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#![feature(proc_macro_diagnostic)]

//! You probably want documentation for the [`hotpatch`](https://docs.rs/hotpatch) crate.

use proc_macro::TokenStream;
use syn::{ItemFn, parse::Nothing, Path};
use std::sync::RwLock;
use quote::ToTokens;

mod item_fn;

lazy_static::lazy_static! {
    static ref EXPORTNUM: RwLock<usize> = RwLock::new(0);
}

/// Transforms a function into a [`Patchable`](struct.Patchable.html) capable of having
/// its behavior redefined at runtime.
///
/// Takes a single optional arguement: `modpath`. Used to spoof the module
/// path.
///
/// ## Example
/// ```
/// #[patchable]
/// fn foo() {}
///
/// #[patchable(mymod::baz)] // will look for the function ::mymod::baz instead of ::bar
/// fn bar() {
///   foo(); // foo is callable, just as a functor
/// }
/// ```
#[proc_macro_attribute]
pub fn patchable(attr: TokenStream, input: TokenStream) -> TokenStream {
    let modpath = get_modpath(attr);
    if modpath.is_err() {
	return TokenStream::new();
    }
    if let Ok(fn_item) = syn::parse::<ItemFn>(input) {
	item_fn::patchable(fn_item, modpath.unwrap())
    } else {
	panic!("I can't hotpatch this yet!");
    }
}

/// Transforms a function into a [`HotpatchExport`](struct.HotpatchExport.html) capable of
/// being exported and changing the behavior of a function in a seperate binary
/// at runtime. **The original function is preserved.** 
///
/// Takes a single optional arguement: `modpath`. Used to spoof the module
/// path.
///
/// ## Example
/// ```
/// #[patch]
/// fn foo() {}
///
/// #[patch(mymod::baz)] // looks like: mod mymod { fn baz() {} }
/// fn bar() {
///   foo(); // can still call foo
/// }
/// ```
#[proc_macro_attribute]
pub fn patch(attr: TokenStream, input: TokenStream) -> TokenStream {
    let modpath = get_modpath(attr);
    if modpath.is_err() {
	return TokenStream::new();
    }
    if let Ok(fn_item) = syn::parse::<ItemFn>(input) {
	item_fn::patch(fn_item, modpath.unwrap())
    } else {
	panic!("I can't patch this yet!");
    }
}

fn get_modpath(attr: TokenStream) -> Result<Option<String>, ()> {
    if syn::parse::<Nothing>(attr.clone()).is_ok() {
	Ok(None)
    } else {
	let path = syn::parse::<Path>(attr.clone());
	if path.is_err() {
	    proc_macro::Span::call_site().error("Expected module path")
		.help("Just use #[patchable]; it's already module aware.")
		.help("If you're trying to spoof a module path, the supplied arguement is an invalid path")
		.emit();
	    return Err(());
	}
	let mut ts = syn::export::TokenStream2::new();
	path.unwrap().to_tokens(&mut ts);
	Ok(Some(ts.to_string().replace(" ", "")))
    }
}