monero-serai: fee calculation parity with Monero's wallet2 (#301)

* monero-serai: fee calculation parity with Monero's wallet2

* Minor lint

---------

Co-authored-by: Luke Parker <lukeparker5132@gmail.com>

coins/monero/src/wallet/send/builder.rs

@@ -5,18 +5,18 @@ use zeroize::{Zeroize, ZeroizeOnDrop, Zeroizing};
 use crate::{
   Protocol,
   wallet::{
-    address::MoneroAddress, Fee, SpendableOutput, Change, SignableTransaction, TransactionError,
-    extra::MAX_ARBITRARY_DATA_SIZE,
+    address::MoneroAddress, Fee, SpendableOutput, Change, Decoys, SignableTransaction,
+    TransactionError, extra::MAX_ARBITRARY_DATA_SIZE,
   },
 };
 
 #[derive(Clone, PartialEq, Eq, Debug, Zeroize, ZeroizeOnDrop)]
 struct SignableTransactionBuilderInternal {
   protocol: Protocol,
-  fee: Fee,
+  fee_rate: Fee,
 
   r_seed: Option<Zeroizing<[u8; 32]>>,
-  inputs: Vec<SpendableOutput>,
+  inputs: Vec<(SpendableOutput, Decoys)>,
   payments: Vec<(MoneroAddress, u64)>,
   change_address: Option<Change>,
   data: Vec<Vec<u8>>,
@@ -25,10 +25,10 @@ struct SignableTransactionBuilderInternal {
 impl SignableTransactionBuilderInternal {
   // Takes in the change address so users don't miss that they have to manually set one
   // If they don't, all leftover funds will become part of the fee
-  fn new(protocol: Protocol, fee: Fee, change_address: Option<Change>) -> Self {
+  fn new(protocol: Protocol, fee_rate: Fee, change_address: Option<Change>) -> Self {
     Self {
       protocol,
-      fee,
+      fee_rate,
       r_seed: None,
       inputs: vec![],
       payments: vec![],
@@ -41,10 +41,10 @@ impl SignableTransactionBuilderInternal {
     self.r_seed = Some(r_seed);
   }
 
-  fn add_input(&mut self, input: SpendableOutput) {
+  fn add_input(&mut self, input: (SpendableOutput, Decoys)) {
     self.inputs.push(input);
   }
-  fn add_inputs(&mut self, inputs: &[SpendableOutput]) {
+  fn add_inputs(&mut self, inputs: &[(SpendableOutput, Decoys)]) {
     self.inputs.extend(inputs.iter().cloned());
   }
 
@@ -90,10 +90,10 @@ impl SignableTransactionBuilder {
     Self(self.0.clone())
   }
 
-  pub fn new(protocol: Protocol, fee: Fee, change_address: Option<Change>) -> Self {
+  pub fn new(protocol: Protocol, fee_rate: Fee, change_address: Option<Change>) -> Self {
     Self(Arc::new(RwLock::new(SignableTransactionBuilderInternal::new(
       protocol,
-      fee,
+      fee_rate,
       change_address,
     ))))
   }
@@ -103,11 +103,11 @@ impl SignableTransactionBuilder {
     self.shallow_copy()
   }
 
-  pub fn add_input(&mut self, input: SpendableOutput) -> Self {
+  pub fn add_input(&mut self, input: (SpendableOutput, Decoys)) -> Self {
     self.0.write().unwrap().add_input(input);
     self.shallow_copy()
   }
-  pub fn add_inputs(&mut self, inputs: &[SpendableOutput]) -> Self {
+  pub fn add_inputs(&mut self, inputs: &[(SpendableOutput, Decoys)]) -> Self {
     self.0.write().unwrap().add_inputs(inputs);
     self.shallow_copy()
   }
@@ -138,7 +138,7 @@ impl SignableTransactionBuilder {
       read.payments.clone(),
       read.change_address.clone(),
       read.data.clone(),
-      read.fee,
+      read.fee_rate,
     )
   }
 }