replacing the average claps in session with median to determine a harmful authority

Signed-off-by: Uncle Stinky <uncle.stinky@ghostchain.io>

pallets/slow-clap/Cargo.toml

@@ -1,6 +1,6 @@
 [package]
 name = "ghost-slow-clap"
-version = "0.3.17"
+version = "0.3.18"
 description = "Applause protocol for the EVM bridge"
 license.workspace = true
 authors.workspace = true

pallets/slow-clap/src/lib.rs

@@ -858,9 +858,9 @@ impl<T: Config> Pallet<T> {
     fn is_good_actor(
         authority_index: usize, 
         session_index: SessionIndex,
-        average_claps: u32,
+        median_claps: u32,
     ) -> bool {
-        if average_claps == 0 {
+        if median_claps == 0 {
             return true;
         }
 
@@ -869,10 +869,10 @@ impl<T: Config> Pallet<T> {
             .or_default()
             .claps;
 
-        let authority_deviation = if number_of_claps < average_claps {
+        let authority_deviation = if number_of_claps < median_claps {
-            Perbill::from_rational(average_claps - number_of_claps, average_claps)
+            Perbill::from_rational(median_claps - number_of_claps, median_claps)
         } else {
-            Perbill::from_rational(number_of_claps - average_claps, average_claps)
+            Perbill::from_rational(number_of_claps - median_claps, median_claps)
         };
         authority_deviation < Perbill::from_percent(T::OffenceThreshold::get())
     }
@@ -886,6 +886,28 @@ impl<T: Config> Pallet<T> {
         }    
     }
 
+    fn calculate_median_claps(session_index: &SessionIndex) -> u32 {
+        let mut claps_in_session = ClapsInSession::<T>::get(session_index)
+            .values()
+            .filter_map(|value| (!value.disabled).then(|| value.claps))
+            .collect::<Vec<_>>();
+
+        if claps_in_session.is_empty() {
+            return 0;
+        }
+
+        claps_in_session.sort();
+        let number_of_claps = claps_in_session.len();
+
+        if number_of_claps % 2 == 0 {
+            let mid_left = claps_in_session[number_of_claps / 2 - 1];
+            let mid_right = claps_in_session[number_of_claps / 2];
+            (mid_left + mid_right) / 2
+        } else {
+            claps_in_session[number_of_claps / 2]
+        }
+    }
+
     #[cfg(test)]
     fn set_test_authorities(authorities: Vec<T::AuthorityId>) {
         let bounded_authorities = WeakBoundedVec::<_, T::MaxAuthorities>::try_from(authorities)
@@ -931,21 +953,12 @@ impl<T: Config> OneSessionHandler<T::AccountId> for Pallet<T> {
         let validators = T::ValidatorSet::validators();
         let authorities = Authorities::<T>::get();
 
-        let (sum_claps, total_claps) = ClapsInSession::<T>::get(&session_index)
+        let median_claps = Self::calculate_median_claps(&session_index);
-            .iter()
-            .filter(|(_, value)| !value.disabled)
-            .fold((0u32, 0u32), |(sum, total), (_, value)| 
-                (sum.saturating_add(value.claps), total.saturating_add(1))
-            );
-
-        let average_claps = sum_claps
-            .checked_div(total_claps)
-            .unwrap_or_default();
 
         let offenders = validators
             .into_iter()
             .enumerate()
-            .filter(|(index, _)| !Self::is_good_actor(*index, session_index, average_claps))
+            .filter(|(index, _)| !Self::is_good_actor(*index, session_index, median_claps))
             .filter_map(|(_, id)| {
                 <T::ValidatorSet as ValidatorSetWithIdentification<T::AccountId>>::IdentificationOf::convert(
                     id.clone(),