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use std::cell::UnsafeCell;

pub struct SyncUnsafeCell<T> {
    value: UnsafeCell<T>,
}

unsafe impl<T> Sync for SyncUnsafeCell<T> {}

impl<T> SyncUnsafeCell<T> {
    /// Constructs a new instance of `SyncUnsafeCell` which will wrap the specified value.
    #[inline]
    pub const fn new(value: T) -> Self {
        Self { value: UnsafeCell::new(value) }
    }
}

impl<T> SyncUnsafeCell<T> {
    /// Gets a mutable pointer to the wrapped value.
    ///
    /// This can be cast to a pointer of any kind.
    /// Ensure that the access is unique (no active references, mutable or not)
    /// when casting to `&mut T`, and ensure that there are no mutations
    /// or mutable aliases going on when casting to `&T`
    #[inline]
    pub const fn get(&self) -> *mut T {
        self.value.get()
    }

    /// Gets a mutable pointer to the wrapped value.
    ///
    /// See [`UnsafeCell::get`] for details.
    #[inline]
    pub const fn raw_get(this: *const Self) -> *mut T {
        // We can just cast the pointer from `SyncUnsafeCell<T>` to `T` because
        // of #[repr(transparent)] on both SyncUnsafeCell and UnsafeCell.
        // See UnsafeCell::raw_get.
        this as *const T as *mut T
    }
}

impl<T: Default> Default for SyncUnsafeCell<T> {
    /// Creates an `SyncUnsafeCell`, with the `Default` value for T.
    fn default() -> SyncUnsafeCell<T> {
        SyncUnsafeCell::new(Default::default())
    }
}

impl<T> From<T> for SyncUnsafeCell<T> {
    /// Creates a new `SyncUnsafeCell<T>` containing the given value.
    fn from(t: T) -> SyncUnsafeCell<T> {
        SyncUnsafeCell::new(t)
    }
}