@ui5/fs/lib/ReaderCollection.js

UI5 Build and Development Tooling - File System Abstraction

const AbstractReader = require("./AbstractReader");

/**
 * Resource Locator ReaderCollection
 *
 * @public
 * @memberof module:@ui5/fs
 * @augments module:@ui5/fs.AbstractReader
 */
class ReaderCollection extends AbstractReader {
	/**
	 * The constructor.
	 *
	 * @param {Object} parameters Parameters
	 * @param {module:@ui5/fs.AbstractReader[]} parameters.readers List of resource readers (all tried in parallel)
	 * @param {string} parameters.name The collection name
	 */
	constructor({readers, name}) {
		super();
		this._name = name;
		this._readers = readers;
	}

	/**
	 * Locates resources by GLOB.
	 *
	 * @private
	 * @param {string} pattern GLOB pattern
	 * @param {Object} options GLOB options
	 * @param {module:@ui5/fs.tracing.Trace} trace Trace instance
	 * @returns {Promise<module:@ui5/fs.Resource[]>} Promise resolving to list of resources
	 */
	_byGlob(pattern, options, trace) {
		return Promise.all(this._readers.map(function(resourceLocator) {
			return resourceLocator._byGlob(pattern, options, trace);
		})).then((result) => {
			trace.collection(this._name);
			return Array.prototype.concat.apply([], result);
		});
	}

	/**
	 * Locates resources by path.
	 *
	 * @private
	 * @param {string} virPath Virtual path
	 * @param {Object} options Options
	 * @param {module:@ui5/fs.tracing.Trace} trace Trace instance
	 * @returns {Promise<module:@ui5/fs.Resource>} Promise resolving to a single resource
	 */
	_byPath(virPath, options, trace) {
		const that = this;
		const resourceLocatorCount = this._readers.length;
		let resolveCount = 0;

		if (this._readers.length === 0) {
			// Promise.race doesn't resolve for empty arrays
			return Promise.resolve();
		}

		/* Promise.race to cover the following (self defined) requirement:
			Deliver files that can be found fast at the cost of slower response times for files that cannot be found.
		*/
		return Promise.race(this._readers.map(function(resourceLocator) {
			return resourceLocator._byPath(virPath, options, trace).then(function(resource) {
				return new Promise(function(resolve, reject) {
					trace.collection(that._name);
					resolveCount++;
					if (resource) {
						resource.pushCollection(that._name);
						resolve(resource);
					} else if (resolveCount === resourceLocatorCount) {
						resolve(null);
					}
				});
			});
		}));
	}
}

module.exports = ReaderCollection;