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use std::fmt::{self, Display};
use header::{self, Header, HeaderFormat, EntityTag, HttpDate};

/// `If-Range` header, defined in [RFC7233](http://tools.ietf.org/html/rfc7233#section-3.2)
///
/// If a client has a partial copy of a representation and wishes to have
/// an up-to-date copy of the entire representation, it could use the
/// Range header field with a conditional GET (using either or both of
/// If-Unmodified-Since and If-Match.)  However, if the precondition
/// fails because the representation has been modified, the client would
/// then have to make a second request to obtain the entire current
/// representation.
///
/// The `If-Range` header field allows a client to \"short-circuit\" the
/// second request.  Informally, its meaning is as follows: if the
/// representation is unchanged, send me the part(s) that I am requesting
/// in Range; otherwise, send me the entire representation.
///
/// # ABNF
/// ```plain
/// If-Range = entity-tag / HTTP-date
/// ```
///
/// # Example values
/// * `Sat, 29 Oct 1994 19:43:31 GMT`
/// * `\"xyzzy\"`
#[derive(Clone, Debug, PartialEq)]
pub enum IfRange {
    /// The entity-tag the client has of the resource
    EntityTag(EntityTag),
    /// The date when the client retrieved the resource
    Date(HttpDate),
}

impl Header for IfRange {
    fn header_name() -> &'static str {
        "If-Range"
    }
    fn parse_header(raw: &[Vec<u8>]) -> Option<IfRange> {
        let etag: Option<EntityTag> = header::parsing::from_one_raw_str(raw);
        if etag != None {
            return Some(IfRange::EntityTag(etag.unwrap()));
        }
        let date: Option<HttpDate> = header::parsing::from_one_raw_str(raw);
        if date != None {
            return Some(IfRange::Date(date.unwrap()));
        }
        None
    }
}

impl HeaderFormat for IfRange {
    fn fmt_header(&self, f: &mut ::std::fmt::Formatter) -> ::std::fmt::Result {
        match self {
            &IfRange::EntityTag(ref x) => Display::fmt(x, f),
            &IfRange::Date(ref x) => Display::fmt(x, f),
        }
    }
}

impl Display for IfRange {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        self.fmt_header(f)
    }
}

#[cfg(test)]
mod test_if_range {
    use std::str;
    use header::*;
    use super::IfRange as HeaderField;
    test_header!(test1, vec![b"Sat, 29 Oct 1994 19:43:31 GMT"]);
    test_header!(test2, vec![b"\"xyzzy\""]);
    test_header!(test3, vec![b"this-is-invalid"], None::<IfRange>);
}