sejm-calculator/src/mandates.ts

import {committees, constituencies, pastSupport} from './data';
import {Constituency} from './types';

const calculateLocalSupport = (
	support: number[],
	pastSupportProjection: number[],
	constituency: Constituency,
): number[] => {
	const localPastSupport = constituency.pastSupport;
	const localPastSupportProjection = support.map((committeeSupport, index) => (
		committees[index].pastSupportEquivalence
			.map(pastCommitteeId => localPastSupport[pastCommitteeId])
			.reduce((a, b) => a + b, 0)
	));
	const localSupportDeviation = pastSupportProjection
		.map((pastCommitteSupportProjection, index) => (
			localPastSupportProjection[index] / pastCommitteSupportProjection
		)
	);
	const localSupport = support.map((committeeSupport, index) => (
		committeeSupport * localSupportDeviation[index]
	));
	return localSupport;
}

export const calculateMandates = (support: number[]): number[] => {
	const pastSupportProjection = support.map((committeeSupport, index) => (
		committees[index].pastSupportEquivalence
			.map(pastCommitteeId => pastSupport[pastCommitteeId])
			.reduce((a, b) => a + b, 0)
	));
	const mandates: number[] = new Array(support.length).fill(0);
	constituencies.forEach(constituency => {
		const localSupport = calculateLocalSupport(support, pastSupportProjection, constituency);
		constituency.support = localSupport;
		constituency.mandates = new Array(support.length).fill(0);
		const filteredLocalSupport = localSupport.map((localCommitteeSupport, index) => {
			if (support[index] < committees[index].threshold) return 0;
			return localCommitteeSupport;
		});
		const quotients: {quotient: number; committeeIndex: number}[] = [];
		for (let divisor = 1; divisor <= constituency.size; divisor++) {
			for (let committeeIndex = 0; committeeIndex < localSupport.length; committeeIndex++) {
				quotients.push({
					quotient: filteredLocalSupport[committeeIndex] / divisor,
					committeeIndex,
				});
			}
		}
		quotients.sort((a, b) => b.quotient - a.quotient);
		quotients.slice(0, constituency.size).forEach(quotient => {
			mandates[quotient.committeeIndex]++;
			constituency.mandates![quotient.committeeIndex]++;
		});
	});
	return mandates;
}