use syn;
use quote;

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

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

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

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

	let name = &ast.ident;

	let mut parse_fields = quote!{};
	let mut format_fields = quote!{};
	for field in fields {
		let field_name = field.ident.as_ref().unwrap();

		parse_fields = quote!{#parse_fields
			#field_name: DnsTextData::dns_parse(_context, _data).with_context(|_| format!("failed parsing field {}::{}", stringify!(#name), stringify!(#field_name)))?,
		};

		format_fields = quote!{#format_fields
			DnsTextData::dns_format(&self.#field_name, f)?;
		};
	}

	quote!{
		#[allow(unused_imports)]
		impl ::dnsbox_base::ser::text::DnsTextData for #name {
			fn dns_parse(_context: &::dnsbox_base::ser::text::DnsTextContext, _data: &mut &str) -> ::dnsbox_base::errors::Result<Self> {
				use dnsbox_base::failure::ResultExt;
				use dnsbox_base::ser::text::DnsTextData;
				Ok(#name{ #parse_fields })
			}

			fn dns_format(&self, f: &mut ::dnsbox_base::ser::text::DnsTextFormatter) -> ::std::fmt::Result {
				use dnsbox_base::ser::text::DnsTextData;
				use std::fmt::{self, Write};
				#format_fields
				Ok(())
			}
		}
	}
}