type Predicate = (props: any) => boolean;

type ExtensionRegistration = {
  predicate: Predicate;
  extension: any;
};

/**
 * Binder is responsible for binding plugin extensions to their corresponding extension points.
 * The Binder class is mainly exported for testing, plugins should only use the default export.
 */
export class Binder {
  extensionPoints: {
    [key: string]: Array<ExtensionRegistration>;
  };

  constructor() {
    this.extensionPoints = {};
  }

  /**
   * Binds an extension to the extension point.
   *
   * @param extensionPoint name of extension point
   * @param extension provided extension
   * @param predicate to decide if the extension gets rendered for the given props
   */
  bind(extensionPoint: string, extension: any, predicate?: Predicate) {
    if (!this.extensionPoints[extensionPoint]) {
      this.extensionPoints[extensionPoint] = [];
    }
    const registration = {
      predicate: predicate ? predicate : () => true,
      extension
    };
    this.extensionPoints[extensionPoint].push(registration);
  }

  /**
   * Returns the first extension or null for the given extension point and its props.
   *
   * @param extensionPoint name of extension point
   * @param props of the extension point
   */
  getExtension(extensionPoint: string, props?: object) {
    const extensions = this.getExtensions(extensionPoint, props);
    if (extensions.length > 0) {
      return extensions[0];
    }
    return null;
  }

  /**
   * Returns all registered extensions for the given extension point and its props.
   *
   * @param extensionPoint name of extension point
   * @param props of the extension point
   */
  getExtensions(extensionPoint: string, props?: object): Array<any> {
    let registrations = this.extensionPoints[extensionPoint] || [];
    if (props) {
      registrations = registrations.filter(reg => reg.predicate(props || {}));
    }
    return registrations.map(reg => reg.extension);
  }

  /**
   * Returns true if at least one extension is bound to the extension point and its props.
   */
  hasExtension(extensionPoint: string, props?: object): boolean {
    return this.getExtensions(extensionPoint, props).length > 0;
  }
}

// singleton binder
const binder = new Binder();

export default binder;