add better comments to the critical part for endian conversion (#43)

Signed-off-by: sczembor <stanislaw.czembor@gmail.com>

Author: sczembor

packages/btcindexer/src/btcindexer.ts

@@ -258,6 +258,9 @@ export class Indexer {
 		if (!block.transactions || block.transactions.length === 0) {
 			return null;
 		}
+		// NOTE: The `merkletreejs` library expects its input leaves to be in big-endian format.
+		// However, `tx.getHash()` from `bitcoinjs-lib` returns the little-endian format used by the Bitcoin protocol.
+		// We must reverse each hash to convert it to big-endian before creating the tree.
 		const leaves = block.transactions.map((tx) => Buffer.from(tx.getHash()).reverse());
 		return new MerkleTree(leaves, SHA256, { isBitcoinTree: true });
 	}

packages/btcindexer/src/sui_client.ts

@@ -43,7 +43,7 @@ export class SuiClient {
 		const target = `${this.nbtcPkg}::${this.nbtcModule}::mint` as const;
 		const serializedTx = serializeBtcTx(transaction);
 
-		// NOTE: the contract is expecting the proofs to be in big-endian format, while the bitcon-js lib operates internally on little-endian.
+		// NOTE: the contract is expecting the proofs to be in little-endian format, while the merkletreejs lib operates internally on big-endian.
 		const proofBigEndian = proof.proofPath.map((p) => Array.from(Buffer.from(p).reverse()));
 
 		tx.moveCall({