Wrap versions list in virtual scroll

Signed-off-by: Louis Chemineau <louis@chmn.me>

2 files changed, 396 insertions, 16 deletions

diff --git a/apps/files_versions/src/components/VirtualScrolling.vue b/apps/files_versions/src/components/VirtualScrolling.vue
new file mode 100644
index 00000000000..fc199edd2ef
--- /dev/null
+++ b/apps/files_versions/src/components/VirtualScrolling.vue
@@ -0,0 +1,363 @@
+<!--
+ - @copyright Copyright (c) 2022 Louis Chemineau <louis@chmn.me>
+ -
+ - @author Louis Chemineau <louis@chmn.me>
+ -
+ - @license AGPL-3.0-or-later
+ -
+ - This program is free software: you can redistribute it and/or modify
+ - it under the terms of the GNU Affero General Public License as
+ - published by the Free Software Foundation, either version 3 of the
+ - License, or (at your option) any later version.
+ -
+ - 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 Affero General Public License for more details.
+ -
+ - You should have received a copy of the GNU Affero General Public License
+ - along with this program. If not, see <http://www.gnu.org/licenses/>.
+ -
+ -->
+<template>
+	<div v-if="!useWindow && containerElement === null" ref="container" class="vs-container">
+		<div ref="rowsContainer"
+			class="vs-rows-container"
+			:style="rowsContainerStyle">
+			<slot :visible-sections="visibleSections" />
+			<slot name="loader" />
+		</div>
+	</div>
+	<div v-else
+		ref="rowsContainer"
+		class="vs-rows-container"
+		:style="rowsContainerStyle">
+		<slot :visible-sections="visibleSections" />
+		<slot name="loader" />
+	</div>
+</template>
+
+<script lang="ts">
+import { defineComponent, type PropType } from 'vue'
+
+import logger from '../utils/logger.js'
+
+interface RowItem {
+	id: string // Unique id for the item.
+	key?: string // Unique key for the item.
+}
+
+interface Row {
+	key: string // Unique key for the row.
+	height: number // The height of the row.
+	sectionKey: string // Unique key for the row.
+	items: RowItem[] // List of items in the row.
+}
+
+interface VisibleRow extends Row {
+	distance: number // The distance from the visible viewport
+}
+
+interface Section {
+	key: string, // Unique key for the section.
+	rows: Row[], // The height of the row.
+	height: number, // Height of the section, excluding the header.
+}
+
+interface VisibleSection extends Section {
+	rows: VisibleRow[], // The height of the row.
+}
+
+export default defineComponent({
+	name: 'VirtualScrolling',
+
+	props: {
+		sections: {
+			type: Array as PropType<Section[]>,
+			required: true,
+		},
+
+		containerElement: {
+			type: HTMLElement,
+			default: null,
+		},
+
+		useWindow: {
+			type: Boolean,
+			default: false,
+		},
+
+		headerHeight: {
+			type: Number,
+			default: 75,
+		},
+		renderDistance: {
+			type: Number,
+			default: 0.5,
+		},
+		bottomBufferRatio: {
+			type: Number,
+			default: 2,
+		},
+		scrollToKey: {
+			type: String,
+			default: '',
+		},
+	},
+
+	data() {
+		return {
+			scrollPosition: 0,
+			containerHeight: 0,
+			rowsContainerHeight: 0,
+			resizeObserver: null as ResizeObserver|null,
+		}
+	},
+
+	computed: {
+		visibleSections(): VisibleSection[] {
+			logger.debug('[VirtualScrolling] Computing visible section', { sections: this.sections })
+
+			// Optimization: get those computed properties once to not go through vue's internal every time we need them.
+			const containerHeight = this.containerHeight
+			const containerTop = this.scrollPosition
+			const containerBottom = containerTop + containerHeight
+
+			let currentRowTop = 0
+			let currentRowBottom = 0
+
+			// Compute whether a row should be included in the DOM (shouldRender)
+			// And how visible the row is.
+			const visibleSections = this.sections
+				.map(section => {
+					currentRowBottom += this.headerHeight
+
+					return {
+						...section,
+						rows: section.rows.reduce((visibleRows, row) => {
+							currentRowTop = currentRowBottom
+							currentRowBottom += row.height
+
+							let distance = 0
+
+							if (currentRowBottom < containerTop) {
+								distance = (containerTop - currentRowBottom) / containerHeight
+							} else if (currentRowTop > containerBottom) {
+								distance = (currentRowTop - containerBottom) / containerHeight
+							}
+
+							if (distance > this.renderDistance) {
+								return visibleRows
+							}
+
+							return [
+								...visibleRows,
+								{
+									...row,
+									distance,
+								},
+							]
+						}, [] as VisibleRow[]),
+					}
+				})
+				.filter(section => section.rows.length > 0)
+
+			// To allow vue to recycle the DOM elements instead of adding and deleting new ones,
+			// we assign a random key to each items. When a item removed, we recycle its key for new items,
+			// so vue can replace the content of removed DOM elements with the content of new items, but keep the other DOM elements untouched.
+			const visibleItems = visibleSections
+				.flatMap(({ rows }) => rows)
+				.flatMap(({ items }) => items)
+
+			const rowIdToKeyMap = this._rowIdToKeyMap as {[key: string]: string}
+
+			visibleItems.forEach(item => (item.key = rowIdToKeyMap[item.id]))
+
+			const usedTokens = visibleItems
+				.map(({ key }) => key)
+				.filter(key => key !== undefined)
+
+			const unusedTokens = Object.values(rowIdToKeyMap).filter(key => !usedTokens.includes(key))
+
+			visibleItems
+				.filter(({ key }) => key === undefined)
+				.forEach(item => (item.key = unusedTokens.pop() ?? Math.random().toString(36).substr(2)))
+
+			// this._rowIdToKeyMap is created in the beforeCreate hook, so value changes are not tracked.
+			// Therefore, we wont trigger the computation of visibleSections again if we alter the value of this._rowIdToKeyMap.
+			// eslint-disable-next-line vue/no-side-effects-in-computed-properties
+			this._rowIdToKeyMap = visibleItems.reduce((finalMapping, { id, key }) => ({ ...finalMapping, [`${id}`]: key }), {})
+
+			return visibleSections
+		},
+
+		/**
+		 * Total height of all the rows + some room for the loader.
+		 */
+		totalHeight(): number {
+			const loaderHeight = 0
+
+			return this.sections
+				.map(section => this.headerHeight + section.height)
+				.reduce((totalHeight, sectionHeight) => totalHeight + sectionHeight, 0) + loaderHeight
+		},
+
+		paddingTop(): number {
+			if (this.visibleSections.length === 0) {
+				return 0
+			}
+
+			let paddingTop = 0
+
+			for (const section of this.sections) {
+				if (section.key !== this.visibleSections[0].rows[0].sectionKey) {
+					paddingTop += this.headerHeight + section.height
+					continue
+				}
+
+				for (const row of section.rows) {
+					if (row.key === this.visibleSections[0].rows[0].key) {
+						return paddingTop
+					}
+
+					paddingTop += row.height
+				}
+
+				paddingTop += this.headerHeight
+			}
+
+			return paddingTop
+		},
+
+		/**
+		 * padding-top is used to replace not included item in the container.
+		 */
+		rowsContainerStyle(): { height: string; paddingTop: string } {
+			return {
+				height: `${this.totalHeight}px`,
+				paddingTop: `${this.paddingTop}px`,
+			}
+		},
+
+		/**
+		 * Whether the user is near the bottom.
+		 * If true, then the need-content event will be emitted.
+		 */
+		isNearBottom(): boolean {
+			const buffer = this.containerHeight * this.bottomBufferRatio
+			return this.scrollPosition + this.containerHeight >= this.totalHeight - buffer
+		},
+
+		container() {
+			logger.debug('[VirtualScrolling] Computing container')
+			if (this.containerElement !== null) {
+				return this.containerElement
+			} else if (this.useWindow) {
+				return window
+			} else {
+				return this.$refs.container as Element
+			}
+		},
+	},
+
+	watch: {
+		isNearBottom(value) {
+			logger.debug('[VirtualScrolling] isNearBottom changed', { value })
+			if (value) {
+				this.$emit('need-content')
+			}
+		},
+
+		visibleSections() {
+			// Re-emit need-content when rows is updated and isNearBottom is still true.
+			// If the height of added rows is under `bottomBufferRatio`, `isNearBottom` will still be true so we need more content.
+			if (this.isNearBottom) {
+				this.$emit('need-content')
+			}
+		},
+
+		scrollToKey(key) {
+			let currentRowTopDistanceFromTop = 0
+
+			for (const section of this.sections) {
+				if (section.key !== key) {
+					currentRowTopDistanceFromTop += this.headerHeight + section.height
+					continue
+				}
+
+				break
+			}
+
+			logger.debug('[VirtualScrolling] Scrolling to', { currentRowTopDistanceFromTop })
+			this.container.scrollTo({ top: currentRowTopDistanceFromTop, behavior: 'smooth' })
+		},
+	},
+
+	beforeCreate() {
+		this._rowIdToKeyMap = {}
+	},
+
+	mounted() {
+		this.resizeObserver = new ResizeObserver(entries => {
+			for (const entry of entries) {
+				const cr = entry.contentRect
+				if (entry.target === this.container) {
+					this.containerHeight = cr.height
+				}
+				if (entry.target.classList.contains('vs-rows-container')) {
+					this.rowsContainerHeight = cr.height
+				}
+			}
+		})
+
+		if (this.useWindow) {
+			window.addEventListener('resize', this.updateContainerSize, { passive: true })
+			this.containerHeight = window.innerHeight
+		} else {
+			this.resizeObserver.observe(this.container as HTMLElement|Element)
+		}
+
+		this.resizeObserver.observe(this.$refs.rowsContainer as Element)
+		this.container.addEventListener('scroll', this.updateScrollPosition, { passive: true })
+	},
+
+	beforeDestroy() {
+		if (this.useWindow) {
+			window.removeEventListener('resize', this.updateContainerSize)
+		}
+
+		this.resizeObserver?.disconnect()
+		this.container.removeEventListener('scroll', this.updateScrollPosition)
+	},
+
+	methods: {
+		updateScrollPosition() {
+			this._onScrollHandle ??= requestAnimationFrame(() => {
+				this._onScrollHandle = null
+				if (this.useWindow) {
+					this.scrollPosition = (this.container as Window).scrollY
+				} else {
+					this.scrollPosition = (this.container as HTMLElement|Element).scrollTop
+				}
+			})
+		},
+
+		updateContainerSize() {
+			this.containerHeight = window.innerHeight
+		},
+	},
+})
+</script>
+
+<style scoped lang="scss">
+.vs-container {
+	overflow-y: scroll;
+	height: 100%;
+}
+
+.vs-rows-container {
+	box-sizing: border-box;
+	will-change: scroll-position, padding;
+	contain: layout paint style;
+}
+</style>
diff --git a/apps/files_versions/src/views/VersionTab.vue b/apps/files_versions/src/views/VersionTab.vue
index 932e37e8918..c039e4a6c3a 100644
--- a/apps/files_versions/src/views/VersionTab.vue
+++ b/apps/files_versions/src/views/VersionTab.vue
@@ -16,22 +16,30 @@
  - along with this program. If not, see <http://www.gnu.org/licenses/>.
  -->
 <template>
-	<ul data-files-versions-versions-list>
-		<Version v-for="version in orderedVersions"
-			:key="version.mtime"
-			:can-view="canView"
-			:can-compare="canCompare"
-			:load-preview="isActive"
-			:version="version"
-			:file-info="fileInfo"
-			:is-current="version.mtime === fileInfo.mtime"
-			:is-first-version="version.mtime === initialVersionMtime"
-			@click="openVersion"
-			@compare="compareVersion"
-			@restore="handleRestore"
-			@label-update="handleLabelUpdate"
-			@delete="handleDelete" />
-	</ul>
+	<VirtualScrolling :sections="sections"
+		:header-height="0">
+		<template slot-scope="{visibleSections}">
+			<ul data-files-versions-versions-list>
+				<template v-if="visibleSections.length === 1">
+					<Version v-for="(row) of visibleSections[0].rows"
+						:key="row.items[0].mtime"
+						:can-view="canView"
+						:can-compare="canCompare"
+						:load-preview="isActive"
+						:version="row.items[0]"
+						:file-info="fileInfo"
+						:is-current="row.items[0].mtime === fileInfo.mtime"
+						:is-first-version="row.items[0].mtime === initialVersionMtime"
+						@click="openVersion"
+						@compare="compareVersion"
+						@restore="handleRestore"
+						@label-update="handleLabelUpdate"
+						@delete="handleDelete" />
+				</template>
+			</ul>
+		</template>
+		<NcLoadingIcon v-if="loading" slot="loader" class="files-list-viewer__loader" />
+	</VirtualScrolling>
 </template>
 
 <script>
@@ -41,14 +49,18 @@ import { showError, showSuccess } from '@nextcloud/dialogs'
 import isMobile from '@nextcloud/vue/dist/Mixins/isMobile.js'
 import { emit, subscribe, unsubscribe } from '@nextcloud/event-bus'
 import { getCurrentUser } from '@nextcloud/auth'
+import { NcLoadingIcon } from '@nextcloud/vue'
 
 import { fetchVersions, deleteVersion, restoreVersion, setVersionLabel } from '../utils/versions.js'
 import Version from '../components/Version.vue'
+import VirtualScrolling from '../components/VirtualScrolling.vue'
 
 export default {
 	name: 'VersionTab',
 	components: {
 		Version,
+		VirtualScrolling,
+		NcLoadingIcon,
 	},
 	mixins: [
 		isMobile,
@@ -69,6 +81,11 @@ export default {
 		unsubscribe('files_versions:restore:restored', this.fetchVersions)
 	},
 	computed: {
+		sections() {
+			const rows = this.orderedVersions.map(version => ({ key: version.mtime, height: 68, sectionKey: 'versions', items: [version] }))
+			return [{ key: 'versions', rows, height: 68 * this.orderedVersions.length }]
+		},
+
 		/**
 		 * Order versions by mtime.
 		 * Put the current version at the top.