// This file is part of Substrate.

// Copyright (C) Parity Technologies (UK) Ltd.
// SPDX-License-Identifier: Apache-2.0

// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// 	http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! Traits and associated data structures concerned with voting, and moving between tokens and
//! votes.

use crate::dispatch::{DispatchError, Parameter};
use codec::{HasCompact, MaxEncodedLen};
use sp_arithmetic::{
	traits::{SaturatedConversion, UniqueSaturatedFrom, UniqueSaturatedInto},
	Perbill,
};
use sp_runtime::traits::Member;
use sp_std::prelude::*;

/// A trait similar to `Convert` to convert values from `B` an abstract balance type
/// into u64 and back from u128. (This conversion is used in election and other places where complex
/// calculation over balance type is needed)
///
/// Total issuance of the currency is passed in, but an implementation of this trait may or may not
/// use it.
///
/// # WARNING
///
/// the total issuance being passed in implies that the implementation must be aware of the fact
/// that its values can affect the outcome. This implies that if the vote value is dependent on the
/// total issuance, it should never ber written to storage for later re-use.
pub trait CurrencyToVote<B> {
	/// Convert balance to u64.
	fn to_vote(value: B, issuance: B) -> u64;

	/// Convert u128 to balance.
	fn to_currency(value: u128, issuance: B) -> B;
}

/// An implementation of `CurrencyToVote` tailored for chain's that have a balance type of u128.
///
/// The factor is the `(total_issuance / u64::MAX).max(1)`, represented as u64. Let's look at the
/// important cases:
///
/// If the chain's total issuance is less than u64::MAX, this will always be 1, which means that
/// the factor will not have any effect. In this case, any account's balance is also less. Thus,
/// both of the conversions are basically an `as`; Any balance can fit in u64.
///
/// If the chain's total issuance is more than 2*u64::MAX, then a factor might be multiplied and
/// divided upon conversion.
pub struct U128CurrencyToVote;

impl U128CurrencyToVote {
	fn factor(issuance: u128) -> u128 {
		(issuance / u64::MAX as u128).max(1)
	}
}

impl CurrencyToVote<u128> for U128CurrencyToVote {
	fn to_vote(value: u128, issuance: u128) -> u64 {
		(value / Self::factor(issuance)).saturated_into()
	}

	fn to_currency(value: u128, issuance: u128) -> u128 {
		value.saturating_mul(Self::factor(issuance))
	}
}

/// A naive implementation of `CurrencyConvert` that simply saturates all conversions.
///
/// # Warning
///
/// This is designed to be used mostly for testing. Use with care, and think about the consequences.
pub struct SaturatingCurrencyToVote;

impl<B: UniqueSaturatedInto<u64> + UniqueSaturatedFrom<u128>> CurrencyToVote<B>
	for SaturatingCurrencyToVote
{
	fn to_vote(value: B, _: B) -> u64 {
		value.unique_saturated_into()
	}

	fn to_currency(value: u128, _: B) -> B {
		B::unique_saturated_from(value)
	}
}

pub trait VoteTally<Votes, Class> {
	fn new(_: Class) -> Self;
	fn ayes(&self, class: Class) -> Votes;
	fn support(&self, class: Class) -> Perbill;
	fn approval(&self, class: Class) -> Perbill;
	#[cfg(feature = "runtime-benchmarks")]
	fn unanimity(class: Class) -> Self;
	#[cfg(feature = "runtime-benchmarks")]
	fn rejection(class: Class) -> Self;
	#[cfg(feature = "runtime-benchmarks")]
	fn from_requirements(support: Perbill, approval: Perbill, class: Class) -> Self;
	#[cfg(feature = "runtime-benchmarks")]
	/// A function that should be called before any use of the `runtime-benchmarks` gated functions
	/// of the `VoteTally` trait.
	///
	/// Should be used to set up any needed state in a Pallet which implements `VoteTally` so that
	/// benchmarks that execute will complete successfully. `class` can be used to set up a
	/// particular class of voters, and `granularity` is used to determine the weight of one vote
	/// relative to total unanimity.
	///
	/// For example, in the case where there are a number of unique voters, and each voter has equal
	/// voting weight, a granularity of `Perbill::from_rational(1, 1000)` should create `1_000`
	/// users.
	fn setup(class: Class, granularity: Perbill);
}
pub enum PollStatus<Tally, Moment, Class> {
	None,
	Ongoing(Tally, Class),
	Completed(Moment, bool),
}

impl<Tally, Moment, Class> PollStatus<Tally, Moment, Class> {
	pub fn ensure_ongoing(self) -> Option<(Tally, Class)> {
		match self {
			Self::Ongoing(t, c) => Some((t, c)),
			_ => None,
		}
	}
}

pub struct ClassCountOf<P, T>(sp_std::marker::PhantomData<(P, T)>);
impl<T, P: Polling<T>> sp_runtime::traits::Get<u32> for ClassCountOf<P, T> {
	fn get() -> u32 {
		P::classes().len() as u32
	}
}

pub trait Polling<Tally> {
	type Index: Parameter + Member + Ord + PartialOrd + Copy + HasCompact + MaxEncodedLen;
	type Votes: Parameter + Member + Ord + PartialOrd + Copy + HasCompact + MaxEncodedLen;
	type Class: Parameter + Member + Ord + PartialOrd + MaxEncodedLen;
	type Moment;

	/// Provides a vec of values that `T` may take.
	fn classes() -> Vec<Self::Class>;

	/// `Some` if the referendum `index` can be voted on, along with the tally and class of
	/// referendum.
	///
	/// Don't use this if you might mutate - use `try_access_poll` instead.
	fn as_ongoing(index: Self::Index) -> Option<(Tally, Self::Class)>;

	fn access_poll<R>(
		index: Self::Index,
		f: impl FnOnce(PollStatus<&mut Tally, Self::Moment, Self::Class>) -> R,
	) -> R;

	fn try_access_poll<R>(
		index: Self::Index,
		f: impl FnOnce(PollStatus<&mut Tally, Self::Moment, Self::Class>) -> Result<R, DispatchError>,
	) -> Result<R, DispatchError>;

	/// Create an ongoing majority-carries poll of given class lasting given period for the purpose
	/// of benchmarking.
	///
	/// May return `Err` if it is impossible.
	#[cfg(feature = "runtime-benchmarks")]
	fn create_ongoing(class: Self::Class) -> Result<Self::Index, ()>;

	/// End the given ongoing poll and return the result.
	///
	/// Returns `Err` if `index` is not an ongoing poll.
	#[cfg(feature = "runtime-benchmarks")]
	fn end_ongoing(index: Self::Index, approved: bool) -> Result<(), ()>;

	/// The maximum amount of ongoing polls within any single class. By default it practically
	/// unlimited (`u32::max_value()`).
	#[cfg(feature = "runtime-benchmarks")]
	fn max_ongoing() -> (Self::Class, u32) {
		(Self::classes().into_iter().next().expect("Always one class"), u32::max_value())
	}
}