Estimates fedimint fee

mutiny-core/src/lib.rs

@@ -1071,6 +1071,66 @@ impl<S: MutinyStorage> MutinyWallet<S> {
         }
     }
 
+    /// Estimates the lightning fee for a transaction. Amount is either from the invoice
+    /// if one is available or a passed in amount (priority). It will try to predict either
+    /// sending the payment through a federation or through lightning, depending on balances.
+    /// The amount and fee is in satoshis.
+    /// Returns None if it has no good way to calculate fee.
+    pub async fn estimate_ln_fee(
+        &self,
+        inv: Option<&Bolt11Invoice>,
+        amt_sats: Option<u64>,
+    ) -> Result<Option<u64>, MutinyError> {
+        let amt = if let Some(a) = amt_sats {
+            a
+        } else if let Some(i) = inv {
+            if let Some(a) = i.amount_milli_satoshis() {
+                a
+            } else {
+                return Err(MutinyError::BadAmountError);
+            }
+        } else {
+            return Err(MutinyError::BadAmountError);
+        };
+
+        // check balances first
+        let total_balances = self.get_balance().await?;
+        if total_balances.federation > amt {
+            let federation_ids = self.list_federation_ids().await?;
+            for federation_id in federation_ids {
+                // Check if the federation has enough balance
+                if let Some(fedimint_client) = self.federations.read().await.get(&federation_id) {
+                    let current_balance = fedimint_client.get_balance().await?;
+                    log_info!(
+                        self.logger,
+                        "current fedimint client balance: {}",
+                        current_balance
+                    );
+
+                    let fees = fedimint_client.gateway_fee().await?;
+                    let max_spendable = max_spendable_amount(current_balance, fees.clone())
+                        .map_or(Err(MutinyError::InsufficientBalance), Ok)?;
+
+                    if max_spendable >= amt {
+                        let prop_fee_msat =
+                            (amt as f64 * 1_000.0 * fees.proportional_millionths as f64)
+                                / 1_000_000.0;
+
+                        let total_fee = fees.base_msat as f64 + prop_fee_msat;
+                        return Ok(Some((total_fee / 1_000.0).floor() as u64));
+                    }
+                }
+            }
+        }
+
+        if total_balances.lightning > amt {
+            // TODO try something to try to get lightning fee
+            return Ok(None);
+        }
+
+        Err(MutinyError::InsufficientBalance)
+    }
+
     /// Creates a BIP 21 invoice. This creates a new address and a lightning invoice.
     /// The lightning invoice may return errors related to the LSP. Check the error and
     /// fallback to `get_new_address` and warn the user that Lightning is not available.

mutiny-wasm/src/lib.rs

@@ -608,6 +608,26 @@ impl MutinyWallet {
             .estimate_sweep_channel_open_fee(fee_rate)?)
     }
 
+    /// Estimates the lightning fee for a transaction. Amount is either from the invoice
+    /// if one is available or a passed in amount (priority). It will try to predict either
+    /// sending the payment through a federation or through lightning, depending on balances.
+    /// The amount and fee is in satoshis.
+    /// Returns None if it has no good way to calculate fee.
+    pub async fn estimate_ln_fee(
+        &self,
+        invoice_str: Option<String>,
+        amt_sats: Option<u64>,
+    ) -> Result<Option<u64>, MutinyJsError> {
+        let invoice = match invoice_str {
+            Some(i) => Some(Bolt11Invoice::from_str(&i)?),
+            None => None,
+        };
+        Ok(self
+            .inner
+            .estimate_ln_fee(invoice.as_ref(), amt_sats)
+            .await?)
+    }
+
     /// Bumps the given transaction by replacing the given tx with a transaction at
     /// the new given fee rate in sats/vbyte
     pub async fn bump_fee(&self, txid: String, fee_rate: f32) -> Result<String, MutinyJsError> {