extern crate proc_macro;
extern crate syn;
#[macro_use]
extern crate quote;

use proc_macro::TokenStream;

#[proc_macro_derive(MakeSingleton)]
pub fn hello_world(input: TokenStream) -> TokenStream {
    // Construct a string representation of the type definition
    let s = input.to_string();

    // Parse the string representation
    let ast = syn::parse_derive_input(&s).unwrap();

    // Build the impl
    let gen = impl_make_singelton(&ast);

    // Return the generated impl
    gen.parse().unwrap()
}

fn impl_make_singelton(ast: &syn::DeriveInput) -> quote::Tokens {
    let name = &ast.ident;
    quote! {

        pub trait MakeSingletonTrait<T> {
            fn instance_thread_safe() -> Arc<Mutex<T>>;
            fn instance_ptr() -> *const T;
        }


        impl MakeSingletonTrait<#name> for #name {
            fn instance_thread_safe() -> Arc<Mutex<#name>> {
                unsafe {
                    static mut INSTANCE: *const Arc<Mutex<#name>> = 0 as *const Arc<Mutex<#name>>;
                    static ONCE: Once = Once::new();

                    ONCE.call_once(||{
                        let tmp_instance = Arc::new(Mutex::new(#name{}));
                        INSTANCE = mem::transmute(#name::instance_ptr());
                    });

                    (*INSTANCE).clone()
                }
            }

            fn instance_ptr() -> *const #name {
                unsafe {
                    static mut INSTANCE: *const #name = 0 as *const #name;
                    static ONCE: Once = Once::new();

                    ONCE.call_once(||{
                        let tmp_instance = #name{};
                        INSTANCE = mem::transmute(Box::new(tmp_instance));
                    });
                    INSTANCE
                }
            }
        }
    }
}