fix txbuilder remaining multi asset amount

Author: tacmota

pycardano/txbuilder.py

@@ -1350,12 +1350,9 @@ def build(
 
         unfulfilled_amount = requested_amount - trimmed_selected_amount
 
-        can_use_again_multi_asset = unfulfilled_amount.multi_asset.filter(
-            lambda p, n, v: v < 0
-        )
-        can_use_again = Value(
-            min(0, unfulfilled_amount.coin) * -1, can_use_again_multi_asset
-        )
+        remaining = trimmed_selected_amount - requested_amount
+        remaining.multi_asset = remaining.multi_asset.filter(lambda p, n, v: v > 0)
+        remaining.coin = max(0, remaining.coin)
 
         if change_address is not None and not can_merge_change:
             # If change address is provided and remainder is smaller than minimum ADA required in change,
@@ -1415,7 +1412,7 @@ def build(
                         self.context,
                         include_max_fee=False,
                         respect_min_utxo=not can_merge_change,
-                        existing_amount=can_use_again,
+                        existing_amount=remaining,
                     )
 
                     for s in selected:

test/pycardano/test_txbuilder.py

@@ -443,7 +443,7 @@ def test_tx_builder_burn_multi_asset(chain_context):
     tx_builder = TransactionBuilder(chain_context)
     sender = "addr_test1vrm9x2zsux7va6w892g38tvchnzahvcd9tykqf3ygnmwtaqyfg52x"
     sender_address: Address = Address.from_primitive(sender)
-    print("1")
+
     # Add sender address as input
     to_burn = MultiAsset.from_primitive({policy_id.payload: {b"Token1": -1}})
     tx_input = TransactionInput.from_primitive([b"1" * 32, 123])
@@ -455,13 +455,12 @@ def test_tx_builder_burn_multi_asset(chain_context):
             ),
         )
     )
-    print("2")
+
     tx_builder.add_input_address(sender).add_output(
         TransactionOutput.from_primitive([sender, 3000000])
     ).add_output(TransactionOutput.from_primitive([sender, 2000000]))
 
     tx_builder.mint = to_burn
-    print("3")
     tx_body = tx_builder.build(change_address=sender_address)
 
     assert tx_input in tx_body.inputs
@@ -2401,7 +2400,6 @@ def test_token_transfer_with_change(chain_context):
             ),
         )
         tx_builder.add_output(TransactionOutput(receiver_address, output_value))
-        # print(tx_builder)
 
         # Build transaction with change going back to vault
         tx = tx_builder.build(change_address=vault_address, merge_change=True)
@@ -2422,4 +2420,4 @@ def test_token_transfer_with_change(chain_context):
         assert (
             change_output.amount.multi_asset[token_policy_id][token_name]
             == 1876083 - 382
-        )
+        )