pip-services4-components-node/src/build/CompositeFactory.ts

Portable Component Model in Node.js / ES2017

/** @module build */
import { IFactory } from './IFactory';
import { CreateException } from './CreateException';

/**
 * Aggregates multiple factories into a single factory component.
 * When a new component is requested, it iterates through 
 * factories to locate the one able to create the requested component.
 * 
 * This component is used to conveniently keep all supported factories in a single place.
 * 
 * ### Example ###
 * 
 *     let factory = new CompositeFactory();
 *     factory.add(new DefaultLoggerFactory());
 *     factory.add(new DefaultCountersFactory());
 *     
 *     let loggerLocator = new Descriptor("*", "logger", "*", "*", "1.0");
 *     factory.canCreate(loggerLocator);         // Result: Descriptor("pip-service", "logger", "null", "default", "1.0")
 *     factory.create(loggerLocator);             // Result: created NullLogger
 */
export class CompositeFactory implements IFactory {
    private _factories: IFactory[] = [];
    
    /**
     * Creates a new instance of the factory.
     * 
     * @param factories     a list of factories to embed into this factory.
     */
    public constructor(...factories: IFactory[]) {
        if (factories != null) {
            this._factories = this._factories.concat(factories);
        }
    }
    
    /**
     * Adds a factory into the list of embedded factories.
     * 
     * @param factory     a factory to be added.
     */
    public add(factory: IFactory): void {
        if (factory == null) {
            throw new Error("Factory cannot be null");
        }
        
        this._factories.push(factory);
    }
    
    /**
     * Removes a factory from the list of embedded factories.
     * 
     * @param factory     the factory to remove.
     */
    public remove(factory: IFactory): void {
        this._factories = this._factories.filter((f) => f != factory);
    }
    
    /**
     * Checks if this factory is able to create component by given locator.
     * 
     * This method searches for all registered components and returns
     * a locator for component it is able to create that matches the given locator.
     * If the factory is not able to create a requested component is returns null.
     * 
     * @param locator     a locator to identify component to be created.
     * @returns            a locator for a component that the factory is able to create.
     */
    public canCreate(locator: any): any {
        if (locator == null) {
            throw new Error("Locator cannot be null");
        }
        
        // Iterate from the latest factories
        for (let index = this._factories.length - 1; index >= 0; index--) {
            const thisLocator = this._factories[index].canCreate(locator);
            if (thisLocator != null) {
                return thisLocator;
            }
        }
        
        return null;
    }
    
    /**
     * Creates a component identified by given locator.
     * 
     * @param locator     a locator to identify component to be created.
     * @returns the created component.
     * 
     * @throws a CreateException if the factory is not able to create the component.
     */
    public create(locator: any): any {
        if (locator == null) {
            throw new Error("Locator cannot be null");
        }
        
        // Iterate from the latest factories
        for (let index = this._factories.length - 1; index >= 0; index--) {
            const factory = this._factories[index];
            if (factory.canCreate(locator) != null) {
                return factory.create(locator);
            }
        }
        
        throw new CreateException(null, locator);
    }
    
}