From 043335f11afcd49522707d96e9584349a5bf0d51 Mon Sep 17 00:00:00 2001
From: PaulVMo <paul.moceri@gmail.com>
Date: Thu, 15 Jul 2021 09:24:26 -0500
Subject: [PATCH] HIP-28 support - add consensus reward grace period

---
 .../v1/blockchain_txn_vars_v1.erl             |  2 +-
 .../v2/blockchain_txn_rewards_v2.erl          | 61 ++++++++++++++++++-
 2 files changed, 59 insertions(+), 4 deletions(-)

diff --git a/src/transactions/v1/blockchain_txn_vars_v1.erl b/src/transactions/v1/blockchain_txn_vars_v1.erl
index 737fd285ca..766ebce82a 100644
--- a/src/transactions/v1/blockchain_txn_vars_v1.erl
+++ b/src/transactions/v1/blockchain_txn_vars_v1.erl
@@ -987,7 +987,7 @@ validate_var(?poc_reward_decay_rate, Value) ->
     validate_float(Value, "poc_reward_decay_rate", 0.0, 1.0);
 validate_var(?reward_version, Value) ->
     case Value of
-        N when is_integer(N), N >= 1,  N =< 5 ->
+        N when is_integer(N), N >= 1,  N =< 6 ->
             ok;
         _ ->
             throw({error, {invalid_reward_version, Value}})
diff --git a/src/transactions/v2/blockchain_txn_rewards_v2.erl b/src/transactions/v2/blockchain_txn_rewards_v2.erl
index 8923630b5d..f780387323 100644
--- a/src/transactions/v2/blockchain_txn_rewards_v2.erl
+++ b/src/transactions/v2/blockchain_txn_rewards_v2.erl
@@ -277,10 +277,18 @@ calculate_rewards_metadata(Start, End, Chain) ->
         Results0 = fold_blocks_for_rewards(Start, End, Chain,
                                           Vars, Ledger, AccInit),
 
-        %% Forcing calculation of the EpochReward amount for the CG to always
+        %% Prior to HIP 28 (reward_version <6), force EpochReward amount for the CG to always
         %% be around ElectionInterval (30 blocks) so that there is less incentive
-        %% to stay in the consensus group
-        ConsensusEpochReward = calculate_epoch_reward(1, Start, End, Ledger),
+        %% to stay in the consensus group. With HIP 28, relax that to be up to election_interval +
+        %% election_retry_interval to allow for time for election to complete.
+        ConsensusEpochReward = 
+            case maps:get(reward_version,Vars) of
+               RewardVersion when RewardVersion >= 6 ->
+                    calculate_consensus_epoch_reward(Start, End, Vars);
+                _ ->
+                    calculate_epoch_reward(1, Start, End, Ledger)
+            end,
+
         Vars1 = Vars#{ consensus_epoch_reward => ConsensusEpochReward },
 
         Results = finalize_reward_calculations(Results0, Ledger, Vars1),
@@ -667,6 +675,16 @@ calculate_epoch_reward(Version, Start, End, Ledger) ->
 
 -spec calculate_epoch_reward(pos_integer(), pos_integer(), pos_integer(),
                              pos_integer(), pos_integer(), pos_integer()) -> float().
+calculate_epoch_reward(Version, Start, End, BlockTime0, _ElectionInterval, MonthlyReward) when Version >= 6 ->
+    BlockTime1 = (BlockTime0/1000),
+    % Convert to blocks per min
+    BlockPerMin = 60/BlockTime1,
+    % Convert to blocks per hour
+    BlockPerHour = BlockPerMin*60,
+    % Calculate election interval in blocks
+    ElectionInterval = End - Start + 1, % epoch is inclusive of start and end
+    ElectionPerHour = BlockPerHour/ElectionInterval,
+    MonthlyReward/30/24/ElectionPerHour;
 calculate_epoch_reward(Version, Start, End, BlockTime0, _ElectionInterval, MonthlyReward) when Version >= 2 ->
     BlockTime1 = (BlockTime0/1000),
     % Convert to blocks per min
@@ -687,6 +705,24 @@ calculate_epoch_reward(_Version, _Start, _End, BlockTime0, ElectionInterval, Mon
     ElectionPerHour = BlockPerHour/ElectionInterval,
     MonthlyReward/30/24/ElectionPerHour.
 
+
+
+-spec calculate_consensus_epoch_reward(pos_integer(), pos_integer(), reward_vars()) -> float().
+calculate_consensus_epoch_reward(Start, End, #{ block_time := BlockTime0,
+                                                election_interval := ElectionInterval, 
+                                                election_restart_interval := ElectionRestartInterval, 
+                                                monthly_reward := MonthlyReward }) ->
+
+    BlockTime1 = (BlockTime0/1000),
+    % Convert to blocks per min
+    BlockPerMin = 60/BlockTime1,
+    % Convert to blocks per month
+    BlockPerMonth = BlockPerMin*60*24*30,
+    % Calculate epoch length in blocks, cap at election interval + grace period
+    EpochLength = erlang:min(End - Start + 1, ElectionInterval + ElectionRestartInterval),
+    MonthlyReward/BlockPerMonth*EpochLength.
+
+
 -spec consensus_members_rewards(blockchain_ledger_v1:ledger(),
                                 reward_vars(),
                                 non_neg_integer()) -> rewards_map().
@@ -1819,4 +1855,23 @@ common_poc_vars() ->
         ?poc_v5_target_prob_randomness_wt => 0.0
     }.
 
+
+hip28_calc_test() ->
+    % set test vars such that rewards are 1 per block
+    Vars = #{ block_time => 60000, 
+              election_interval => 30, 
+              election_restart_interval => 5, 
+              monthly_reward => 43200,
+              reward_version => 6 },
+    ?assertEqual(30.0, calculate_consensus_epoch_reward(1,30,Vars)),
+    ?assertEqual(35.0, calculate_consensus_epoch_reward(1,50,Vars)).
+
+consensus_epoch_reward_test() ->
+    % using test values such that reward is 1 per block
+    % should always return the election interval as the answer
+    ?assertEqual(30.0,calculate_epoch_reward(1,1,25,60000,30,43200)),
+
+    % more than 30 blocks should return 30
+    ?assertEqual(30.0,calculate_epoch_reward(1,1,50,60000,30,43200)).
+
 -endif.