// force-host

#![feature(plugin_registrar)]
#![feature(box_syntax)]
#![feature(rustc_private)]

extern crate syntax;
extern crate syntax_ext;
extern crate syntax_pos;
extern crate rustc;
extern crate rustc_plugin;

use syntax::ast;
use syntax::ext::base::{MultiDecorator, ExtCtxt, Annotatable};
use syntax::ext::build::AstBuilder;
use syntax::symbol::Symbol;
use syntax_ext::deriving::generic::{cs_fold, TraitDef, MethodDef, combine_substructure};
use syntax_ext::deriving::generic::ty::{Literal, LifetimeBounds, Path, borrowed_explicit_self};
use syntax_pos::Span;
use rustc_plugin::Registry;

#[plugin_registrar]
pub fn plugin_registrar(reg: &mut Registry) {
    reg.register_syntax_extension(
        Symbol::intern("derive_TotalSum"),
        MultiDecorator(box expand));

    reg.register_syntax_extension(
        Symbol::intern("derive_Nothing"),
        MultiDecorator(box noop));
}

fn noop(_: &mut ExtCtxt, _: Span, _: &ast::MetaItem, _: &Annotatable, _: &mut FnMut(Annotatable)) {}

fn expand(cx: &mut ExtCtxt,
          span: Span,
          mitem: &ast::MetaItem,
          item: &Annotatable,
          push: &mut FnMut(Annotatable)) {
    let trait_def = TraitDef {
        span: span,
        attributes: vec![],
        path: Path::new_local("TotalSum"),
        additional_bounds: vec![],
        generics: LifetimeBounds::empty(),
        associated_types: vec![],
        is_unsafe: false,
        supports_unions: false,
        methods: vec![
            MethodDef {
                name: "total_sum",
                generics: LifetimeBounds::empty(),
                explicit_self: borrowed_explicit_self(),
                args: vec![],
                ret_ty: Literal(Path::new_local("isize")),
                attributes: vec![],
                is_unsafe: false,
                unify_fieldless_variants: true,
                combine_substructure: combine_substructure(box |cx, span, substr| {
                    let zero = cx.expr_isize(span, 0);
                    cs_fold(false,
                            |cx, span, subexpr, field, _| {
                                cx.expr_binary(span, ast::BinOpKind::Add, subexpr,
                                    cx.expr_method_call(span, field,
                                        ast::Ident::from_str("total_sum"), vec![]))
                            },
                            zero,
                            box |cx, span, _, _| { cx.span_bug(span, "wtf??"); },
                            cx, span, substr)
                }),
            },
        ],
    };

    trait_def.expand(cx, mitem, item, push)
}