Add unfinished progress on BeaconChain struct

beacon_chain/chain/src/maps.rs

@@ -0,0 +1,45 @@
+use types::{
+    AttesterMap,
+    CrystallizedState,
+    ProposerMap,
+};
+
+#[derive(Debug, PartialEq)]
+pub enum AttesterAndProposerMapError {
+    NoShardAndCommitteeForSlot,
+    NoAvailableProposer,
+}
+
+/// Generate a map of `(slot, shard) |--> committee`.
+///
+/// The attester map is used to optimise the lookup of a committee.
+pub fn generate_attester_and_proposer_maps(cry_state: &CrystallizedState, start_slot: u64)
+    -> Result<(AttesterMap, ProposerMap), AttesterAndProposerMapError>
+{
+    let mut attester_map = AttesterMap::new();
+    let mut proposer_map = ProposerMap::new();
+    for (i, slot) in cry_state.shard_and_committee_for_slots.iter().enumerate() {
+        /*
+         * Store the proposer for the block.
+         */
+        let slot_number = (i as u64).saturating_add(start_slot);
+        let first_committee = {
+            let first_shard_and_committee = slot.get(0)
+                .ok_or(AttesterAndProposerMapError::NoShardAndCommitteeForSlot)?;
+            first_shard_and_committee.committee.clone()
+        };
+        println!("{:?}", slot);
+        let proposer_index = (slot_number as usize).checked_rem(first_committee.len())
+            .ok_or(AttesterAndProposerMapError::NoAvailableProposer)?;
+        proposer_map.insert(slot_number, proposer_index);
+
+        /*
+         * Loop through the shards and extend the attester map.
+         */
+        for shard_and_committee in slot {
+            let committee = shard_and_committee.committee.clone();
+            attester_map.insert((slot_number, shard_and_committee.shard), committee);
+        }
+    };
+    Ok((attester_map, proposer_map))
+}