m_has_error;
    }

    int error()
    {
        expect(has_error(), "Result::error() called on a Result that holds a value");
        return m_error;
    }

    Error release_error()
    {
        expect(has_error(), "Result::release_error() called on a Result that holds a value");
        return {m_error};
    }

    const char* error_string()
    {
        expect(has_error(), "Result::error_string() called on a Result that holds a value");
        return ::error_string(m_error);
    }

    void value()
    {
        expect(has_value(), "Result::value() called on a Result that holds an error");
        return;
    }

    void expect_value(const char* reason)
    {
        expect(has_value(), reason);
        return;
    }

    void release_value()
    {
        expect(has_value(), "Result::release_value() called on a Result that holds an error");
        return;
    }

    void expect_release_value(const char* reason)
    {
        expect(has_value(), reason);
        return;
    }

  private:
    int m_error;
    bool m_has_error;
};

// clang-format off
#define err(x) Error{x}
// clang-format on

#define TRY(expr)                                                                                                      \
    ({                                                                                                                 \
        auto _expr_rc = (expr);                                                                                        \
        if (!_expr_rc.has_value()) return _expr_rc.release_error();                                                    \
        _expr_rc.expect_release_value("sanity check failed: has_error() returned false, yet result has no value");     \
    })