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use cosmwasm_schema::cw_serde;
use cosmwasm_std::{Decimal, StdError};
use thiserror::Error;
/// This defines the different ways tallies can happen.
///
/// The total_weight used for calculating success as well as the weights of each
/// individual voter used in tallying should be snapshotted at the beginning of
/// the block at which the proposal starts (this is likely the responsibility of a
/// correct cw4 implementation).
/// See also `ThresholdResponse` in the cw3 spec.
#[cw_serde]
pub enum Threshold {
/// Declares that a fixed weight of Yes votes is needed to pass.
/// See `ThresholdResponse.AbsoluteCount` in the cw3 spec for details.
AbsoluteCount { weight: u64 },
/// Declares a percentage of the total weight that must cast Yes votes in order for
/// a proposal to pass.
/// See `ThresholdResponse.AbsolutePercentage` in the cw3 spec for details.
AbsolutePercentage { percentage: Decimal },
/// Declares a `quorum` of the total votes that must participate in the election in order
/// for the vote to be considered at all.
/// See `ThresholdResponse.ThresholdQuorum` in the cw3 spec for details.
ThresholdQuorum { threshold: Decimal, quorum: Decimal },
}
impl Threshold {
/// returns error if this is an unreachable value,
/// given a total weight of all members in the group
pub fn validate(&self, total_weight: u64) -> Result<(), ThresholdError> {
match self {
Threshold::AbsoluteCount {
weight: weight_needed,
} => {
if *weight_needed == 0 {
Err(ThresholdError::ZeroWeight {})
} else if *weight_needed > total_weight {
Err(ThresholdError::UnreachableWeight {})
} else {
Ok(())
}
}
Threshold::AbsolutePercentage {
percentage: percentage_needed,
} => valid_threshold(percentage_needed),
Threshold::ThresholdQuorum {
threshold,
quorum: quroum,
} => {
valid_threshold(threshold)?;
valid_quorum(quroum)
}
}
}
/// Creates a response from the saved data, just missing the total_weight info
pub fn to_response(&self, total_weight: u64) -> ThresholdResponse {
match self.clone() {
Threshold::AbsoluteCount { weight } => ThresholdResponse::AbsoluteCount {
weight,
total_weight,
},
Threshold::AbsolutePercentage { percentage } => ThresholdResponse::AbsolutePercentage {
percentage,
total_weight,
},
Threshold::ThresholdQuorum { threshold, quorum } => {
ThresholdResponse::ThresholdQuorum {
threshold,
quorum,
total_weight,
}
}
}
}
}
/// Asserts that the 0.5 < percent <= 1.0
fn valid_threshold(percent: &Decimal) -> Result<(), ThresholdError> {
if *percent > Decimal::percent(100) || *percent < Decimal::percent(50) {
Err(ThresholdError::InvalidThreshold {})
} else {
Ok(())
}
}
/// Asserts that the 0.5 < percent <= 1.0
fn valid_quorum(percent: &Decimal) -> Result<(), ThresholdError> {
if percent.is_zero() {
Err(ThresholdError::ZeroQuorumThreshold {})
} else if *percent > Decimal::one() {
Err(ThresholdError::UnreachableQuorumThreshold {})
} else {
Ok(())
}
}
/// This defines the different ways tallies can happen.
/// Every contract should support a subset of these, ideally all.
///
/// The total_weight used for calculating success as well as the weights of each
/// individual voter used in tallying should be snapshotted at the beginning of
/// the block at which the proposal starts (this is likely the responsibility of a
/// correct cw4 implementation).
#[cw_serde]
pub enum ThresholdResponse {
/// Declares that a fixed weight of yes votes is needed to pass.
/// It does not matter how many no votes are cast, or how many do not vote,
/// as long as `weight` yes votes are cast.
///
/// This is the simplest format and usually suitable for small multisigs of trusted parties,
/// like 3 of 5. (weight: 3, total_weight: 5)
///
/// A proposal of this type can pass early as soon as the needed weight of yes votes has been cast.
AbsoluteCount { weight: u64, total_weight: u64 },
/// Declares a percentage of the total weight that must cast Yes votes, in order for
/// a proposal to pass. The passing weight is computed over the total weight minus the weight of the
/// abstained votes.
///
/// This is useful for similar circumstances as `AbsoluteCount`, where we have a relatively
/// small set of voters, and participation is required.
/// It is understood that if the voting set (group) changes between different proposals that
/// refer to the same group, each proposal will work with a different set of voter weights
/// (the ones snapshotted at proposal creation), and the passing weight for each proposal
/// will be computed based on the absolute percentage, times the total weights of the members
/// at the time of each proposal creation.
///
/// Example: we set `percentage` to 51%. Proposal 1 starts when there is a `total_weight` of 5.
/// This will require 3 weight of Yes votes in order to pass. Later, the Proposal 2 starts but the
/// `total_weight` of the group has increased to 9. That proposal will then automatically
/// require 5 Yes of 9 to pass, rather than 3 yes of 9 as would be the case with `AbsoluteCount`.
AbsolutePercentage {
percentage: Decimal,
total_weight: u64,
},
/// In addition to a `threshold`, declares a `quorum` of the total votes that must participate
/// in the election in order for the vote to be considered at all. Within the votes that
/// were cast, it requires `threshold` votes in favor. That is calculated by ignoring
/// the Abstain votes (they count towards `quorum`, but do not influence `threshold`).
/// That is, we calculate `Yes / (Yes + No + Veto)` and compare it with `threshold` to consider
/// if the proposal was passed.
///
/// It is rather difficult for a proposal of this type to pass early. That can only happen if
/// the required quorum has been already met, and there are already enough Yes votes for the
/// proposal to pass.
///
/// 30% Yes votes, 10% No votes, and 20% Abstain would pass early if quorum <= 60%
/// (who has cast votes) and if the threshold is <= 37.5% (the remaining 40% voting
/// no => 30% yes + 50% no). Once the voting period has passed with no additional votes,
/// that same proposal would be considered successful if quorum <= 60% and threshold <= 75%
/// (percent in favor if we ignore abstain votes).
///
/// This type is more common in general elections, where participation is often expected to
/// be low, and `AbsolutePercentage` would either be too high to pass anything,
/// or allow low percentages to pass, independently of if there was high participation in the
/// election or not.
ThresholdQuorum {
threshold: Decimal,
quorum: Decimal,
total_weight: u64,
},
}
#[derive(Error, Debug, PartialEq)]
pub enum ThresholdError {
#[error("{0}")]
Std(#[from] StdError),
#[error("Invalid voting threshold percentage, must be in the 0.5-1.0 range")]
InvalidThreshold {},
#[error("Required quorum threshold cannot be zero")]
ZeroQuorumThreshold {},
#[error("Not possible to reach required quorum threshold")]
UnreachableQuorumThreshold {},
#[error("Required weight cannot be zero")]
ZeroWeight {},
#[error("Not possible to reach required (passing) weight")]
UnreachableWeight {},
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn validate_quorum_percentage() {
// TODO: test the error messages
// 0 is never a valid percentage
let err = valid_quorum(&Decimal::zero()).unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::ZeroQuorumThreshold {}.to_string()
);
// 100% is
valid_quorum(&Decimal::one()).unwrap();
// 101% is not
let err = valid_quorum(&Decimal::percent(101)).unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::UnreachableQuorumThreshold {}.to_string()
);
// not 100.1%
let err = valid_quorum(&Decimal::permille(1001)).unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::UnreachableQuorumThreshold {}.to_string()
);
}
#[test]
fn validate_threshold_percentage() {
// other values in between 0.5 and 1 are valid
valid_threshold(&Decimal::percent(51)).unwrap();
valid_threshold(&Decimal::percent(67)).unwrap();
valid_threshold(&Decimal::percent(99)).unwrap();
let err = valid_threshold(&Decimal::percent(101)).unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::InvalidThreshold {}.to_string()
);
}
#[test]
fn validate_threshold() {
// absolute count ensures 0 < required <= total_weight
let err = Threshold::AbsoluteCount { weight: 0 }
.validate(5)
.unwrap_err();
// TODO: remove to_string() when PartialEq implemented
assert_eq!(err.to_string(), ThresholdError::ZeroWeight {}.to_string());
let err = Threshold::AbsoluteCount { weight: 6 }
.validate(5)
.unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::UnreachableWeight {}.to_string()
);
Threshold::AbsoluteCount { weight: 1 }.validate(5).unwrap();
Threshold::AbsoluteCount { weight: 5 }.validate(5).unwrap();
// AbsolutePercentage just enforces valid_percentage (tested above)
let err = Threshold::AbsolutePercentage {
percentage: Decimal::zero(),
}
.validate(5)
.unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::InvalidThreshold {}.to_string()
);
Threshold::AbsolutePercentage {
percentage: Decimal::percent(51),
}
.validate(5)
.unwrap();
// Quorum enforces both valid just enforces valid_percentage (tested above)
Threshold::ThresholdQuorum {
threshold: Decimal::percent(51),
quorum: Decimal::percent(40),
}
.validate(5)
.unwrap();
let err = Threshold::ThresholdQuorum {
threshold: Decimal::percent(101),
quorum: Decimal::percent(40),
}
.validate(5)
.unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::InvalidThreshold {}.to_string()
);
let err = Threshold::ThresholdQuorum {
threshold: Decimal::percent(51),
quorum: Decimal::percent(0),
}
.validate(5)
.unwrap_err();
assert_eq!(
err.to_string(),
ThresholdError::ZeroQuorumThreshold {}.to_string()
);
}
#[test]
fn threshold_response() {
let total_weight: u64 = 100;
let res = Threshold::AbsoluteCount { weight: 42 }.to_response(total_weight);
assert_eq!(
res,
ThresholdResponse::AbsoluteCount {
weight: 42,
total_weight
}
);
let res = Threshold::AbsolutePercentage {
percentage: Decimal::percent(51),
}
.to_response(total_weight);
assert_eq!(
res,
ThresholdResponse::AbsolutePercentage {
percentage: Decimal::percent(51),
total_weight
}
);
let res = Threshold::ThresholdQuorum {
threshold: Decimal::percent(66),
quorum: Decimal::percent(50),
}
.to_response(total_weight);
assert_eq!(
res,
ThresholdResponse::ThresholdQuorum {
threshold: Decimal::percent(66),
quorum: Decimal::percent(50),
total_weight
}
);
}
}