Add NFT trait. (#309)

traits/src/lib.rs

@@ -17,6 +17,7 @@ pub use currency::{
 };
 pub use data_provider::{DataFeeder, DataProvider, DataProviderExtended};
 pub use get_by_key::GetByKey;
+pub use nft::NFT;
 pub use price::{DefaultPriceProvider, PriceProvider};
 pub use rewards::RewardHandler;
 
@@ -25,6 +26,7 @@ pub mod auction;
 pub mod currency;
 pub mod data_provider;
 pub mod get_by_key;
+pub mod nft;
 pub mod price;
 pub mod rewards;
 

traits/src/nft.rs

+use codec::FullCodec;
+use sp_runtime::{
+	traits::{AtLeast32BitUnsigned, MaybeSerializeDeserialize},
+	DispatchResult,
+};
+use sp_std::fmt::Debug;
+
+/// Abstraction over a non-fungible token system.
+pub trait NFT<AccountId> {
+	/// The NFT class identifier.
+	type ClassId: Default + Copy;
+
+	/// The NFT token identifier.
+	type TokenId: Default + Copy;
+
+	/// The balance of account.
+	type Balance: AtLeast32BitUnsigned + FullCodec + Copy + MaybeSerializeDeserialize + Debug + Default;
+
+	/// The number of NFTs assigned to `who`.
+	fn balance(who: &AccountId) -> Self::Balance;
+
+	/// The owner of the given token ID. Returns `None` if the token does not
+	/// exist.
+	fn owner(token: (Self::ClassId, Self::TokenId)) -> Option<AccountId>;
+
+	/// Transfer the given token ID from one account to another.
+	fn transfer(from: &AccountId, to: &AccountId, token: (Self::ClassId, Self::TokenId)) -> DispatchResult;
+}