Add incomplete progress on fixing test harness

beacon_node/beacon_chain/src/cached_beacon_state.rs

@@ -0,0 +1,49 @@
+use types::{beacon_state::BeaconStateError, BeaconState, ChainSpec, Epoch, Slot};
+
+pub const CACHED_EPOCHS: usize = 3; // previous, current, next.
+
+pub type CrosslinkCommittees = Vec<(Vec<usize>, u64)>;
+
+pub struct CachedBeaconState<'a> {
+    state: BeaconState,
+    crosslinks: Vec<Vec<CrosslinkCommittees>>,
+    spec: &'a ChainSpec,
+}
+
+impl<'a> CachedBeaconState<'a> {
+    pub fn from_beacon_state(
+        state: BeaconState,
+        spec: &'a ChainSpec,
+    ) -> Result<Self, BeaconStateError> {
+        let current_epoch = state.current_epoch(spec);
+        let previous_epoch = if current_epoch == spec.genesis_epoch {
+            current_epoch
+        } else {
+            current_epoch.saturating_sub(1_u64)
+        };
+        let next_epoch = state.next_epoch(spec);
+
+        let mut crosslinks: Vec<Vec<CrosslinkCommittees>> = Vec::with_capacity(3);
+        crosslinks.push(committees_for_all_slots(&state, previous_epoch, spec)?);
+        crosslinks.push(committees_for_all_slots(&state, current_epoch, spec)?);
+        crosslinks.push(committees_for_all_slots(&state, next_epoch, spec)?);
+
+        Ok(Self {
+            state,
+            crosslinks,
+            spec,
+        })
+    }
+}
+
+fn committees_for_all_slots(
+    state: &BeaconState,
+    epoch: Epoch,
+    spec: &ChainSpec,
+) -> Result<Vec<CrosslinkCommittees>, BeaconStateError> {
+    let mut crosslinks: Vec<CrosslinkCommittees> = Vec::with_capacity(spec.epoch_length as usize);
+    for slot in epoch.slot_iter(spec.epoch_length) {
+        crosslinks.push(state.get_crosslink_committees_at_slot(slot, false, spec)?)
+    }
+    Ok(crosslinks)
+}