mediawiki-extensions-MultimediaViewer/resources/mmv/provider/mmv.provider.GuessedThumbnailInfo.js

/*
 * This file is part of the MediaWiki extension MediaViewer.
 *
 * MediaViewer is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * MediaViewer is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with MediaViewer.  If not, see <http://www.gnu.org/licenses/>.
 */

const Thumbnail = require( '../model/mmv.model.Thumbnail.js' );

/**
 * This provider is similar to ThumbnailInfo, but instead of making an API call
 * to get the thumbnail URL, it tries to guess it. There are two failure modes:
 * - known failure: in the given situation it does not seem possible or safe to guess the URL.
 *   It is up to the caller to obtain it by falling back to the normal provider.
 * - unexpected failure: we guess an URL but it does not work. The current implementation is
 *   conservative so at least on WMF wikis this probably won't happen, but should be reckoned
 *   with anyway. On other wikis (especially ones which do not generate thumbnails on demand
 *   via the 404 handler) this could be more frequent. Again, it is the caller's responsibility
 *   to handle this by detecting image loading errors and falling back to the normal provider.
 */
class GuessedThumbnailInfo {

	/**
	 * File extensions which are vector types (as opposed to bitmap).
	 * Thumbnails of vector types can be larger than the original file.
	 *
	 * @return {Object.<string, number>}
	 */
	get vectorExtensions() {
		return {
			svg: 1
		};
	}

	/**
	 * File extensions which can be displayed in the browser.
	 * Other file types need to be thumbnailed even if the size of the original file would be right.
	 *
	 * @return {Object.<string, number>}
	 */
	get displayableExtensions() {
		return {
			png: 1,
			jpg: 1,
			jpeg: 1,
			gif: 1
		};
	}

	/**
	 * Try to guess the thumbnailinfo for a thumbnail without doing an API request.
	 * An existing thumbnail URL is required.
	 *
	 * There is no guarantee this function will be successful - in some cases, it is impossible
	 * to guess how the URL would look. If that's the case, the promise just rejects.
	 *
	 * @param {mw.Title} file
	 * @param {string} sampleUrl a thumbnail URL for the same file (but with different size).
	 * @param {number} width thumbnail width in pixels
	 * @param {number} originalWidth width of original image in pixels
	 * @param {number} originalHeight height of original image in pixels
	 * @return {jQuery.Promise.<Thumbnail>}
	 */
	get( file, sampleUrl, width, originalWidth, originalHeight ) {
		const url = this.getUrl( file, sampleUrl, width, originalWidth );
		if ( url ) {
			return $.Deferred().resolve( new Thumbnail(
				url,
				this.guessWidth( file, width, originalWidth ),
				this.guessHeight( file, width, originalWidth, originalHeight )
			) );
		} else {
			return $.Deferred().reject( 'Could not guess thumbnail URL' );
		}
	}

	/**
	 * Try to guess the URL of a thumbnail without doing an API request.
	 * See #get().
	 *
	 * @param {mw.Title} file
	 * @param {string} sampleUrl a thumbnail URL for the same file (but with different size)
	 * @param {number} width thumbnail width in pixels
	 * @param {number} originalWidth width of original image in pixels
	 * @return {string|undefined} a thumbnail URL or nothing
	 */
	getUrl( file, sampleUrl, width, originalWidth ) {
		const needsFullSize = this.needsOriginal( file, width, originalWidth );
		const sampleIsFullSize = this.isFullSizeUrl( sampleUrl, file );

		if ( sampleIsFullSize && needsFullSize ) {
			// sample thumbnail uses full size, and we need full size as well - the sample URL
			// happens to be just the right one for us
			return sampleUrl;
		} else if ( !sampleIsFullSize && !needsFullSize ) {
			// need to convert a scaled thumbnail URL to another scaled thumbnail URL
			return this.replaceSize( file, sampleUrl, width );
		} else if ( !sampleIsFullSize && needsFullSize ) {
			if ( this.canBeDisplayedInBrowser( file ) ) {
				// the size requested is larger than the original - we need to return an URL
				// to the original file instead
				return this.guessFullUrl( file, sampleUrl );
			} else {
				// the size requested is larger than the original, but this file type cannot
				// be displayed by all browsers, so needs to be thumbnailed anyway,
				// but the thumbnail still cannot be larger than the original file
				return this.replaceSize( file, sampleUrl, originalWidth );
			}
		} else { // sampleIsFullSize && !needsOriginal
			return this.guessThumbUrl( file, sampleUrl, width );
		}
	}

	/**
	 * True if the original image needs to be used as a thumbnail.
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {number} width thumbnail width in pixels
	 * @param {number} originalWidth width of original image in pixels
	 * @return {boolean}
	 */
	needsOriginal( file, width, originalWidth ) {
		return width >= originalWidth && !this.canHaveLargerThumbnailThanOriginal( file );
	}

	/**
	 * Checks if a given thumbnail URL is full-size (the original image) or scaled
	 *
	 * @protected
	 * @param {string} url a thumbnail URL
	 * @param {mw.Title} file
	 * @return {boolean}
	 */
	isFullSizeUrl( url, file ) {
		return !this.obscureFilename( url, file ).match( '/thumb/' );
	}

	/**
	 * Removes the filename in a reversible way. This is useful because the filename can be nearly
	 * anything and could cause false positives when looking for patterns.
	 *
	 * @protected
	 * @param {string} url a thumbnail URL
	 * @param {mw.Title} file
	 * @return {string} thumbnail URL with occurrences of the filename replaced by `<filename>`
	 */
	obscureFilename( url, file ) {
		// corresponds to File::getUrlRel() which uses rawurlencode()
		const filenameInUrl = mw.util.rawurlencode( file.getMain() );

		// In the URL to the original file the filename occurs once. In a thumbnail URL it usually
		// occurs twice, but can occur once if it is too short. We replace twice, can't hurt.
		return url.replace( filenameInUrl, '<filename>' ).replace( filenameInUrl, '<filename>' );
	}

	/**
	 * Undoes #obscureFilename().
	 *
	 * @protected
	 * @param {string} url a thumbnail URL (with obscured filename)
	 * @param {mw.Title} file
	 * @return {string} original thumbnail URL
	 */
	restoreFilename( url, file ) {
		// corresponds to File::getUrlRel() which uses rawurlencode()
		const filenameInUrl = mw.util.rawurlencode( file.getMain() );

		// <> cannot be used in titles, so this is safe
		return url.replace( '<filename>', filenameInUrl ).replace( '<filename>', filenameInUrl );
	}

	/**
	 * True if the file is of a type for which the thumbnail can be scaled beyond the original size.
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @return {boolean}
	 */
	canHaveLargerThumbnailThanOriginal( file ) {
		return ( file.getExtension().toLowerCase() in this.vectorExtensions );
	}

	/**
	 * True if the file type can be displayed in most browsers, false if it needs thumbnailing
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @return {boolean}
	 */
	canBeDisplayedInBrowser( file ) {
		return ( file.getExtension().toLowerCase() in this.displayableExtensions );
	}

	/**
	 * Guess what will be the width of the thumbnail. (Thumbnails for most file formats cannot be
	 * larger than the original file so this might be smaller than the requested width.)
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {number} width thumbnail width in pixels
	 * @param {number} originalWidth width of original image in pixels
	 * @return {number} guessed width
	 */
	guessWidth( file, width, originalWidth ) {
		if ( width >= originalWidth && !this.canHaveLargerThumbnailThanOriginal( file ) ) {
			return originalWidth;
		} else {
			return width;
		}
	}

	/**
	 * Guess what will be the height of the thumbnail, given its width.
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {number} width thumbnail width in pixels
	 * @param {number} originalWidth width of original image in pixels
	 * @param {number} originalHeight height of original image in pixels
	 * @return {number} guessed height
	 */
	guessHeight( file, width, originalWidth, originalHeight ) {
		if ( width >= originalWidth && !this.canHaveLargerThumbnailThanOriginal( file ) ) {
			return originalHeight;
		} else {
			// might be off 1px due to rounding (we don't know what exact scaling method the
			// backend uses) but that should not cause any issues
			return Math.round( width * ( originalHeight / originalWidth ) );
		}
	}

	/**
	 * Given a thumbnail URL with a wrong size, returns one with the right size.
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {string} sampleUrl a thumbnail URL for the same file (but with different size)
	 * @param {number} width thumbnail width in pixels
	 * @return {string|undefined} thumbnail URL with the correct size
	 */
	replaceSize( file, sampleUrl, width ) {
		let url = this.obscureFilename( sampleUrl, file );
		const sizeRegexp = /\b\d{1,5}px\b/;

		// this should never happen, but let's play it safe - returning the sample URL and believing
		// it is the resized one would be bad. Returning a wrong filename is not catastrophic
		// as long as we return a non-working wrong filename, which would not be the case here.
		if ( !url.match( sizeRegexp ) ) {
			return undefined;
		}

		// we are assuming here that the other thumbnail parameters do not look like a size
		url = url.replace( sizeRegexp, `${ width }px` );

		return this.restoreFilename( url, file );
	}

	/**
	 * Try to guess the original URL to the file, from a thumb URL.
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {string} thumbnailUrl
	 * @return {string} URL of the original file
	 */
	guessFullUrl( file, thumbnailUrl ) {
		let url = this.obscureFilename( thumbnailUrl, file );

		if ( url === thumbnailUrl ) {
			// Did not find the filename, maybe due to URL encoding issues. Bail out.
			return undefined;
		}

		// this depends on some config settings, but will work with default or WMF settings.
		url = url.replace( /<filename>.*/, '<filename>' );
		url = url.replace( '/thumb', '' );

		return this.restoreFilename( url, file );
	}

	/**
	 * Hardest version: try to guess thumbnail URL from original
	 *
	 * @protected
	 * @param {mw.Title} file
	 * @param {string} originalUrl URL for the original file
	 * @param {number} width thumbnail width in pixels
	 * @return {string|undefined} thumbnail URL
	 */
	guessThumbUrl() {
		// Not implemented. This can be very complicated (the thumbnail might have other
		// parameters than the size, which are impossible to guess, might be converted to some
		// other format, might have a special shortened format depending on the length of the
		// filename) and it is unlikely to be useful - it would be only called when we need
		// a thumbnail that is smaller than the sample (the thumbnail which is already on the page).
		return undefined;
	}
}

module.exports = GuessedThumbnailInfo;