solti-observe 0.0.2

use std::fmt;

use time::{OffsetDateTime, UtcOffset, format_description::well_known::Rfc3339};
use tracing_subscriber::fmt::{format::Writer, time::FormatTime};

use crate::logger::object::timezone::{LoggerTimeZone, get_or_detect_local_offset};

/// RFC 3339 timestamp formatter for [`tracing_subscriber`] that respects the configured [`LoggerTimeZone`].
///
/// Implements [`FormatTime`](tracing_subscriber::fmt::time::FormatTime) and is injected into the `fmt::Layer` by [`crate::init_logger`].
///
/// ## Behaviour
///
/// | Timezone                  | Offset source                 | Example output                 |
/// |---------------------------|-------------------------------|--------------------------------|
/// | [`LoggerTimeZone::Utc`]   | Always `+00:00`               | `2025-01-15T10:30:00+00:00`    |
/// | [`LoggerTimeZone::Local`] | Cached local offset (per-call)| `2025-01-15T13:30:00+03:00`    |
///
/// In `Local` mode the cached offset is read on **every** call, so DST changes picked up
/// by [`timezone_sync`](crate::timezone_sync) are reflected without restarting the logger.
///
/// ## Also
///
/// - [`init_local_offset`](crate::init_local_offset) — must be called before tokio for `Local` mode.
/// - [`LoggerTimeZone`] — timezone configuration.
#[derive(Debug, Clone, Copy)]
pub struct LoggerRfc3339 {
    tz: LoggerTimeZone,
}

impl LoggerRfc3339 {
    /// Create a formatter for the given timezone setting.
    pub fn new(tz: LoggerTimeZone) -> Self {
        Self { tz }
    }
}

impl FormatTime for LoggerRfc3339 {
    fn format_time(&self, w: &mut Writer<'_>) -> fmt::Result {
        let offset = match self.tz {
            LoggerTimeZone::Utc => UtcOffset::UTC,
            LoggerTimeZone::Local => get_or_detect_local_offset(),
        };

        let ts = OffsetDateTime::now_utc().to_offset(offset);

        match ts.format(&Rfc3339) {
            Ok(s) => write!(w, "{s} "),
            Err(_) => write!(w, "<invalid-time> "),
        }
    }
}