Introduce currency swap related primitives

crates/primitives-currency-swap/Cargo.toml

@@ -0,0 +1,13 @@
+[package]
+name = "primitives-currency-swap"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
+frame-support = { default-features = false, git = "https://github.com/humanode-network/substrate", branch = "locked/polkadot-v0.9.38" }
+
+[features]
+default = ["std"]
+std = ["frame-support/std"]
+try-runtime = ["frame-support/try-runtime"]

crates/primitives-currency-swap/src/lib.rs

@@ -0,0 +1,23 @@
+//! Currency swap related primitives.
+
+// Either generate code at stadard mode, or `no_std`, based on the `std` feature presence.
+#![cfg_attr(not(feature = "std"), no_std)]
+
+use frame_support::{sp_runtime::DispatchError, traits::Currency};
+
+/// Currency swap interface.
+pub trait CurrencySwap<AccountIdFrom, AccountIdTo> {
+    /// The currency type balances send from.
+    type From: Currency<AccountIdFrom>;
+
+    /// The currency type balances send to.
+    type To: Currency<AccountIdTo>;
+
+    /// A possible error happens during the actual swap logic.
+    type Error: Into<DispatchError>;
+
+    /// The actual swap logic.
+    fn swap(
+        imbalance: <Self::From as Currency<AccountIdFrom>>::NegativeImbalance,
+    ) -> Result<<Self::To as Currency<AccountIdTo>>::NegativeImbalance, Self::Error>;
+}