From bdff698344f52a80eed2db6d7d438715607d98a2 Mon Sep 17 00:00:00 2001
From: harkamal <gajinder@g11.in>
Date: Tue, 27 Sep 2022 21:33:28 +0530
Subject: [PATCH] further simplify the fn and add test to enhance coverage

---
 packages/common/src/common.ts           | 23 ++++++++++++++---------
 packages/common/tests/hardforks.spec.ts | 14 ++++++++++++++
 2 files changed, 28 insertions(+), 9 deletions(-)

diff --git a/packages/common/src/common.ts b/packages/common/src/common.ts
index 4abf0dfe276..3cf7ee43417 100644
--- a/packages/common/src/common.ts
+++ b/packages/common/src/common.ts
@@ -308,27 +308,32 @@ export class Common extends EventEmitter {
         continue
       }
 
-      if (hf.ttd !== undefined && hf.ttd !== null) {
-        // Only one hardfork merge is based on ttd, if mergeTTDSeen already seen than throw error
-        if (passedMergeHF !== undefined) {
-          throw new Error(
-            `Invalid hardfork config with repeat ttd hardfork=${hf.name} ttd=${hf.ttd}, previous seen at hardfork=${passedMergeHF.name} ttd=${passedMergeHF.ttd}`
-          )
-        }
+      if (hf.ttd !== undefined && hf.ttd !== null && preMergeHF === undefined) {
+        // Ok, this is the hardfork with ttd
         preMergeHF = hardfork
       }
 
-      // If merge hardfork has block null set, we will make determination of that hardfork if no future hardforks qualify
+      // If merge hardfork has block null set, we will make determination if this is merge hardfork or preMergeHF
+      //  - if no future hardforks qualify by block number
+      // So we assume it to quality for now to move to check future post merge hardfork qualitfication
+      //
+      // For the hardforks with block specified we check for qualification
       if (hf.block !== null) {
         if (blockNumber < BigInt(hf.block)) {
           break
         }
       }
 
-      // Move the candidate hardfork pointer to this hf else we would have broken out of loop
+      // hf qualifies else we would have broken out of the loop till now
       if (hardfork?.ttd !== undefined && hardfork?.ttd !== null) {
         passedMergeHF = hardfork!
       }
+      // If passedMergeHF, the next hardforks can't have ttd specified
+      if (passedMergeHF !== undefined && hf.ttd !== undefined && hf.ttd !== null) {
+        throw new Error(
+          `Invalid hardfork config with repeat ttd hardfork=${hf.name} ttd=${hf.ttd}, previous seen at hardfork=${passedMergeHF.name} ttd=${passedMergeHF.ttd}`
+        )
+      }
       hardfork = hf
     }
 
diff --git a/packages/common/tests/hardforks.spec.ts b/packages/common/tests/hardforks.spec.ts
index 39d3d1b14f5..18f1f6feeee 100644
--- a/packages/common/tests/hardforks.spec.ts
+++ b/packages/common/tests/hardforks.spec.ts
@@ -114,6 +114,20 @@ tape('[Common]: Hardfork logic', function (t: tape.Test) {
     st.end()
   })
 
+  t.test('should reject two hardforks  with ttd specified', function (st: tape.Test) {
+    const c = new Common({ chain: Chain.Sepolia })
+    c.hardforks().filter((hf) => hf.name === 'mergeForkIdTransition')[0]!['ttd'] =
+      '17000000000000000'
+
+    try {
+      c.setHardforkByBlockNumber(1735371)
+      st.fail('should have thrown as two hardforks with ttd specified')
+    } catch (error) {
+      st.pass('throws error as two hardforks with ttd specified')
+    }
+    st.end()
+  })
+
   t.test(
     'should generate expected hash with london block zero and base fee per gas defined',
     async (st) => {