feat: implement custom cdk virtual scroll behavior

src/app/modules/data/chips/action-chip-list.html

@@ -1,5 +1,5 @@
 <!--
-  ~ Copyright (C) 2022 StApps
+  ~ Copyright (C) 2023 StApps
   ~ This program is free software: you can redistribute it and/or modify it
   ~ under the terms of the GNU General Public License as published by the Free
   ~ Software Foundation, version 3.
@@ -13,8 +13,6 @@
   ~ this program. If not, see <https://www.gnu.org/licenses/>.
   -->
 
-<div>
-  <stapps-locate-action-chip *ngIf="applicable.locate" [item]="item"></stapps-locate-action-chip>
-  <!-- Add Event Chip needs to load data and should be the last -->
-  <stapps-add-event-action-chip *ngIf="applicable.event" [item]="item"></stapps-add-event-action-chip>
-</div>
+<stapps-locate-action-chip *ngIf="applicable.locate" [item]="item"></stapps-locate-action-chip>
+<!-- Add Event Chip needs to load data and should be the last -->
+<stapps-add-event-action-chip *ngIf="applicable.event" [item]="item"></stapps-add-event-action-chip>

src/app/modules/data/chips/action-chip-list.scss

@@ -1,5 +1,24 @@
-div {
+/*!
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+:host {
   display: flex;
   flex-direction: row;
   width: fit-content;
+
+  &:has(*) {
+    height: 48px;
+  }
 }

src/app/modules/data/chips/data/add-event-action-chip.scss

@@ -1,5 +1,5 @@
 /*!
- * Copyright (C) 2022 StApps
+ * Copyright (C) 2023 StApps
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation, version 3.

src/app/modules/data/data.module.ts

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2022 StApps
+ * Copyright (C) 2023 StApps
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the Free
  * Software Foundation, version 3.
@@ -95,6 +95,9 @@ import {BookDetailContentComponent} from './types/book/book-detail-content.compo
 import {BookListItemComponent} from './types/book/book-list-item.component';
 import {PeriodicalListItemComponent} from './types/periodical/periodical-list-item.component';
 import {PeriodicalDetailContentComponent} from './types/periodical/periodical-detail-content.component';
+import {SCThingListItemVirtualScrollStrategyDirective} from './list/sc-thing-list-item-virtual-scroll-strategy.directive';
+import {DataListItemHostDirective} from './list/data-list-item-host.directive';
+import {DataListItemHostDefaultComponent} from './list/data-list-item-host-default.component';
 
 /**
  * Module for handling data
@@ -141,8 +144,11 @@ import {PeriodicalDetailContentComponent} from './types/periodical/periodical-de
     PlaceListItemComponent,
     PlaceMensaDetailComponent,
     SearchPageComponent,
+    SCThingListItemVirtualScrollStrategyDirective,
     SemesterDetailContentComponent,
     SemesterListItemComponent,
+    DataListItemHostDirective,
+    DataListItemHostDefaultComponent,
     SimpleCardComponent,
     SkeletonListItemComponent,
     SkeletonSegmentComponent,
@@ -195,6 +201,7 @@ import {PeriodicalDetailContentComponent} from './types/periodical/periodical-de
     SettingsProvider,
   ],
   exports: [
+    SCThingListItemVirtualScrollStrategyDirective,
     DataDetailComponent,
     DataDetailContentComponent,
     DataIconPipe,

src/app/modules/data/list/data-list-item-host-default.component.ts

@@ -0,0 +1,25 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {Component, Input} from '@angular/core';
+import {SCThings} from '@openstapps/core';
+
+@Component({
+  selector: 'data-list-item-host-default',
+  templateUrl: 'data-list-item-host-default.html',
+})
+export class DataListItemHostDefaultComponent {
+  @Input() item: SCThings;
+}

src/app/modules/data/list/data-list-item-host-default.html

@@ -0,0 +1,24 @@
+<!--
+  ~ Copyright (C) 2023 StApps
+  ~ This program is free software: you can redistribute it and/or modify it
+  ~ under the terms of the GNU General Public License as published by the Free
+  ~ Software Foundation, version 3.
+  ~
+  ~ This program is distributed in the hope that it will be useful, but WITHOUT
+  ~ ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+  ~ FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+  ~ more details.
+  ~
+  ~ You should have received a copy of the GNU General Public License along with
+  ~ this program. If not, see <https://www.gnu.org/licenses/>.
+  -->
+
+<h2>
+  {{ 'name' | thingTranslate: item }}
+</h2>
+<p *ngIf="item.description">
+  <stapps-long-inline-text
+    [text]="'description' | thingTranslate: item"
+    [size]="80"
+  ></stapps-long-inline-text>
+</p>

src/app/modules/data/list/data-list-item-host.directive.ts

@@ -0,0 +1,84 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+import {ComponentRef, Directive, Input, Type, ViewContainerRef} from '@angular/core';
+import {SCThings, SCThingType} from '@openstapps/core';
+import {BookListItemComponent} from '../types/book/book-list-item.component';
+import {CatalogListItemComponent} from '../types/catalog/catalog-list-item.component';
+import {DateSeriesListItemComponent} from '../types/date-series/date-series-list-item.component';
+import {EventListItemComponent} from '../types/event/event-list-item.component';
+import {FavoriteListItemComponent} from '../types/favorite/favorite-list-item.component';
+import {MessageListItemComponent} from '../types/message/message-list-item.component';
+import {OrganizationListItemComponent} from '../types/organization/organization-list-item.component';
+import {PersonListItemComponent} from '../types/person/person-list-item.component';
+import {PlaceListItemComponent} from '../types/place/place-list-item.component';
+import {SemesterListItemComponent} from '../types/semester/semester-list-item.component';
+import {VideoListItemComponent} from '../types/video/video-list-item.component';
+import {PeriodicalListItemComponent} from '../types/periodical/periodical-list-item.component';
+import {DataListItemHostDefaultComponent} from './data-list-item-host-default.component';
+import {ArticleListItemComponent} from '../types/article/article-item.component';
+import {DishListItemComponent} from '../types/dish/dish-list-item.component';
+
+export interface DataListItem {
+  item: SCThings;
+}
+
+const DataListItemIndex: Partial<Record<SCThingType, Type<DataListItem>>> = {
+  [SCThingType.Catalog]: CatalogListItemComponent,
+  [SCThingType.Dish]: DishListItemComponent,
+  [SCThingType.DateSeries]: DateSeriesListItemComponent,
+  [SCThingType.AcademicEvent]: EventListItemComponent,
+  [SCThingType.SportCourse]: DateSeriesListItemComponent,
+  [SCThingType.Favorite]: FavoriteListItemComponent,
+  [SCThingType.Message]: MessageListItemComponent,
+  [SCThingType.Organization]: OrganizationListItemComponent,
+  [SCThingType.Person]: PersonListItemComponent,
+  [SCThingType.Building]: PlaceListItemComponent,
+  [SCThingType.Floor]: PlaceListItemComponent,
+  [SCThingType.PointOfInterest]: PlaceListItemComponent,
+  [SCThingType.Room]: PlaceListItemComponent,
+  [SCThingType.Semester]: SemesterListItemComponent,
+  [SCThingType.Video]: VideoListItemComponent,
+  [SCThingType.Periodical]: PeriodicalListItemComponent,
+  [SCThingType.Book]: BookListItemComponent,
+  [SCThingType.Article]: ArticleListItemComponent,
+};
+
+@Directive({
+  selector: '[dataListItemHost]',
+})
+export class DataListItemHostDirective {
+  private type?: Type<DataListItem>;
+
+  private component?: ComponentRef<DataListItem>;
+
+  constructor(readonly viewContainerRef: ViewContainerRef) {}
+
+  @Input() set dataListItemHost(value: SCThings | undefined) {
+    if (!value) {
+      this.viewContainerRef.clear();
+      delete this.type;
+      delete this.component;
+      return;
+    }
+
+    const type = DataListItemIndex[value.type] || DataListItemHostDefaultComponent;
+    if (this.type !== type || !this.component) {
+      this.type = type;
+      this.viewContainerRef.clear();
+      this.component = this.viewContainerRef.createComponent(this.type);
+    }
+    this.component.instance.item = value;
+  }
+}

src/app/modules/data/list/data-list-item.component.ts

@@ -27,7 +27,7 @@ import {DataListContext} from './data-list.component';
 })
 export class DataListItemComponent {
   /**
-   * Whether or not the list item should show a thumbnail
+   * Whether the list item should show a thumbnail
    */
   @Input() hideThumbnail = false;
 
@@ -40,6 +40,10 @@ export class DataListItemComponent {
 
   @Input() lines = 'inset';
 
+  @Input() forceHeight = false;
+
+  height?: string;
+
   @Input() appearance: 'normal' | 'square' = 'normal';
 
   @ContentChild(TemplateRef) contentTemplateRef: TemplateRef<DataListContext<SCThings>>;

src/app/modules/data/list/data-list-item.html

@@ -36,82 +36,9 @@
 </ion-item>
 
 <ng-template #defaultContent>
-  <ion-label class="ion-text-wrap" [ngSwitch]="true">
+  <ion-label class="ion-text-wrap">
     <div>
-      <stapps-catalog-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'catalog'"
-      ></stapps-catalog-list-item>
-      <stapps-date-series-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'date series'"
-      ></stapps-date-series-list-item>
-      <stapps-dish-list-item [item]="$any(item)" *ngSwitchCase="item.type === 'dish'"></stapps-dish-list-item>
-      <stapps-event-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'academic event'"
-      ></stapps-event-list-item>
-      <stapps-event-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'sport course'"
-      ></stapps-event-list-item>
-      <stapps-favorite-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'favorite'"
-      ></stapps-favorite-list-item>
-      <stapps-message-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'message'"
-      ></stapps-message-list-item>
-      <stapps-organization-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'organization'"
-      ></stapps-organization-list-item>
-      <stapps-person-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'person'"
-      ></stapps-person-list-item>
-      <stapps-place-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'building'"
-      ></stapps-place-list-item>
-      <stapps-place-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'floor'"
-      ></stapps-place-list-item>
-      <stapps-place-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'point of interest'"
-      ></stapps-place-list-item>
-      <stapps-place-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'room'"
-      ></stapps-place-list-item>
-      <stapps-semester-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'semester'"
-      ></stapps-semester-list-item>
-      <stapps-video-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'video'"
-      ></stapps-video-list-item>
-      <stapps-book-list-item [item]="$any(item)" *ngSwitchCase="item.type === 'book'"></stapps-book-list-item>
-      <stapps-periodical-list-item
-        [item]="$any(item)"
-        *ngSwitchCase="item.type === 'periodical'"
-      ></stapps-periodical-list-item>
-      <stapps-article-item [item]="$any(item)" *ngSwitchCase="item.type === 'article'"></stapps-article-item>
-      <div *ngSwitchDefault>
-        <h2>
-          {{ 'name' | thingTranslate: item }}
-        </h2>
-        <p *ngIf="item.description">
-          <stapps-long-inline-text
-            [text]="'description' | thingTranslate: item"
-            [size]="80"
-          ></stapps-long-inline-text>
-        </p>
-      </div>
+      <ng-template [dataListItemHost]="item"></ng-template>
       <stapps-action-chip-list
         *ngIf="appearance !== 'square'"
         slot="end"

src/app/modules/data/list/data-list-item.scss

@@ -15,6 +15,21 @@
 @import 'src/theme/util/_mixins.scss';
 @import 'src/theme/common/_helper.scss';
 
+:host {
+  display: block;
+}
+
+ion-item::part(native) {
+  height: 100%;
+}
+
+.ion-text-wrap ::ng-deep ion-label {
+  white-space: normal !important;
+  display: -webkit-box;
+  -webkit-box-orient: vertical;
+  -webkit-line-clamp: 3;
+}
+
 ion-item {
   --border-color: transparent;
   @include border-radius-in-parallax(var(--border-radius-default));

src/app/modules/data/list/data-list.html

@@ -1,5 +1,5 @@
 <!--
-  ~ Copyright (C) 2022 StApps
+  ~ Copyright (C) 2023 StApps
   ~ This program is free software: you can redistribute it and/or modify it
   ~ under the terms of the GNU General Public License as published by the Free
   ~ Software Foundation, version 3.
@@ -14,21 +14,17 @@
   -->
 
 <ng-container *ngIf="itemStream | async as items">
+  <ng-content select="[header]"></ng-content>
   <cdk-virtual-scroll-viewport
-    itemSize="80"
-    minBufferPx="1500"
-    maxBufferPx="2000"
-    (scrolledIndexChange)="scrolled($event)"
+    scThingListItemVirtualScrollStrategy
     [style.display]="items && items.length ? 'block' : 'none'"
+    (loadMore)="notifyLoadMore()"
   >
-    <ng-content select="[header]"></ng-content>
-    <ion-list>
-      <ng-container *cdkVirtualFor="let item of items; trackBy: identifyItem">
-        <ng-container
-          *ngTemplateOutlet="listItemTemplateRef || defaultListItem; context: {$implicit: item}"
-        ></ng-container>
-      </ng-container>
-    </ion-list>
+    <ng-container *cdkVirtualFor="let item of items; trackBy: identifyItem">
+      <ng-container
+        *ngTemplateOutlet="listItemTemplateRef || defaultListItem; context: {$implicit: item}"
+      ></ng-container>
+    </ng-container>
   </cdk-virtual-scroll-viewport>
 </ng-container>
 <div [style.display]="!loading && items && items.length === 0 ? 'block' : 'none'">

src/app/modules/data/list/data-list.scss

@@ -1,10 +1,21 @@
+/*!
+ * Copyright (C) 2022 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
 cdk-virtual-scroll-viewport {
   height: 100%;
   width: 100%;
-
-  ion-list {
-    background: transparent;
-  }
 }
 
 ::ng-deep {

src/app/modules/data/list/sc-thing-list-item-virtual-scroll-strategy.directive.ts

@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {Directive, forwardRef, Input, Output, ViewChild} from '@angular/core';
+import {CdkVirtualForOf, VIRTUAL_SCROLL_STRATEGY} from '@angular/cdk/scrolling';
+import {ScThingListItemVirtualScrollStrategy} from './sc-thing-list-item-virtual-scroll-strategy';
+
+/**
+ *
+ */
+function factory(directive: SCThingListItemVirtualScrollStrategyDirective) {
+  return directive.scrollStrategy;
+}
+
+@Directive({
+  selector: 'cdk-virtual-scroll-viewport[scThingListItemVirtualScrollStrategy]',
+  providers: [
+    {
+      provide: VIRTUAL_SCROLL_STRATEGY,
+      useFactory: factory,
+      deps: [forwardRef(() => SCThingListItemVirtualScrollStrategyDirective)],
+    },
+  ],
+})
+export class SCThingListItemVirtualScrollStrategyDirective {
+  scrollStrategy = new ScThingListItemVirtualScrollStrategy();
+
+  @ViewChild(CdkVirtualForOf) virtualForOf: CdkVirtualForOf<unknown>;
+
+  @Output() readonly loadMore = this.scrollStrategy.loadMore;
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  @Input() set trackGroupBy(value: (item: any) => unknown) {
+    this.scrollStrategy.trackGroupBy = value;
+  }
+
+  @Input() set minimumHeight(value: number) {
+    this.scrollStrategy.approximateItemHeight = value;
+  }
+
+  @Input() set buffer(value: number) {
+    this.scrollStrategy.buffer = value;
+  }
+
+  @Input() set gap(value: number) {
+    this.scrollStrategy.gap = value;
+  }
+
+  @Input() set itemRenderTimeout(value: number) {
+    this.scrollStrategy.itemRenderTimeout = value;
+  }
+}

src/app/modules/data/list/sc-thing-list-item-virtual-scroll-strategy.ts

@@ -0,0 +1,286 @@
+/*
+ * Copyright (C) 2023 StApps
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation, version 3.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along with
+ * this program. If not, see <https://www.gnu.org/licenses/>.
+ */
+
+import {CdkVirtualForOf, CdkVirtualScrollViewport, VirtualScrollStrategy} from '@angular/cdk/scrolling';
+import {BehaviorSubject, Subject, Subscription, takeUntil, timer} from 'rxjs';
+import {debounceTime, distinctUntilChanged, tap} from 'rxjs/operators';
+import {SCThingType} from '@openstapps/core';
+
+export class ScThingListItemVirtualScrollStrategy implements VirtualScrollStrategy {
+  private viewport?: CdkVirtualScrollViewport;
+
+  private virtualForOf?: CdkVirtualForOf<unknown>;
+
+  private index$ = new Subject<number>();
+
+  private heights = new Map<unknown, number | undefined>();
+
+  private groupHeights = new Map<unknown, number | undefined>();
+
+  private offsets: number[] = [];
+
+  private totalHeight = 0;
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  private _items?: readonly unknown[];
+
+  private _groups?: readonly unknown[];
+
+  /**
+   * We use this to track loadMore
+   */
+  private currentLength = 0;
+
+  private dataStreamSubscription?: Subscription;
+
+  private mutationObserver?: MutationObserver;
+
+  approximateItemHeight = 67;
+
+  approximateGroupSizes: Map<unknown, number> = new Map([[SCThingType.AcademicEvent, 139]]);
+
+  buffer = 4000;
+
+  gap = 8;
+
+  itemRenderTimeout = 1000;
+
+  heightUpdateDebounceTime = 25;
+
+  heightSetDebounceTime = 100;
+
+  loadMore = new Subject<void>();
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  trackGroupBy: (value: any) => unknown = it => it.type;
+
+  attach(viewport: CdkVirtualScrollViewport): void {
+    this.viewport = viewport;
+    // @ts-expect-error private property
+    this.virtualForOf = viewport._forOf;
+    this.dataStreamSubscription = this.virtualForOf?.dataStream.subscribe(items => {
+      this.items = items;
+    });
+
+    this.mutationObserver = new MutationObserver(() => {
+      const renderedItems = this.renderedItems;
+      if (!renderedItems) {
+        this.mutationObserver?.disconnect();
+        return this.onPrematureDisconnect();
+      }
+
+      this.intersectionObserver?.disconnect();
+      this.intersectionObserver = new IntersectionObserver(this.observeIntersection.bind(this), {
+        rootMargin: `${this.buffer - 64}px`,
+        threshold: 1,
+      });
+
+      for (const node of renderedItems) {
+        const [item, group] = this.getItemByNode(node, renderedItems);
+
+        if (!this.heights.has(item)) {
+          this.intersectionObserver.observe(node);
+        } else {
+          node.style.height = `${this.getHeight(item, group)}px`;
+        }
+      }
+    });
+
+    const contentWrapper = this.contentWrapper;
+    if (!contentWrapper) return this.onPrematureDisconnect();
+    this.mutationObserver.observe(contentWrapper, {childList: true, subtree: true});
+
+    this.setTotalContentSize();
+  }
+
+  detach(): void {
+    this.index$.complete();
+    this.dataStreamSubscription?.unsubscribe();
+    this.mutationObserver?.disconnect();
+    delete this.viewport;
+  }
+
+  private getHeight(item: unknown, group: unknown) {
+    return (
+      this.heights.get(item) ||
+      this.groupHeights.get(group) ||
+      this.approximateGroupSizes.get(group) ||
+      this.approximateItemHeight
+    );
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  private set items(value: readonly unknown[]) {
+    const trackBy = this.virtualForOf?.cdkVirtualForTrackBy;
+    const tracks = value.map((it, i) => (trackBy ? trackBy(i, it) : it));
+    if (
+      this._items &&
+      tracks.length === this._items.length &&
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      tracks.every((it, i) => it === this._items![i])
+    )
+      return;
+
+    this._items = tracks;
+    this._groups = value.map(this.trackGroupBy);
+    this.currentLength = tracks.length;
+
+    this.updateHeights();
+  }
+
+  scrolledIndexChange = this.index$.pipe(distinctUntilChanged());
+
+  private getOffsetFromIndex(index: number): number {
+    return this.offsets[index];
+  }
+
+  private getIndexFromOffset(offset: number): number {
+    return Math.max(
+      0,
+      this.offsets.findIndex((it, i, array) => it >= offset || i === array.length - 1),
+    );
+  }
+
+  private updateHeights() {
+    if (!this._items) return;
+    const heights = this._items.map((it, i) => this.getHeight(it, this._groups![i]) + this.gap);
+    this.offsets = Array.from({length: heights.length}, () => 0);
+    this.totalHeight = heights.reduce((a, b, index) => (this.offsets[index + 1] = a + b), 0) + this.gap;
+
+    this.setTotalContentSize();
+    this.updateRenderedRange();
+  }
+
+  private updateRenderedRange() {
+    if (!this.viewport) return;
+    const offset = this.viewport.measureScrollOffset('top');
+    const viewportSize = this.viewport.getViewportSize();
+    const firstVisibleIndex = Math.max(0, this.getIndexFromOffset(offset) - 1);
+    const range = {
+      start: this.getIndexFromOffset(Math.max(0, offset - this.buffer)),
+      end: this.getIndexFromOffset(offset + viewportSize + this.buffer),
+    };
+    const {start, end} = this.viewport.getRenderedRange();
+    if (range.start === start && range.end === end) return;
+
+    if (this.currentLength !== 0 && range.end === this.currentLength) {
+      this.currentLength++;
+      this.loadMore.next();
+    }
+
+    this.viewport.setRenderedRange(range);
+    this.viewport.setRenderedContentOffset(this.getOffsetFromIndex(range.start), 'to-start');
+
+    this.index$.next(firstVisibleIndex);
+  }
+
+  private setTotalContentSize() {
+    this.viewport?.setTotalContentSize(this.totalHeight);
+    // @ts-expect-error TODO
+    this.viewport?._measureViewportSize();
+  }
+
+  observeIntersection(entries: IntersectionObserverEntry[], observer: IntersectionObserver) {
+    const renderedItems = this.renderedItems;
+    if (!renderedItems) return this.onPrematureDisconnect();
+
+    const update = new Subject<void>();
+    for (const entry of entries) {
+      if (!entry.isIntersecting) continue;
+
+      const outerNode = entry.target as HTMLElement;
+      const [item] = this.getItemByNode(outerNode, renderedItems);
+      const node = outerNode.firstChild! as HTMLElement;
+
+      const height = new BehaviorSubject(node.offsetHeight);
+      const resizeObserver = new ResizeObserver(() => {
+        const renderedItems = this.renderedItems;
+        if (!renderedItems) {
+          resizeObserver.disconnect();
+          return this.onPrematureDisconnect();
+        }
+        const [newItem] = this.getItemByNode(node, renderedItems);
+        if (newItem !== item) {
+          this.heights.delete(item);
+          resizeObserver.disconnect();
+          return;
+        }
+        height.next(node.offsetHeight);
+      });
+      resizeObserver.observe(node);
+      height
+        .pipe(
+          distinctUntilChanged(),
+          debounceTime(this.heightSetDebounceTime),
+          takeUntil(timer(this.itemRenderTimeout)),
+          tap({complete: () => resizeObserver.disconnect()}),
+        )
+        .subscribe(height => {
+          this.heights.set(item, height);
+          outerNode.style.height = `${height}px`;
+          update.next();
+        });
+
+      observer.unobserve(node);
+    }
+    update
+      .pipe(debounceTime(this.heightUpdateDebounceTime), takeUntil(timer(this.itemRenderTimeout)))
+      .subscribe(() => {
+        this.updateHeights();
+      });
+  }
+
+  intersectionObserver?: IntersectionObserver;
+
+  get contentWrapper() {
+    return this.viewport?._contentWrapper.nativeElement;
+  }
+
+  get renderedItems() {
+    const contentWrapper = this.contentWrapper;
+    return contentWrapper
+      ? // eslint-disable-next-line unicorn/prefer-spread
+        (Array.from(contentWrapper.children).filter(it => it instanceof HTMLElement) as HTMLElement[])
+      : undefined;
+  }
+
+  getItemByNode(node: HTMLElement, renderedItems: HTMLElement[]) {
+    const {start} = this.viewport!.getRenderedRange();
+    const index = renderedItems.indexOf(node) + start;
+    return [this._items![index], this._groups![index]];
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-empty-function
+  onContentRendered(): void {}
+
+  onContentScrolled() {
+    this.updateRenderedRange();
+  }
+
+  onPrematureDisconnect() {
+    console.warn('Virtual Scroll strategy was disconnected unexpectedly', new Error('foo').stack);
+  }
+
+  onDataLengthChanged(): void {
+    this.setTotalContentSize();
+  }
+
+  // eslint-disable-next-line @typescript-eslint/no-empty-function
+  onRenderedOffsetChanged(): void {}
+
+  scrollToIndex(index: number, behavior: ScrollBehavior): void {
+    this.viewport?.scrollToOffset(this.getOffsetFromIndex(index), behavior);
+  }
+}

src/app/modules/data/list/search-page.component.ts

@@ -216,18 +216,20 @@ export class SearchPageComponent implements OnInit, OnDestroy {
       const result = await this.dataProvider.search(searchOptions);
       this.singleTypeResponse = result.facets.find(facet => facet.field === 'type')?.buckets.length === 1;
       if (append) {
-        let items = await this.items;
         // append results
-        items = [...items, ...result.data];
-        this.items = (async () => items)();
+        this.items = this.items.then(it =>
+          // fix for some very short results
+          it.length === result.pagination.total ? it : [...it, ...result.data],
+        );
       } else {
         // override items with results
-        this.items = (async () => {
-          this.updateContextFilter(result.facets);
-
-          return result.data;
-        })();
+        this.updateContextFilter(result.facets);
+        this.items = Promise.resolve(result.data);
       }
+
+      this.items.then(it => {
+        if (it.length === result.pagination.total) console.log('final page loaded');
+      });
     } catch (error) {
       this.logger.error(error);
     } finally {