merkle root is the txid if there is only one (#75)

Signed-off-by: Darren Kellenschwiler <d.kellenschwiler@bsvblockchain.org>

bump.go

@@ -141,6 +141,9 @@ func (bump *BUMP) String() (string, error) {
 
 // CalculateRootGivenTxid calculates the root of the Merkle tree given a txid.
 func (bump *BUMP) CalculateRootGivenTxid(txid string) (string, error) {
+	if len(bump.Path) < 2 {
+		return txid, nil
+	}
 	// Find the index of the txid at the lowest level of the Merkle tree
 	var index uint64
 	txidFound := false
@@ -241,7 +244,7 @@ func NewBUMPFromMerkleTreeAndIndex(blockHeight uint64, merkleTree []*chainhash.H
 	} else {
 		sh := merkleTree[0].String()
 		o := uint64(0)
-		bump.Path[0][0] = leaf{Hash: &sh, Offset: &o, Txid: &t}
+		bump.Path = [][]leaf{{leaf{Hash: &sh, Offset: &o, Txid: &t}}}
 	}
 
 	return bump, nil

bump_test.go

@@ -15,6 +15,7 @@ const (
 	txidExample          = `3ecead27a44d013ad1aae40038acbb1883ac9242406808bb4667c15b4f164eac`
 	rootOfBlockTxExample = `1a1e779cd7dfc59f603b4e88842121001af822b2dc5d3b167ae66152e586a6b0`
 	fakeMadeUpNum        = 814435
+	txidSmallBlock       = `be7853d7685ed5b5ec61a0ca8e3f193a7b0632cb2db950528c2041ee5d7dd95d`
 )
 
 var blockTxExample = []string{
@@ -28,6 +29,20 @@ var blockTxExample = []string{
 	"397fe2ae4d1d24efcc868a02daae42d1b419289d9a1ded3a5fe771efcc1219d9",
 }
 
+func TestNewBUMPFromMerkleTreeWithOnlyOneTxid(t *testing.T) {
+	chainHashBlock := make([]*chainhash.Hash, 0)
+	hash, err := chainhash.NewHashFromStr(txidSmallBlock)
+	require.NoError(t, err)
+	chainHashBlock = append(chainHashBlock, hash)
+	merkles, err := BuildMerkleTreeStoreChainHash(chainHashBlock)
+	require.NoError(t, err)
+	bump, err := NewBUMPFromMerkleTreeAndIndex(fakeMadeUpNum, merkles, uint64(0))
+	require.NoError(t, err)
+	root, err := bump.CalculateRootGivenTxid(txidSmallBlock)
+	require.NoError(t, err)
+	require.Equal(t, txidSmallBlock, root)
+}
+
 func TestNewBUMPFromMerkleTree(t *testing.T) {
 	chainHashBlock := make([]*chainhash.Hash, 0)
 	for _, txid := range blockTxExample {