From ab2b8accd4503011eaeb399acd45988f46fba906 Mon Sep 17 00:00:00 2001
From: Paul Hauner <paul@paulhauner.com>
Date: Tue, 3 Sep 2019 15:22:00 +1000
Subject: [PATCH] Add first pass at Eth1Chain trait

---
 beacon_node/beacon_chain/src/eth1_chain.rs | 61 ++++++++++++++++++++++
 beacon_node/beacon_chain/src/lib.rs        |  1 +
 2 files changed, 62 insertions(+)
 create mode 100644 beacon_node/beacon_chain/src/eth1_chain.rs

diff --git a/beacon_node/beacon_chain/src/eth1_chain.rs b/beacon_node/beacon_chain/src/eth1_chain.rs
new file mode 100644
index 000000000..5f148cd9b
--- /dev/null
+++ b/beacon_node/beacon_chain/src/eth1_chain.rs
@@ -0,0 +1,61 @@
+use crate::BeaconChainTypes;
+use eth2_hashing::hash;
+use std::marker::PhantomData;
+use types::{BeaconState, Deposit, DepositData, Eth1Data, EthSpec, Hash256};
+
+type Result<T> = std::result::Result<T, Error>;
+
+pub enum Error {
+    /// Unable to return an Eth1Data for the given epoch.
+    EpochUnavailable,
+    /// An error from the backend service (e.g., the web3 data fetcher).
+    BackendError(String),
+}
+
+pub trait Eth1Chain<T: BeaconChainTypes> {
+    /// Returns the `Eth1Data` that should be included in a block being produced for the given
+    /// `state`.
+    fn eth1_data_for_epoch(&self, beacon_state: &BeaconState<T::EthSpec>) -> Result<Eth1Data>;
+
+    /// Returns all `Deposits` between `state.eth1_deposit_index` and
+    /// `state.eth1_data.deposit_count`.
+    ///
+    /// # Note:
+    ///
+    /// It is possible that not all returned `Deposits` can be included in a block. E.g., there may
+    /// be more than `MAX_DEPOSIT_COUNT` or the churn may be too high.
+    fn queued_deposits(&self, beacon_state: &BeaconState<T::EthSpec>) -> Result<Vec<Deposit>>;
+}
+
+pub struct InteropEth1Chain<T: BeaconChainTypes> {
+    _phantom: PhantomData<T>,
+}
+
+impl<T: BeaconChainTypes> Eth1Chain<T> for InteropEth1Chain<T> {
+    fn eth1_data_for_epoch(&self, state: &BeaconState<T::EthSpec>) -> Result<Eth1Data> {
+        let current_epoch = state.current_epoch();
+        let slots_per_voting_period = T::EthSpec::slots_per_eth1_voting_period() as u64;
+        let current_voting_period: u64 = current_epoch.as_u64() / slots_per_voting_period;
+
+        // TODO: confirm that `int_to_bytes32` is correct.
+        let deposit_root = hash(&int_to_bytes32(current_voting_period));
+        let block_hash = hash(&deposit_root);
+
+        Ok(Eth1Data {
+            deposit_root: Hash256::from_slice(&deposit_root),
+            deposit_count: state.eth1_deposit_index,
+            block_hash: Hash256::from_slice(&block_hash),
+        })
+    }
+
+    fn queued_deposits(&self, beacon_state: &BeaconState<T::EthSpec>) -> Result<Vec<Deposit>> {
+        Ok(vec![])
+    }
+}
+
+/// Returns `int` as little-endian bytes with a length of 32.
+fn int_to_bytes32(int: u64) -> Vec<u8> {
+    let mut vec = int.to_le_bytes().to_vec();
+    vec.resize(32, 0);
+    vec
+}
diff --git a/beacon_node/beacon_chain/src/lib.rs b/beacon_node/beacon_chain/src/lib.rs
index 9c833f778..25f8b74eb 100644
--- a/beacon_node/beacon_chain/src/lib.rs
+++ b/beacon_node/beacon_chain/src/lib.rs
@@ -6,6 +6,7 @@ mod beacon_chain;
 mod beacon_chain_builder;
 mod checkpoint;
 mod errors;
+mod eth1_chain;
 mod fork_choice;
 mod iter;
 mod metrics;