66391: expandedNodes (&loadingNode) is now retrieved/sent to the store

at component initialisation/destruction so the state of the tree persists
& documentation

src/app/app.reducer.ts

@@ -1,5 +1,6 @@
 import { ActionReducerMap, createSelector, MemoizedSelector } from '@ngrx/store';
 import * as fromRouter from '@ngrx/router-store';
+import { CommunityListReducer, CommunityListState } from './community-list-page/community-list.reducer';
 import { hostWindowReducer, HostWindowState } from './shared/host-window.reducer';
 import { formReducer, FormState } from './shared/form/form.reducer';
 import {
@@ -43,6 +44,7 @@ export interface AppState {
   cssVariables: CSSVariablesState;
   menus: MenusState;
   objectSelection: ObjectSelectionListState;
+  communityList: CommunityListState;
 }
 
 export const appReducers: ActionReducerMap<AppState> = {
@@ -58,7 +60,8 @@ export const appReducers: ActionReducerMap<AppState> = {
   truncatable: truncatableReducer,
   cssVariables: cssVariablesReducer,
   menus: menusReducer,
-  objectSelection: objectSelectionReducer
+  objectSelection: objectSelectionReducer,
+  communityList: CommunityListReducer,
 };
 
 export const routerStateSelector = (state: AppState) => state.router;

src/app/community-list-page/community-list-datasource.ts

@@ -3,6 +3,12 @@ import { CollectionViewer, DataSource } from '@angular/cdk/typings/collections';
 import { BehaviorSubject, Observable, } from 'rxjs';
 import { finalize, take, } from 'rxjs/operators';
 
+/**
+ * DataSource object needed by a CDK Tree to render its nodes.
+ * The list of FlatNodes that this DataSource object represents gets created in the CommunityListService at
+ *    the beginning (initial page-limited top communities) and re-calculated any time the tree state changes
+ *    (a node gets expanded or page-limited result become larger by triggering a show more node)
+ */
 export class CommunityListDatasource implements DataSource<FlatNode> {
 
   private communityList$ = new BehaviorSubject<FlatNode[]>([]);
@@ -12,7 +18,6 @@ export class CommunityListDatasource implements DataSource<FlatNode> {
   }
 
   connect(collectionViewer: CollectionViewer): Observable<FlatNode[]> {
-    this.loadCommunities(null);
     return this.communityList$.asObservable();
   }
 

src/app/community-list-page/community-list-page.module.ts

@@ -6,6 +6,9 @@ import { CommunityListPageRoutingModule } from './community-list-page.routing.mo
 import { CommunityListComponent } from './community-list/community-list.component';
 import { CdkTreeModule } from '@angular/cdk/tree';
 
+/**
+ * The page which houses a title and the community list, as described in community-list.component
+ */
 @NgModule({
   imports: [
     CommonModule,

src/app/community-list-page/community-list-page.routing.module.ts

@@ -5,6 +5,9 @@ import { CdkTreeModule } from '@angular/cdk/tree';
 import { CommunityListPageComponent } from './community-list-page.component';
 import { CommunityListService } from './community-list-service';
 
+/**
+ * RouterModule to help navigate to the page with the community list tree
+ */
 @NgModule({
   imports: [
     RouterModule.forChild([

src/app/community-list-page/community-list-service.ts

@@ -1,6 +1,8 @@
 import { Injectable } from '@angular/core';
+import { createSelector, Store } from '@ngrx/store';
 import { combineLatest as observableCombineLatest } from 'rxjs/internal/observable/combineLatest';
 import { Observable, of as observableOf } from 'rxjs';
+import { AppState } from '../app.reducer';
 import { CommunityDataService } from '../core/data/community-data.service';
 import { PaginationComponentOptions } from '../shared/pagination/pagination-component-options.model';
 import { SortDirection, SortOptions } from '../core/cache/models/sort-options.model';
@@ -13,7 +15,13 @@ import {PaginatedList} from '../core/data/paginated-list';
 import { getCommunityPageRoute } from '../+community-page/community-page-routing.module';
 import { getCollectionPageRoute } from '../+collection-page/collection-page-routing.module';
 import { CollectionDataService } from '../core/data/collection-data.service';
+import { CommunityListSaveAction } from './community-list.actions';
+import { CommunityListState } from './community-list.reducer';
 
+/**
+ * Each node in the tree is represented by a flatNode which contains info about the node itself and its position and
+ *  state in the tree. There are nodes representing communities, collections and show more links.
+ */
 export interface FlatNode {
   isExpandable$: Observable<boolean>;
   name: string;
@@ -28,15 +36,28 @@ export interface FlatNode {
   currentCollectionPage?: number;
 }
 
+/**
+ * The show more links in the community tree are also represented by a flatNode so we know where in
+ *  the tree it should be rendered an who its parent is (needed for the action resulting in clicking this link)
+ */
 export class ShowMoreFlatNode {
 }
 
+// Helper method to combine an flatten an array of observables of flatNode arrays
 export const combineAndFlatten = (obsList: Array<Observable<FlatNode[]>>): Observable<FlatNode[]> =>
   observableCombineLatest(...obsList).pipe(
     map((matrix: FlatNode[][]) =>
       matrix.reduce((combinedList, currentList: FlatNode[]) => [...combinedList, ...currentList]))
   );
 
+/**
+ * Creates a flatNode from a community or collection
+ * @param c               The community or collection this flatNode represents
+ * @param isExpandable    Whether or not this node is expandable (true if it has children)
+ * @param level           Level indicating how deep in the tree this node should be rendered
+ * @param isExpanded      Whether or not this node already is expanded
+ * @param parent          Parent of this node (flatNode representing its parent community)
+ */
 export const toFlatNode = (
   c: Community | Collection,
   isExpandable: Observable<boolean>,
@@ -55,6 +76,9 @@ export const toFlatNode = (
   route: c instanceof Community ? getCommunityPageRoute(c.id) : getCollectionPageRoute(c.id),
 });
 
+/**
+ * Creates a show More flatnode where only the level and parent are of importance
+ */
 export const showMoreFlatNode = (
   id: string,
   level: number,
@@ -70,6 +94,15 @@ export const showMoreFlatNode = (
   isShowMoreNode: true,
 });
 
+// Selectors the get the communityList data out of the store
+const communityListStateSelector = (state: AppState) => state.communityList;
+const expandedNodesSelector = createSelector(communityListStateSelector, (communityList: CommunityListState) => communityList.expandedNodes);
+const loadingNodeSelector = createSelector(communityListStateSelector, (communityList: CommunityListState) => communityList.loadingNode);
+
+/**
+ * Service class for the community list, responsible for the creating of the flat list used by communityList dataSource
+ *  and connection to the store to retrieve and save the state of the community list
+ */
 // tslint:disable-next-line:max-classes-per-file
 @Injectable()
 export class CommunityListService {
@@ -83,7 +116,8 @@ export class CommunityListService {
   maxSubCommunitiesPerPage: number;
   maxCollectionsPerPage: number;
 
-    constructor(private communityDataService: CommunityDataService, private collectionDataService: CollectionDataService) {
+  constructor(private communityDataService: CommunityDataService, private collectionDataService: CollectionDataService,
+              private store: Store<any>) {
     this.topCommunitiesConfig = new PaginationComponentOptions();
     this.topCommunitiesConfig.id = 'top-level-pagination';
     this.topCommunitiesConfig.pageSize = 10;
@@ -95,6 +129,18 @@ export class CommunityListService {
     this.maxCollectionsPerPage = 3;
   }
 
+  saveCommunityListStateToStore(expandedNodes: FlatNode[], loadingNode: FlatNode): void {
+    this.store.dispatch(new CommunityListSaveAction(expandedNodes, loadingNode));
+  }
+
+  getExpandedNodesFromStore(): Observable<FlatNode[]> {
+    return this.store.select(expandedNodesSelector);
+  }
+
+  getLoadingNodeFromStore(): Observable<FlatNode> {
+    return this.store.select(loadingNodeSelector);
+  }
+
   /**
    * Increases the payload so it contains the next page of top level communities
    */
@@ -114,8 +160,9 @@ export class CommunityListService {
   }
 
   /**
-     * Gets all top communities, limited by page, and transforms this in a list of flatnodes.
+   * Gets all top communities, limited by page, and transforms this in a list of flatNodes.
-     * @param expandedNodes     List of expanded nodes; if a node is not expanded its subcommunities and collections need not be added to the list
+   * @param expandedNodes     List of expanded nodes; if a node is not expanded its subCommunities and collections need
+   *                            not be added to the list
    */
   loadCommunities(expandedNodes: FlatNode[]): Observable<FlatNode[]> {
     const res = this.payloads$.map((payload) => {

src/app/community-list-page/community-list.actions.ts

@@ -0,0 +1,35 @@
+import { Action } from '@ngrx/store';
+import { type } from '../shared/ngrx/type';
+import { FlatNode } from './community-list-service';
+
+/**
+ * All the action types of the community-list
+ */
+
+export const CommunityListActionTypes = {
+  SAVE: type('dspace/community-list-page/SAVE')
+};
+
+/**
+ * Community list SAVE action
+ */
+export class CommunityListSaveAction implements Action {
+
+  type = CommunityListActionTypes.SAVE;
+
+  payload: {
+    expandedNodes: FlatNode[];
+    loadingNode: FlatNode;
+  };
+
+  constructor(expandedNodes: FlatNode[], loadingNode: FlatNode) {
+    this.payload = { expandedNodes, loadingNode }
+  }
+};
+
+/**
+ * Export a type alias of all actions in this action group
+ * so that reducers can easily compose action types
+ */
+
+export type CommunityListActions = CommunityListSaveAction;

src/app/community-list-page/community-list.reducer.ts

@@ -0,0 +1,36 @@
+import { FlatNode } from './community-list-service';
+import { CommunityListActionTypes, CommunityListSaveAction } from './community-list.actions';
+
+/**
+ * States we wish to put in store concerning the community list
+ */
+export interface CommunityListState {
+  expandedNodes: FlatNode[];
+  loadingNode: FlatNode;
+}
+
+/**
+ * Initial starting state of the list of expandedNodes and the current loading node of the community list
+ */
+const initialState: CommunityListState = {
+  expandedNodes: [],
+  loadingNode: null,
+};
+
+/**
+ * Reducer to interact with store concerning objects for the community list
+ * @constructor
+ */
+export function CommunityListReducer(state = initialState, action: CommunityListSaveAction) {
+  switch (action.type) {
+    case CommunityListActionTypes.SAVE: {
+      return Object.assign({}, state, {
+        expandedNodes: (action as CommunityListSaveAction).payload.expandedNodes,
+        loadingNode: (action as CommunityListSaveAction).payload.loadingNode,
+      })
+    }
+    default: {
+      return state;
+    }
+  }
+}

src/app/community-list-page/community-list/community-list.component.ts

@@ -1,14 +1,22 @@
-import { Component, OnInit } from '@angular/core';
+import { Component, OnDestroy, OnInit } from '@angular/core';
+import { take } from 'rxjs/operators';
 import { CommunityListService, FlatNode } from '../community-list-service';
 import { CommunityListDatasource } from '../community-list-datasource';
 import { FlatTreeControl } from '@angular/cdk/tree';
 import { isEmpty } from '../../shared/empty.util';
 
+/**
+ * A tree-structured list of nodes representing the communities, their subCommunities and collections.
+ * Initially only the page-restricted top communities are shown.
+ * Each node can be expanded to show its children and all children are also page-limited.
+ * More pages of a page-limited result can be shown by pressing a show more node/link.
+ * Which nodes were expanded is kept in the store, so this persists across pages.
+ */
 @Component({
   selector: 'ds-community-list',
   templateUrl: './community-list.component.html',
 })
-export class CommunityListComponent implements OnInit {
+export class CommunityListComponent implements OnInit, OnDestroy {
 
   private expandedNodes: FlatNode[] = [];
   public loadingNode: FlatNode;
@@ -24,7 +32,17 @@ export class CommunityListComponent implements OnInit {
 
   ngOnInit() {
     this.dataSource = new CommunityListDatasource(this.communityListService);
-    this.dataSource.loadCommunities(null);
+    this.communityListService.getLoadingNodeFromStore().pipe(take(1)).subscribe((result) => {
+      this.loadingNode = result;
+    });
+    this.communityListService.getExpandedNodesFromStore().pipe(take(1)).subscribe((result) => {
+      this.expandedNodes = [...result];
+      this.dataSource.loadCommunities(this.expandedNodes);
+    });
+  }
+
+  ngOnDestroy(): void {
+    this.communityListService.saveCommunityListStateToStore(this.expandedNodes, this.loadingNode);
   }
 
   // whether or not this node has children (subcommunities or collections)