// Copyright 2017-2019 Parity Technologies (UK) Ltd.
// This file is part of Substrate.

// Substrate 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.

// Substrate 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 Substrate.  If not, see <http://www.gnu.org/licenses/>.

//! # Assets Module
//!
//! A simple, secure module for dealing with fungible assets.
//!
//! ## Overview
//!
//! The Assets module provides functionality for asset management of fungible asset classes
//! with a fixed supply, including:
//!
//! * Asset Issuance
//! * Asset Transfer
//! * Asset Destruction
//!
//! To use it in your runtime, you need to implement the assets [`Trait`](./trait.Trait.html).
//!
//! The supported dispatchable functions are documented in the [`Call`](./enum.Call.html) enum.
//!
//! ### Terminology
//!
//! * **Asset issuance:** The creation of a new asset, whose total supply will belong to the
//!   account that issues the asset.
//! * **Asset transfer:** The action of transferring assets from one account to another.
//! * **Asset destruction:** The process of an account removing its entire holding of an asset.
//! * **Fungible asset:** An asset whose units are interchangeable.
//! * **Non-fungible asset:** An asset for which each unit has unique characteristics.
//!
//! ### Goals
//!
//! The assets system in Substrate is designed to make the following possible:
//!
//! * Issue a unique asset to its creator's account.
//! * Move assets between accounts.
//! * Remove an account's balance of an asset when requested by that account's owner and update
//!   the asset's total supply.
//!
//! ## Interface
//!
//! ### Dispatchable Functions
//!
//! * `issue` - Issues the total supply of a new fungible asset to the account of the caller of the function.
//! * `transfer` - Transfers an `amount` of units of fungible asset `id` from the balance of
//! the function caller's account (`origin`) to a `target` account.
//! * `destroy` - Destroys the entire holding of a fungible asset `id` associated with the account
//! that called the function.
//!
//! Please refer to the [`Call`](./enum.Call.html) enum and its associated variants for documentation on each function.
//!
//! ### Public Functions
//! <!-- Original author of descriptions: @gavofyork -->
//!
//! * `balance` - Get the asset `id` balance of `who`.
//! * `total_supply` - Get the total supply of an asset `id`.
//!
//! Please refer to the [`Module`](./struct.Module.html) struct for details on publicly available functions.
//!
//! ## Usage
//!
//! The following example shows how to use the Assets module in your runtime by exposing public functions to:
//!
//! * Issue a new fungible asset for a token distribution event (airdrop).
//! * Query the fungible asset holding balance of an account.
//! * Query the total supply of a fungible asset that has been issued.
//!
//! ### Prerequisites
//!
//! Import the Assets module and types and derive your runtime's configuration traits from the Assets module trait.
//!
//! ### Simple Code Snippet
//!
//! ```rust,ignore
//! use support::{decl_module, dispatch::Result};
//! use system::ensure_signed;
//!
//! pub trait Trait: assets::Trait { }
//!
//! decl_module! {
//! 	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
//! 		pub fn issue_token_airdrop(origin) -> Result {
//! 			const ACCOUNT_ALICE: u64 = 1;
//! 			const ACCOUNT_BOB: u64 = 2;
//! 			const COUNT_AIRDROP_RECIPIENTS = 2;
//! 			const TOKENS_FIXED_SUPPLY: u64 = 100;
//!
//! 			ensure!(!COUNT_AIRDROP_RECIPIENTS.is_zero(), "Divide by zero error.");
//!
//! 			let sender = ensure_signed(origin)?;
//! 			let asset_id = Self::next_asset_id();
//!
//! 			<NextAssetId<T>>::mutate(|asset_id| *asset_id += 1);
//! 			<Balances<T>>::insert((asset_id, &ACCOUNT_ALICE), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
//! 			<Balances<T>>::insert((asset_id, &ACCOUNT_BOB), TOKENS_FIXED_SUPPLY / COUNT_AIRDROP_RECIPIENTS);
//! 			<TotalSupply<T>>::insert(asset_id, TOKENS_FIXED_SUPPLY);
//!
//! 			Self::deposit_event(RawEvent::Issued(asset_id, sender, TOKENS_FIXED_SUPPLY));
//! 			Ok(())
//! 		}
//! 	}
//! }
//! ```
//!
//! ## Assumptions
//!
//! Below are assumptions that must be held when using this module.  If any of
//! them are violated, the behavior of this module is undefined.
//!
//! * The total count of assets should be less than
//!   `Trait::AssetId::max_value()`.
//!
//! ## Related Modules
//!
//! * [`System`](../srml_system/index.html)
//! * [`Support`](../srml_support/index.html)

// Ensure we're `no_std` when compiling for Wasm.
#![cfg_attr(not(feature = "std"), no_std)]

use srml_support::{StorageValue, StorageMap, Parameter, decl_module, decl_event, decl_storage, ensure};
use primitives::traits::{Member, SimpleArithmetic, Zero, StaticLookup};
use system::ensure_signed;
use primitives::traits::One;

/// The module configuration trait.
pub trait Trait: system::Trait {
	/// The overarching event type.
	type Event: From<Event<Self>> + Into<<Self as system::Trait>::Event>;

	/// The units in which we record balances.
	type Balance: Member + Parameter + SimpleArithmetic + Default + Copy;

	/// The arithmetic type of asset identifier.
	type AssetId: Parameter + SimpleArithmetic + Default + Copy;
}

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		fn deposit_event<T>() = default;
		/// Issue a new class of fungible assets. There are, and will only ever be, `total`
		/// such assets and they'll all belong to the `origin` initially. It will have an
		/// identifier `AssetId` instance: this will be specified in the `Issued` event.
		fn issue(origin, #[compact] total: T::Balance) {
			let origin = ensure_signed(origin)?;

			let id = Self::next_asset_id();
			<NextAssetId<T>>::mutate(|id| *id += One::one());

			<Balances<T>>::insert((id, origin.clone()), total);
			<TotalSupply<T>>::insert(id, total);

			Self::deposit_event(RawEvent::Issued(id, origin, total));
		}

		/// Move some assets from one holder to another.
		fn transfer(origin,
			#[compact] id: T::AssetId,
			target: <T::Lookup as StaticLookup>::Source,
			#[compact] amount: T::Balance
		) {
			let origin = ensure_signed(origin)?;
			let origin_account = (id, origin.clone());
			let origin_balance = <Balances<T>>::get(&origin_account);
			let target = T::Lookup::lookup(target)?;
			ensure!(!amount.is_zero(), "transfer amount should be non-zero");
			ensure!(origin_balance >= amount, "origin account balance must be greater than or equal to the transfer amount");

			Self::deposit_event(RawEvent::Transferred(id, origin, target.clone(), amount));
			<Balances<T>>::insert(origin_account, origin_balance - amount);
			<Balances<T>>::mutate((id, target), |balance| *balance += amount);
		}

		/// Destroy any assets of `id` owned by `origin`.
		fn destroy(origin, #[compact] id: T::AssetId) {
			let origin = ensure_signed(origin)?;
			let balance = <Balances<T>>::take((id, origin.clone()));
			ensure!(!balance.is_zero(), "origin balance should be non-zero");

			<TotalSupply<T>>::mutate(id, |total_supply| *total_supply -= balance);
			Self::deposit_event(RawEvent::Destroyed(id, origin, balance));
		}
	}
}

decl_event!(
	pub enum Event<T>
		where <T as system::Trait>::AccountId,
		      <T as Trait>::Balance,
		      <T as Trait>::AssetId {
		/// Some assets were issued.
		Issued(AssetId, AccountId, Balance),
		/// Some assets were transferred.
		Transferred(AssetId, AccountId, AccountId, Balance),
		/// Some assets were destroyed.
		Destroyed(AssetId, AccountId, Balance),
	}
);

decl_storage! {
	trait Store for Module<T: Trait> as Assets {
		/// The number of units of assets held by any given account.
		Balances: map (T::AssetId, T::AccountId) => T::Balance;
		/// The next asset identifier up for grabs.
		NextAssetId get(next_asset_id): T::AssetId;
		/// The total unit supply of an asset.
		TotalSupply: map T::AssetId => T::Balance;
	}
}

// The main implementation block for the module.
impl<T: Trait> Module<T> {
	// Public immutables

	/// Get the asset `id` balance of `who`.
	pub fn balance(id: T::AssetId, who: T::AccountId) -> T::Balance {
		<Balances<T>>::get((id, who))
	}

	/// Get the total supply of an asset `id`.
	pub fn total_supply(id: T::AssetId) -> T::Balance {
		<TotalSupply<T>>::get(id)
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	use runtime_io::with_externalities;
	use srml_support::{impl_outer_origin, assert_ok, assert_noop, parameter_types};
	use substrate_primitives::{H256, Blake2Hasher};
	// The testing primitives are very useful for avoiding having to work with signatures
	// or public keys. `u64` is used as the `AccountId` and no `Signature`s are required.
	use primitives::{traits::{BlakeTwo256, IdentityLookup}, testing::Header};

	impl_outer_origin! {
		pub enum Origin for Test {}
	}

	// For testing the module, we construct most of a mock runtime. This means
	// first constructing a configuration type (`Test`) which `impl`s each of the
	// configuration traits of modules we want to use.
	#[derive(Clone, Eq, PartialEq)]
	pub struct Test;
	parameter_types! {
		pub const BlockHashCount: u64 = 250;
		pub const MaximumBlockWeight: u32 = 1024;
		pub const MaximumBlockLength: u32 = 2 * 1024;
	}
	impl system::Trait for Test {
		type Origin = Origin;
		type Index = u64;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type AccountId = u64;
		type Lookup = IdentityLookup<Self::AccountId>;
		type Header = Header;
		type WeightMultiplierUpdate = ();
		type Event = ();
		type BlockHashCount = BlockHashCount;
		type MaximumBlockWeight = MaximumBlockWeight;
		type MaximumBlockLength = MaximumBlockLength;
	}
	impl Trait for Test {
		type Event = ();
		type Balance = u64;
		type AssetId = u32;
	}
	type Assets = Module<Test>;

	// This function basically just builds a genesis storage key/value store according to
	// our desired mockup.
	fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
		system::GenesisConfig::default().build_storage::<Test>().unwrap().0.into()
	}

	#[test]
	fn issuing_asset_units_to_issuer_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
		});
	}

	#[test]
	fn querying_total_supply_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_ok!(Assets::transfer(Origin::signed(1), 0, 2, 50));
			assert_eq!(Assets::balance(0, 1), 50);
			assert_eq!(Assets::balance(0, 2), 50);
			assert_ok!(Assets::transfer(Origin::signed(2), 0, 3, 31));
			assert_eq!(Assets::balance(0, 1), 50);
			assert_eq!(Assets::balance(0, 2), 19);
			assert_eq!(Assets::balance(0, 3), 31);
			assert_ok!(Assets::destroy(Origin::signed(3), 0));
			assert_eq!(Assets::total_supply(0), 69);
		});
	}

	#[test]
	fn transferring_amount_above_available_balance_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_ok!(Assets::transfer(Origin::signed(1), 0, 2, 50));
			assert_eq!(Assets::balance(0, 1), 50);
			assert_eq!(Assets::balance(0, 2), 50);
		});
	}

	#[test]
	fn transferring_amount_less_than_available_balance_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_ok!(Assets::transfer(Origin::signed(1), 0, 2, 50));
			assert_eq!(Assets::balance(0, 1), 50);
			assert_eq!(Assets::balance(0, 2), 50);
			assert_ok!(Assets::destroy(Origin::signed(1), 0));
			assert_eq!(Assets::balance(0, 1), 0);
			assert_noop!(Assets::transfer(Origin::signed(1), 0, 1, 50), "origin account balance must be greater than or equal to the transfer amount");
		});
	}

	#[test]
	fn transferring_less_than_one_unit_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_noop!(Assets::transfer(Origin::signed(1), 0, 2, 0), "transfer amount should be non-zero");
		});
	}

	#[test]
	fn transferring_more_units_than_total_supply_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_noop!(Assets::transfer(Origin::signed(1), 0, 2, 101), "origin account balance must be greater than or equal to the transfer amount");
		});
	}

	#[test]
	fn destroying_asset_balance_with_positive_balance_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 1), 100);
			assert_ok!(Assets::destroy(Origin::signed(1), 0));
		});
	}

	#[test]
	fn destroying_asset_balance_with_zero_balance_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_ok!(Assets::issue(Origin::signed(1), 100));
			assert_eq!(Assets::balance(0, 2), 0);
			assert_noop!(Assets::destroy(Origin::signed(2), 0), "origin balance should be non-zero");
		});
	}
}