// Copyright 2015-2020 Parity Technologies (UK) Ltd.
// This file is part of OpenEthereum.

// OpenEthereum is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// OpenEthereum is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with OpenEthereum.  If not, see <http://www.gnu.org/licenses/>.

use proc_macro2::{Span, TokenStream};
use syn;

pub fn impl_encodable(ast: &syn::DeriveInput) -> TokenStream {
    let body = match ast.data {
        syn::Data::Struct(ref s) => s,
        _ => panic!("#[derive(RlpEncodable)] is only defined for structs."),
    };

    let stmts: Vec<_> = body
        .fields
        .iter()
        .enumerate()
        .map(encodable_field_map)
        .collect();
    let name = &ast.ident;

    let stmts_len = stmts.len();
    let stmts_len = quote! { #stmts_len };
    let dummy_const = syn::Ident::new(
        &format!("_IMPL_RLP_ENCODABLE_FOR_{}", name),
        Span::call_site(),
    );
    let impl_block = quote! {
        impl rlp::Encodable for #name {
            fn rlp_append(&self, stream: &mut rlp::RlpStream) {
                stream.begin_list(#stmts_len);
                #(#stmts)*
            }
        }
    };

    quote! {
        #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
        const #dummy_const: () = {
            extern crate rlp;
            #impl_block
        };
    }
}

pub fn impl_encodable_wrapper(ast: &syn::DeriveInput) -> TokenStream {
    let body = match ast.data {
        syn::Data::Struct(ref s) => s,
        _ => panic!("#[derive(RlpEncodableWrapper)] is only defined for structs."),
    };

    let stmt = {
        let fields: Vec<_> = body.fields.iter().collect();
        if fields.len() == 1 {
            let field = fields.first().expect("fields.len() == 1; qed");
            encodable_field(0, field)
        } else {
            panic!("#[derive(RlpEncodableWrapper)] is only defined for structs with one field.")
        }
    };

    let name = &ast.ident;

    let dummy_const = syn::Ident::new(
        &format!("_IMPL_RLP_ENCODABLE_FOR_{}", name),
        Span::call_site(),
    );
    let impl_block = quote! {
        impl rlp::Encodable for #name {
            fn rlp_append(&self, stream: &mut rlp::RlpStream) {
                #stmt
            }
        }
    };

    quote! {
        #[allow(non_upper_case_globals, unused_attributes, unused_qualifications)]
        const #dummy_const: () = {
            extern crate rlp;
            #impl_block
        };
    }
}

fn encodable_field_map(tuple: (usize, &syn::Field)) -> TokenStream {
    encodable_field(tuple.0, tuple.1)
}

fn encodable_field(index: usize, field: &syn::Field) -> TokenStream {
    let ident = match field.ident {
        Some(ref ident) => quote! { #ident },
        None => {
            let index: syn::Index = index.into();
            quote! { #index }
        }
    };

    let id = quote! { self.#ident };

    match field.ty {
        syn::Type::Path(ref path) => {
            let top_segment = path
                .path
                .segments
                .first()
                .expect("there must be at least 1 segment");
            let ident = &top_segment.value().ident;
            if &ident.to_string() == "Vec" {
                let inner_ident = match top_segment.value().arguments {
                    syn::PathArguments::AngleBracketed(ref angle) => {
                        let ty = angle
                            .args
                            .first()
                            .expect("Vec has only one angle bracketed type; qed");
                        match **ty.value() {
                            syn::GenericArgument::Type(syn::Type::Path(ref path)) => {
                                &path
                                    .path
                                    .segments
                                    .first()
                                    .expect("there must be at least 1 segment")
                                    .value()
                                    .ident
                            }
                            _ => panic!("rlp_derive not supported"),
                        }
                    }
                    _ => unreachable!("Vec has only one angle bracketed type; qed"),
                };
                quote! { stream.append_list::<#inner_ident, _>(&#id); }
            } else {
                quote! { stream.append(&#id); }
            }
        }
        _ => panic!("rlp_derive not supported"),
    }
}
