skratchdot/random-picker

/*
 * random-picker
 * https://github.com/skratchdot/random-picker
 *
 * Copyright (c) 2014 skratchdot
 * Licensed under the MIT license.
 */
'use strict';

var randomGenerator = require('random-seed');

var cleanScore = function (score) {
    var num = score === undefined ? 1 : parseFloat(score);
    num = isNaN(num) ? 1 : num;
    if (!Number.isFinite(num) || num < 0) {
        num = 0;
    }
    return num;
};

var Option = function (value, score) {
    this.value = value;
    this.score = cleanScore(score);
};

var Picker = function (seed) {
    var api = this;
    var rand = randomGenerator.create(seed);
    var total = 0;
    var options = [];

    var recalculateTotal = function () {
        total = 0;
        for (var i = 0; i < options.length; i++) {
            total += options[i].score;
        }
    };

    api.pick = function () {
        var runningTotal = 0;
        var randomValue = rand.floatBetween(0, total);
        for (var i = 0; i < options.length; i++) {
            runningTotal += options[i].score;
            if (randomValue < runningTotal) {
                return options[i].value;
            }
        }
        return null;
    };

    api.option = function (value, score) {
        var option = new Option(value, score);
        var added = false;
        if (option.score <= 0) {
            api.remove(value);
        } else {
            for (var i = 0; i < options.length; i++) {
                if (options[i].value === option.value) {
                    options[i] = option;
                    added = true;
                }
            }
            if (!added) {
                options.push(option);
            }
            recalculateTotal();
        }
    };

    api.removeAll = function () {
        total = 0;
        options = [];
    };

    api.remove = function (value) {
        for (var i = options.length - 1; i >= 0; i--) {
            if (options[i].value === value) {
                options.splice(i, 1);
            }
        }
        recalculateTotal();
    };

    api.size = function () {
        return options.length;
    };

    api.totalScore = function () {
        return total;
    };

    api.avgScore = function () {
        var avg = total / options.length;
        return Number.isFinite(avg) ? avg : 0;
    };

    return api;
};

exports.Picker = function (seed) {
    return new Picker(seed);
};