crowdfund.rs

// Copyright 2017-2020 Parity Technologies (UK) Ltd.
// This file is part of Polkadot.

// Polkadot is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.

// Polkadot is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License
// along with Polkadot.  If not, see <http://www.gnu.org/licenses/>.

//! # Parachain Crowdfunding module
//!
//! The point of this module is to allow parachain projects to offer the ability to help fund a
//! deposit for the parachain. When the parachain is retired, the funds may be returned.
//!
//! Contributing funds is permissionless. Each fund has a child-trie which stores all
//! contributors account IDs together with the amount they contributed; the root of this can then be
//! used by the parachain to allow contributors to prove that they made some particular contribution
//! to the project (e.g. to be rewarded through some token or badge). The trie is retained for later
//! (efficient) redistribution back to the contributors.
//!
//! Contributions must be of at least `MinContribution` (to account for the resources taken in
//! tracking contributions), and may never tally greater than the fund's `cap`, set and fixed at the
//! time of creation. The `create` call may be used to create a new fund. In order to do this, then
//! a deposit must be paid of the amount `SubmissionDeposit`. Substantial resources are taken on
//! the main trie in tracking a fund and this accounts for that.
//!
//! Funds may be set up during an auction period; their closing time is fixed at creation (as a
//! block number) and if the fund is not successful by the closing time, then it will become *retired*.
//! Funds may span multiple auctions, and even auctions that sell differing periods. However, for a
//! fund to be active in bidding for an auction, it *must* have had *at least one bid* since the end
//! of the last auction. Until a fund takes a further bid following the end of an auction, then it
//! will be inactive.
//!
//! Contributors may get a refund of their contributions from retired funds. After a period (`RetirementPeriod`)
//! the fund may be dissolved entirely. At this point any non-refunded contributions are considered
//! `orphaned` and are disposed of through the `OrphanedFunds` handler (which may e.g. place them
//! into the treasury).
//!
//! Funds may accept contributions at any point before their success or retirement. When a parachain
//! slot auction enters its ending period, then parachains will each place a bid; the bid will be
//! raised once per block if the parachain had additional funds contributed since the last bid.
//!
//! Funds may set their deploy data (the code hash and head data of their parachain) at any point.
//! It may only be done once and once set cannot be changed. Good procedure would be to set them
//! ahead of receiving any contributions in order that contributors may verify that their parachain
//! contains all expected functionality. However, this is not enforced and deploy data may happen
//! at any point, even after a slot has been successfully won or, indeed, never.
//!
//! Funds that are successful winners of a slot may have their slot claimed through the `onboard`
//! call. This may only be done once and must be after the deploy data has been fixed. Successful
//! funds remain tracked (in the `Funds` storage item and the associated child trie) as long as
//! the parachain remains active. Once it does not, it is up to the parachain to ensure that the
//! funds are returned to this module's fund sub-account in order that they be redistributed back to
//! contributors. *Retirement* may be initiated by any account (using the `begin_retirement` call)
//! once the parachain is removed from the its slot.
//!
//! @WARNING: For funds to be returned, it is imperative that this module's account is provided as
//! the offboarding account for the slot. In the case that a parachain supplemented these funds in
//! order to win a later auction, then it is the parachain's duty to ensure that the right amount of
//! funds ultimately end up in module's fund sub-account.

use frame_support::{
	decl_module, decl_storage, decl_event, decl_error, storage::child, ensure,
	traits::{
		Currency, Get, OnUnbalanced, WithdrawReason, ExistenceRequirement::AllowDeath
	},
	weights::{MINIMUM_WEIGHT, SimpleDispatchInfo},
};
use system::ensure_signed;
use sp_runtime::{ModuleId,
	traits::{AccountIdConversion, Hash, Saturating, Zero, CheckedAdd}
};
use crate::slots;
use codec::{Encode, Decode};
use sp_std::vec::Vec;
use primitives::parachain::{Id as ParaId, HeadData};

const MODULE_ID: ModuleId = ModuleId(*b"py/cfund");

pub type BalanceOf<T> =
	<<T as slots::Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::Balance;
#[allow(dead_code)]
pub type NegativeImbalanceOf<T> =
	<<T as slots::Trait>::Currency as Currency<<T as system::Trait>::AccountId>>::NegativeImbalance;

pub trait Trait: slots::Trait {
	type Event: From<Event<Self>> + Into<<Self as system::Trait>::Event>;

	/// The amount to be held on deposit by the owner of a crowdfund.
	type SubmissionDeposit: Get<BalanceOf<Self>>;

	/// The minimum amount that may be contributed into a crowdfund. Should almost certainly be at
	/// least ExistentialDeposit.
	type MinContribution: Get<BalanceOf<Self>>;

	/// The period of time (in blocks) after an unsuccessful crowdfund ending when
	/// contributors are able to withdraw their funds. After this period, their funds are lost.
	type RetirementPeriod: Get<Self::BlockNumber>;

	/// What to do with funds that were not withdrawn.
	type OrphanedFunds: OnUnbalanced<NegativeImbalanceOf<Self>>;
}

/// Simple index for identifying a fund.
pub type FundIndex = u32;

#[derive(Encode, Decode, Copy, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "std", derive(Debug))]
pub enum LastContribution<BlockNumber> {
	Never,
	PreEnding(slots::AuctionIndex),
	Ending(BlockNumber),
}

#[derive(Encode, Decode, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "std", derive(Debug))]
struct DeployData<Hash> {
	code_hash: Hash,
	code_size: u32,
	initial_head_data: HeadData,
}

#[derive(Encode, Decode, Clone, PartialEq, Eq)]
#[cfg_attr(feature = "std", derive(Debug))]
#[codec(dumb_trait_bound)]
pub struct FundInfo<AccountId, Balance, Hash, BlockNumber> {
	/// The parachain that this fund has funded, if there is one. As long as this is `Some`, then
	/// the funds may not be withdrawn and the fund cannot be dissolved.
	parachain: Option<ParaId>,
	/// The owning account who placed the deposit.
	owner: AccountId,
	/// The amount of deposit placed.
	deposit: Balance,
	/// The total amount raised.
	raised: Balance,
	/// Block number after which the funding must have succeeded. If not successful at this number
	/// then everyone may withdraw their funds.
	end: BlockNumber,
	/// A hard-cap on the amount that may be contributed.
	cap: Balance,
	/// The most recent block that this had a contribution. Determines if we make a bid or not.
	/// If this is `Never`, this fund has never received a contribution.
	/// If this is `PreEnding(n)`, this fund received a contribution sometime in auction
	/// number `n` before the ending period.
	/// If this is `Ending(n)`, this fund received a contribution during the current ending period,
	/// where `n` is how far into the ending period the contribution was made.
	last_contribution: LastContribution<BlockNumber>,
	/// First slot in range to bid on; it's actually a LeasePeriod, but that's the same type as
	/// BlockNumber.
	first_slot: BlockNumber,
	/// Last slot in range to bid on; it's actually a LeasePeriod, but that's the same type as
	/// BlockNumber.
	last_slot: BlockNumber,
	/// The deployment data associated with this fund, if any. Once set it may not be reset. First
	/// is the code hash, second is the code size, third is the initial head data.
	deploy_data: Option<DeployData<Hash>>,
}

decl_storage! {
	trait Store for Module<T: Trait> as Crowdfund {
		/// Info on all of the funds.
		Funds get(fn funds):
			map hasher(twox_64_concat) FundIndex
			=> Option<FundInfo<T::AccountId, BalanceOf<T>, T::Hash, T::BlockNumber>>;

		/// The total number of funds that have so far been allocated.
		FundCount get(fn fund_count): FundIndex;

		/// The funds that have had additional contributions during the last block. This is used
		/// in order to determine which funds should submit new or updated bids.
		NewRaise get(fn new_raise): Vec<FundIndex>;

		/// The number of auctions that have entered into their ending period so far.
		EndingsCount get(fn endings_count): slots::AuctionIndex;
	}
}

decl_event! {
	pub enum Event<T> where
		<T as system::Trait>::AccountId,
		Balance = BalanceOf<T>,
	{
		Created(FundIndex),
		Contributed(AccountId, FundIndex, Balance),
		Withdrew(AccountId, FundIndex, Balance),
		Retiring(FundIndex),
		Dissolved(FundIndex),
		DeployDataFixed(FundIndex),
		Onboarded(FundIndex, ParaId),
	}
}

decl_error! {