random-tables-mcp/dist/adapters/secondary/rng/crypto-random-number-generator.js

An MCP (Model Context Protocol) server for managing and rolling on random-table assets used in tabletop RPGs. Create, update, and roll on random tables with support for nested tables, weighted entries, and range-based results.

import * as crypto from 'crypto';
/**
 * Implementation of the RandomNumberGenerator interface using Node's crypto module.
 * Provides cryptographically secure random numbers.
 */
export class CryptoRandomNumberGenerator {
    /**
     * Generates a cryptographically secure random number between min and max (inclusive).
     * @param min The minimum value (inclusive).
     * @param max The maximum value (inclusive).
     * @returns A random number between min and max.
     */
    getRandomNumber(min, max) {
        // Ensure min is less than or equal to max
        if (min > max) {
            throw new Error('Min must be less than or equal to max');
        }
        // Handle special case where min equals max
        if (min === max) {
            return min;
        }
        // For floating point values between 0 and 1
        if (min === 0 && max === 1) {
            // Generate a random 32-bit unsigned integer and divide by 2^32
            const buffer = crypto.randomBytes(4);
            const randomValue = buffer.readUInt32LE(0) / 0x100000000;
            return randomValue;
        }
        // For integer ranges, use randomInt which is more efficient
        // randomInt is inclusive of min, exclusive of max+1
        return crypto.randomInt(min, max + 1);
    }
    /**
     * Gets a weighted random index based on the provided weights using
     * cryptographically secure random number generation.
     * @param weights An array of weights.
     * @returns A random index, with probability proportional to the weights.
     * @throws Error if the weights array is empty or contains non-positive values.
     */
    getWeightedIndex(weights) {
        if (weights.length === 0) {
            throw new Error('Weights array cannot be empty');
        }
        if (weights.some(weight => weight <= 0)) {
            throw new Error('All weights must be positive');
        }
        const totalWeight = weights.reduce((sum, weight) => sum + weight, 0);
        // Generate a random value between 0 and totalWeight
        const randomValue = this.getRandomNumber(0, 1) * totalWeight;
        let cumulativeWeight = 0;
        for (let i = 0; i < weights.length; i++) {
            cumulativeWeight += weights[i];
            if (randomValue < cumulativeWeight) {
                return i;
            }
        }
        // Fallback (should never happen with proper weights)
        return weights.length - 1;
    }
}
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