// Copyright 2017-2018 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/>.

//! Democratic system: Handles administration of general stakeholder voting.

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

#[cfg(test)]
extern crate substrate_primitives;

#[macro_use]
extern crate parity_codec_derive;
#[cfg_attr(not(feature = "std"), macro_use)]
extern crate sr_std as rstd;
#[macro_use]
extern crate srml_support;

extern crate parity_codec as codec;
extern crate sr_io as runtime_io;
extern crate sr_primitives as primitives;
extern crate srml_balances as balances;
extern crate srml_system as system;

use rstd::prelude::*;
use rstd::result;
use codec::{HasCompact, Compact};
use primitives::traits::{Zero, As};
use srml_support::{StorageValue, StorageMap, Parameter, Dispatchable, IsSubType};
use srml_support::dispatch::Result;
use system::ensure_signed;

mod vote_threshold;
pub use vote_threshold::{Approved, VoteThreshold};

/// A proposal index.
pub type PropIndex = u32;
/// A referendum index.
pub type ReferendumIndex = u32;

pub trait Trait: balances::Trait + Sized {
	type Proposal: Parameter + Dispatchable<Origin=Self::Origin> + IsSubType<Module<Self>>;

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

decl_module! {
	pub struct Module<T: Trait> for enum Call where origin: T::Origin {
		fn deposit_event() = default;

		/// Propose a sensitive action to be taken.
		fn propose(
			origin,
			proposal: Box<T::Proposal>,
			value: <T::Balance as HasCompact>::Type
		) -> Result {
			let who = ensure_signed(origin)?;
			let value = value.into();

			ensure!(value >= Self::minimum_deposit(), "value too low");
			<balances::Module<T>>::reserve(&who, value)
				.map_err(|_| "proposer's balance too low")?;

			let index = Self::public_prop_count();
			<PublicPropCount<T>>::put(index + 1);
			<DepositOf<T>>::insert(index, (value, vec![who.clone()]));

			let mut props = Self::public_props();
			props.push((index, (*proposal).clone(), who));
			<PublicProps<T>>::put(props);
			Ok(())
		}

		/// Propose a sensitive action to be taken.
		fn second(origin, proposal: Compact<PropIndex>) -> Result {
			let who = ensure_signed(origin)?;
			let proposal: PropIndex = proposal.into();
			let mut deposit = Self::deposit_of(proposal)
				.ok_or("can only second an existing proposal")?;
			<balances::Module<T>>::reserve(&who, deposit.0)
				.map_err(|_| "seconder's balance too low")?;
			deposit.1.push(who);
			<DepositOf<T>>::insert(proposal, deposit);
			Ok(())
		}

		/// Vote in a referendum. If `approve_proposal` is true, the vote is to enact the proposal;
		/// false would be a vote to keep the status quo.
		fn vote(origin, ref_index: Compact<ReferendumIndex>, approve_proposal: bool) -> Result {
			let who = ensure_signed(origin)?;
			let ref_index = ref_index.into();
			ensure!(Self::is_active_referendum(ref_index), "vote given for invalid referendum.");
			ensure!(!<balances::Module<T>>::total_balance(&who).is_zero(),
					"transactor must have balance to signal approval.");
			if !<VoteOf<T>>::exists(&(ref_index, who.clone())) {
				<VotersFor<T>>::mutate(ref_index, |voters| voters.push(who.clone()));
			}
			<VoteOf<T>>::insert(&(ref_index, who), approve_proposal);
			Ok(())
		}

		/// Start a referendum.
		fn start_referendum(proposal: Box<T::Proposal>, vote_threshold: VoteThreshold) -> Result {
			Self::inject_referendum(
				<system::Module<T>>::block_number() + Self::voting_period(),
				*proposal,
				vote_threshold
			).map(|_| ())
		}

		/// Remove a referendum.
		fn cancel_referendum(ref_index: Compact<ReferendumIndex>) -> Result {
			Self::clear_referendum(ref_index.into());
			Ok(())
		}

		fn on_finalise(n: T::BlockNumber) {
			if let Err(e) = Self::end_block(n) {
				runtime_io::print(e);
			}
		}
	}
}

decl_storage! {
	trait Store for Module<T: Trait> as Democracy {

		/// The number of (public) proposals that have been made so far.
		pub PublicPropCount get(public_prop_count) build(|_| 0 as PropIndex) : PropIndex;
		/// The public proposals. Unsorted.
		pub PublicProps get(public_props): Vec<(PropIndex, T::Proposal, T::AccountId)>;
		/// Those who have locked a deposit.
		pub DepositOf get(deposit_of): map PropIndex => Option<(T::Balance, Vec<T::AccountId>)>;
		/// How often (in blocks) new public referenda are launched.
		pub LaunchPeriod get(launch_period) config(): T::BlockNumber = T::BlockNumber::sa(1000);
		/// The minimum amount to be used as a deposit for a public referendum proposal.
		pub MinimumDeposit get(minimum_deposit) config(): T::Balance;

		/// How often (in blocks) to check for new votes.
		pub VotingPeriod get(voting_period) config(): T::BlockNumber = T::BlockNumber::sa(1000);

		/// The next free referendum index, aka the number of referendums started so far.
		pub ReferendumCount get(referendum_count) build(|_| 0 as ReferendumIndex): ReferendumIndex;
		/// The next referendum index that should be tallied.
		pub NextTally get(next_tally) build(|_| 0 as ReferendumIndex): ReferendumIndex;
		/// Information concerning any given referendum.
		pub ReferendumInfoOf get(referendum_info): map ReferendumIndex => Option<(T::BlockNumber, T::Proposal, VoteThreshold)>;

		/// Get the voters for the current proposal.
		pub VotersFor get(voters_for): map ReferendumIndex => Vec<T::AccountId>;

		/// Get the vote, if Some, of `who`.
		pub VoteOf get(vote_of): map (ReferendumIndex, T::AccountId) => Option<bool>;
	}
}

decl_event!(
	/// An event in this module.
	pub enum Event<T> where <T as balances::Trait>::Balance, <T as system::Trait>::AccountId {
		Tabled(PropIndex, Balance, Vec<AccountId>),
		Started(ReferendumIndex, VoteThreshold),
		Passed(ReferendumIndex),
		NotPassed(ReferendumIndex),
		Cancelled(ReferendumIndex),
		Executed(ReferendumIndex, bool),
	}
);

impl<T: Trait> Module<T> {
	// exposed immutables.

	/// Get the amount locked in support of `proposal`; `None` if proposal isn't a valid proposal
	/// index.
	pub fn locked_for(proposal: PropIndex) -> Option<T::Balance> {
		Self::deposit_of(proposal).map(|(d, l)| d * T::Balance::sa(l.len() as u64))
	}

	/// Return true if `ref_index` is an on-going referendum.
	pub fn is_active_referendum(ref_index: ReferendumIndex) -> bool {
		<ReferendumInfoOf<T>>::exists(ref_index)
	}

	/// Get all referendums currently active.
	pub fn active_referendums() -> Vec<(ReferendumIndex, T::BlockNumber, T::Proposal, VoteThreshold)> {
		let next = Self::next_tally();
		let last = Self::referendum_count();
		(next..last).into_iter()
			.filter_map(|i| Self::referendum_info(i).map(|(n, p, t)| (i, n, p, t)))
			.collect()
	}

	/// Get all referendums ready for tally at block `n`.
	pub fn maturing_referendums_at(n: T::BlockNumber) -> Vec<(ReferendumIndex, T::BlockNumber, T::Proposal, VoteThreshold)> {
		let next = Self::next_tally();
		let last = Self::referendum_count();
		(next..last).into_iter()
			.filter_map(|i| Self::referendum_info(i).map(|(n, p, t)| (i, n, p, t)))
			.take_while(|&(_, block_number, _, _)| block_number == n)
			.collect()
	}

	/// Get the voters for the current proposal.
	pub fn tally(ref_index: ReferendumIndex) -> (T::Balance, T::Balance) {
		Self::voters_for(ref_index).iter()
			.map(|a| (<balances::Module<T>>::total_balance(a), Self::vote_of((ref_index, a.clone())).unwrap_or(false)/*defensive only: all items come from `voters`; for an item to be in `voters` there must be a vote registered; qed*/))
			.map(|(bal, vote)| if vote { (bal, Zero::zero()) } else { (Zero::zero(), bal) })
			.fold((Zero::zero(), Zero::zero()), |(a, b), (c, d)| (a + c, b + d))
	}

	// Exposed mutables.

	/// Start a referendum. Can be called directly by the council.
	pub fn internal_start_referendum(proposal: T::Proposal, vote_threshold: VoteThreshold) -> result::Result<ReferendumIndex, &'static str> {
		<Module<T>>::inject_referendum(<system::Module<T>>::block_number() + <Module<T>>::voting_period(), proposal, vote_threshold)
	}

	/// Remove a referendum. Can be called directly by the council.
	pub fn internal_cancel_referendum(ref_index: ReferendumIndex) {
		Self::deposit_event(RawEvent::Cancelled(ref_index));
		<Module<T>>::clear_referendum(ref_index);
	}

	// private.

	/// Start a referendum
	fn inject_referendum(
		end: T::BlockNumber,
		proposal: T::Proposal,
		vote_threshold: VoteThreshold
	) -> result::Result<ReferendumIndex, &'static str> {
		let ref_index = Self::referendum_count();
		if ref_index > 0 && Self::referendum_info(ref_index - 1).map(|i| i.0 > end).unwrap_or(false) {
			Err("Cannot inject a referendum that ends earlier than preceeding referendum")?
		}

		<ReferendumCount<T>>::put(ref_index + 1);
		<ReferendumInfoOf<T>>::insert(ref_index, (end, proposal, vote_threshold));
		Self::deposit_event(RawEvent::Started(ref_index, vote_threshold));
		Ok(ref_index)
	}

	/// Remove all info on a referendum.
	fn clear_referendum(ref_index: ReferendumIndex) {
		<ReferendumInfoOf<T>>::remove(ref_index);
		<VotersFor<T>>::remove(ref_index);
		for v in Self::voters_for(ref_index) {
			<VoteOf<T>>::remove((ref_index, v));
		}
	}

	/// Current era is ending; we should finish up any proposals.
	fn end_block(now: T::BlockNumber) -> Result {
		// pick out another public referendum if it's time.
		if (now % Self::launch_period()).is_zero() {
			let mut public_props = Self::public_props();
			if let Some((winner_index, _)) = public_props.iter()
				.enumerate()
				.max_by_key(|x| Self::locked_for((x.1).0).unwrap_or_else(Zero::zero)/*defensive only: All current public proposals have an amount locked*/)
			{
				let (prop_index, proposal, _) = public_props.swap_remove(winner_index);
				<PublicProps<T>>::put(public_props);

				if let Some((deposit, depositors)) = <DepositOf<T>>::take(prop_index) {//: (T::Balance, Vec<T::AccountId>) =
					// refund depositors
					for d in &depositors {
						<balances::Module<T>>::unreserve(d, deposit);
					}
					Self::deposit_event(RawEvent::Tabled(prop_index, deposit, depositors));
					Self::inject_referendum(now + Self::voting_period(), proposal, VoteThreshold::SuperMajorityApprove)?;
				}
			}
		}

		// tally up votes for any expiring referenda.
		for (index, _, proposal, vote_threshold) in Self::maturing_referendums_at(now) {
			let (approve, against) = Self::tally(index);
			let total_issuance = <balances::Module<T>>::total_issuance();
			Self::clear_referendum(index);
			if vote_threshold.approved(approve, against, total_issuance) {
				Self::deposit_event(RawEvent::Passed(index));
				let ok = proposal.dispatch(system::RawOrigin::Root.into()).is_ok();
				Self::deposit_event(RawEvent::Executed(index, ok));
			} else {
				Self::deposit_event(RawEvent::NotPassed(index));
			}
			<NextTally<T>>::put(index + 1);
		}
		Ok(())
	}
}

#[cfg(test)]
mod tests {
	use super::*;
	use runtime_io::with_externalities;
	use substrate_primitives::{H256, Blake2Hasher};
	use primitives::BuildStorage;
	use primitives::traits::{BlakeTwo256};
	use primitives::testing::{Digest, DigestItem, Header};

	impl_outer_origin! {
		pub enum Origin for Test {}
	}

	impl_outer_dispatch! {
		pub enum Call for Test where origin: Origin {
			balances::Balances,
			democracy::Democracy,
		}
	}

	// Workaround for https://github.com/rust-lang/rust/issues/26925 . Remove when sorted.
	#[derive(Clone, Eq, PartialEq, Debug, Serialize, Deserialize)]
	pub struct Test;
	impl system::Trait for Test {
		type Origin = Origin;
		type Index = u64;
		type BlockNumber = u64;
		type Hash = H256;
		type Hashing = BlakeTwo256;
		type Digest = Digest;
		type AccountId = u64;
		type Header = Header;
		type Event = ();
		type Log = DigestItem;
	}
	impl balances::Trait for Test {
		type Balance = u64;
		type AccountIndex = u64;
		type OnFreeBalanceZero = ();
		type EnsureAccountLiquid = ();
		type Event = ();
	}
	impl Trait for Test {
		type Proposal = Call;
		type Event = ();
	}

	fn new_test_ext() -> runtime_io::TestExternalities<Blake2Hasher> {
		let mut t = system::GenesisConfig::<Test>::default().build_storage().unwrap().0;
		t.extend(balances::GenesisConfig::<Test>{
			balances: vec![(1, 10), (2, 20), (3, 30), (4, 40), (5, 50), (6, 60)],
			transaction_base_fee: 0,
			transaction_byte_fee: 0,
			existential_deposit: 0,
			transfer_fee: 0,
			creation_fee: 0,
			reclaim_rebate: 0,
			_genesis_phantom_data: Default::default(),
		}.build_storage().unwrap().0);
		t.extend(GenesisConfig::<Test>{
			launch_period: 1,
			voting_period: 1,
			minimum_deposit: 1,
			_genesis_phantom_data: Default::default(),
		}.build_storage().unwrap().0);
		runtime_io::TestExternalities::new(t)
	}

	type System = system::Module<Test>;
	type Balances = balances::Module<Test>;
	type Democracy = Module<Test>;

	#[test]
	fn params_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_eq!(Democracy::launch_period(), 1);
			assert_eq!(Democracy::voting_period(), 1);
			assert_eq!(Democracy::minimum_deposit(), 1);
			assert_eq!(Democracy::referendum_count(), 0);
			assert_eq!(Balances::free_balance(&42), 0);
			assert_eq!(Balances::total_issuance(), 210);
		});
	}

	fn set_balance_proposal(value: u64) -> Call {
		Call::Balances(balances::Call::set_balance(balances::address::Address::Id(42), value.into(), 0.into()))
	}

	fn propose_set_balance(who: u64, value: u64, locked: u64) -> super::Result {
		Democracy::propose(Origin::signed(who), Box::new(set_balance_proposal(value)), locked.into())
	}

	#[test]
	fn locked_for_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_ok!(propose_set_balance(1, 2, 2));
			assert_ok!(propose_set_balance(1, 4, 4));
			assert_ok!(propose_set_balance(1, 3, 3));
			assert_eq!(Democracy::locked_for(0), Some(2));
			assert_eq!(Democracy::locked_for(1), Some(4));
			assert_eq!(Democracy::locked_for(2), Some(3));
		});
	}

	#[test]
	fn single_proposal_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_ok!(propose_set_balance(1, 2, 1));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			System::set_block_number(2);
			let r = 0;
			assert_ok!(Democracy::vote(Origin::signed(1), r.into(), true));

			assert_eq!(Democracy::referendum_count(), 1);
			assert_eq!(Democracy::voters_for(r), vec![1]);
			assert_eq!(Democracy::vote_of((r, 1)), Some(true));
			assert_eq!(Democracy::tally(r), (10, 0));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 2);
		});
	}

	#[test]
	fn deposit_for_proposals_should_be_taken() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_ok!(propose_set_balance(1, 2, 5));
			assert_ok!(Democracy::second(Origin::signed(2), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_eq!(Balances::free_balance(&1), 5);
			assert_eq!(Balances::free_balance(&2), 15);
			assert_eq!(Balances::free_balance(&5), 35);
		});
	}

	#[test]
	fn deposit_for_proposals_should_be_returned() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_ok!(propose_set_balance(1, 2, 5));
			assert_ok!(Democracy::second(Origin::signed(2), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_ok!(Democracy::second(Origin::signed(5), 0.into()));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));
			assert_eq!(Balances::free_balance(&1), 10);
			assert_eq!(Balances::free_balance(&2), 20);
			assert_eq!(Balances::free_balance(&5), 50);
		});
	}

	#[test]
	fn proposal_with_deposit_below_minimum_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_noop!(propose_set_balance(1, 2, 0), "value too low");
		});
	}

	#[test]
	fn poor_proposer_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_noop!(propose_set_balance(1, 2, 11), "proposer\'s balance too low");
		});
	}

	#[test]
	fn poor_seconder_should_not_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			assert_ok!(propose_set_balance(2, 2, 11));
			assert_noop!(Democracy::second(Origin::signed(1), 0.into()), "seconder\'s balance too low");
		});
	}

	#[test]
	fn runners_up_should_come_after() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(0);
			assert_ok!(propose_set_balance(1, 2, 2));
			assert_ok!(propose_set_balance(1, 4, 4));
			assert_ok!(propose_set_balance(1, 3, 3));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			System::set_block_number(1);
			assert_ok!(Democracy::vote(Origin::signed(1), 0.into(), true));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));
			assert_eq!(Balances::free_balance(&42), 4);

			System::set_block_number(2);
			assert_ok!(Democracy::vote(Origin::signed(1), 1.into(), true));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));
			assert_eq!(Balances::free_balance(&42), 3);

			System::set_block_number(3);
			assert_ok!(Democracy::vote(Origin::signed(1), 2.into(), true));
			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));
		});
	}

	#[test]
	fn simple_passing_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(1), r.into(), true));

			assert_eq!(Democracy::voters_for(r), vec![1]);
			assert_eq!(Democracy::vote_of((r, 1)), Some(true));
			assert_eq!(Democracy::tally(r), (10, 0));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 2);
		});
	}

	#[test]
	fn cancel_referendum_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(1), r.into(), true));
			assert_ok!(Democracy::cancel_referendum(r.into()));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 0);
		});
	}

	#[test]
	fn simple_failing_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(1), r.into(), false));

			assert_eq!(Democracy::voters_for(r), vec![1]);
			assert_eq!(Democracy::vote_of((r, 1)), Some(false));
			assert_eq!(Democracy::tally(r), (0, 10));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 0);
		});
	}

	#[test]
	fn controversial_voting_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(1), r.into(), true));
			assert_ok!(Democracy::vote(Origin::signed(2), r.into(), false));
			assert_ok!(Democracy::vote(Origin::signed(3), r.into(), false));
			assert_ok!(Democracy::vote(Origin::signed(4), r.into(), true));
			assert_ok!(Democracy::vote(Origin::signed(5), r.into(), false));
			assert_ok!(Democracy::vote(Origin::signed(6), r.into(), true));

			assert_eq!(Democracy::tally(r), (110, 100));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 2);
		});
	}

	#[test]
	fn controversial_low_turnout_voting_should_work() {
		with_externalities(&mut new_test_ext(), || {
			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(5), r.into(), false));
			assert_ok!(Democracy::vote(Origin::signed(6), r.into(), true));

			assert_eq!(Democracy::tally(r), (60, 50));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 0);
		});
	}

	#[test]
	fn passing_low_turnout_voting_should_work() {
		with_externalities(&mut new_test_ext(), || {
			assert_eq!(Balances::free_balance(&42), 0);
			assert_eq!(Balances::total_issuance(), 210);

			System::set_block_number(1);
			let r = Democracy::inject_referendum(1, set_balance_proposal(2), VoteThreshold::SuperMajorityApprove).unwrap();
			assert_ok!(Democracy::vote(Origin::signed(4), r.into(), true));
			assert_ok!(Democracy::vote(Origin::signed(5), r.into(), false));
			assert_ok!(Democracy::vote(Origin::signed(6), r.into(), true));

			assert_eq!(Democracy::tally(r), (100, 50));

			assert_eq!(Democracy::end_block(System::block_number()), Ok(()));

			assert_eq!(Balances::free_balance(&42), 2);
		});
	}
}