ffi: added 2 functions, wallet_preview_coin_split and wallet_preview_…

…coin_join (#4264)

Description
---
Added 2 preview functions for coin split and join

Motivation and Context
---
To let mobile users appraise the fee and expected outputs without performing the actual split/join operation.

How Has This Been Tested?
---
unit tests

base_layer/wallet/src/output_manager_service/handle.rs

@@ -110,6 +110,8 @@ pub enum OutputManagerRequest {
     RevalidateTxos,
     CreateCoinSplit((Vec<Commitment>, MicroTari, usize, MicroTari)),
     CreateCoinSplitEven((Vec<Commitment>, usize, MicroTari)),
+    PreviewCoinJoin((Vec<Commitment>, MicroTari)),
+    PreviewCoinSplitEven((Vec<Commitment>, usize, MicroTari)),
     CreateCoinJoin {
         commitments: Vec<Commitment>,
         fee_per_gram: MicroTari,
@@ -177,6 +179,16 @@ impl fmt::Display for OutputManagerRequest {
             GetInvalidOutputs => write!(f, "GetInvalidOutputs"),
             ValidateUtxos => write!(f, "ValidateUtxos"),
             RevalidateTxos => write!(f, "RevalidateTxos"),
+            PreviewCoinJoin((commitments, fee_per_gram)) => write!(
+                f,
+                "PreviewCoinJoin(commitments={:#?}, fee_per_gram={})",
+                commitments, fee_per_gram
+            ),
+            PreviewCoinSplitEven((commitments, number_of_splits, fee_per_gram)) => write!(
+                f,
+                "PreviewCoinSplitEven(commitments={:#?}, number_of_splits={}, fee_per_gram={})",
+                commitments, number_of_splits, fee_per_gram
+            ),
             CreateCoinSplit(v) => write!(f, "CreateCoinSplit ({:?})", v.0),
             CreateCoinSplitEven(v) => write!(f, "CreateCoinSplitEven ({:?})", v.0),
             CreateCoinJoin {
@@ -272,6 +284,7 @@ pub enum OutputManagerResponse {
     CoinbaseAbandonedSet,
     ClaimHtlcTransaction((TxId, MicroTari, MicroTari, Transaction)),
     OutputStatusesByTxId(OutputStatusesByTxId),
+    CoinPreview((Vec<MicroTari>, MicroTari)),
 }
 
 pub type OutputManagerEventSender = broadcast::Sender<Arc<OutputManagerEvent>>;
@@ -673,6 +686,41 @@ impl OutputManagerHandle {
         }
     }
 
+    pub async fn preview_coin_join_with_commitments(
+        &mut self,
+        commitments: Vec<Commitment>,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), OutputManagerError> {
+        match self
+            .handle
+            .call(OutputManagerRequest::PreviewCoinJoin((commitments, fee_per_gram)))
+            .await??
+        {
+            OutputManagerResponse::CoinPreview((expected_outputs, fee)) => Ok((expected_outputs, fee)),
+            _ => Err(OutputManagerError::UnexpectedApiResponse),
+        }
+    }
+
+    pub async fn preview_coin_split_with_commitments_no_amount(
+        &mut self,
+        commitments: Vec<Commitment>,
+        split_count: usize,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), OutputManagerError> {
+        match self
+            .handle
+            .call(OutputManagerRequest::PreviewCoinSplitEven((
+                commitments,
+                split_count,
+                fee_per_gram,
+            )))
+            .await??
+        {
+            OutputManagerResponse::CoinPreview((expected_outputs, fee)) => Ok((expected_outputs, fee)),
+            _ => Err(OutputManagerError::UnexpectedApiResponse),
+        }
+    }
+
     /// Create a coin split transaction.
     /// Returns (tx_id, tx, utxos_total_value).
     pub async fn create_coin_split(

base_layer/wallet/src/output_manager_service/service.rs

@@ -382,6 +382,18 @@ where
                 let outputs = self.fetch_invalid_outputs()?.into_iter().map(|v| v.into()).collect();
                 Ok(OutputManagerResponse::InvalidOutputs(outputs))
             },
+            OutputManagerRequest::PreviewCoinJoin((commitments, fee_per_gram)) => {
+                Ok(OutputManagerResponse::CoinPreview(
+                    self.preview_coin_join_with_commitments(commitments, fee_per_gram)
+                        .await?,
+                ))
+            },
+            OutputManagerRequest::PreviewCoinSplitEven((commitments, number_of_splits, fee_per_gram)) => {
+                Ok(OutputManagerResponse::CoinPreview(
+                    self.preview_coin_split_with_commitments_no_amount(commitments, number_of_splits, fee_per_gram)
+                        .await?,
+                ))
+            },
             OutputManagerRequest::CreateCoinSplit((commitments, amount_per_split, split_count, fee_per_gram)) => {
                 if commitments.is_empty() {
                     self.create_coin_split_auto(Some(amount_per_split), split_count, fee_per_gram)
@@ -1716,6 +1728,78 @@ where
             )
     }
 
+    pub async fn preview_coin_join_with_commitments(
+        &self,
+        commitments: Vec<Commitment>,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), OutputManagerError> {
+        let src_outputs = self.resources.db.fetch_unspent_outputs_for_spending(
+            UtxoSelectionCriteria::specific(commitments),
+            MicroTari::zero(),
+            None,
+        )?;
+
+        let accumulated_amount = src_outputs
+            .iter()
+            .fold(MicroTari::zero(), |acc, x| acc + x.unblinded_output.value);
+
+        let fee = self
+            .get_fee_calc()
+            .calculate(fee_per_gram, 1, src_outputs.len(), 1, self.default_metadata_size());
+
+        Ok((vec![accumulated_amount.saturating_sub(fee)], fee))
+    }
+
+    pub async fn preview_coin_split_with_commitments_no_amount(
+        &mut self,
+        commitments: Vec<Commitment>,
+        number_of_splits: usize,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), OutputManagerError> {
+        if commitments.is_empty() {
+            return Err(OutputManagerError::NoCommitmentsProvided);
+        }
+
+        if number_of_splits == 0 {
+            return Err(OutputManagerError::InvalidArgument(
+                "number_of_splits must be greater than 0".to_string(),
+            ));
+        }
+
+        let src_outputs = self.resources.db.fetch_unspent_outputs_for_spending(
+            UtxoSelectionCriteria::specific(commitments),
+            MicroTari::zero(),
+            None,
+        )?;
+
+        let fee = self.get_fee_calc().calculate(
+            fee_per_gram,
+            1,
+            src_outputs.len(),
+            number_of_splits,
+            self.default_metadata_size() * number_of_splits,
+        );
+
+        let accumulated_amount = src_outputs
+            .iter()
+            .fold(MicroTari::zero(), |acc, x| acc + x.unblinded_output.value);
+
+        let aftertax_amount = accumulated_amount.saturating_sub(fee);
+        let amount_per_split = MicroTari(aftertax_amount.as_u64() / number_of_splits as u64);
+        let unspent_remainder = MicroTari(aftertax_amount.as_u64() % amount_per_split.as_u64());
+        let mut expected_outputs = vec![];
+
+        for i in 1..=number_of_splits {
+            expected_outputs.push(if i == number_of_splits {
+                amount_per_split + unspent_remainder
+            } else {
+                amount_per_split
+            });
+        }
+
+        Ok((expected_outputs, fee))
+    }
+
     async fn create_coin_split_with_commitments(
         &mut self,
         commitments: Vec<Commitment>,

base_layer/wallet/src/wallet.rs

@@ -536,6 +536,31 @@ where
         signature.verify_challenge(&public_key, challenge.clone().as_slice())
     }
 
+    /// Appraise the expected outputs and a fee
+    pub async fn preview_coin_split_with_commitments_no_amount(
+        &mut self,
+        commitments: Vec<Commitment>,
+        split_count: usize,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), WalletError> {
+        self.output_manager_service
+            .preview_coin_split_with_commitments_no_amount(commitments, split_count, fee_per_gram)
+            .await
+            .map_err(WalletError::OutputManagerError)
+    }
+
+    /// Appraise the expected outputs and a fee
+    pub async fn preview_coin_join_with_commitments(
+        &mut self,
+        commitments: Vec<Commitment>,
+        fee_per_gram: MicroTari,
+    ) -> Result<(Vec<MicroTari>, MicroTari), WalletError> {
+        self.output_manager_service
+            .preview_coin_join_with_commitments(commitments, fee_per_gram)
+            .await
+            .map_err(WalletError::OutputManagerError)
+    }
+
     /// Do a coin split
     pub async fn coin_split(
         &mut self,
@@ -593,6 +618,34 @@ where
         }
     }
 
+    /// Do a coin split
+    pub async fn coin_split_even_with_commitments(
+        &mut self,
+        commitments: Vec<Commitment>,
+        split_count: usize,
+        fee_per_gram: MicroTari,
+        message: String,
+    ) -> Result<TxId, WalletError> {
+        let coin_split_tx = self
+            .output_manager_service
+            .create_coin_split_even(commitments, split_count, fee_per_gram)
+            .await;
+
+        match coin_split_tx {
+            Ok((tx_id, split_tx, amount)) => {
+                let coin_tx = self
+                    .transaction_service
+                    .submit_transaction(tx_id, split_tx, amount, message)
+                    .await;
+                match coin_tx {
+                    Ok(_) => Ok(tx_id),
+                    Err(e) => Err(WalletError::TransactionServiceError(e)),
+                }
+            },
+            Err(e) => Err(WalletError::OutputManagerError(e)),
+        }
+    }
+
     pub async fn coin_join(
         &mut self,
         commitments: Vec<Commitment>,