external-api: add get_quote_amount helper

external-api/src/http/external_match.rs

@@ -161,7 +161,7 @@ impl ExternalOrder {
     ///
     /// The price here is expected to be decimal corrected; i.e. multiplied by
     /// the decimal diff for the two tokens
-    fn get_base_amount(&self, price: FixedPoint) -> Amount {
+    pub fn get_base_amount(&self, price: FixedPoint) -> Amount {
         if self.base_amount != 0 {
             return self.base_amount;
         }
@@ -170,6 +170,20 @@ impl ExternalOrder {
         scalar_to_u128(&implied_base_amount)
     }
 
+    /// Get the quote amount of the order implied by the external order
+    ///
+    /// The price here is expected to be decimal corrected; i.e. multiplied by
+    /// the decimal diff for the two tokens
+    pub fn get_quote_amount(&self, price: FixedPoint) -> Amount {
+        if self.quote_amount != 0 {
+            return self.quote_amount;
+        }
+
+        let base_amount_scalar = Scalar::from(self.base_amount);
+        let implied_quote_amount = price * base_amount_scalar;
+        scalar_to_u128(&implied_quote_amount.floor())
+    }
+
     /// Get the min fill size in units of the base token
     ///
     /// If the order size is specified in the `base_amount` field, this is