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#[doc(hidden)]
#[macro_export]
#[cfg(radium_atomic_8)]
macro_rules! __radium_if_atomic_8 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($a)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(not(radium_atomic_8))]
macro_rules! __radium_if_atomic_8 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($b)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(radium_atomic_16)]
macro_rules! __radium_if_atomic_16 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($a)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(not(radium_atomic_16))]
macro_rules! __radium_if_atomic_16 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($b)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(radium_atomic_32)]
macro_rules! __radium_if_atomic_32 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($a)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(not(radium_atomic_32))]
macro_rules! __radium_if_atomic_32 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($b)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(radium_atomic_64)]
macro_rules! __radium_if_atomic_64 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($a)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(not(radium_atomic_64))]
macro_rules! __radium_if_atomic_64 {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($b)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(radium_atomic_ptr)]
macro_rules! __radium_if_atomic_ptr {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($a)* }
}

#[doc(hidden)]
#[macro_export]
#[cfg(not(radium_atomic_ptr))]
macro_rules! __radium_if_atomic_ptr {
    ( [ $( $a:tt )* ] [ $( $b:tt )* ] ) => { $($b)* }
}

/// Conditional compilation based on the presence of atomic instructions.
///
/// This macro allows you to write `if`/`else` clauses, evaluated at
/// compile-time, that test the presence of atomic instructions and preserve or
/// destroy their guarded code accordingly.
///
/// The `if atomic(WIDTH)` test preserves the contents of its block when the
/// target architecture has atomic instructions for the requested `WIDTH`, and
/// removes them from the syntax tree when the target does not. If an `else`
/// clause is provided, the contents of the `else` block are used as a
/// substitute when the `if` is destroyed.
///
/// This macro can be used in any position. When it is used in item or statement
/// position, it can contain multiple `if` clauses, and each will be evaluated
/// in turn. Expression and type positions can only accept exactly one code
/// span, and so may only have exactly one `if`/`else` clause. An `else` clause
/// is required here so that the macro will always expand to something; an empty
/// expansion is a parse error.
///
/// # Macro Syntax
///
/// The macro contents `if atomic() {} else {}` are part of the macro
/// invocation. Only the contents of the two blocks are actual Rust code.
///
/// The acceptable arguments to `atomic()` are:
///
/// - `8`
/// - `16`
/// - `32`
/// - `64`
/// - `ptr`
/// - `bool`: alias for `8`
/// - `size`: alias for `ptr`
///
/// In addition, the `atomic()` test can be inverted, as `!atomic()`, to reverse
/// the preserve/destroy behavior of the `if` and `else` blocks.
///
/// # Examples
///
/// This demonstrates the use of `if_atomic!` to produce multiple statements,
/// and then to produce a single type-name.
///
/// ```rust
/// radium::if_atomic! {
///   if atomic(size) { use core::sync::atomic::AtomicUsize; }
///   if !atomic(size) { use core::cell::Cell; }
/// }
///
/// struct RadiumRc<T: ?Sized> {
///   strong: radium::if_atomic! {
///     if atomic(ptr) { AtomicUsize }
///     else { Cell<usize> }
///   },
///   weak: radium::types::RadiumUsize,
///   data: T,
/// }
/// ```
#[macro_export]
macro_rules! if_atomic {
    ( if atomic(8) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::__radium_if_atomic_8! {
            [ $($a)* ] [ $( $($b)* )? ]
        }
        $($crate::if_atomic! { if $($rest)* })?
    };

    ( if atomic(16) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::__radium_if_atomic_16! {
            [ $($a)* ] [ $( $($b)* )? ]
        }
        $( $crate::if_atomic! { if $($rest)* } )?
    };

    ( if atomic(32) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::__radium_if_atomic_32! {
            [ $($a)* ] [ $( $($b)* )? ]
        }
        $( $crate::if_atomic! { if $($rest)* } )?
    };

    ( if atomic(64) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::__radium_if_atomic_64! {
            [ $($a)* ] [ $( $($b)* )? ]
        }
        $( $crate::if_atomic! { if $($rest)* } )?
    };

    ( if atomic(ptr) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::__radium_if_atomic_ptr! {
            [ $($a)* ] [ $( $($b)* )? ]
        }
        $( $crate::if_atomic! { if $($rest)* } )?
    };

    ( if atomic(bool) $($rest:tt)* ) => {
        $crate::if_atomic! { if atomic(8) $($rest)* }
    };

    ( if atomic(size) $($rest:tt)* ) => {
        $crate::if_atomic! { if atomic(ptr) $($rest)* }
    };

    ( if ! atomic( $t:tt ) { $($a:tt)* } $( else { $($b:tt)* } )? $( if $($rest:tt)* )? ) => {
        $crate::if_atomic! {
            if atomic($t) { $( $($b)* )? } else { $($a)* } $( if $($rest)* )?
        }
    };
}