wikimedia/mediawiki-extensions-MobileFrontend

const sizeBuckets = [ 320, 640, 800, 1024, 1280, 1920, 2560, 2880 ],
    actionParams = require( './../mobile.startup/actionParams' ),
    util = require( './../mobile.startup/util' );

/**
 * Gets the first size larger than or equal to the provided size
 *
 * @memberof ImageGateway
 * @param {number} size
 * @return {number}
 */
function findSizeBucket( size ) {
    let i = 0;
    while ( size > sizeBuckets[i] && i < sizeBuckets.length - 1 ) {
        ++i;
    }
    return sizeBuckets[i];
}

/**
 * API for retrieving image thumbnails for a given page
 *
 * @param {Object} options Configuration options
 * @param {mw.Api} options.api
 * @private
 */
function ImageGateway( options ) {
    this._cache = {};
    this.api = options.api;
}
/**
 * Get thumbnail via the API and cache it. Return the result from the cache if exists.
 *
 * @param {string} title Url of image
 * @return {jQuery.Deferred} with the image info
 */
ImageGateway.prototype.getThumb = function ( title ) {
    const cachedThumb = this._cache[title],
        $window = util.getWindow(),
        imageSizeMultiplier = ( window.devicePixelRatio && window.devicePixelRatio > 1 ) ?
            window.devicePixelRatio : 1;

    if ( !cachedThumb ) {
        this._cache[title] = this.api.get( actionParams( {
            prop: 'imageinfo',
            titles: title,
            iiprop: [ 'url', 'extmetadata' ],
            // request an image devicePixelRatio times bigger than the reported screen size
            // for retina displays and zooming
            iiurlwidth: findSizeBucket( $window.width() * imageSizeMultiplier ),
            iiurlheight: findSizeBucket( $window.height() * imageSizeMultiplier )
        } ) ).then( function ( resp ) {
            // imageinfo is undefined for missing pages.
            if ( resp.query && resp.query.pages &&
                resp.query.pages[0] && resp.query.pages[0].imageinfo ) {
                return resp.query.pages[0].imageinfo[0];
            }
            throw new Error( 'The API failed to return any pages matching the titles.' );
        } );
    }

    return this._cache[title];
};

ImageGateway._findSizeBucket = findSizeBucket;
module.exports = ImageGateway;