Backbone Collection: iterate & search effectively

Question

What I have: I'm writing my very trivial media player. So somewhere in it I have collection of subtitles (let's say about 2 thousands per movie). So each subtitle looks like:

Object {
  id: "1"
  startTime: 2468
  endTime: 4743
  text: "Test subtitle."
}

I want: Very effectively do two things:

1. .next() method which should get me the next subtitle.
2. .getByTime(neededTime) which make something like binary search through the whole subtitles collection in effective way. The point is that the neededTime could be something in between the startTime and endTime attributes (i.e. 3000).

Question: I gonna use Backbone collection for my subtitles but how will it handle those two requirements? I mean maybe it'd be better to implement Iterator pattern and binary search manually?

Answer 1

Don't know whether it's the best solution, but I end with:

if (!Number.isInteger) {
    Number.isInteger = function isInteger (nVal) {
        return typeof nVal === "number" && isFinite(nVal) && nVal > -9007199254740992 && nVal < 9007199254740992 && Math.floor(nVal) === nVal;
    };
}

/**
 * Model
 */
var Subtitle = Backbone.Model.extend({
    defaults: {
        'startTime': '',
        'endTime': '',
        'text': ''
    },

    validate: function(attrs) {
        if (!this.get('startTime')) return 'You missed startTime';
        if (!this.get('endTime')) return 'You missed endTime';
        if (!this.get('text')) return 'You missed text';
        if (this.get('startTime') > this.get('endTime')) return 'startTime cannot be greater than endTime';
    },

    /**
     * Compare two time periods
     * @param that Subtitle with which we compare the current one
     * @returns {number} positive if {@code this} is greater than {@code that}, negative if {@code this} is less than {@code that}
     * and zero if they are equals or overlaps or one time period contains another.
     */
    equals: function(that) {
        if (!(that instanceof Subtitle)) throw Error('Cannot compare with element that does not belong to Subtitle type');
        if (this.get('startTime') > that.get('endTime')) return 1;
        else if (that.get('startTime') > this.get('endTime')) return -1;
        else return 0;
    },

    /**
     *
     * @param moment moment for which we need to find a time period
     * @returns {number} positive if {@code moment} belongs to time period greater than {@code this},
     * negative if {@code moment} belongs to time period less than {@code this}
     * and zero if the curect time period contain the {@code moment}.
     */
    containMoment: function(moment) {
        if (!Number.isInteger(moment)) throw Error('Moment should be an Integer');

        if (moment >= this.get('startTime') && moment <= this.get('endTime')) return 0;
        else if (moment < this.get('startTime')) return -1;
        else if (moment > this.get('endTime')) return +1;
        else throw Error('Impossible case :-)');
    }
});

/**
 * Collection
 */
var Subtitles = Backbone.Collection.extend({
    model: Subtitle,
    index: 0,

    next: function() {
        return this.at(this.index++);
    },

    getByMoment: function(moment) {
        return this._binarySearch(this.toArray(), moment);
    },

    _binarySearch: function(array, moment) {
        'use strict';

        var minIndex = 0;
        var maxIndex = array.length - 1;
        var currentIndex;
        var currentElement;

        while (minIndex <= maxIndex) {
            currentIndex = (minIndex + maxIndex) / 2 | 0;
            currentElement = array[currentIndex];

            if (currentElement.containMoment(moment) > 0) {
                minIndex = currentIndex + 1;
            }
            else if (currentElement.containMoment(moment) < 0) {
                maxIndex = currentIndex - 1;
            }
            else {
                return array[currentIndex];
            }
        }

        throw Error('No subtitle for this moment');
    }
});

/**
 * Test
 */
var data = [ 
  { id: '1',
    startTime: 2468,
    endTime: 4743,
    text: 'Here\'s little Ben nodding off.' },
  { id: '2',
    startTime: 5389,
    endTime: 7698,
    text: 'Look at Aunt Monica\'s Little boy.' },
  { id: '3',
    startTime: 7948,
    endTime: 11099,
    text: '-Look, he\'s got Ross\' hair cut.\n-Let me see.' },
  { id: '4',
    startTime: 11948,
    endTime: 14907,
    text: 'Oh, God!\nIs he just the sweetest thing?' },
  { id: '5',
    startTime: 15148,
    endTime: 17946,
    text: 'You must just want\nto kiss him all over.' }
];
var subtitles = new Subtitles();
subtitles.add(data);

var moment = 3000;
console.log(subtitles.next().attributes);
console.log(subtitles.next().attributes);
console.log(subtitles.next().attributes);
console.log(subtitles.next().attributes);
console.log(subtitles.getByMoment(moment).attributes);