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// This file is part of Soil.
// Copyright (C) Soil contributors.
// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0 OR GPL-3.0-or-later WITH Classpath-exception-2.0
//! Traits for dealing with on-chain randomness.
/// A trait that is able to provide randomness.
///
/// Being a deterministic blockchain, real randomness is difficult to come by, different
/// implementations of this trait will provide different security guarantees. At best,
/// this will be randomness which was hard to predict a long time ago, but that has become
/// easy to predict recently.
pub trait Randomness<Output, BlockNumber> {
/// Get the most recently determined random seed, along with the time in the past
/// since when it was determinable by chain observers.
///
/// `subject` is a context identifier and allows you to get a different result to
/// other callers of this function; use it like `random(&b"my context"[..])`.
///
/// NOTE: The returned seed should only be used to distinguish commitments made before
/// the returned block number. If the block number is too early (i.e. commitments were
/// made afterwards), then ensure no further commitments may be made and repeatedly
/// call this on later blocks until the block number returned is later than the latest
/// commitment.
fn random(subject: &[u8]) -> (Output, BlockNumber);
/// Get the basic random seed.
///
/// In general you won't want to use this, but rather `Self::random` which allows
/// you to give a subject for the random result and whose value will be
/// independently low-influence random from any other such seeds.
///
/// NOTE: The returned seed should only be used to distinguish commitments made before
/// the returned block number. If the block number is too early (i.e. commitments were
/// made afterwards), then ensure no further commitments may be made and repeatedly
/// call this on later blocks until the block number returned is later than the latest
/// commitment.
fn random_seed() -> (Output, BlockNumber) {
Self::random(&[][..])
}
}