Factor out calculation for ms duration

Author: JosephTLyons

src/persevero.gleam

@@ -208,6 +208,14 @@ fn configure_wait_stream(
   case mode {
     MaxAttempts(max_attempts) -> wait_stream |> yielder.take(max_attempts)
     Expiry(_) -> wait_stream
+
+fn duration_ms(left: Timestamp, right: Timestamp) -> Int {
+  left
+  |> timestamp.difference(right)
+  |> duration.to_seconds_and_nanoseconds
+  |> fn(seconds_nanoseconds) {
+    let #(seconds, nanoseconds) = seconds_nanoseconds
+    seconds * 1000 + nanoseconds / 1_000_000
   }
 }
 
@@ -233,16 +241,7 @@ fn do_execute(
     True, yielder.Next(wait_time, wait_stream) -> {
       wait_function(wait_time)
       let wait_time_acc = [wait_time, ..wait_time_acc]
-
-      let duration =
-        start_time
-        |> timestamp.difference(clock.now(clock))
-        |> duration.to_seconds_and_nanoseconds
-        |> fn(seconds_nanoseconds) {
-          let #(seconds, nanoseconds) = seconds_nanoseconds
-          let milliseconds = seconds * 1000 + nanoseconds / 1_000_000
-          milliseconds
-        }
+      let duration = duration_ms(start_time, clock.now(clock))
 
       case operation(attempt) {
         Ok(result) ->