Optimize start_snapshotting? function

apps/explorer/lib/explorer/staking/contract_state.ex

@@ -233,8 +233,6 @@ defmodule Explorer.Staking.ContractState do
 
     epoch_very_beginning = global_responses.epoch_start_block == block_number + 1
 
-    start_snapshotting = start_snapshotting?(global_responses, state, block_number)
-
     # determine if something changed in contracts state since the previous seen block.
     # if something changed or the `fetch_state` function is called for the first time
     # or we are at the beginning of staking epoch or snapshotting recently finished
@@ -242,6 +240,8 @@ defmodule Explorer.Staking.ContractState do
     last_change_block =
       max(global_responses.staking_last_change_block, global_responses.validator_set_last_change_block)
 
+    start_snapshotting = start_snapshotting?(global_responses, state, block_number, last_change_block)
+
     first_fetch = get(:epoch_end_block, 0) == 0
 
     should_update_db =
@@ -350,7 +350,7 @@ defmodule Explorer.Staking.ContractState do
     end
   end
 
-  defp start_snapshotting?(global_responses, state, block_number) do
+  defp start_snapshotting?(global_responses, state, block_number, last_change_block) do
     if global_responses.epoch_number == 0 do
       # we never snapshot at initial staking epoch
       false
@@ -365,6 +365,8 @@ defmodule Explorer.Staking.ContractState do
         :ets.insert(@table_name, snapshotting_scheduled: false)
         true
       else
+        change_pool_address_events =
+          if last_change_block > get(:last_change_block) do
             # check for ChangedMiningAddress and ChangedStakingAddress events
             # from the ValidatorSetAuRa contract: if one of these events
             # emitted, we need to do snapshotting
@@ -377,7 +379,6 @@ defmodule Explorer.Staking.ContractState do
                 block_number
               end
 
-        change_pool_address_events =
             ContractReader.get_contract_events(
               state.contracts.validator_set,
               from_block,
@@ -389,6 +390,9 @@ defmodule Explorer.Staking.ContractState do
                 "0x5c44164828293bba0353472e907f7ee26a8659f916e6311fe826a7c70510e352"
               ]
             )
+          else
+            []
+          end
 
         if Enum.count(change_pool_address_events) > 0 do
           # we see at least one of the events, so start snapshotting