use syn;
use quote;

pub fn build(ast: &syn::DeriveInput) -> quote::Tokens {
	let fields = match ast.body {
		syn::Body::Enum(_) => panic!("Deriving DnsPacketData not supported for enum types"),
		syn::Body::Struct(syn::VariantData::Struct(ref s)) => s,
		syn::Body::Struct(_) => panic!("Deriving DnsPacketData not supported for unit / tuple struct types"),
	};

	if !ast.generics.ty_params.is_empty() {
		panic!("Type parameters not supported for deriving DnsPacketData");
	}

	if !ast.generics.where_clause.predicates.is_empty() {
		panic!("Where clauses not supported for deriving DnsPacketData");
	}

	if !ast.generics.lifetimes.is_empty() {
		panic!("Lifetimes not supported for deriving DnsPacketData");
	}

	let name = &ast.ident;

	let mut parse_fields = quote!{};
	for field in fields {
		let field_name = field.ident.as_ref().unwrap();
		let ctx_msg = format!("failed parsing field {}::{}", name, field_name);

		parse_fields = quote!{#parse_fields
			#field_name: DnsPacketData::deserialize(_data).context(#ctx_msg)?,
		};
	}

	quote!{
		impl ::dnsbox_base::ser::DnsPacketData for #name {
			#[allow(unused_imports)]
			fn deserialize(_data: &mut ::std::io::Cursor<::dnsbox_base::bytes::Bytes>) -> ::dnsbox_base::errors::Result<Self> {
				use ::dnsbox_base::failure::ResultExt;
				use ::dnsbox_base::ser::DnsPacketData;
				Ok(#name{ #parse_fields })
			}
		}
	}
}