Create Rating System Final

createRatingSystem.ts

export type KFactorOption =
    | KFactorFunctionWithPlayers
    | KFactorFunction
    | number

export function createRatingSystem(kFactor: KFactorOption = 32, exponentDenominator: number = 400, exponentBase: number = 10): RatingSystem {

    let resolvedKFactor: KFactorFunctionWithPlayers

    if (typeof kFactor === 'number') {
        resolvedKFactor = () => kFactor
    }
    else {
        resolvedKFactor = kFactor
    }

    // Standard Elo implementation with symmetric kfactor functions for each player
    // This would be a true zero-sum game where A(-x) = B(+x)
    const symmetricKFactorFn = (rating: number) => resolvedKFactor(rating, undefined)
    const getPlayerProbabilities = createPlayerProbabilitiesFn(exponentBase, exponentDenominator)
    const getNextRating = createNextRatingFn(symmetricKFactorFn)

    // Modified Elo implementation with potentially *asymmetric* kfactor functions (e.g. One play kfactor is higher than the others)
    // This means one player may gain or lose more than the other player would in similar
    const aKFactor = (rating: number) => resolvedKFactor(rating, 0)
    const getNextARating = createNextRatingFn(aKFactor)
    const bKFactor = (rating: number) => resolvedKFactor(rating, 1)
    const getNextBRating = createNextRatingFn(bKFactor)
    const getNextRatings = createNextRatingsFn(getPlayerProbabilities, getNextARating, getNextBRating)

    return {
        getPlayerProbabilities,
        getNextRating,
        getNextRatings
    }
}