refactor spend_from_wallet and add checks for spend_amount.

- check whether the given amount is feasible to spend or not.
- refactor the api to improve efficiency.

src/wallet/direct_send.rs

@@ -72,8 +72,18 @@ impl Wallet {
  coins_to_spend: &[(ListUnspentResultEntry, UTXOSpendInfo)],
  ) -> Result<Transaction, WalletError> {
  log::info!("Creating Direct-Spend from Wallet.");
- let mut tx_inputs = Vec::<TxIn>::new();
- let mut spend_infos = Vec::new();
+
+ // Set the Anti-Fee-Snipping locktime
+ let current_height = self.rpc.get_block_count()?;
+ let lock_time = LockTime::from_height(current_height as u32)?;
+
+ let mut tx = Transaction {
+ version: Version::TWO,
+ lock_time,
+ input: vec![],
+ output: vec![],
+ };
+
  let mut total_input_value = Amount::ZERO;
 
  for (utxo_data, spend_info) in coins_to_spend {
@@ -93,24 +103,16 @@ impl Wallet {
  _ => 0,
  };
 
- tx_inputs.push(TxIn {
+ tx.input.push(TxIn {
  previous_output: OutPoint::new(utxo_data.txid, utxo_data.vout),
  sequence: Sequence(sequence),
  witness: Witness::new(),
  script_sig: ScriptBuf::new(),
  });
 
- spend_infos.push(spend_info);
-
  total_input_value += utxo_data.amount;
  }
 
- if tx_inputs.len() != coins_to_spend.len() {
- return Err(WalletError::Protocol(
- "Could not fetch all inputs.".to_string(),
- ));
- }
-
  log::info!("Total Input Amount: {} | Fees: {}", total_input_value, fee);
 
  let dest_addr = match destination {
@@ -133,12 +135,19 @@ impl Wallet {
  }
  };
 
- let mut output = Vec::<TxOut>::new();
-
  let txout = {
  let value = match send_amount {
  SendAmount::Max => (total_input_value - fee).to_sat(),
- SendAmount::Amount(a) => a.to_sat(),
+ SendAmount::Amount(a) => {
+ if a + fee <= total_input_value {
+ a.to_sat()
+ } else {
+ return Err(WalletError::Protocol(
+ "Insufficient funds: Amount plus fees exceeds available UTXOs."
+ .to_string(),
+ ));
+ }
+ }
  };
  log::info!("Sending {} to {}.", value, dest_addr);
  TxOut {
@@ -147,31 +156,21 @@ impl Wallet {
  }
  };
 
- output.push(txout);
+ tx.output.push(txout);
 
  // Only include change if remaining > dust
  if let SendAmount::Amount(amount) = send_amount {
  let internal_spk = self.get_next_internal_addresses(1)?[0].script_pubkey();
  let remaining = total_input_value - amount - fee;
  if remaining > internal_spk.minimal_non_dust() {
  log::info!("Adding Change {}:{}", internal_spk, remaining);
- output.push(TxOut {
+ tx.output.push(TxOut {
  script_pubkey: internal_spk,
  value: remaining,
  });
  }
  }
 
- // Set the Anti-Fee-Snipping locktime
- let current_height = self.rpc.get_block_count()?;
- let lock_time = LockTime::from_height(current_height as u32)?;
-
- let mut tx = Transaction {
- input: tx_inputs,
- output,
- lock_time,
- version: Version::TWO,
- };
  self.sign_transaction(
  &mut tx,
  &mut coins_to_spend.iter().map(|(_, usi)| usi.clone()),