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use time::OffsetDateTime;
/// The `MeasurementVisitor` trait represents the capability to visit a series of measurements, possibly grouped.
///
/// Here is an implementation of the `MeasurementVisitor` trait that prints the measurements:
///
/// ```
/// # use thin_edge_json::measurement::*;
/// # use time::{OffsetDateTime, format_description};
///
/// struct MeasurementPrinter {
/// group: Option<String>,
/// }
///
/// #[derive(thiserror::Error, Debug)]
/// pub enum MeasurementError {
/// #[error("Unexpected time stamp within a group")]
/// UnexpectedTimestamp,
///
/// #[error("Unexpected end of group")]
/// UnexpectedEndOfGroup,
///
/// #[error("Unexpected start of group")]
/// UnexpectedStartOfGroup,
/// }
///
/// impl MeasurementVisitor for MeasurementPrinter {
/// type Error = MeasurementError;
///
/// fn visit_timestamp(&mut self, timestamp: OffsetDateTime) -> Result<(), Self::Error> {
/// let format =
/// format_description::parse("[day] [month repr:short] [year] [hour repr:24]:[minute]:[seconds] [offset_hour sign:mandatory]:[offset_minute]").unwrap();
/// if self.group.is_none() {
/// Ok(println!("time = {}", timestamp.format(&format).unwrap()))
/// } else {
/// Err(MeasurementError::UnexpectedTimestamp)
/// }
/// }
///
/// fn visit_measurement(&mut self, name: &str, value: f64) -> Result<(), Self::Error> {
/// if let Some(group_name) = self.group.as_ref() {
/// Ok(println!("{}.{} = {}", group_name, name, value))
/// } else {
/// Ok(println!("{} = {}", name, value))
/// }
/// }
///
/// fn visit_start_group(&mut self, group: &str) -> Result<(), Self::Error> {
/// if self.group.is_none() {
/// self.group = Some(group.to_owned());
/// Ok(())
/// } else {
/// Err(MeasurementError::UnexpectedStartOfGroup)
/// }
/// }
///
/// fn visit_end_group(&mut self) -> Result<(), Self::Error> {
/// if self.group.is_none() {
/// Err(MeasurementError::UnexpectedEndOfGroup)
/// } else {
/// self.group = None;
/// Ok(())
/// }
/// }
/// }
/// ```
pub trait MeasurementVisitor {
/// Error type specific to this visitor.
type Error: std::error::Error + std::fmt::Debug;
/// Set the timestamp shared by all the measurements of this series.
fn visit_timestamp(&mut self, value: OffsetDateTime) -> Result<(), Self::Error>;
/// Add a new measurement, attached to the current group if any.
fn visit_measurement(&mut self, name: &str, value: f64) -> Result<(), Self::Error>;
/// Start to gather measurements for a group.
fn visit_start_group(&mut self, group: &str) -> Result<(), Self::Error>;
/// End to gather measurements for the current group.
fn visit_end_group(&mut self) -> Result<(), Self::Error>;
/// A single measurement contained in `group`. Defaults to a sequence of
/// `visit_start_group`, `visit_measurement` and `visit_end_group`.
fn visit_grouped_measurement(
&mut self,
group: &str,
name: &str,
value: f64,
) -> Result<(), Self::Error> {
self.visit_start_group(group)?;
self.visit_measurement(name, value)?;
self.visit_end_group()?;
Ok(())
}
}
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