//! Common builder types shared across all builders
//!
//! Generates the Set, Unset, IsSet, IsUnset types that all builders use.
//! These are generated once per crate and re-used by all builders.

use proc_macro2::TokenStream;
use quote::quote;

/// Generate the common builder types module
///
/// This should be generated once at the root of the generated code
/// (e.g., in lib.rs or a builder_types module).
pub fn generate_common_types() -> TokenStream {
    quote! {
        /// Marker type indicating a builder field has been set
        pub struct Set<T>(pub T);

        impl<T> Set<T> {
            /// Extract the inner value
            #[inline]
            pub fn into_inner(self) -> T {
                self.0
            }
        }

        /// Marker type indicating a builder field has not been set
        pub struct Unset;

        /// Trait indicating a builder field is set (has a value)
        #[rustversion::attr(
            since(1.78.0),
            diagnostic::on_unimplemented(
                message = "the field `{Self}` was not set, but this method requires it to be set",
                label = "the field `{Self}` was not set"
            )
        )]
        pub trait IsSet: private::Sealed {}

        /// Trait indicating a builder field is unset (no value yet)
        #[rustversion::attr(
            since(1.78.0),
            diagnostic::on_unimplemented(
                message = "the field `{Self}` was already set, but this method requires it to be unset",
                label = "the field `{Self}` was already set"
            )
        )]
        pub trait IsUnset: private::Sealed {}

        impl<T> IsSet for Set<T> {}
        impl IsUnset for Unset {}

        mod private {
            /// Sealed trait to prevent external implementations
            pub trait Sealed {}
            impl<T> Sealed for super::Set<T> {}
            impl Sealed for super::Unset {}
        }
    }
}