type contactPredicate = (contact: Contact) => boolean;
type contactLike = Contact | string | SelectedContact;

@Injectable()
export class ContactService {
  private selectedContactId: string = '';
  public selectedContactSubject: BehaviorSubject<contactLike>;

  public get SelectedContact(): contactLike {
    const contact: Contact = this.contactList.find((v) => v.Id === this.selectedContactId);

    return contact ? contact : null;
  }

  public set SelectedContact(value: contactLike) {
    this.selectedContactId = typeof value === 'string' ? value as string : value.Id;
    this.selectedContactSubject.next(this.findContact(this.selectedContactId));
  }

  constructor() {
    this.selectedContactSubject = new BehaviorSubject<Contact>(this.findContact(this.selectedContactId));
  }

}

import { ContactService } from './contact.service';

@Injectable()
export class FileService {

  constructor(
    private httpServiceProvider: HttpServiceProvider,
    private userService: UserService,
    private contactService: ContactService) {
  }

  getFiles(fileType: string, contactType: ContactType, skip: number, pageSize: number, organisationId: string): Observable<any> {
    let myUserId = this.userService.userId;

    let selectedContact: SelectedContact;
    this.contactService.selectedContactSubject.subscribe(v => {
      selectedContact = (v as SelectedContact);
    });
    let selectedContactId = selectedContact.Id;
    let params: HttpParams = new HttpParams();

    params = params.set('category', fileType)
      .append('senderId', myUserId)
      .append('receiverId', selectedContactId)
      .append('Skip', skip.toString())
      .append('PageSize', pageSize.toString())
      .append('contactType', String(contactType))
      .append('organisationId', organisationId);

    return this.httpServiceProvider.httpGet(CONFIGURATION.GetFiles.url, params);
  }

}