feat(common): add IAsyncProvider interface definition

This is a commonly reusable interface that objects/classes
can choose to implement to express that they have
the ability to provide a certain value.
Helps a lot while authoring methods that must be able
to accept injected providers as parameters for example
in order to allow them to be customizable without
doing an actual source code rewrite of the
functions itself.

Signed-off-by: Peter Somogyvari <peter.somogyvari@accenture.com>

packages/cactus-common/src/main/typescript/i-async-provider.ts

@@ -0,0 +1,12 @@
+/**
+ * A generic interface to be implemented by objects/classes that want to express
+ * their ability of returning a certain type of object or value in an async
+ * manner (e.g. by returning a Promise of what is actually being provided).
+ */
+export interface IAsyncProvider<T> {
+  /**
+   * Obtains the value/object meant to be provided by this `IAsyncProvider`
+   * implementation.
+   */
+  get(): Promise<T>;
+}

packages/cactus-common/src/main/typescript/public-api.ts

@@ -18,3 +18,4 @@ export {
 export { ISignerKeyPair } from "./signer-key-pair";
 export { Secp256k1Keys } from "./secp256k1-keys";
 export { KeyFormat, KeyConverter } from "./key-converter";
+export { IAsyncProvider } from "./i-async-provider";