1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176

//! # Asset
//!
//! The asset module provides functionality for handling bridged asset balances.
//!
//! ## Overview
//!
//! This module is used by the ETH and ERC20 pallets to store account balances for bridged assets.
//!
//! Each asset is identified by a unique `H160` hash. This is useful for tracking ERC20 tokens which on Ethereum are identified by a 20-byte contract address.
//!
//! For various reasons, we built our own asset pallet instead of reusing existing work:
//! - `assets`: Too high-level and limited for our needs
//! - `generic-asset`: Its enforced permissions system implies trusted operations. But our system is designed to be trustless.
//! - `balances`: Only stores balances for a single asset. Our ERC20 pallet supports multiple different ERC20 assets.
//!
//! Additionally, we need to store balances using `U256`, which seemed difficult or impossible to plug into the above pallets.
//!
//! ## Interface
//!
//! ### Dispatchable Calls
//!
//! - `transfer`: Transferring a balance between accounts.
//!
//! ### Public Functions
//!
//! - `do_mint`: Mint to an account's free balance.
//! - `do_burn`: Burn an account's free balance.
//!

#![cfg_attr(not(feature = "std"), no_std)]

use sp_std::prelude::*;
use sp_core::{U256, RuntimeDebug};
use frame_system::{self as system, ensure_signed};
use frame_support::{
	decl_error, decl_event, decl_module, decl_storage,
	dispatch::{DispatchResult, DispatchError},
};

use codec::{Encode, Decode};

use artemis_core::BridgedAssetId;

#[cfg(test)]
mod mock;

#[cfg(test)]
mod tests;

#[derive(Encode, Decode, Clone, PartialEq, Eq, Default, RuntimeDebug)]
pub struct AccountData {
	pub free: U256
}

type AssetAccountData = AccountData;

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

decl_storage! {
	trait Store for Module<T: Trait> as Asset {
		pub TotalIssuance: map        hasher(blake2_128_concat) BridgedAssetId => U256;
		pub Account:       double_map hasher(blake2_128_concat) BridgedAssetId, hasher(blake2_128_concat) T::AccountId => AssetAccountData;
	}
}

decl_event!(
	pub enum Event<T>
	where
		AccountId = <T as system::Trait>::AccountId,
	{
		Burned(BridgedAssetId, AccountId, U256),
		Minted(BridgedAssetId, AccountId, U256),
		Transferred(BridgedAssetId, AccountId, AccountId, U256),
	}
);

decl_error! {
	pub enum Error for Module<T: Trait> {
		/// Free balance got overflowed after transfer.
		FreeTransferOverflow,
		/// Total issuance got overflowed after minting.
		TotalMintingOverflow,
		/// Free balance got overflowed after minting.
		FreeMintingOverflow,
		/// Total issuance got underflowed after burning.
		TotalBurningUnderflow,
		/// Free balance got underflowed after burning.
		FreeBurningUnderflow,
		InsufficientBalance,
	}
}

decl_module! {

	pub struct Module<T: Trait> for enum Call where origin: T::Origin {

		type Error = Error<T>;

		fn deposit_event() = default;

		/// Transfer some free balance to another account.
		// TODO: Calculate weight
		#[weight = 0]
		pub fn transfer(origin, asset_id: BridgedAssetId, to: T::AccountId, amount: U256) -> DispatchResult {
			let who = ensure_signed(origin)?;
			Self::do_transfer(asset_id, &who, &to, amount)?;
			Ok(())
		}

	}
}

impl<T: Trait> Module<T> {

	pub fn free_balance(asset_id: BridgedAssetId, who: &T::AccountId) -> U256 {
		<Account<T>>::get(asset_id, who).free
	}

	pub fn do_mint(asset_id: BridgedAssetId, who: &T::AccountId, amount: U256) -> DispatchResult  {
		if amount.is_zero() {
			return Ok(())
		}
		<Account<T>>::try_mutate(asset_id, who, |account| -> Result<(), DispatchError> {
			let current_total_issuance = <TotalIssuance>::get(asset_id);
			let new_total_issuance = current_total_issuance.checked_add(amount)
			.ok_or(Error::<T>::TotalMintingOverflow)?;
			account.free = account.free.checked_add(amount)
				.ok_or(Error::<T>::FreeMintingOverflow)?;
			<TotalIssuance>::insert(asset_id, new_total_issuance);
			Ok(())
		})?;
		Self::deposit_event(RawEvent::Minted(asset_id, who.clone(), amount));
		Ok(())
	}

	pub fn do_burn(asset_id: BridgedAssetId, who: &T::AccountId, amount: U256) -> DispatchResult  {
		if amount.is_zero() {
			return Ok(())
		}
		<Account<T>>::try_mutate(asset_id, who, |account| -> Result<(), DispatchError> {
			let current_total_issuance = <TotalIssuance>::get(asset_id);
			let new_total_issuance = current_total_issuance.checked_sub(amount)
			.ok_or(Error::<T>::TotalBurningUnderflow)?;
			account.free = account.free.checked_sub(amount)
				.ok_or(Error::<T>::FreeBurningUnderflow)?;
			<TotalIssuance>::insert(asset_id, new_total_issuance);
			Ok(())
		})?;
		Self::deposit_event(RawEvent::Burned(asset_id, who.clone(), amount));
		Ok(())
	}

	fn do_transfer(
		asset_id: BridgedAssetId,
		from: &T::AccountId,
		to: &T::AccountId,
		amount: U256)
	-> DispatchResult {
		if amount.is_zero() || from == to {
			return Ok(())
		}
		<Account<T>>::try_mutate(asset_id, from, |from_account| -> DispatchResult {
			<Account<T>>::try_mutate(asset_id, to, |to_account| -> DispatchResult {
				from_account.free = from_account.free.checked_sub(amount).ok_or(Error::<T>::InsufficientBalance)?;
				// In theory we'll never hit overflow here since Sum(Account.free) == TotalIssuance.
				to_account.free = to_account.free.checked_add(amount).ok_or(Error::<T>::FreeTransferOverflow)?;
				Ok(())
			})
		})?;
		Self::deposit_event(RawEvent::Transferred(asset_id, from.clone(), to.clone(), amount));
		Ok(())
	}

}