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extern crate proc_macro;
extern crate proc_macro2;
extern crate quote;
extern crate syn;

use std::mem;

use proc_macro::TokenStream;
use quote::quote;
use syn::{
    parse::{Parse, Parser},
    spanned::Spanned,
    parse_quote,
};


#[proc_macro_attribute]
pub fn quickcheck(_args: TokenStream, input: TokenStream) -> TokenStream {
    let output = match syn::Item::parse.parse(input.clone()) {
        Ok(syn::Item::Fn(mut item_fn)) => {
            let mut inputs = syn::punctuated::Punctuated::new();
            let mut errors = Vec::new();

            item_fn.decl.inputs.iter().for_each(|input| match *input {
                syn::FnArg::Captured(syn::ArgCaptured { ref ty, .. }) => {
                    inputs.push(parse_quote!(_: #ty));
                },
                _ => {
                    errors.push(syn::parse::Error::new(
                        input.span(),
                        "unsupported kind of function argument",
                    ))
                },
            });

            if errors.is_empty() {
                let attrs = mem::replace(&mut item_fn.attrs, Vec::new());
                let name = &item_fn.ident;
                let fn_type = syn::TypeBareFn {
                    lifetimes: None,
                    unsafety: item_fn.unsafety.clone(),
                    abi: item_fn.abi.clone(),
                    fn_token: <syn::Token![fn]>::default(),
                    paren_token: syn::token::Paren::default(),
                    inputs,
                    variadic: item_fn.decl.variadic.clone(),
                    output: item_fn.decl.output.clone(),
                };

                quote! {
                    #[test]
                    #(#attrs)*
                    fn #name() {
                        #item_fn
                       ::quickcheck::quickcheck(#name as #fn_type)
                    }
                }
            } else {
                errors.iter().map(syn::parse::Error::to_compile_error).collect()
            }
        },
        Ok(syn::Item::Static(mut item_static)) => {
            let attrs = mem::replace(&mut item_static.attrs, Vec::new());
            let name = &item_static.ident;

            quote! {
                #[test]
                #(#attrs)*
                fn #name() {
                    #item_static
                    ::quickcheck::quickcheck(#name)
                }
            }
        },
        _ => {
            let span = proc_macro2::TokenStream::from(input).span();
            let msg = "#[quickcheck] is only supported on statics and functions";

            syn::parse::Error::new(span, msg).to_compile_error()
        }
    };

    output.into()
}