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use std::time::SystemTime;
/// Find the earliest item in a collection based on a custom iteratee function.
/// If the collection is empty, returns `None`.
///
/// # Arguments
///
/// * `collection` - A slice of items.
/// * `iteratee` - A function that takes an item and returns a `SystemTime` used for comparison.
///
/// # Returns
///
/// * `Option<T>` - The earliest item based on the iteratee function, or `None` if the collection is empty.
///
/// # Examples
/// ```rust
/// use std::time::{SystemTime, Duration};
/// use lowdash::earliest_by;
///
/// let t1 = SystemTime::UNIX_EPOCH;
/// let t2 = t1 + Duration::new(60, 0);
/// let t3 = t1 + Duration::new(120, 0);
/// let times = vec![t2, t1, t3];
/// let earliest_time = earliest_by(×, |&t| t);
/// assert_eq!(earliest_time, Some(t1));
///
/// #[derive(Debug, PartialEq, Clone)]
/// struct Event {
/// name: String,
/// timestamp: SystemTime,
/// }
///
/// let events = vec![
/// Event {
/// name: "Event1".to_string(),
/// timestamp: t2,
/// },
/// Event {
/// name: "Event2".to_string(),
/// timestamp: t1,
/// },
/// Event {
/// name: "Event3".to_string(),
/// timestamp: t3,
/// },
/// ];
///
/// let earliest_event = earliest_by(&events, |e| e.timestamp);
/// assert_eq!(
/// earliest_event,
/// Some(Event {
/// name: "Event2".to_string(),
/// timestamp: t1,
/// })
/// );
/// ```
pub fn earliest_by<T, F>(collection: &[T], iteratee: F) -> Option<T>
where
T: Clone,
F: Fn(&T) -> SystemTime,
{
if collection.is_empty() {
return None;
}
let mut earliest = collection[0].clone();
let mut earliest_time = iteratee(&earliest);
for item in &collection[1..] {
let item_time = iteratee(item);
if item_time < earliest_time {
earliest = item.clone();
earliest_time = item_time;
}
}
Some(earliest)
}
#[cfg(test)]
mod tests {
use super::*;
use std::time::{Duration, SystemTime};
#[derive(Debug, PartialEq, Clone)]
struct Event {
name: String,
timestamp: SystemTime,
}
#[test]
fn test_earliest_by_with_multiple_items() {
let t1 = SystemTime::UNIX_EPOCH;
let t2 = t1 + Duration::new(60, 0);
let t3 = t1 + Duration::new(120, 0);
let times = vec![t2, t1, t3];
let result = earliest_by(×, |&t| t);
assert_eq!(result, Some(t1));
}
#[test]
fn test_earliest_by_with_single_item() {
let t = SystemTime::now();
let times = vec![t];
let result = earliest_by(×, |&t| t);
assert_eq!(result, Some(t));
}
#[test]
fn test_earliest_by_empty_collection() {
let times: Vec<SystemTime> = vec![];
let result = earliest_by(×, |&t| t);
assert_eq!(result, None);
}
#[test]
fn test_earliest_by_all_same_times() {
let t = SystemTime::now();
let times = vec![t, t, t];
let result = earliest_by(×, |&t| t);
assert_eq!(result, Some(t));
}
#[test]
fn test_earliest_by_custom_struct() {
let t1 = SystemTime::UNIX_EPOCH;
let t2 = t1 + Duration::new(30, 0);
let t3 = t1 + Duration::new(60, 0);
let t4 = t1 + Duration::new(90, 0);
let events = vec![
Event {
name: "Event1".to_string(),
timestamp: t2,
},
Event {
name: "Event2".to_string(),
timestamp: t1,
},
Event {
name: "Event3".to_string(),
timestamp: t4,
},
Event {
name: "Event4".to_string(),
timestamp: t3,
},
];
let result = earliest_by(&events, |e| e.timestamp);
assert_eq!(
result,
Some(Event {
name: "Event2".to_string(),
timestamp: t1,
})
);
}
#[test]
fn test_earliest_by_varied_times() {
let t1 = SystemTime::UNIX_EPOCH;
let t2 = t1 + Duration::new(15, 0);
let t3 = t1 + Duration::new(45, 0);
let t4 = t1 + Duration::new(30, 0);
let t5 = t1 + Duration::new(60, 0);
let times = vec![t3, t2, t5, t1, t4];
let result = earliest_by(×, |&t| t);
assert_eq!(result, Some(t1));
}
}