/*  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/>.
 */

#![allow(mutable_borrow_reservation_conflict)]

use crate::numbers::Number;
use crate::election::{Candidate, CandidateState, CountCard, CountState, Parcel, Vote};

use std::collections::HashMap;
use std::ops::Sub;

struct NextPreferencesResult<'a, N> {
	candidates: HashMap<&'a Candidate, NextPreferencesEntry<'a, N>>,
	exhausted: NextPreferencesEntry<'a, N>,
	total_ballots: N,
}

struct NextPreferencesEntry<'a, N> {
	//count_card: Option<&'a CountCard<'a, N>>,
	votes: Vec<Vote<'a, N>>,
	num_ballots: N,
	num_votes: N,
}

fn next_preferences<'a, N: Number>(state: &CountState<'a, N>, votes: Vec<Vote<'a, N>>) -> NextPreferencesResult<'a, N> {
	let mut result = NextPreferencesResult {
		candidates: HashMap::new(),
		exhausted: NextPreferencesEntry {
			votes: Vec::new(),
			num_ballots: N::new(),
			num_votes: N::new(),
		},
		total_ballots: N::new(),
	};
	
	for mut vote in votes.into_iter() {
		result.total_ballots += &vote.ballot.orig_value;
		
		let mut next_candidate = None;
		
		for (i, preference) in vote.ballot.preferences.iter().enumerate().skip(vote.up_to_pref) {
			let candidate = &state.election.candidates[*preference];
			let count_card = state.candidates.get(candidate).unwrap();
			
			if let CandidateState::HOPEFUL | CandidateState::GUARDED = count_card.state {
				next_candidate = Some(candidate);
				vote.up_to_pref = i + 1;
				break;
			}
		}
		
		// Have to structure like this to satisfy Rust's borrow checker
		if let Some(candidate) = next_candidate {
			if result.candidates.contains_key(candidate) {
				let entry = result.candidates.get_mut(candidate).unwrap();
				entry.num_ballots += &vote.ballot.orig_value;
				entry.num_votes += &vote.value;
				entry.votes.push(vote);
			} else {
				let entry = NextPreferencesEntry {
					num_ballots: vote.ballot.orig_value.clone(),
					num_votes: vote.value.clone(),
					votes: vec![vote],
				};
				result.candidates.insert(candidate, entry);
			}
		} else {
			result.exhausted.num_ballots += &vote.ballot.orig_value;
			result.exhausted.num_votes += &vote.value;
			result.exhausted.votes.push(vote);
		}
	}
	
	return result;
}

pub fn distribute_first_preferences<N: Number>(state: &mut CountState<N>) {
	let mut votes = Vec::new();
	for ballot in state.election.ballots.iter() {
		let vote = Vote {
			ballot: ballot,
			value: ballot.orig_value.clone(),
			up_to_pref: 0,
		};
		votes.push(vote);
	}
	
	let result = next_preferences(state, votes);
	
	// Transfer candidate votes
	for (candidate, entry) in result.candidates.into_iter() {
		let parcel = entry.votes as Parcel<N>;
		let count_card = state.candidates.get_mut(candidate).unwrap();
		count_card.parcels.push(parcel);
		count_card.transfer(&entry.num_votes);
	}
	
	// Transfer exhausted votes
	let parcel = result.exhausted.votes as Parcel<N>;
	state.exhausted.parcels.push(parcel);
	state.exhausted.transfer(&result.exhausted.num_votes);
}

pub fn calculate_quota<N: Number>(state: &mut CountState<N>) {
	// Calculate the total vote
	state.quota = N::zero();
	for count_card in state.candidates.values() {
		state.quota += &count_card.votes;
	}
	
	// TODO: Different quotas
	state.quota /= N::from(state.election.seats + 1);
	
	// TODO: Different rounding rules
	state.quota += N::one();
	state.quota.floor_mut();
}

fn meets_quota<N: Number>(quota: &N, count_card: &CountCard<N>) -> bool {
	// TODO: Different quota rules
	return count_card.votes >= *quota;
}

pub fn elect_meeting_quota<N: Number>(state: &mut CountState<N>) {
	// Can't use filter(...) magic because of conflict with borrow checker
	let mut cands_meeting_quota = Vec::new();
	for (candidate, count_card) in state.candidates.iter_mut() {
		if count_card.state == CandidateState::HOPEFUL && meets_quota(&state.quota, count_card) {
			cands_meeting_quota.push((candidate, count_card));
		}
	}
	
	if cands_meeting_quota.len() > 0 {
		// Sort by votes
		cands_meeting_quota.sort_unstable_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
		
		// Declare elected in descending order of votes
		for (_, count_card) in cands_meeting_quota.into_iter().rev() {
			// TODO: Log
			count_card.state = CandidateState::ELECTED;
			state.num_elected += 1;
			count_card.order_elected = state.num_elected as isize;
		}
	}
}

pub fn distribute_surpluses<N: Number>(state: &mut CountState<N>) -> bool where for<'r> &'r N: Sub<&'r N, Output=N> {
	// As above regarding filter(...)
	let mut has_surplus = Vec::new();
	for (candidate, count_card) in state.candidates.iter() {
		if count_card.votes > state.quota {
			has_surplus.push((candidate, count_card));
		}
	}
	
	if has_surplus.len() > 0 {
		// TODO: Different sorting orders
		has_surplus.sort_unstable_by(|a, b| a.1.order_elected.partial_cmp(&b.1.order_elected).unwrap());
		
		// Distribute top candidate's surplus
		// TODO: Handle ties
		let elected_candidate = has_surplus.first_mut().unwrap().0;
		distribute_surplus(state, elected_candidate);
		
		return true;
	}
	return false;
}

fn distribute_surplus<N: Number>(state: &mut CountState<N>, elected_candidate: &Candidate) where for<'r> &'r N: Sub<&'r N, Output=N> {
	let count_card = state.candidates.get(elected_candidate).unwrap();
	let surplus = &count_card.votes - &state.quota;
	
	// Inclusive Gregory
	// TODO: Other methods
	let votes = state.candidates.get(elected_candidate).unwrap().parcels.concat();
	
	// Count next preferences
	let result = next_preferences(state, votes);
	
	// Transfer candidate votes
	// Unweighted inclusive Gregory
	// TODO: Other methods
	let transfer_value = surplus.clone() / &result.total_ballots;
	
	for (candidate, entry) in result.candidates.into_iter() {
		let mut parcel = entry.votes as Parcel<N>;
		
		// Reweight votes
		for vote in parcel.iter_mut() {
			vote.value = vote.ballot.orig_value.clone() * &transfer_value;
		}
		
		let count_card = state.candidates.get_mut(candidate).unwrap();
		count_card.parcels.push(parcel);
		
		let mut total_transferred = entry.num_ballots * &surplus / &result.total_ballots;
		// Round transfers
		// TODO: Make configurable
		total_transferred.floor_mut();
		count_card.transfer(&total_transferred);
	}
	
	// Transfer exhausted votes
	let parcel = result.exhausted.votes as Parcel<N>;
	state.exhausted.parcels.push(parcel);
	state.exhausted.transfer(&result.exhausted.num_votes);
	
	// Finalise candidate votes
	let count_card = state.candidates.get_mut(elected_candidate).unwrap();
	count_card.transfers = -surplus;
	count_card.votes.assign(&state.quota);
}

pub fn bulk_elect<N: Number>(state: &mut CountState<N>) -> bool {
	if state.election.candidates.len() - state.num_excluded <= state.election.seats {
		// Bulk elect all remaining candidates
		let mut hopefuls = Vec::new();
		for (candidate, count_card) in state.candidates.iter_mut() {
			if count_card.state == CandidateState::HOPEFUL {
				hopefuls.push((candidate, count_card));
			}
		}
		// TODO: Handle ties
		hopefuls.sort_unstable_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
		
		for (_, count_card) in hopefuls.into_iter() {
			count_card.state = CandidateState::ELECTED;
			state.num_elected += 1;
			count_card.order_elected = state.num_elected as isize;
		}
		
		return true;
	}
	return false;
}

pub fn exclude_hopefuls<N: Number>(state: &mut CountState<N>) -> bool {
	let mut hopefuls = Vec::new();
	for (candidate, count_card) in state.candidates.iter() {
		if count_card.state == CandidateState::HOPEFUL {
			hopefuls.push((candidate, count_card));
		}
	}
	
	// Sort by votes
	// TODO: Handle ties
	hopefuls.sort_unstable_by(|a, b| a.1.votes.partial_cmp(&b.1.votes).unwrap());
	
	// Exclude lowest ranked candidate
	let excluded_candidate = hopefuls.first().unwrap().0;
	exclude_candidate(state, excluded_candidate);
	
	return true;
}

pub fn continue_exclusion<N: Number>(state: &mut CountState<N>) -> bool {
	let mut excluded_with_votes = Vec::new();
	for (candidate, count_card) in state.candidates.iter() {
		if count_card.state == CandidateState::EXCLUDED && !count_card.votes.is_zero() {
			excluded_with_votes.push((candidate, count_card));
		}
	}
	
	if excluded_with_votes.len() > 0 {
		excluded_with_votes.sort_unstable_by(|a, b| a.1.order_elected.partial_cmp(&b.1.order_elected).unwrap());
		let excluded_candidate = excluded_with_votes.first().unwrap().0;
		exclude_candidate(state, excluded_candidate);
		return true;
	}
	
	return false;
}

fn exclude_candidate<N: Number>(state: &mut CountState<N>, excluded_candidate: &Candidate) {
	let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
	count_card.state = CandidateState::EXCLUDED;
	state.num_excluded += 1;
	count_card.order_elected = -(state.num_excluded as isize);
	
	// Exclude in one round
	// TODO: Exclude by parcel
	let votes = state.candidates.get(excluded_candidate).unwrap().parcels.concat();
	
	// Count next preferences
	let result = next_preferences(state, votes);
	
	// Transfer candidate votes
	for (candidate, entry) in result.candidates.into_iter() {
		let parcel = entry.votes as Parcel<N>;
		let count_card = state.candidates.get_mut(candidate).unwrap();
		count_card.parcels.push(parcel);
		
		count_card.transfer(&entry.num_votes);
	}
	
	// Transfer exhausted votes
	let parcel = result.exhausted.votes as Parcel<N>;
	state.exhausted.parcels.push(parcel);
	state.exhausted.transfer(&result.exhausted.num_votes);
	
	// Finalise candidate votes
	let count_card = state.candidates.get_mut(excluded_candidate).unwrap();
	count_card.transfers = -count_card.votes.clone();
	count_card.votes = N::new();
}

pub fn finished_before_stage<N: Number>(state: &CountState<N>) -> bool {
	if state.num_elected >= state.election.seats {
		return true;
	}
	return false;
}