From ed91b3f57b92bc1e4e02a04234dd1d8d17955dec Mon Sep 17 00:00:00 2001
From: Jim Hamill <zuccon@gmail.com>
Date: Mon, 14 Jul 2025 00:27:00 +0000
Subject: [PATCH] fix(BlockchainInMemory): BIP30 protections and fetchChainTip

---
 .../src/blockchain/blockchain-inmemory.ts     | 41 +++++++++++++------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/packages/stack/src/blockchain/blockchain-inmemory.ts b/packages/stack/src/blockchain/blockchain-inmemory.ts
index 95509e5..bb345fd 100644
--- a/packages/stack/src/blockchain/blockchain-inmemory.ts
+++ b/packages/stack/src/blockchain/blockchain-inmemory.ts
@@ -23,8 +23,9 @@ import {
   createVirtualMachineBCH,
 } from '@bitauth/libauth';
 
-// Local Blockchain Adapter.
-// This simulates the BCH Blockchain.
+/**
+ * @remarks This provider DOES NOT enforce the 100 confirmations Coinbase Transaction rule.
+ **/
 export class BlockchainInMemory extends BaseBlockchain {
   static async from<T extends typeof BlockchainInMemory>(this: T) {
     const blockchain = new this();
@@ -104,10 +105,14 @@ export class BlockchainInMemory extends BaseBlockchain {
     return blockHeader;
   }
 
-  // TODO: Implement a method for fetching the chain tip.
-  //       This is a placeholder for now.
   async fetchChainTip(): Promise<BlockchainChainTip> {
-    throw new Error('Not implemented yet');
+    const height = this.blockHeaders.length;
+    const blockHeader = this.blockHeaders[height - 1];
+
+    return {
+      height,
+      blockHeader,
+    };
   }
 
   async broadcastTransaction(
@@ -347,14 +352,6 @@ export class BlockchainInMemory extends BaseBlockchain {
   }
 
   async mineBlock(outputs: Array<Output>): Promise<void> {
-    // Create a block header from the current timestamp.
-    const newBlockHeader = BlockHeader.generateRandom(
-      Math.floor(Date.now() / 1000),
-    );
-
-    // Add it to our list of block headers.
-    this.blockHeaders.push(newBlockHeader);
-
     // Create a transaction that pays to our subscribed address.
     const transaction = Transaction.fromRaw({
       version: 2,
@@ -370,6 +367,24 @@ export class BlockchainInMemory extends BaseBlockchain {
       outputs,
     });
 
+    // Calculate the hash of this transaction.
+    const coinbaseTxHash = transaction.toHash();
+
+    // Ensure that this transaction hash does not already exist (as per BIP30).
+    if (this.transactions.has(coinbaseTxHash.toHex())) {
+      throw new Error(
+        `Transaction ID "${coinbaseTxHash.toHex()}" already exists (see BIP30 for details)`,
+      );
+    }
+
+    // Create a block header from the current timestamp.
+    const newBlockHeader = BlockHeader.generateRandom(
+      Math.floor(Date.now() / 1000),
+    );
+
+    // Add it to our list of block headers.
+    this.blockHeaders.push(newBlockHeader);
+
     // Broadcast that transaction.
     await this.broadcastTransaction(transaction, { skipValidation: true });
   }