D&D 4th Edition Encounter Level Calculator

4e-xp.js

/**
 * 4e-xp.js
 * D&D 4th Edition Encounter Level Calculator
 *
 * Copyright (C) 2012  Duane Sibilly <[email protected]>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 * 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 *
 * Usage: node 4e-xp.js -pcs [4-6] -xp [total encounter XP]
 */
(function () {
    'use strict';
    
    var print = console.log,
        
        // 4e XP tables don't cleanly map to smooth functions,so it is
        // faster to store them as hashtables for quick lookup.
        targetXP = {
            four: [
            0, 400, 500, 600, 700, 800, 1000, 1200, 1400, 1600, 2000, 2400, 2800, 3200, 4000, 4800, 5600, 6400, 8000, 9600, 11200, 12800, 16600, 20400, 24200, 28000, 36000, 44000, 52000, 60000, 76000],

            five: [
            0, 500, 625, 750, 875, 1000, 1250, 1500, 1750, 2000, 2500, 3000, 3500, 4000, 5000, 6000, 7000, 8000, 10000, 12000, 14000, 16000, 20750, 25500, 30250, 35000, 45000, 55000, 65000, 75000, 95000],

            six: [
            0, 600, 750, 900, 1050, 1200, 1500, 1800, 2100, 2400, 3000, 3600, 4200, 4800, 6000, 7200, 8400, 9600, 12000, 14400, 16800, 19200, 24900, 30600, 36300, 42000, 54000, 66000, 78000, 90000, 114000]
        },

        // What is the estimated encounter level based on the XP total
        // for the encounter and the number of PCs?
        calculateEncounterLevel = function (XP, players) {
            var key, EL, found = false;

            switch (players) {
            case 5:
                key = 'five';
                break;

            case 6:
                key = 'six';
                break;

            default:
                key = 'four';
            }

            EL = targetXP[key].reduce(function (prev, curr, idx, arr) {
                if (! found) {
                    if (XP === curr) {
                        found = true;
                        return idx;
                    }

                    if (XP < curr) {
                        found = true;
                        return (idx - 1) + ((XP - arr[idx - 1]) / (curr - arr[idx - 1]));
                    }
                }

                return prev;
            });

            print('Encounter XP: ' + XP);
            print('No. of Players: ' + players);
            print('Encounter Level: ' + EL.toFixed(1));
        },

        parse = function (args) {
            var opts = {},
                curSwitch, i, len, arg;

            args = args || process.argv;

            for (i = 0, len = args.length; i < len; i += 1) {
                arg = args[i];

                // it's a switch
                if (/^(-|--)/.test(arg) || !curSwitch) {
                    opts[arg] = true;
                    curSwitch = arg;
                } else {
                    if ('false' === arg) {
                        arg = false;
                    } else if ('true' === arg) {
                        arg = true;
                    } else if (! isNaN(arg)) {
                        arg = Number(arg);
                    }

                    if (typeof opts[curSwitch] === 'boolean') {
                        opts[curSwitch] = arg;
                    } else if (Array.isArray(opts[curSwitch])) {
                        opts[curSwitch].push(arg);
                    } else {
                        opts[curSwitch] = [opts[curSwitch], arg];
                    }
                }
            }

            return opts;
        },

        args = parse(),
        xp = args['-xp'],
        pcs = args['-pcs'];

    if (! xp) {
        print('You must provide an XP value with the -xp switch');
        return;
    }

    if (pcs < 4 || pcs > 6) {
        print('Party size is limited to 4, 5 or 6 PCs');
        return;
    }

    if (pcs) {
        calculateEncounterLevel(xp, pcs);
    } else {
        calculateEncounterLevel(xp);
    }
}());