From 1af6117155f0b887ae2b4350a2bfe38300272ae6 Mon Sep 17 00:00:00 2001
From: Luke Parker <lukeparker5132@gmail.com>
Date: Sun, 30 Oct 2022 04:27:15 -0400
Subject: [PATCH] Move TendermintMachine from start_num, time to last_num, time

Provides an explicitly clear API clearer to program around.

Also adds additional time code to handle an edge case.
---
 substrate/tendermint/client/src/tendermint.rs | 10 ++---
 substrate/tendermint/machine/src/lib.rs       | 45 ++++++++++++-------
 2 files changed, 35 insertions(+), 20 deletions(-)

diff --git a/substrate/tendermint/client/src/tendermint.rs b/substrate/tendermint/client/src/tendermint.rs
index f70e3c9a..7b8051c4 100644
--- a/substrate/tendermint/client/src/tendermint.rs
+++ b/substrate/tendermint/client/src/tendermint.rs
@@ -61,11 +61,11 @@ impl<T: TendermintValidator> TendermintAuthority<T> {
     let info = self.0.client.info();
 
     // Header::Number: TryInto<u64> doesn't implement Debug and can't be unwrapped
-    let start_number = match TryInto::<u64>::try_into(info.best_number) {
-      Ok(best) => BlockNumber(best + 1),
+    let last_number = match info.best_number.try_into() {
+      Ok(best) => BlockNumber(best),
       Err(_) => panic!("BlockNumber exceeded u64"),
     };
-    let start_time = Commit::<TendermintValidators<T>>::decode(
+    let last_time = Commit::<TendermintValidators<T>>::decode(
       &mut self
         .0
         .client
@@ -76,7 +76,7 @@ impl<T: TendermintValidator> TendermintAuthority<T> {
         .as_ref(),
     )
     .map(|commit| commit.end_time)
-    // TODO: Genesis start time
+    // TODO: Genesis start time + BLOCK_TIME
     .unwrap_or_else(|_| SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs());
 
     let proposal = self
@@ -88,7 +88,7 @@ impl<T: TendermintValidator> TendermintAuthority<T> {
       self.0.clone(),
       // TODO
       0, // ValidatorId
-      (start_number, start_time),
+      (last_number, last_time),
       proposal,
     ));
   }
diff --git a/substrate/tendermint/machine/src/lib.rs b/substrate/tendermint/machine/src/lib.rs
index 7fb02bf6..cb73bcf0 100644
--- a/substrate/tendermint/machine/src/lib.rs
+++ b/substrate/tendermint/machine/src/lib.rs
@@ -242,24 +242,32 @@ impl<N: Network + 'static> TendermintMachine<N> {
   pub fn new(
     network: N,
     proposer: N::ValidatorId,
-    start: (BlockNumber, u64),
+    last: (BlockNumber, u64),
     proposal: N::Block,
   ) -> TendermintHandle<N> {
-    // Convert the start time to an instant
-    // This is imprecise yet should be precise enough
-    let start_time = {
-      let instant_now = Instant::now();
-      let sys_now = SystemTime::now();
-      instant_now -
-        sys_now
-          .duration_since(UNIX_EPOCH + Duration::from_secs(start.1))
-          .unwrap_or(Duration::ZERO)
-    };
-
     let (msg_send, mut msg_recv) = mpsc::channel(100); // Backlog to accept. Currently arbitrary
     TendermintHandle {
       messages: msg_send,
       handle: tokio::spawn(async move {
+        let last_end = UNIX_EPOCH + Duration::from_secs(last.1);
+
+        // If the last block hasn't ended yet, sleep until it has
+        {
+          let now = SystemTime::now();
+          if last_end > now {
+            sleep(last_end.duration_since(now).unwrap_or(Duration::ZERO)).await;
+          }
+        }
+
+        // Convert the last time to an instant
+        // This is imprecise yet should be precise enough, given this library only has
+        // second accuracy
+        let last_time = {
+          let instant_now = Instant::now();
+          let sys_now = SystemTime::now();
+          instant_now - sys_now.duration_since(last_end).unwrap_or(Duration::ZERO)
+        };
+
         let signer = network.signature_scheme();
         let weights = network.weights();
         let network = Arc::new(RwLock::new(network));
@@ -270,9 +278,16 @@ impl<N: Network + 'static> TendermintMachine<N> {
           weights: weights.clone(),
           proposer,
 
-          number: start.0,
-          canonical_start_time: start.1,
-          start_time,
+          number: BlockNumber(last.0.0 + 1),
+          canonical_start_time: last.1,
+          // The end time of the last block is the start time for this one
+          // The Commit explicitly contains the end time, so loading the last commit will provide
+          // this. The only exception is for the genesis block, which doesn't have a commit
+          // Using the genesis time in place will cause this block to be created immediately after
+          // it, without the standard amount of separation (so their times will be equivalent or
+          // minimally offset)
+          // For callers wishing to avoid this, they should pass (0, GENESIS + BLOCK_TIME)
+          start_time: last_time,
           personal_proposal: proposal,
 
           queue: vec![],