use deriving::{self, pathvec_std, path_std};
use deriving::generic::*;
use deriving::generic::ty::*;

use syntax::ast::{Expr, MetaItem, Mutability};
use syntax::ext::base::{Annotatable, ExtCtxt};
use syntax::ext::build::AstBuilder;
use syntax::ptr::P;
use syntax_pos::Span;

pub fn expand_deriving_hash(cx: &mut ExtCtxt,
                            span: Span,
                            mitem: &MetaItem,
                            item: &Annotatable,
                            push: &mut dyn FnMut(Annotatable)) {

    let path = Path::new_(pathvec_std!(cx, hash::Hash), None, vec![], PathKind::Std);

    let typaram = &*deriving::hygienic_type_parameter(item, "__H");

    let arg = Path::new_local(typaram);
    let hash_trait_def = TraitDef {
        span,
        attributes: Vec::new(),
        path,
        additional_bounds: Vec::new(),
        generics: LifetimeBounds::empty(),
        is_unsafe: false,
        supports_unions: false,
        methods: vec![MethodDef {
                          name: "hash",
                          generics: LifetimeBounds {
                              lifetimes: Vec::new(),
                              bounds: vec![(typaram, vec![path_std!(cx, hash::Hasher)])],
                          },
                          explicit_self: borrowed_explicit_self(),
                          args: vec![(Ptr(Box::new(Literal(arg)),
                                         Borrowed(None, Mutability::Mutable)), "state")],
                          ret_ty: nil_ty(),
                          attributes: vec![],
                          is_unsafe: false,
                          unify_fieldless_variants: true,
                          combine_substructure: combine_substructure(Box::new(|a, b, c| {
                              hash_substructure(a, b, c)
                          })),
                      }],
        associated_types: Vec::new(),
    };

    hash_trait_def.expand(cx, mitem, item, push);
}

fn hash_substructure(cx: &mut ExtCtxt, trait_span: Span, substr: &Substructure) -> P<Expr> {
    let state_expr = match (substr.nonself_args.len(), substr.nonself_args.get(0)) {
        (1, Some(o_f)) => o_f,
        _ => {
            cx.span_bug(trait_span,
                        "incorrect number of arguments in `derive(Hash)`")
        }
    };
    let call_hash = |span, thing_expr| {
        let hash_path = {
            let strs = cx.std_path(&["hash", "Hash", "hash"]);

            cx.expr_path(cx.path_global(span, strs))
        };
        let ref_thing = cx.expr_addr_of(span, thing_expr);
        let expr = cx.expr_call(span, hash_path, vec![ref_thing, state_expr.clone()]);
        cx.stmt_expr(expr)
    };
    let mut stmts = Vec::new();

    let fields = match *substr.fields {
        Struct(_, ref fs) | EnumMatching(_, 1, .., ref fs) => fs,
        EnumMatching(.., ref fs) => {
            let variant_value = deriving::call_intrinsic(cx,
                                                         trait_span,
                                                         "discriminant_value",
                                                         vec![cx.expr_self(trait_span)]);

            stmts.push(call_hash(trait_span, variant_value));

            fs
        }
        _ => cx.span_bug(trait_span, "impossible substructure in `derive(Hash)`"),
    };

    stmts.extend(fields.iter().map(|FieldInfo { ref self_, span, .. }|
        call_hash(*span, self_.clone())));

    cx.expr_block(cx.block(trait_span, stmts))
}
