Refactor winning root logic

eth2/state_processing/src/per_epoch_processing/inclusion_distance.rs

@@ -0,0 +1,61 @@
+use super::errors::InclusionError;
+use types::*;
+
+/// Returns the distance between the first included attestation for some validator and this
+/// slot.
+///
+/// Note: In the spec this is defined "inline", not as a helper function.
+///
+/// Spec v0.4.0
+pub fn inclusion_distance(
+    state: &BeaconState,
+    attestations: &[&PendingAttestation],
+    validator_index: usize,
+    spec: &ChainSpec,
+) -> Result<u64, InclusionError> {
+    let attestation = earliest_included_attestation(state, attestations, validator_index, spec)?;
+    Ok((attestation.inclusion_slot - attestation.data.slot).as_u64())
+}
+
+/// Returns the slot of the earliest included attestation for some validator.
+///
+/// Note: In the spec this is defined "inline", not as a helper function.
+///
+/// Spec v0.4.0
+pub fn inclusion_slot(
+    state: &BeaconState,
+    attestations: &[&PendingAttestation],
+    validator_index: usize,
+    spec: &ChainSpec,
+) -> Result<Slot, InclusionError> {
+    let attestation = earliest_included_attestation(state, attestations, validator_index, spec)?;
+    Ok(attestation.inclusion_slot)
+}
+
+/// Finds the earliest included attestation for some validator.
+///
+/// Note: In the spec this is defined "inline", not as a helper function.
+///
+/// Spec v0.4.0
+fn earliest_included_attestation(
+    state: &BeaconState,
+    attestations: &[&PendingAttestation],
+    validator_index: usize,
+    spec: &ChainSpec,
+) -> Result<PendingAttestation, InclusionError> {
+    let mut included_attestations = vec![];
+
+    for (i, a) in attestations.iter().enumerate() {
+        let participants =
+            state.get_attestation_participants(&a.data, &a.aggregation_bitfield, spec)?;
+        if participants.iter().any(|i| *i == validator_index) {
+            included_attestations.push(i);
+        }
+    }
+
+    let earliest_attestation_index = included_attestations
+        .iter()
+        .min_by_key(|i| attestations[**i].inclusion_slot)
+        .ok_or_else(|| InclusionError::NoAttestationsForValidator)?;
+    Ok(attestations[*earliest_attestation_index].clone())
+}