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    use std::fmt;

    use once_cell::sync::Lazy;
    use regex::Regex;
    use serde::de;

    use crate::{AsResult, Error, Parse};

    /// A timeout duration in milliseconds or seconds.
    #[derive(Debug, Clone, PartialEq, Eq, Hash)]
    pub enum Timeout {
        /// The default timeout. Depends on context.
        Default,

        /// Timeout in milliseconds.
        Milliseconds(usize),

        /// Timeout in seconds.
        Seconds(usize),
    }

    impl Parse for Timeout {
        fn parse(string: &str) -> AsResult<Self> {
            pub static FMT: Lazy<Regex> = Lazy::new(|| {
                Regex::new(r"^\d+ (milliseconds|seconds)$").expect("Failed to compile regex: FMT")
            });

            pub static DIGITS: Lazy<Regex> =
                Lazy::new(|| Regex::new(r"^\d+").expect("Failed to compile regex: DIGITS"));

            pub static UNIT: Lazy<Regex> = Lazy::new(|| {
                Regex::new(r"(milliseconds|seconds)$").expect("Failed to compile regex: UNIT")
            });

            macro_rules! invalid_value {
                ($got:expr) => {
                    Err(InvalidValue! {
                        expected: "a string of the format \"N seconds\" or \"N milliseconds\" where N is an integer > 0",
                        got: $got,
                    })
                }
            }

            match string {
                "default" => Ok(Timeout::Default),

                string if !FMT.is_match(string) => invalid_value!(string),

                string => match (DIGITS.find(string), UNIT.find(string)) {
                    (None, _) | (_, None) => invalid_value!(string),

                    (Some(digits), Some(unit)) => {
                        let digits = &string[digits.range()];
                        let unit = &string[unit.range()];

                        match (digits.parse(), unit) {
                            (Ok(n), "milliseconds") => Ok(Timeout::Milliseconds(n)),
                            (Ok(n), "seconds") => Ok(Timeout::Seconds(n)),
                            _ => invalid_value!(string),
                        }
                    }
                },
            }
        }
    }

    impl<'de> de::Deserialize<'de> for Timeout {
        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
        where
            D: de::Deserializer<'de>,
        {
            struct TimeoutVisitor;

            impl<'de> de::Visitor<'de> for TimeoutVisitor {
                type Value = Timeout;

                fn expecting(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
                    let msg = "Either \"default\", \"disabled\", \"os\", or a string of the format \"N seconds\" where N is an integer > 0";
                    f.write_str(msg)
                }

                fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
                where
                    E: de::Error,
                {
                    match Timeout::parse(value) {
                        Ok(num_workers) => Ok(num_workers),
                        Err(Error::InvalidValue { expected, got, .. }) => Err(
                            de::Error::invalid_value(de::Unexpected::Str(&got), &expected),
                        ),
                        Err(_) => unreachable!(),
                    }
                }
            }

            deserializer.deserialize_string(TimeoutVisitor)
        }
    }