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use chrono::prelude::*;
use failure::{bail, Error};
use serde::{de, ser};
use std::fmt;
use std::str::FromStr;

/// A wrapper type around chrono's DateTime, which supports parsing from WMI-format strings.
///
#[derive(Debug)]
pub struct WMIDateTime(pub DateTime<FixedOffset>);

impl FromStr for WMIDateTime {
    type Err = Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        if s.len() < 21 {
            bail!("Expected {:?} to be at least 21 chars", s)
        }

        let (datetime_part, tz_part) = s.split_at(21);

        let tz_min: i32 = tz_part.parse()?;

        let tz = FixedOffset::east(tz_min * 60);

        let dt = tz.datetime_from_str(datetime_part, "%Y%m%d%H%M%S.%f")?;

        Ok(Self(dt))
    }
}

struct DateTimeVisitor;

impl<'de> de::Visitor<'de> for DateTimeVisitor {
    type Value = WMIDateTime;

    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
        write!(formatter, "a timestamp in WMI format")
    }

    fn visit_str<E>(self, value: &str) -> Result<Self::Value, E>
    where
        E: de::Error,
    {
        value.parse().map_err(|err| E::custom(format!("{}", err)))
    }
}

impl<'de> de::Deserialize<'de> for WMIDateTime {
    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
    where
        D: de::Deserializer<'de>,
    {
        deserializer.deserialize_str(DateTimeVisitor)
    }
}

impl ser::Serialize for WMIDateTime {
    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
    where
        S: ser::Serializer,
    {
        serializer.serialize_str(&self.0.to_rfc3339())
    }
}

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

    #[test]
    fn it_works_with_negative_offset() {
        let dt: WMIDateTime = "20190113200517.500000-180".parse().unwrap();

        assert_eq!(dt.0.to_rfc3339(), "2019-01-13T20:05:17.000500-03:00");
    }

    #[test]
    fn it_works_with_positive_offset() {
        let dt: WMIDateTime = "20190113200517.500000+060".parse().unwrap();

        assert_eq!(dt.0.to_rfc3339(), "2019-01-13T20:05:17.000500+01:00");
    }

    #[test]
    fn it_fails_with_malformed_str() {
        let dt_res: Result<WMIDateTime, _> = "20190113200517".parse();

        assert!(dt_res.is_err());
    }

    #[test]
    fn it_fails_with_malformed_str_with_no_tz() {
        let dt_res: Result<WMIDateTime, _> = "20190113200517.000500".parse();

        assert!(dt_res.is_err());
    }

    #[test]
    fn it_serializes_to_rfc() {
        let dt: WMIDateTime = "20190113200517.500000+060".parse().unwrap();

        let v = serde_json::to_string(&dt).unwrap();
        assert_eq!(v, "\"2019-01-13T20:05:17.000500+01:00\"");
    }
}