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use std::fmt;

/// The `Expect` header.
///
/// > The "Expect" header field in a request indicates a certain set of
/// > behaviors (expectations) that need to be supported by the server in
/// > order to properly handle this request.  The only such expectation
/// > defined by this specification is 100-continue.
/// >
/// >    Expect  = "100-continue"
///
/// # Example
///
/// ```
/// # extern crate headers_ext as headers;
/// use headers::Expect;
///
/// let expect = Expect::CONTINUE;
/// ```
#[derive(Clone, PartialEq)]
pub struct Expect(());

impl Expect {
    /// "100-continue"
    pub const CONTINUE: Expect = Expect(());
}

impl ::Header for Expect {
    const NAME: &'static ::HeaderName = &::http::header::EXPECT;

    fn decode(values: &mut ::Values) -> Option<Expect> {
        if values.next()? == "100-continue" {
            Some(Expect::CONTINUE)
        } else {
            None
        }
    }

    fn encode(&self, values: &mut ::ToValues) {
        values.append(::HeaderValue::from_static("100-continue"));
    }
}

impl fmt::Debug for Expect {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        f.debug_tuple("Expect")
            .field(&"100-continue")
            .finish()
    }
}

#[cfg(test)]
mod tests {
    use super::Expect;
    use super::super::test_decode;

    #[test]
    fn expect_continue() {
        assert_eq!(
            test_decode::<Expect>(&["100-continue"]),
            Some(Expect::CONTINUE),
        );
    }

    #[test]
    fn expectation_failed() {
        assert_eq!(
            test_decode::<Expect>(&["sandwich"]),
            None,
        );
    }

    #[test]
    fn too_many_values() {
        assert_eq!(
            test_decode::<Expect>(&["100-continue", "100-continue"]),
            None,
        );
    }
}