#4512 inactivity calculation for Altair (#4807)

## Issue Addressed
#4512 
Which issue # does this PR address?

## Proposed Changes
Add inactivity calculation for Altair

Please list or describe the changes introduced by this PR.
Add inactivity calculation for Altair

## Additional Info

Please provide any additional information. For example, future considerations
or information useful for reviewers.


Co-authored-by: Jimmy Chen <jchen.tc@gmail.com>

beacon_node/beacon_chain/src/attestation_rewards.rs

@@ -5,6 +5,7 @@ use participation_cache::ParticipationCache;
 use safe_arith::SafeArith;
 use serde_utils::quoted_u64::Quoted;
 use slog::debug;
+use state_processing::per_epoch_processing::altair::process_inactivity_updates;
 use state_processing::{
     common::altair::BaseRewardPerIncrement,
     per_epoch_processing::altair::{participation_cache, rewards_and_penalties::get_flag_weight},
@@ -124,6 +125,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
 
         // Calculate ideal_rewards
         let participation_cache = ParticipationCache::new(&state, spec)?;
+        process_inactivity_updates(&mut state, &participation_cache, spec)?;
 
         let previous_epoch = state.previous_epoch();
 
@@ -190,6 +192,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             let mut head_reward = 0i64;
             let mut target_reward = 0i64;
             let mut source_reward = 0i64;
+            let mut inactivity_penalty = 0i64;
 
             if eligible {
                 let effective_balance = state.get_effective_balance(*validator_index)?;
@@ -215,6 +218,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                         head_reward = 0;
                     } else if flag_index == TIMELY_TARGET_FLAG_INDEX {
                         target_reward = *penalty;
+
+                        let penalty_numerator = effective_balance
+                            .safe_mul(state.get_inactivity_score(*validator_index)?)?;
+                        let penalty_denominator = spec
+                            .inactivity_score_bias
+                            .safe_mul(spec.inactivity_penalty_quotient_for_state(&state))?;
+                        inactivity_penalty =
+                            -(penalty_numerator.safe_div(penalty_denominator)? as i64);
                     } else if flag_index == TIMELY_SOURCE_FLAG_INDEX {
                         source_reward = *penalty;
                     }
@@ -226,8 +237,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 target: target_reward,
                 source: source_reward,
                 inclusion_delay: None,
-                // TODO: altair calculation logic needs to be updated to include inactivity penalty
-                inactivity: 0,
+                inactivity: inactivity_penalty,
             });
         }
 
@@ -250,7 +260,6 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                             target: 0,
                             source: 0,
                             inclusion_delay: None,
-                            // TODO: altair calculation logic needs to be updated to include inactivity penalty
                             inactivity: 0,
                         });
                     match *flag_index {

beacon_node/beacon_chain/src/test_utils.rs

@@ -2350,6 +2350,29 @@ where
         .await
     }
 
+    /// Uses `Self::extend_chain` to `num_slots` blocks.
+    ///
+    /// Utilizes:
+    ///
+    ///  - BlockStrategy::OnCanonicalHead,
+    ///  - AttestationStrategy::SomeValidators(validators),
+    pub async fn extend_slots_some_validators(
+        &self,
+        num_slots: usize,
+        validators: Vec<usize>,
+    ) -> Hash256 {
+        if self.chain.slot().unwrap() == self.chain.canonical_head.cached_head().head_slot() {
+            self.advance_slot();
+        }
+
+        self.extend_chain(
+            num_slots,
+            BlockStrategy::OnCanonicalHead,
+            AttestationStrategy::SomeValidators(validators),
+        )
+        .await
+    }
+
     /// Extend the `BeaconChain` with some blocks and attestations. Returns the root of the
     /// last-produced block (the head of the chain).
     ///