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#![feature(associated_consts)]
extern crate rocket;

use rocket::request::{FromForm, FormItems};

/// This trait is used to get the names of the fields of the structures.
pub trait NamedFields {
    const FIELDS: &'static [&'static str];
}

pub struct QueryParamGroup<T>(T);

impl<T> QueryParamGroup<T> {
    pub fn get(&self) -> &T {
        &self.0
    }

    pub fn get_owned(self) -> T {
        self.0
    }
}

macro_rules! peel {
    ($name:ident, $($other:ident,)*) => (query_param_group! { $($other,)* })
}

macro_rules! query_param_group {
  () => {};
  ($($name:ident,)+) => {
    impl<'f, $($name),*> FromForm<'f> for QueryParamGroup<($($name,)*)>
      where $($name: for<'x> FromForm<'x> + NamedFields),*
    {
      type Error = ();
      fn from_form_items(form_items: &mut FormItems<'f>) -> Result<Self, ()> {
        $(
          let query_string_items: Vec<String> = FormItems::from(form_items.inner_str())
            .filter(|&(ref k, _)| $name::FIELDS.contains(k))
            .map(|(k,v)| format!("{}={}", k, v))
            .collect();

          let query_string = query_string_items.join("&");
          let mut items: FormItems = FormItems::from(query_string.as_str());

          #[allow(non_snake_case)]
          let $name = $name::from_form_items(&mut items).map_err(|_| ())?;
        )*
        Ok(QueryParamGroup(($($name,)*)))
      }
    }

    peel! { $($name,)* }
  }
}

query_param_group! { T0, T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, }