add specific network/coin/balance types (#619)

* add specific network/coin/balance types

* misc fixes

* fix clippy

* misc fixes

* fix pr comments

* Make halting for external networks

* fix encode/decode

substrate/primitives/src/balance.rs

@@ -11,7 +11,7 @@ use serde::{Serialize, Deserialize};
 use scale::{Encode, Decode, MaxEncodedLen};
 use scale_info::TypeInfo;
 
-use crate::{Coin, Amount};
+use crate::{Amount, Coin, ExternalCoin};
 
 /// The type used for balances (a Coin and Balance).
 #[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, MaxEncodedLen, TypeInfo)]
@@ -23,6 +23,34 @@ pub struct Balance {
   pub amount: Amount,
 }
 
+/// The type used for balances (a Coin and Balance).
+#[derive(Clone, Copy, PartialEq, Eq, Debug, Encode, Decode, MaxEncodedLen, TypeInfo)]
+#[cfg_attr(feature = "std", derive(Zeroize))]
+#[cfg_attr(feature = "borsh", derive(BorshSerialize, BorshDeserialize))]
+#[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
+pub struct ExternalBalance {
+  pub coin: ExternalCoin,
+  pub amount: Amount,
+}
+
+impl From<ExternalBalance> for Balance {
+  fn from(balance: ExternalBalance) -> Self {
+    Balance { coin: balance.coin.into(), amount: balance.amount }
+  }
+}
+
+impl TryFrom<Balance> for ExternalBalance {
+  type Error = ();
+
+  fn try_from(balance: Balance) -> Result<Self, Self::Error> {
+    match balance.coin {
+      Coin::Serai => Err(())?,
+      Coin::External(coin) => Ok(ExternalBalance { coin, amount: balance.amount }),
+    }
+  }
+}
+
+// TODO: these impl either should be removed or return errors in case of overflows
 impl Add<Amount> for Balance {
   type Output = Balance;
   fn add(self, other: Amount) -> Balance {