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use serde::ser::{Serialize, Serializer};
use std::time::{Duration, SystemTime, UNIX_EPOCH};

/// A timestamp which anchors the profile in absolute time.
///
/// In the profile JSON, this uses a UNIX timestamp.
///
/// All timestamps in the profile are relative to this reference timestamp.
#[derive(Debug, Clone, Copy, PartialOrd, PartialEq)]
pub struct ReferenceTimestamp {
    ms_since_unix_epoch: f64,
}

impl ReferenceTimestamp {
    /// Create a reference timestamp from a [`Duration`] since the UNIX epoch.
    pub fn from_duration_since_unix_epoch(duration: Duration) -> Self {
        Self::from_millis_since_unix_epoch(duration.as_secs_f64() * 1000.0)
    }

    /// Create a reference timestamp from milliseconds since the UNIX epoch.
    pub fn from_millis_since_unix_epoch(ms_since_unix_epoch: f64) -> Self {
        Self {
            ms_since_unix_epoch,
        }
    }

    /// Create a reference timestamp from a [`SystemTime`].
    pub fn from_system_time(system_time: SystemTime) -> Self {
        Self::from_duration_since_unix_epoch(system_time.duration_since(UNIX_EPOCH).unwrap())
    }
}

impl From<SystemTime> for ReferenceTimestamp {
    fn from(system_time: SystemTime) -> Self {
        Self::from_system_time(system_time)
    }
}

impl Serialize for ReferenceTimestamp {
    fn serialize<S: Serializer>(&self, serializer: S) -> Result<S::Ok, S::Error> {
        self.ms_since_unix_epoch.serialize(serializer)
    }
}