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use std::fmt;
use std::str::FromStr;
use std::time::Instant;

/// Absolute time.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Time(f64);

impl Time {
    /// Convert into seconds.
    pub fn as_secs(self) -> f64 {
        self.0
    }

    /// Wrap time with a given duration.
    pub fn wrap_around(self, t: Time) -> Self {
        Time(self.0 % t.0)
    }

    /// Offset a time by a given amount of time.
    pub fn offset(self, t: Time) -> Self {
        Time(self.0 + t.0)
    }
}

impl fmt::Display for Time {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        self.0.fmt(f)
    }
}

impl From<DurationSpec> for Time {
    fn from(spec: DurationSpec) -> Self {
        Time(spec.mins as f64 * 60. + spec.secs as f64)
    }
}

/// Monotonic time.
#[derive(Clone, Copy, Debug, PartialEq)]
pub struct Monotonic(Instant);

impl Monotonic {
    pub fn now() -> Self {
        Monotonic(Instant::now())
    }

    pub fn elapsed_secs(&self) -> Time {
        let dur = self.0.elapsed();
        let secs = dur.as_secs() as f64;
        let nanos = dur.subsec_nanos() as f64;

        Time(secs + nanos * 1e-9)
    }
}

/// A way to specify a duration with minutes and seconds.
///
/// The string format is the following:
///
///   - `MmSs`, if you want minutes (e.g. `3m43s`).
///   - `Ss`, if you only have seconds (e.g. `23s`).
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub struct DurationSpec {
    mins: u8,
    secs: u8,
}

impl Default for DurationSpec {
    fn default() -> Self {
        DurationSpec { mins: 0, secs: 0 }
    }
}

impl FromStr for DurationSpec {
    type Err = DurationSpecError;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if !s.ends_with('s') {
            if s.ends_with('m') {
                // only minutes
                let mins = s
                    .trim_end_matches('m')
                    .parse()
                    .map_err(|_| DurationSpecError::CannotParseMinutes)?;

                Ok(DurationSpec { mins, secs: 0 })
            } else {
                Err(DurationSpecError::MissingSecondsSuffix)
            }
        } else if s.contains('m') {
            // the first argument represents minutes, so let’s take them out first
            let mut iter = s.split('m');
            let mins = iter
                .next()
                .and_then(|x| x.parse().ok())
                .ok_or(DurationSpecError::CannotParseMinutes)?;
            let secs = iter
                .next()
                .and_then(|x| x.trim_end_matches('s').parse().ok())
                .ok_or(DurationSpecError::CannotParseSeconds)?;

            Ok(DurationSpec { mins, secs })
        } else {
            // only seconds
            let secs = s
                .trim_end_matches('s')
                .parse()
                .map_err(|_| DurationSpecError::CannotParseSeconds)?;

            Ok(DurationSpec { mins: 0, secs })
        }
    }
}

/// Possible error than can occurr while parsing a `DurationSpec` from a string.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum DurationSpecError {
    MissingSecondsSuffix,
    CannotParseMinutes,
    CannotParseSeconds,
}

impl fmt::Display for DurationSpecError {
    fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
        match *self {
            DurationSpecError::MissingSecondsSuffix => f.write_str("missing the seconds suffix"),
            DurationSpecError::CannotParseMinutes => f.write_str("cannot parse minutes"),
            DurationSpecError::CannotParseSeconds => f.write_str("cannot parse seconds"),
        }
    }
}

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

    #[test]
    fn parse_duration_spec() {
        assert_eq!(
            "1s".parse::<DurationSpec>().unwrap(),
            DurationSpec { mins: 0, secs: 1 }
        );
        assert_eq!(
            "2m".parse::<DurationSpec>().unwrap(),
            DurationSpec { mins: 2, secs: 0 }
        );
        assert_eq!(
            "3m12s".parse::<DurationSpec>().unwrap(),
            DurationSpec { mins: 3, secs: 12 }
        );
        assert_eq!(
            "3m12".parse::<DurationSpec>(),
            Err(DurationSpecError::MissingSecondsSuffix)
        );
    }
}