edx-platform/xmodule/assets/video/public/js/00_sjson.js

'use strict';

let Sjson = function(data) {
    let sjson = {
            start: data.start.concat(),
            text: data.text.concat()
        },
        module = {};

    let getter = function(propertyName) {
        return function() {
            return sjson[propertyName];
        };
    };

    let getStartTimes = getter('start');

    let getCaptions = getter('text');

    let size = function() {
        return sjson.text.length;
    };

    function search(time, startTime, endTime) {
        let start = getStartTimes(),
            max = size() - 1,
            min = 0,
            results,
            index;

        // if we specify a start and end time to search,
        // search the filtered list of captions in between
        // the start / end times.
        // Else, search the unfiltered list.
        if (typeof startTime !== 'undefined'
    && typeof endTime !== 'undefined') {
            results = filter(startTime, endTime);
            start = results.start;
            max = results.captions.length - 1;
        } else {
            start = getStartTimes();
        }
        while (min < max) {
            index = Math.ceil((max + min) / 2);

            if (time < start[index]) {
                max = index - 1;
            }

            if (time >= start[index]) {
                min = index;
            }
        }

        return min;
    }

    function filter(start, end) {
        /* filters captions that occur between inputs
         * `start` and `end`. Start and end should
         * be Numbers (doubles) corresponding to the
         * number of seconds elapsed since the beginning
         * of the video.
         *
         * Returns an object with properties
         * "start" and "captions" representing
         * parallel arrays of start times and
         * their corresponding captions.
         */
        let filteredTimes = [];
        let filteredCaptions = [];
        let startTimes = getStartTimes();
        let captions = getCaptions();

        if (startTimes.length !== captions.length) {
            console.warn('video caption and start time arrays do not match in length');
        }

        // if end is null, then it's been set to
        // some erroneous value, so filter using the
        // entire array as long as it's not empty
        if (end === null && startTimes.length) {
            end = startTimes[startTimes.length - 1];
        }

        _.filter(startTimes, function(currentStartTime, i) {
            if (currentStartTime >= start && currentStartTime <= end) {
                filteredTimes.push(currentStartTime);
                filteredCaptions.push(captions[i]);
            }
        });

        return {
            start: filteredTimes,
            captions: filteredCaptions
        };
    }

    return {
        getCaptions: getCaptions,
        getStartTimes: getStartTimes,
        getSize: size,
        filter: filter,
        search: search
    };
};

export default Sjson;