feat:pallets/price-feed: introduce price feed types and price feed trait

pallets/price-feed/src/traits.rs

@@ -0,0 +1,17 @@
+// Copyright 2021 ChainSafe Systems
+// SPDX-License-Identifier: LGPL-3.0-only
+
+use crate::types::AssetPricePair;
+use frame_support::dispatch::DispatchError;
+
+/// An interface to access price data
+pub trait PriceFeed<AssetId, Balance> {
+    /// Returns the current price pair for `base/quote` where `base` is the native token
+    fn get_price(quote: AssetId) -> Result<AssetPricePair<AssetId, Balance>, DispatchError>;
+
+    /// Returns the current price pair for `base/quote`
+    fn get_price_pair(
+        base: AssetId,
+        quote: AssetId,
+    ) -> Result<AssetPricePair<AssetId, Balance>, DispatchError>;
+}

pallets/price-feed/src/types.rs

@@ -0,0 +1,74 @@
+// Copyright 2021 ChainSafe Systems
+// SPDX-License-Identifier: LGPL-3.0-only
+
+use frame_support::pallet_prelude::*;
+use frame_support::sp_runtime::traits::AtLeast32BitUnsigned;
+use frame_support::sp_runtime::{PerThing, SaturatedConversion};
+
+/// Defines an asset pair identifier
+#[derive(PartialEq, Eq, Clone, Encode, Decode, RuntimeDebug)]
+pub struct AssetPricePair<AssetId, Price> {
+    /// The base asset id of this pair.
+    pub base: AssetId,
+    /// The quote asset
+    pub quote: AssetId,
+    /// The price for `base/quote`
+    price: Price,
+}
+
+impl<AssetId, Price> AssetPricePair<AssetId, Price>
+where
+    AssetId: Member,
+    Price: PerThing,
+{
+    /// Whether this pair involves the `asset`
+    pub fn involves_asset(&self, asset: &AssetId) -> bool {
+        self.is_base(asset) || self.is_quote(asset)
+    }
+
+    /// Whether the provided asset is the `base` asset of this price pair
+    pub fn is_base(&self, asset: &AssetId) -> bool {
+        self.base == *asset
+    }
+
+    /// Whether the provided asset is the `quote` asset of this price pair
+    pub fn is_quote(&self, asset: &AssetId) -> bool {
+        self.quote == *asset
+    }
+
+    /// Returns the price fraction `base/quote`
+    pub fn price(&self) -> &Price {
+        &self.price
+    }
+
+    /// Calculates the total volume of the provided units of the `quote` assetId w.r.t. price pair
+    pub fn volume<N>(&self, units: N) -> Price
+    where
+        N: Into<Price>,
+    {
+        self.price * Price::saturated_from(units)
+    }
+
+    /// Calculates the total volume of the provided units of the `base` assetId w.r.t. price pair
+    pub fn reciprocal_volume<N>(&self, units: N) -> u128
+    where
+        N: Into<u128>,
+    {
+        self.price.saturating_reciprocal_mul(units.into())
+    }
+}
+
+impl<AssetId, Price> AssetPricePair<AssetId, Price>
+where
+    AssetId: Member,
+    Price: PerThing + From<u128>,
+{
+    /// Turns this price pair of `base/quote` into a price pair of `quote/base`
+    pub fn invert(self) -> Self {
+        Self {
+            base: self.quote,
+            quote: self.base,
+            price: self.price.saturating_reciprocal_mul(1).into(),
+        }
+    }
+}