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    use std::cmp;
    use std::default::Default;
    use std::fmt;
    use std::str;

    use self::internal::IntoQuality;

    /// Represents a quality used in quality values.
    ///
    /// Can be created with the `q` function.
    ///
    /// # Implementation notes
    ///
    /// The quality value is defined as a number between 0 and 1 with three decimal
    /// places. This means there are 1001 possible values. Since floating point
    /// numbers are not exact and the smallest floating point data type (`f32`)
    /// consumes four bytes, hyper uses an `u16` value to store the
    /// quality internally. For performance reasons you may set quality directly to
    /// a value between 0 and 1000 e.g. `Quality(532)` matches the quality
    /// `q=0.532`.
    ///
    /// [RFC7231 Section 5.3.1](https://tools.ietf.org/html/rfc7231#section-5.3.1)
    /// gives more information on quality values in HTTP header fields.
    #[derive(Copy, Clone, Debug, Eq, Ord, PartialEq, PartialOrd)]
    pub struct Quality(u16);

    impl Default for Quality {
        fn default() -> Quality {
            Quality(1000)
        }
    }

    /// Represents an item with a quality value as defined in
    /// [RFC7231](https://tools.ietf.org/html/rfc7231#section-5.3.1).
    #[derive(Clone, PartialEq, Debug)]
    pub struct QualityItem<T> {
        /// The actual contents of the field.
        pub item: T,
        /// The quality (client or server preference) for the value.
        pub quality: Quality,
    }

    impl<T> QualityItem<T> {
        /// Creates a new `QualityItem` from an item and a quality.
        /// The item can be of any type.
        /// The quality should be a value in the range [0, 1].
        pub fn new(item: T, quality: Quality) -> QualityItem<T> {
            QualityItem { item, quality }
        }
    }

    impl<T: PartialEq> cmp::PartialOrd for QualityItem<T> {
        fn partial_cmp(&self, other: &QualityItem<T>) -> Option<cmp::Ordering> {
            self.quality.partial_cmp(&other.quality)
        }
    }

    impl<T: fmt::Display> fmt::Display for QualityItem<T> {
        fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
            fmt::Display::fmt(&self.item, f)?;
            match self.quality.0 {
                1000 => Ok(()),
                0 => f.write_str("; q=0"),
                x => write!(f, "; q=0.{}", format!("{:03}", x).trim_right_matches('0')),
            }
        }
    }

    impl<T: str::FromStr> str::FromStr for QualityItem<T> {
        type Err = ::error::ParseError;

        fn from_str(s: &str) -> Result<QualityItem<T>, ::error::ParseError> {
            if !s.is_ascii() {
                return Err(::error::ParseError::Header);
            }
            // Set defaults used if parsing fails.
            let mut raw_item = s;
            let mut quality = 1f32;

            let parts: Vec<&str> = s.rsplitn(2, ';').map(|x| x.trim()).collect();
            if parts.len() == 2 {
                if parts[0].len() < 2 {
                    return Err(::error::ParseError::Header);
                }
                let start = &parts[0][0..2];
                if start == "q=" || start == "Q=" {
                    let q_part = &parts[0][2..parts[0].len()];
                    if q_part.len() > 5 {
                        return Err(::error::ParseError::Header);
                    }
                    match q_part.parse::<f32>() {
                        Ok(q_value) => {
                            if 0f32 <= q_value && q_value <= 1f32 {
                                quality = q_value;
                                raw_item = parts[1];
                            } else {
                                return Err(::error::ParseError::Header);
                            }
                        }
                        Err(_) => return Err(::error::ParseError::Header),
                    }
                }
            }
            match raw_item.parse::<T>() {
                // we already checked above that the quality is within range
                Ok(item) => Ok(QualityItem::new(item, from_f32(quality))),
                Err(_) => Err(::error::ParseError::Header),
            }
        }
    }

    #[inline]
    fn from_f32(f: f32) -> Quality {
        // this function is only used internally. A check that `f` is within range
        // should be done before calling this method. Just in case, this
        // debug_assert should catch if we were forgetful
        debug_assert!(
            f >= 0f32 && f <= 1f32,
            "q value must be between 0.0 and 1.0"
        );
        Quality((f * 1000f32) as u16)
    }

    /// Convenience function to wrap a value in a `QualityItem`
    /// Sets `q` to the default 1.0
    pub fn qitem<T>(item: T) -> QualityItem<T> {
        QualityItem::new(item, Default::default())
    }

    /// Convenience function to create a `Quality` from a float or integer.
    ///
    /// Implemented for `u16` and `f32`. Panics if value is out of range.
    pub fn q<T: IntoQuality>(val: T) -> Quality {
        val.into_quality()
    }

    mod internal {
        use super::Quality;

        // TryFrom is probably better, but it's not stable. For now, we want to
        // keep the functionality of the `q` function, while allowing it to be
        // generic over `f32` and `u16`.
        //
        // `q` would panic before, so keep that behavior. `TryFrom` can be
        // introduced later for a non-panicking conversion.

        pub trait IntoQuality: Sealed + Sized {
            fn into_quality(self) -> Quality;
        }

        impl IntoQuality for f32 {
            fn into_quality(self) -> Quality {
                assert!(
                    self >= 0f32 && self <= 1f32,
                    "float must be between 0.0 and 1.0"
                );
                super::from_f32(self)
            }
        }

        impl IntoQuality for u16 {
            fn into_quality(self) -> Quality {
                assert!(self <= 1000, "u16 must be between 0 and 1000");
                Quality(self)
            }
        }

        pub trait Sealed {}
        impl Sealed for u16 {}
        impl Sealed for f32 {}
    }

    #[cfg(test)]
    mod tests {
        use super::super::encoding::*;
        use super::*;

        #[test]
        fn test_quality_item_fmt_q_1() {
            let x = qitem(Chunked);
            assert_eq!(format!("{}", x), "chunked");
        }
        #[test]
        fn test_quality_item_fmt_q_0001() {
            let x = QualityItem::new(Chunked, Quality(1));
            assert_eq!(format!("{}", x), "chunked; q=0.001");
        }
        #[test]
        fn test_quality_item_fmt_q_05() {
            // Custom value
            let x = QualityItem {
                item: EncodingExt("identity".to_owned()),
                quality: Quality(500),
            };
            assert_eq!(format!("{}", x), "identity; q=0.5");
        }

        #[test]
        fn test_quality_item_fmt_q_0() {
            // Custom value
            let x = QualityItem {
                item: EncodingExt("identity".to_owned()),
                quality: Quality(0),
            };
            assert_eq!(x.to_string(), "identity; q=0");
        }

        #[test]
        fn test_quality_item_from_str1() {
            let x: Result<QualityItem<Encoding>, _> = "chunked".parse();
            assert_eq!(
                x.unwrap(),
                QualityItem {
                    item: Chunked,
                    quality: Quality(1000),
                }
            );
        }
        #[test]
        fn test_quality_item_from_str2() {
            let x: Result<QualityItem<Encoding>, _> = "chunked; q=1".parse();
            assert_eq!(
                x.unwrap(),
                QualityItem {
                    item: Chunked,
                    quality: Quality(1000),
                }
            );
        }
        #[test]
        fn test_quality_item_from_str3() {
            let x: Result<QualityItem<Encoding>, _> = "gzip; q=0.5".parse();
            assert_eq!(
                x.unwrap(),
                QualityItem {
                    item: Gzip,
                    quality: Quality(500),
                }
            );
        }
        #[test]
        fn test_quality_item_from_str4() {
            let x: Result<QualityItem<Encoding>, _> = "gzip; q=0.273".parse();
            assert_eq!(
                x.unwrap(),
                QualityItem {
                    item: Gzip,
                    quality: Quality(273),
                }
            );
        }
        #[test]
        fn test_quality_item_from_str5() {
            let x: Result<QualityItem<Encoding>, _> = "gzip; q=0.2739999".parse();
            assert!(x.is_err());
        }
        #[test]
        fn test_quality_item_from_str6() {
            let x: Result<QualityItem<Encoding>, _> = "gzip; q=2".parse();
            assert!(x.is_err());
        }
        #[test]
        fn test_quality_item_ordering() {
            let x: QualityItem<Encoding> = "gzip; q=0.5".parse().ok().unwrap();
            let y: QualityItem<Encoding> = "gzip; q=0.273".parse().ok().unwrap();
            let comparision_result: bool = x.gt(&y);
            assert!(comparision_result)
        }

        #[test]
        fn test_quality() {
            assert_eq!(q(0.5), Quality(500));
        }

        #[test]
        #[should_panic] // FIXME - 32-bit msvc unwinding broken
        #[cfg_attr(all(target_arch = "x86", target_env = "msvc"), ignore)]
        fn test_quality_invalid() {
            q(-1.0);
        }

        #[test]
        #[should_panic] // FIXME - 32-bit msvc unwinding broken
        #[cfg_attr(all(target_arch = "x86", target_env = "msvc"), ignore)]
        fn test_quality_invalid2() {
            q(2.0);
        }

        #[test]
        fn test_fuzzing_bugs() {
            assert!("99999;".parse::<QualityItem<String>>().is_err());
            assert!("\x0d;;;=\u{d6aa}==".parse::<QualityItem<String>>().is_err())
        }
    }

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