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use crate::ptr::NullPtr;
use crate::{CppBox, CppDeletable, Ptr, Ref, StaticUpcast};

/// Performs some of the conversions that are available implicitly in C++.
///
/// `CastInto` is automatically implemented for all `CastFrom` conversions,
/// similar to `From` and `Into` traits from `std`.
pub trait CastFrom<T>: Sized {
    /// Performs the conversion.
    ///
    /// ### Safety
    ///
    /// This operation is safe as long as `value` is valid.
    unsafe fn cast_from(value: T) -> Self;
}

/// Performs some of the conversions that are available implicitly in C++.
///
/// `CastInto` is automatically implemented for all `CastFrom` conversions,
/// similar to `From` and `Into` traits from `std`.
pub trait CastInto<T>: Sized {
    /// Performs the conversion.
    ///
    /// ### Safety
    ///
    /// This operation is safe as long as `self` is valid.
    unsafe fn cast_into(self) -> T;
}

impl<T, U: CastFrom<T>> CastInto<U> for T {
    unsafe fn cast_into(self) -> U {
        U::cast_from(self)
    }
}

impl<T, U> CastFrom<Ref<U>> for Ptr<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: Ref<U>) -> Self {
        StaticUpcast::static_upcast(value.as_ptr())
    }
}

impl<'a, T, U: CppDeletable> CastFrom<&'a CppBox<U>> for Ptr<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: &'a CppBox<U>) -> Self {
        StaticUpcast::static_upcast(value.as_ptr())
    }
}

impl<'a, T, U: CppDeletable> CastFrom<&'a CppBox<U>> for Ref<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: &'a CppBox<U>) -> Self {
        StaticUpcast::static_upcast(value.as_ptr())
            .as_ref()
            .expect("StaticUpcast returned null on CppBox input")
    }
}

impl<T, U> CastFrom<Ptr<U>> for Ptr<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: Ptr<U>) -> Self {
        StaticUpcast::static_upcast(value)
    }
}

impl<T, U> CastFrom<Ref<U>> for Ref<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: Ref<U>) -> Self {
        StaticUpcast::static_upcast(value.as_ptr())
            .as_ref()
            .expect("StaticUpcast returned null on Ref input")
    }
}

impl<T> CastFrom<NullPtr> for Ptr<T> {
    unsafe fn cast_from(_value: NullPtr) -> Self {
        Self::null()
    }
}

impl<T, U> CastFrom<*const U> for Ptr<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: *const U) -> Self {
        Self::cast_from(Ptr::from_raw(value))
    }
}

impl<T, U> CastFrom<*mut U> for Ptr<T>
where
    U: StaticUpcast<T>,
{
    unsafe fn cast_from(value: *mut U) -> Self {
        Self::cast_from(Ptr::from_raw(value))
    }
}