likwid/backend/src/voting/mod.rs

//! Advanced Voting Methods
//!
//! Implements various voting algorithms as described in the Democracy Design manifesto:
//! - Schulze Method (Condorcet-consistent pairwise comparison)
//! - STAR Voting (Score Then Automatic Runoff)
//! - Quadratic Voting (intensity-weighted preferences)
//! - Ranked Choice / Instant Runoff

pub mod schulze;
pub mod star;
pub mod quadratic;
pub mod ranked_choice;

use serde::{Deserialize, Serialize};
use uuid::Uuid;

/// Voting method types
/// Used by voting calculation services when tallying results.
#[allow(dead_code)]
#[derive(Debug, Default, Clone, Copy, PartialEq, Eq, Serialize, Deserialize)]
#[serde(rename_all = "snake_case")]
pub enum VotingMethod {
    /// Simple approval voting (vote for multiple options)
    #[default]
    Approval,
    /// Ranked choice / instant runoff
    RankedChoice,
    /// Schulze method (Condorcet)
    Schulze,
    /// STAR voting (Score Then Automatic Runoff)
    Star,
    /// Quadratic voting (intensity-weighted)
    Quadratic,
}

impl std::fmt::Display for VotingMethod {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            VotingMethod::Approval => write!(f, "approval"),
            VotingMethod::RankedChoice => write!(f, "ranked_choice"),
            VotingMethod::Schulze => write!(f, "schulze"),
            VotingMethod::Star => write!(f, "star"),
            VotingMethod::Quadratic => write!(f, "quadratic"),
        }
    }
}

/// Result of a voting calculation
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct VotingResult {
    /// The winning option (if any)
    pub winner: Option<Uuid>,
    /// Full ranking of options
    pub ranking: Vec<RankedOption>,
    /// Method-specific details
    pub details: VotingDetails,
    /// Total number of ballots counted
    pub total_ballots: usize,
}

/// An option with its rank and score
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RankedOption {
    pub option_id: Uuid,
    pub rank: usize,
    pub score: f64,
}

/// Method-specific voting details
#[derive(Debug, Clone, Serialize, Deserialize)]
#[serde(tag = "method")]
pub enum VotingDetails {
    Approval {
        vote_counts: Vec<(Uuid, i64)>,
    },
    RankedChoice {
        rounds: Vec<RoundResult>,
        eliminated: Vec<Uuid>,
    },
    Schulze {
        pairwise_matrix: Vec<Vec<i32>>,
        strongest_paths: Vec<Vec<i32>>,
        option_ids: Vec<Uuid>,
    },
    Star {
        score_totals: Vec<(Uuid, i64)>,
        finalists: (Uuid, Uuid),
        runoff_votes: (i64, i64),
    },
    Quadratic {
        vote_totals: Vec<(Uuid, i64)>,
        total_credits_spent: i64,
    },
}

/// Result of a single round in ranked choice voting
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct RoundResult {
    pub round: usize,
    pub vote_counts: Vec<(Uuid, i64)>,
    pub eliminated: Option<Uuid>,
}