@seroh/roll/dist/randomizer/WeightedRandomizer.js

An RPG dice-rolling library with a variety of built-in roll mechanics.

import { Randomizer } from "./Randomizer";
export class WeightedRandomizer extends Randomizer {
    weights;
    cumulativeWeights;
    constructor(weights) {
        super();
        this.validateWeights(weights);
        this.weights = Object.values(weights);
        this.cumulativeWeights = this.convertToCumulativeWeights(this.weights);
    }
    generator() {
        return this.mapToWeightedValue(Math.random(), this.cumulativeWeights);
    }
    validateWeights(weights) {
        const entries = Object.entries(weights);
        let maxFace = 0;
        let weightSum = 0;
        for (const [key, value] of entries) {
            const face = Number(key);
            // Validate key
            if (key === "" || !Number.isInteger(face) || face <= 0) {
                throw new Error(`Invalid key "${key}": All keys must be positive integers.`);
            }
            // Validate value
            if (typeof value !== "number" || value > 1 || value < 0 || isNaN(value)) {
                throw new Error(`Invalid value for key "${key}": All values must be a number between 0 and 1 (inclusive). Received "${value}".`);
            }
            if (face > maxFace) {
                maxFace = face;
            }
            weightSum += value;
        }
        if (maxFace !== entries.length) {
            throw new Error(`Incorrect number of weight entries: Expected entries from 1 to ${maxFace}, but received ${entries.length} entries total.`);
        }
        if (weightSum != 1) {
            throw new Error(`Incorrect weights provided, the total of all weights expected to be 1. Got ${weightSum}`);
        }
    }
    convertToCumulativeWeights(weights) {
        const cumulativeWeights = [];
        let cumulativeSum = 0;
        for (let i = 0; i < weights.length; i++) {
            cumulativeSum += weights[i];
            cumulativeWeights.push(cumulativeSum);
        }
        return cumulativeWeights;
    }
    mapToWeightedValue(randomValue, cumulativeWeights) {
        for (let i = 0; i < cumulativeWeights.length; i++) {
            if (randomValue < cumulativeWeights[i]) {
                return i + 1;
            }
        }
        // Should not reach here if weights are valid
        throw new Error("Invalid weights or random value.");
    }
    scaleToRange(weightedRoll) {
        return weightedRoll;
    }
}
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