OpenTally/src/ties.rs

/*  OpenTally: Open-source election vote counting
 *  Copyright © 2021 Lee Yingtong Li (RunasSudo)
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU Affero General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program 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 Affero General Public License for more details.
 *
 *  You should have received a copy of the GNU Affero General Public License
 *  along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */

use crate::election::{Candidate, CountState};
use crate::logger::smart_join;
use crate::numbers::Number;
use crate::stv::STVError;

#[allow(unused_imports)]
use wasm_bindgen::prelude::wasm_bindgen;

#[allow(unused_imports)]
use std::io::{stdin, stdout, Write};

/// Strategy for breaking ties
#[derive(PartialEq)]
pub enum TieStrategy {
	/// Break ties according to the candidate who first had more/fewer votes
	Forwards,
	/// Break ties according to the candidate who most recently had more/fewer votes
	Backwards,
	/// Break ties randomly (see [crate::sharandom])
	Random(String),
	/// Prompt the user to break ties
	Prompt,
}

impl TieStrategy {
	/// Convert to CLI argument representation
	pub fn describe(&self) -> String {
		match self {
			Self::Forwards => "forwards",
			Self::Backwards => "backwards",
			Self::Random(_) => "random",
			Self::Prompt => "prompt",
		}.to_string()
	}
	
	/// Break a tie between the given candidates, selecting the highest candidate
	///
	/// The given candidates are assumed to be tied in this round
	pub fn choose_highest<'c, N: Number>(&self, state: &mut CountState<N>, candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
		match self {
			Self::Forwards => {
				let mut candidates = candidates.clone();
				candidates.sort_unstable_by(|a, b|
					// Compare b to a to sort high-to-low
					state.forwards_tiebreak.as_ref().unwrap()[b]
						.cmp(&state.forwards_tiebreak.as_ref().unwrap()[a])
					);
				if state.forwards_tiebreak.as_ref().unwrap()[candidates[0]] == state.forwards_tiebreak.as_ref().unwrap()[candidates[1]] {
					return Err(STVError::UnresolvedTie);
				} else {
					state.logger.log_literal(format!("Tie between {} broken forwards.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
					return Ok(candidates[0]);
				}
			}
			Self::Backwards => {
				let mut candidates = candidates.clone();
				candidates.sort_unstable_by(|a, b|
					state.backwards_tiebreak.as_ref().unwrap()[b]
						.cmp(&state.backwards_tiebreak.as_ref().unwrap()[a])
					);
				if state.backwards_tiebreak.as_ref().unwrap()[candidates[0]] == state.backwards_tiebreak.as_ref().unwrap()[candidates[1]] {
					return Err(STVError::UnresolvedTie);
				} else {
					state.logger.log_literal(format!("Tie between {} broken backwards.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
					return Ok(candidates[0]);
				}
			}
			Self::Random(_) => {
				state.logger.log_literal(format!("Tie between {} broken at random.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
				return Ok(candidates[state.random.as_mut().unwrap().next(candidates.len())]);
			}
			Self::Prompt => {
				match prompt(candidates) {
					Ok(c) => {
						state.logger.log_literal(format!("Tie between {} broken by manual intervention.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
						return Ok(c);
					}
					Err(e) => { return Err(e); }
				}
			}
		}
	}
	
	/// Break a tie between the given candidates, selecting the lowest candidate
	///
	/// The given candidates are assumed to be tied in this round
	pub fn choose_lowest<'c, N: Number>(&self, state: &mut CountState<N>, candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
		match self {
			Self::Forwards => {
				let mut candidates = candidates.clone();
				candidates.sort_unstable_by(|a, b|
					state.forwards_tiebreak.as_ref().unwrap()[a]
						.cmp(&state.forwards_tiebreak.as_ref().unwrap()[b])
					);
				if state.forwards_tiebreak.as_ref().unwrap()[candidates[0]] == state.forwards_tiebreak.as_ref().unwrap()[candidates[1]] {
					return Err(STVError::UnresolvedTie);
				} else {
					state.logger.log_literal(format!("Tie between {} broken forwards.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
					return Ok(candidates[0]);
				}
			}
			Self::Backwards => {
				let mut candidates = candidates.clone();
				candidates.sort_unstable_by(|a, b|
					state.backwards_tiebreak.as_ref().unwrap()[a]
						.cmp(&state.backwards_tiebreak.as_ref().unwrap()[b])
					);
				if state.backwards_tiebreak.as_ref().unwrap()[candidates[0]] == state.backwards_tiebreak.as_ref().unwrap()[candidates[1]] {
					return Err(STVError::UnresolvedTie);
				} else {
					state.logger.log_literal(format!("Tie between {} broken backwards.", smart_join(&candidates.iter().map(|c| c.name.as_str()).collect())));
					return Ok(candidates[0]);
				}
			}
			Self::Random(_seed) => {
				return self.choose_highest(state, candidates);
			}
			Self::Prompt => {
				return self.choose_highest(state, candidates);
			}
		}
	}
}

/// Return all maximal items according to the given key
pub fn multiple_max_by<E: Copy, K, C: Ord>(items: &Vec<E>, key: K) -> Vec<E>
where
	K: Fn(&E) -> C
{
	let mut max_key = None;
	let mut max_items = Vec::new();
	for item in items.iter() {
		let item_key = key(item);
		match &max_key {
			Some(v) => {
				if &item_key > v {
					max_key = Some(item_key);
					max_items.clear();
					max_items.push(*item);
				} else if &item_key == v {
					max_items.push(*item);
				}
			}
			None => {
				max_key = Some(item_key);
				max_items.clear();
				max_items.push(*item);
			}
		}
	}
	return max_items;
}

/// Return all minimal items according to the given key
pub fn multiple_min_by<E: Copy, K, C: Ord>(items: &Vec<E>, key: K) -> Vec<E>
where
	K: Fn(&E) -> C
{
	let mut min_key = None;
	let mut min_items = Vec::new();
	for item in items.iter() {
		let item_key = key(item);
		match &min_key {
			Some(v) => {
				if &item_key < v {
					min_key = Some(item_key);
					min_items.clear();
					min_items.push(*item);
				} else if &item_key == v {
					min_items.push(*item);
				}
			}
			None => {
				min_key = Some(item_key);
				min_items.clear();
				min_items.push(*item);
			}
		}
	}
	return min_items;
}

/// Prompt the candidate for input, depending on CLI or WebAssembly target
// FIXME: This may have unexpected behaviour if the tie occurs in the middle of a stage
#[cfg(not(target_arch = "wasm32"))]
fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
	println!("Multiple tied candidates:");
	for (i, candidate) in candidates.iter().enumerate() {
		println!("{}. {}", i + 1, candidate.name);
	}
	let mut buffer = String::new();
	loop {
		print!("Which candidate to select? [1-{}] ", candidates.len());
		stdout().flush().expect("IO Error");
		stdin().read_line(&mut buffer).expect("IO Error");
		match buffer.trim().parse::<usize>() {
			Ok(val) => {
				if val >= 1 && val <= candidates.len() {
					println!();
					return Ok(candidates[val - 1]);
				} else {
					println!("Invalid selection");
					continue;
				}
			}
			Err(_) => {
				println!("Invalid selection");
				continue;
			}
		}
	}
}

#[cfg(target_arch = "wasm32")]
#[wasm_bindgen]
extern "C" {
	fn read_user_input_buffer(s: &str) -> Option<String>;
}

#[cfg(target_arch = "wasm32")]
fn prompt<'c>(candidates: &Vec<&'c Candidate>) -> Result<&'c Candidate, STVError> {
	let mut message = String::from("Multiple tied candidates:\n");
	for (i, candidate) in candidates.iter().enumerate() {
		message.push_str(&format!("{}. {}\n", i + 1, candidate.name));
	}
	message.push_str(&format!("Which candidate to select? [1-{}] ", candidates.len()));
	
	match read_user_input_buffer(&message) {
		Some(response) => {
			match response.trim().parse::<usize>() {
				Ok(val) => {
					if val >= 1 && val <= candidates.len() {
						return Ok(candidates[val - 1]);
					} else {
						let _ = read_user_input_buffer(&message);
						return Err(STVError::RequireInput);
					}
				}
				Err(_) => {
					let _ = read_user_input_buffer(&message);
					return Err(STVError::RequireInput);
				}
			}
		}
		None => {
			return Err(STVError::RequireInput);
		}
	}
}