refactor guess time/freq res into guess interval

src/context/helpers.rs

@@ -1,3 +1,5 @@
+use std::ops::Sub;
+
 use mwa_hyperdrive_common::{
     hifitime::{Duration, Epoch, Unit},
     itertools::Itertools,
@@ -8,20 +10,22 @@ lazy_static::lazy_static! {
     static ref DURATION_MAX: Duration = Duration::from_f64(f64::MAX, Unit::Second);
 }
 
-pub fn guess_time_res(timestamps: Vec<Epoch>) -> Option<Duration> {
-    timestamps
+pub fn guess_interval<T, O>(elements: &[T]) -> Option<O>
+where
+    T: Sub<Output = O> + Copy,
+    O: PartialOrd,
+{
+    elements
         .iter()
         .tuple_windows()
-        .fold(None, |result, (&past, &future)| {
-            Some(result.unwrap_or(*DURATION_MAX).min(future - past))
-        })
+        .map(|(&a, &b)| b.sub(a))
+        .min_by(|a, b| a.partial_cmp(b).unwrap())
+}
+
+pub fn guess_time_res(timestamps: Vec<Epoch>) -> Option<Duration> {
+    guess_interval(&timestamps)
 }
 
 pub fn guess_freq_res(frequencies: Vec<f64>) -> Option<f64> {
-    frequencies
-        .iter()
-        .tuple_windows()
-        .fold(None, |result, (&low, &high)| {
-            Some(result.unwrap_or(f64::MAX).min(high - low))
-        })
+    guess_interval(&frequencies)
 }