dspace-angular/src/app/core/cache/builders/remote-data-build.service.ts

import { Injectable } from '@angular/core';
import { Observable } from 'rxjs/Observable';
import { distinctUntilChanged, filter, flatMap, map, startWith, switchMap } from 'rxjs/operators';
import { hasValue, hasValueOperator, isEmpty, isNotEmpty } from '../../../shared/empty.util';
import { PaginatedList } from '../../data/paginated-list';
import { RemoteData } from '../../data/remote-data';
import { RemoteDataError } from '../../data/remote-data-error';
import { GetRequest } from '../../data/request.models';
import { RequestEntry } from '../../data/request.reducer';
import { RequestService } from '../../data/request.service';

import { NormalizedObject } from '../models/normalized-object.model';
import { ObjectCacheService } from '../object-cache.service';
import { DSOSuccessResponse, ErrorResponse } from '../response-cache.models';
import { ResponseCacheEntry } from '../response-cache.reducer';
import { ResponseCacheService } from '../response-cache.service';
import { getMapsTo, getRelationMetadata, getRelationships } from './build-decorators';
import { PageInfo } from '../../shared/page-info.model';
import {
  getRequestFromSelflink,
  getResourceLinksFromResponse,
  getResponseFromSelflink,
  filterSuccessfulResponses
} from '../../shared/operators';

@Injectable()
export class RemoteDataBuildService {
  constructor(protected objectCache: ObjectCacheService,
              protected responseCache: ResponseCacheService,
              protected requestService: RequestService) {
  }

  buildSingle<TNormalized extends NormalizedObject, TDomain>(href$: string | Observable<string>): Observable<RemoteData<TDomain>> {
    if (typeof href$ === 'string') {
      href$ = Observable.of(href$);
    }
    const requestHref$ = href$.pipe(flatMap((href: string) =>
      this.objectCache.getRequestHrefBySelfLink(href)));

    const requestEntry$ = Observable.race(
      href$.pipe(getRequestFromSelflink(this.requestService)),
      requestHref$.pipe(getRequestFromSelflink(this.requestService))
    );

    const responseCache$ = Observable.race(
      href$.pipe(getResponseFromSelflink(this.responseCache)),
      requestHref$.pipe(getResponseFromSelflink(this.responseCache))
    );

    // always use self link if that is cached, only if it isn't, get it via the response.
    const payload$ =
      Observable.combineLatest(
        href$.pipe(
          flatMap((href: string) => this.objectCache.getBySelfLink<TNormalized>(href)),
          startWith(undefined)
        ),
        responseCache$.pipe(
          getResourceLinksFromResponse(),
          flatMap((resourceSelfLinks: string[]) => {
            if (isNotEmpty(resourceSelfLinks)) {
              return this.objectCache.getBySelfLink(resourceSelfLinks[0]);
            } else {
              return Observable.of(undefined);
            }
          }),
          distinctUntilChanged(),
          startWith(undefined)
        ),
        (fromSelfLink, fromResponse) => {
          if (hasValue(fromSelfLink)) {
            return fromSelfLink;
          } else {
            return fromResponse;
          }
        }
      ).pipe(
        hasValueOperator(),
        map((normalized: TNormalized) => {
          return this.build<TNormalized, TDomain>(normalized);
        }),
        startWith(undefined),
        distinctUntilChanged()
      );
    return this.toRemoteDataObservable(requestEntry$, responseCache$, payload$);
  }

  toRemoteDataObservable<T>(requestEntry$: Observable<RequestEntry>, responseCache$: Observable<ResponseCacheEntry>, payload$: Observable<T>) {
    return Observable.combineLatest(requestEntry$, responseCache$.startWith(undefined), payload$,
      (reqEntry: RequestEntry, resEntry: ResponseCacheEntry, payload: T) => {
        const requestPending = hasValue(reqEntry.requestPending) ? reqEntry.requestPending : true;
        const responsePending = hasValue(reqEntry.responsePending) ? reqEntry.responsePending : false;
        let isSuccessful: boolean;
        let error: RemoteDataError;
        if (hasValue(resEntry) && hasValue(resEntry.response)) {
          isSuccessful = resEntry.response.isSuccessful;
          const errorMessage = isSuccessful === false ? (resEntry.response as ErrorResponse).errorMessage : undefined;
          if (hasValue(errorMessage)) {
            error = new RemoteDataError(resEntry.response.statusCode, errorMessage);
          }
        }
        return new RemoteData(
          requestPending,
          responsePending,
          isSuccessful,
          error,
          payload
        );
      });
  }

  buildList<TNormalized extends NormalizedObject, TDomain>(href$: string | Observable<string>): Observable<RemoteData<PaginatedList<TDomain>>> {
    if (typeof href$ === 'string') {
      href$ = Observable.of(href$);
    }

    const requestEntry$ = href$.pipe(getRequestFromSelflink(this.requestService));
    const responseCache$ = href$.pipe(getResponseFromSelflink(this.responseCache));

    const tDomainList$ = responseCache$.pipe(
      getResourceLinksFromResponse(),
      flatMap((resourceUUIDs: string[]) => {
        return this.objectCache.getList(resourceUUIDs)
          .map((normList: TNormalized[]) => {
            return normList.map((normalized: TNormalized) => {
              return this.build<TNormalized, TDomain>(normalized);
            });
          });
      }),
      startWith([]),
      distinctUntilChanged()
    );

    const pageInfo$ = responseCache$.pipe(
      filterSuccessfulResponses(),
      map((entry: ResponseCacheEntry) => {
        if (hasValue((entry.response as DSOSuccessResponse).pageInfo)) {
          const resPageInfo = (entry.response as DSOSuccessResponse).pageInfo;
          if (isNotEmpty(resPageInfo) && resPageInfo.currentPage >= 0) {
            return Object.assign({}, resPageInfo, { currentPage: resPageInfo.currentPage + 1 });
          } else {
            return resPageInfo;
          }
        }
      })
  );

    const payload$ = Observable.combineLatest(tDomainList$, pageInfo$, (tDomainList, pageInfo) => {
      return new PaginatedList(pageInfo, tDomainList);
    });

    return this.toRemoteDataObservable(requestEntry$, responseCache$, payload$);
  }

  build<TNormalized, TDomain>(normalized: TNormalized): TDomain {
    const links: any = {};

    const relationships = getRelationships(normalized.constructor) || [];

    relationships.forEach((relationship: string) => {
      let result;
      if (hasValue(normalized[relationship])) {
        const { resourceType, isList } = getRelationMetadata(normalized, relationship);
        const objectList = normalized[relationship].page || normalized[relationship];
        if (typeof objectList !== 'string') {
          objectList.forEach((href: string) => {
            this.requestService.configure(new GetRequest(this.requestService.generateRequestId(), href))
          });

          const rdArr = [];
          objectList.forEach((href: string) => {
            rdArr.push(this.buildSingle(href));
          });

          if (isList) {
            result = this.aggregate(rdArr);
          } else if (rdArr.length === 1) {
            result = rdArr[0];
          }
        } else {
          this.requestService.configure(new GetRequest(this.requestService.generateRequestId(), objectList));

          // The rest API can return a single URL to represent a list of resources (e.g. /items/:id/bitstreams)
          // in that case only 1 href will be stored in the normalized obj (so the isArray above fails),
          // but it should still be built as a list
          if (isList) {
            result = this.buildList(objectList);
          } else {
            result = this.buildSingle(objectList);
          }
        }

        if (hasValue(normalized[relationship].page)) {
          links[relationship] = this.toPaginatedList(result, normalized[relationship].pageInfo);
        } else {
          links[relationship] = result;
        }
      }
    });

    const domainModel = getMapsTo(normalized.constructor);
    return Object.assign(new domainModel(), normalized, links);
  }

  aggregate<T>(input: Array<Observable<RemoteData<T>>>): Observable<RemoteData<T[]>> {

    if (isEmpty(input)) {
      return Observable.of(new RemoteData(false, false, true, null, []));
    }

    return Observable.combineLatest(
      ...input,
      (...arr: Array<RemoteData<T>>) => {
        const requestPending: boolean = arr
          .map((d: RemoteData<T>) => d.isRequestPending)
          .every((b: boolean) => b === true);

        const responsePending: boolean = arr
          .map((d: RemoteData<T>) => d.isResponsePending)
          .every((b: boolean) => b === true);

        const isSuccessful: boolean = arr
          .map((d: RemoteData<T>) => d.hasSucceeded)
          .every((b: boolean) => b === true);

        const errorMessage: string = arr
          .map((d: RemoteData<T>) => d.error)
          .map((e: RemoteDataError, idx: number) => {
            if (hasValue(e)) {
              return `[${idx}]: ${e.message}`;
            }
          }).filter((e: string) => hasValue(e))
          .join(', ');

        const statusCode: string = arr
          .map((d: RemoteData<T>) => d.error)
          .map((e: RemoteDataError, idx: number) => {
            if (hasValue(e)) {
              return `[${idx}]: ${e.statusCode}`;
            }
          }).filter((c: string) => hasValue(c))
          .join(', ');

        const error = new RemoteDataError(statusCode, errorMessage);

        const payload: T[] = arr.map((d: RemoteData<T>) => d.payload);

        return new RemoteData(
          requestPending,
          responsePending,
          isSuccessful,
          error,
          payload
        );
      })
  }

  private toPaginatedList<T>(input: Observable<RemoteData<T[] | PaginatedList<T>>>, pageInfo: PageInfo): Observable<RemoteData<PaginatedList<T>>> {
    return input.map((rd: RemoteData<T[] | PaginatedList<T>>) => {
      if (Array.isArray(rd.payload)) {
        return Object.assign(rd, { payload: new PaginatedList(pageInfo, rd.payload) })
      } else {
        return Object.assign(rd, { payload: new PaginatedList(pageInfo, rd.payload.page) });
      }
    });
  }

}