//! Formatters for event timestamps.
use crate::fmt::format::Writer;
use std::fmt;
use std::time::Instant;

mod datetime;

#[cfg(feature = "time")]
mod time_crate;
#[cfg(feature = "time")]
#[cfg_attr(docsrs, doc(cfg(feature = "time")))]
pub use time_crate::UtcTime;

#[cfg(feature = "local-time")]
#[cfg_attr(docsrs, doc(cfg(unsound_local_offset, feature = "local-time")))]
pub use time_crate::LocalTime;

#[cfg(feature = "time")]
#[cfg_attr(docsrs, doc(cfg(feature = "time")))]
pub use time_crate::OffsetTime;

/// A type that can measure and format the current time.
///
/// This trait is used by `Format` to include a timestamp with each `Event` when it is logged.
///
/// Notable default implementations of this trait are `SystemTime` and `()`. The former prints the
/// current time as reported by `std::time::SystemTime`, and the latter does not print the current
/// time at all. `FormatTime` is also automatically implemented for any function pointer with the
/// appropriate signature.
///
/// The full list of provided implementations can be found in [`time`].
///
/// [`time`]: self
pub trait FormatTime {
    /// Measure and write out the current time.
    ///
    /// When `format_time` is called, implementors should get the current time using their desired
    /// mechanism, and write it out to the given `fmt::Write`. Implementors must insert a trailing
    /// space themselves if they wish to separate the time from subsequent log message text.
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result;
}

/// Returns a new `SystemTime` timestamp provider.
///
/// This can then be configured further to determine how timestamps should be
/// configured.
///
/// This is equivalent to calling
/// ```rust
/// # fn timer() -> tracing_subscriber::fmt::time::SystemTime {
/// tracing_subscriber::fmt::time::SystemTime::default()
/// # }
/// ```
pub fn time() -> SystemTime {
    SystemTime::default()
}

/// Returns a new `Uptime` timestamp provider.
///
/// With this timer, timestamps will be formatted with the amount of time
/// elapsed since the timestamp provider was constructed.
///
/// This can then be configured further to determine how timestamps should be
/// configured.
///
/// This is equivalent to calling
/// ```rust
/// # fn timer() -> tracing_subscriber::fmt::time::Uptime {
/// tracing_subscriber::fmt::time::Uptime::default()
/// # }
/// ```
pub fn uptime() -> Uptime {
    Uptime::default()
}

impl<'a, F> FormatTime for &'a F
where
    F: FormatTime,
{
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result {
        (*self).format_time(w)
    }
}

impl FormatTime for () {
    fn format_time(&self, _: &mut Writer<'_>) -> fmt::Result {
        Ok(())
    }
}

impl FormatTime for fn(&mut Writer<'_>) -> fmt::Result {
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result {
        (*self)(w)
    }
}

/// Retrieve and print the current wall-clock time.
#[derive(Debug, Clone, Copy, Eq, PartialEq, Default)]
pub struct SystemTime;

/// Retrieve and print the relative elapsed wall-clock time since an epoch.
///
/// The `Default` implementation for `Uptime` makes the epoch the current time.
#[derive(Debug, Clone, Copy, Eq, PartialEq)]
pub struct Uptime {
    epoch: Instant,
}

impl Default for Uptime {
    fn default() -> Self {
        Uptime {
            epoch: Instant::now(),
        }
    }
}

impl From<Instant> for Uptime {
    fn from(epoch: Instant) -> Self {
        Uptime { epoch }
    }
}

impl FormatTime for SystemTime {
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result {
        write!(
            w,
            "{}",
            datetime::DateTime::from(std::time::SystemTime::now())
        )
    }
}

impl FormatTime for Uptime {
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result {
        let e = self.epoch.elapsed();
        write!(w, "{:4}.{:09}s", e.as_secs(), e.subsec_nanos())
    }
}
