Merge pull request #938 from vector-im/bwindels/dateheaders-with-model

Add date headers in timeline (second stab)

src/domain/ViewModel.ts

@@ -29,6 +29,7 @@ import type {ILogger} from "../logging/types";
 import type {Navigation} from "./navigation/Navigation";
 import type {SegmentType} from "./navigation/index";
 import type {IURLRouter} from "./navigation/URLRouter";
+import type { ITimeFormatter } from "../platform/types/types";
 
 export type Options<T extends object = SegmentType> = {
     platform: Platform;
@@ -145,4 +146,8 @@ export class ViewModel<N extends object = SegmentType, O extends Options<N> = Op
         // typescript needs a little help here
         return this._options.navigation as unknown as Navigation<N>;
     }
+
+    get timeFormatter(): ITimeFormatter {
+        return this._options.platform.timeFormatter;
+    }
 }

src/domain/session/room/timeline/TilesCollection.js

@@ -16,6 +16,7 @@ limitations under the License.
 
 import {BaseObservableList} from "../../../../observable/list/BaseObservableList";
 import {sortedIndex} from "../../../../utils/sortedIndex";
+import {TileShape} from "./tiles/ITile";
 
 // maps 1..n entries to 0..1 tile. Entries are what is stored in the timeline, either an event or fragmentboundary
 // for now, tileClassForEntry should be stable in whether it returns a tile or not.
@@ -51,6 +52,7 @@ export class TilesCollection extends BaseObservableList {
     }
 
     _populateTiles() {
+        this._silent = true;
         this._tiles = [];
         let currentTile = null;
         for (let entry of this._entries) {
@@ -72,11 +74,20 @@ export class TilesCollection extends BaseObservableList {
         if (prevTile) {
             prevTile.updateNextSibling(null);
         }
+        // add date headers here
+        for (let idx = 0; idx < this._tiles.length; idx += 1) {
+            const tile = this._tiles[idx];
+            if (tile.needsDateSeparator) {
+                this._addTileAt(idx, tile.createDateSeparator(), true);
+                idx += 1; // tile's index moved one up, don't process it again
+            }
+        }
         // now everything is wired up,
         // allow tiles to emit updates
         for (const tile of this._tiles) {
             tile.setUpdateEmit(this._emitSpontanousUpdate);
         }
+        this._silent = false;
     }
 
     _findTileIdx(entry) {
@@ -130,25 +141,57 @@ export class TilesCollection extends BaseObservableList {
 
         const newTile = this._createTile(entry);
         if (newTile) {
-            if (prevTile) {
-                prevTile.updateNextSibling(newTile);
-                // this emits an update while the add hasn't been emitted yet
-                newTile.updatePreviousSibling(prevTile);
-            }
-            if (nextTile) {
-                newTile.updateNextSibling(nextTile);
-                nextTile.updatePreviousSibling(newTile);
-            }
-            this._tiles.splice(tileIdx, 0, newTile);
-            this.emitAdd(tileIdx, newTile);
-            // add event is emitted, now the tile
-            // can emit updates
-            newTile.setUpdateEmit(this._emitSpontanousUpdate);
+            this._addTileAt(tileIdx, newTile);
+            this._evaluateDateHeaderAtIdx(tileIdx);
         }
         // find position by sort key
         // ask siblings to be included? both? yes, twice: a (insert c here) b, ask a(c), if yes ask b(a), else ask b(c)? if yes then b(a)?
     }
 
+    _evaluateDateHeaderAtIdx(tileIdx) {
+        // consider two tiles after the inserted tile, because
+        // the first of the two tiles may be a DateTile in which case,
+        // we remove it after looking at the needsDateSeparator prop of the
+        // next next tile
+        for (let i = 0; i < 3; i += 1) {
+            const idx = tileIdx + i;
+            if (idx >= this._tiles.length) {
+                break;
+            }
+            const tile = this._tiles[idx];
+            const prevTile = idx > 0 ? this._tiles[idx - 1] : undefined;
+            const hasDateSeparator = prevTile?.shape === TileShape.DateHeader;
+            if (tile.needsDateSeparator && !hasDateSeparator) {
+                // adding a tile shift all the indices we need to consider
+                // especially given we consider removals for the tile that
+                // comes after a datetile
+                tileIdx += 1;
+                this._addTileAt(idx, tile.createDateSeparator());
+            } else if (!tile.needsDateSeparator && hasDateSeparator) {
+                // this is never triggered because needsDateSeparator is not cleared
+                // when loading more items because we don't do anything once the
+                // direct sibling is a DateTile
+                this._removeTile(idx - 1, prevTile);
+            }
+        }
+    }
+
+    _addTileAt(idx, newTile, silent = false) {
+        const prevTile = idx > 0 ? this._tiles[idx - 1] : undefined;
+        const nextTile = this._tiles[idx];
+        prevTile?.updateNextSibling(newTile);
+        newTile.updatePreviousSibling(prevTile);
+        newTile.updateNextSibling(nextTile);
+        nextTile?.updatePreviousSibling(newTile);
+        this._tiles.splice(idx, 0, newTile);
+        if (!silent) {
+            this.emitAdd(idx, newTile);
+        }
+        // add event is emitted, now the tile
+        // can emit updates
+        newTile.setUpdateEmit(this._emitSpontanousUpdate);
+    }
+
     onUpdate(index, entry, params) {
         // if an update is emitted while calling source.subscribe() from onSubscribeFirst, ignore it
         if (!this._tiles) {
@@ -210,11 +253,16 @@ export class TilesCollection extends BaseObservableList {
         this.emitRemove(tileIdx, tile);
         prevTile?.updateNextSibling(nextTile);
         nextTile?.updatePreviousSibling(prevTile);
+
+        if (prevTile && prevTile.shape === TileShape.DateHeader && (!nextTile || !nextTile.needsDateSeparator)) {
+            this._removeTile(tileIdx - 1, prevTile);
+        }
     }
 
     // would also be called when unloading a part of the timeline
     onRemove(index, entry) {
         const tileIdx = this._findTileIdx(entry);
+        
         const tile = this._findTileAtIdx(entry, tileIdx);
         if (tile) {
             const removeTile = tile.removeEntry(entry);
@@ -268,6 +316,7 @@ export function tests() {
         constructor(entry) {
             this.entry = entry;
             this.update = null;
+            this.needsDateSeparator = false;
         }
         setUpdateEmit(update) {
             this.update = update;
@@ -297,6 +346,34 @@ export function tests() {
         dispose() {}
     }
 
+    class DateHeaderTile extends TestTile {
+        get shape() { return TileShape.DateHeader; }
+        updateNextSibling(next) {
+            this.next = next;
+        }
+        updatePreviousSibling(prev) {
+            this.next?.updatePreviousSibling(prev);
+        }
+        compareEntry(b) {
+            // important that date tiles as sorted before their next item, but after their previous sibling
+            return this.next.compareEntry(b) - 0.5;
+        }
+    }
+
+    class MessageNeedingDateHeaderTile extends TestTile {
+        get shape() { return TileShape.Message; }
+
+        createDateSeparator() {
+            return new DateHeaderTile(this.entry);
+        }
+        updatePreviousSibling(prev) {
+            if (prev?.shape !== TileShape.DateHeader) {
+                // 1 day is 10 
+                this.needsDateSeparator = !prev || Math.floor(prev.entry.n / 10) !== Math.floor(this.entry.n / 10);
+            }
+        }
+    }
+
     return {
         "don't emit update before add": assert => {
             class UpdateOnSiblingTile extends TestTile {
@@ -355,6 +432,73 @@ export function tests() {
             });
             entries.remove(1);
             assert.deepEqual(events, ["remove", "update"]);
+        },
+        "date tile is added when needed when populating": assert => {
+            const entries = new ObservableArray([{n: 15}]);
+            const tileOptions = {
+                tileClassForEntry: () => MessageNeedingDateHeaderTile,
+            };
+            const tiles = new TilesCollection(entries, tileOptions);
+            tiles.subscribe({});
+            const tilesArray = Array.from(tiles);
+            assert.equal(tilesArray.length, 2);
+            assert.equal(tilesArray[0].shape, TileShape.DateHeader);
+            assert.equal(tilesArray[1].shape, TileShape.Message);
+        },
+        "date header is added when receiving addition": assert => {
+            const entries = new ObservableArray([{n: 15}]);
+            const tileOptions = {
+                tileClassForEntry: () => MessageNeedingDateHeaderTile,
+            };
+            const tiles = new TilesCollection(entries, tileOptions);
+            tiles.subscribe({
+                onAdd() {},
+                onRemove() {}
+            });
+            entries.insert(0, {n: 5});
+            const tilesArray = Array.from(tiles);
+            assert.equal(tilesArray[0].shape, TileShape.DateHeader);
+            assert.equal(tilesArray[1].shape, TileShape.Message);
+            assert.equal(tilesArray[2].shape, TileShape.DateHeader);
+            assert.equal(tilesArray[3].shape, TileShape.Message);
+            assert.equal(tilesArray.length, 4);
+        },
+        "date header is removed and added when loading more messages for the same day": assert => {
+            const entries = new ObservableArray([{n: 15}]);
+            const tileOptions = {
+                tileClassForEntry: () => MessageNeedingDateHeaderTile,
+            };
+            const tiles = new TilesCollection(entries, tileOptions);
+            tiles.subscribe({
+                onAdd() {},
+                onRemove() {}
+            });
+            entries.insert(0, {n: 12});
+            const tilesArray = Array.from(tiles);
+            assert.equal(tilesArray[0].shape, TileShape.DateHeader);
+            assert.equal(tilesArray[1].shape, TileShape.Message);
+            assert.equal(tilesArray[2].shape, TileShape.Message);
+            assert.equal(tilesArray.length, 3);
+        },
+        "date header is removed at the end of the timeline": assert => {
+            const entries = new ObservableArray([{n: 5}, {n: 15}]);
+            const tileOptions = {
+                tileClassForEntry: () => MessageNeedingDateHeaderTile,
+            };
+            const tiles = new TilesCollection(entries, tileOptions);
+            let removals = 0;
+            tiles.subscribe({
+                onAdd() {},
+                onRemove() {
+                    removals += 1;
+                }
+            });
+            entries.remove(1);
+            const tilesArray = Array.from(tiles);
+            assert.equal(tilesArray[0].shape, TileShape.DateHeader);
+            assert.equal(tilesArray[1].shape, TileShape.Message);
+            assert.equal(tilesArray.length, 2);
+            assert.equal(removals, 2);
         }
     }
 }

src/domain/session/room/timeline/tiles/BaseMessageTile.js

@@ -21,7 +21,6 @@ import {getIdentifierColorNumber, avatarInitials, getAvatarHttpUrl} from "../../
 export class BaseMessageTile extends SimpleTile {
     constructor(entry, options) {
         super(entry, options);
-        this._date = this._entry.timestamp ? new Date(this._entry.timestamp) : null;
         this._isContinuation = false;
         this._reactions = null;
         this._replyTile = null;
@@ -78,12 +77,8 @@ export class BaseMessageTile extends SimpleTile {
         return this.sender;
     }
 
-    get date() {
-        return this._date && this._date.toLocaleDateString({}, {month: "numeric", day: "numeric"});
-    }
-
     get time() {
-        return this._date && this._date.toLocaleTimeString({}, {hour: "numeric", minute: "2-digit"});
+        return this._date && this.timeFormatter.formatTime(this._date);
     }
 
     get isOwn() {

src/domain/session/room/timeline/tiles/DateTile.ts

@@ -0,0 +1,181 @@
+import {ITile, TileShape, EmitUpdateFn} from "./ITile";
+import {UpdateAction} from "../UpdateAction";
+import {BaseEntry} from "../../../../../matrix/room/timeline/entries/BaseEntry";
+import {BaseEventEntry} from "../../../../../matrix/room/timeline/entries/BaseEventEntry";
+import {ViewModel} from "../../../../ViewModel";
+import type {Options} from "../../../../ViewModel";
+
+/**
+ * edge cases:
+ *  - be able to remove the tile in response to the sibling changing,
+ *    probably by letting updateNextSibling/updatePreviousSibling
+ *    return an UpdateAction and change TilesCollection accordingly.
+ *    this is relevant when next becomes undefined there when
+ *    a pending event is removed on remote echo.
+ * */
+
+export class DateTile extends ViewModel implements ITile<BaseEventEntry> {
+    private _emitUpdate?: EmitUpdateFn;
+    private _dateString?: string;
+    private _machineReadableString?: string;
+    
+    constructor(private _firstTileInDay: ITile<BaseEventEntry>, options: Options) {
+        super(options);
+    }
+
+    setUpdateEmit(emitUpdate: EmitUpdateFn): void {
+        this._emitUpdate = emitUpdate;
+    }
+
+    get upperEntry(): BaseEventEntry {
+        return this.refEntry;
+    }
+
+    get lowerEntry(): BaseEventEntry {
+        return this.refEntry;
+    }
+
+    /** the entry reference by this datetile, e.g. the entry of the first tile for this day */
+    private get refEntry(): BaseEventEntry {
+        // lowerEntry is the first entry... i think?
+        // so given the date header always comes before,
+        // this is our closest entry.
+        return this._firstTileInDay.lowerEntry;
+    }
+
+    compare(tile: ITile<BaseEntry>): number {
+        return this.compareEntry(tile.upperEntry);
+    }
+
+    get relativeDate(): string {
+        if (!this._dateString) {
+            this._dateString = this.timeFormatter.formatRelativeDate(new Date(this.refEntry.timestamp));
+        }
+        return this._dateString;
+    }
+
+    get machineReadableDate(): string {
+        if (!this._machineReadableString) {
+            this._machineReadableString = this.timeFormatter.formatMachineReadableDate(new Date(this.refEntry.timestamp));
+        }
+        return this._machineReadableString;
+    }
+
+    get shape(): TileShape {
+        return TileShape.DateHeader;
+    }
+
+    get needsDateSeparator(): boolean {
+        return false;
+    }
+
+    createDateSeparator(): undefined {
+        return undefined;
+    }
+
+/**
+ * _findTileIdx in TilesCollection should never return
+ * the index of a DateTile as that is mainly used
+ * for mapping incoming event indices coming from the Timeline
+ * to the tile index to propage the event.
+ * This is not a path that is relevant to date headers as they
+ * are added as a side-effect of adding other tiles and are generally
+ * not updated (only removed in some cases). _findTileIdx is also
+ * used for emitting spontanous updates, but that should also not be
+ * needed for a DateTile.
+ * The problem is basically that _findTileIdx maps an entry to
+ * a tile, and DateTile adopts the entry of it's sibling tile (_firstTileInDay)
+ * so now we have the entry pointing to two tiles. So we should avoid
+ * returning the DateTile itself from the compare method.
+ * We will always return -1 or 1 from here to signal an entry comes before or after us,
+ * never 0
+ * */
+    compareEntry(entry: BaseEntry): number {
+        const result = this.refEntry.compare(entry);
+        if (result === 0) {
+            // if it's a match for the reference entry (e.g. _firstTileInDay),
+            // say it comes after us as the date tile always comes at the top
+            // of the day.
+            return -1;
+        }
+        // otherwise, assume the given entry is never for ourselves
+        // as we don't have our own entry, we only borrow one from _firstTileInDay
+        return result;
+    }
+
+    // update received for already included (falls within sort keys) entry
+    updateEntry(entry, param): UpdateAction {
+        return UpdateAction.Nothing();
+    }
+
+    // return whether the tile should be removed
+    // as SimpleTile only has one entry, the tile should be removed
+    removeEntry(entry: BaseEntry): boolean {
+        return false;
+    }
+
+    // SimpleTile can only contain 1 entry
+    tryIncludeEntry(): boolean {
+        return false;
+    }
+
+    // let item know it has a new sibling
+    updatePreviousSibling(prev: ITile<BaseEntry> | undefined): void {
+        // forward the sibling update to our next tile, so it is informed
+        // about it's previous sibling beyond the date header (which is it's direct previous sibling)
+        // so it can recalculate whether it still needs a date header
+        this._firstTileInDay.updatePreviousSibling(prev);
+    }
+
+    // let item know it has a new sibling
+    updateNextSibling(next: ITile<BaseEntry> | undefined): UpdateAction {
+        if(!next) {
+            // If we are the DateTile for the last tile in the timeline,
+            // and that tile gets removed, next would be undefined
+            // and this DateTile would be removed as well,
+            // so do nothing
+            return;
+        }
+        this._firstTileInDay = next;
+        const prevDateString = this._dateString;
+        this._dateString = undefined;
+        this._machineReadableString = undefined;
+        if (prevDateString && prevDateString !== this.relativeDate) {
+            this._emitUpdate?.(this, "relativeDate");
+        }
+    }
+
+    notifyVisible(): void {
+        // trigger sticky logic here?
+    }
+
+    dispose(): void {
+
+    }
+}
+
+import { EventEntry } from "../../../../../matrix/room/timeline/entries/EventEntry.js";
+import { SimpleTile } from "./SimpleTile";
+
+export function tests() {
+    return {
+        "date tile sorts before reference tile": assert => {
+            const a = new SimpleTile(new EventEntry({
+                event: {},
+                eventIndex: 2,
+                fragmentId: 1
+            }, undefined), {});
+            const b = new SimpleTile(new EventEntry({
+                event: {},
+                eventIndex: 3,
+                fragmentId: 1
+            }, undefined), {});
+            const d = new DateTile(b, {} as any);
+            const tiles = [d, b, a];
+            tiles.sort((a, b) => a.compare(b));
+            assert.equal(tiles[0], a);
+            assert.equal(tiles[1], d);
+            assert.equal(tiles[2], b);
+        }
+    }
+}

src/domain/session/room/timeline/tiles/GapTile.js

@@ -19,6 +19,7 @@ import {UpdateAction} from "../UpdateAction.js";
 import {ConnectionError} from "../../../../../matrix/error.js";
 import {ConnectionStatus} from "../../../../../matrix/net/Reconnector";
 
+// TODO: should this become an ITile and SimpleTile become EventTile?
 export class GapTile extends SimpleTile {
     constructor(entry, options) {
         super(entry, options);
@@ -29,6 +30,10 @@ export class GapTile extends SimpleTile {
         this._showSpinner = false;
     }
 
+    get needsDateSeparator() {
+        return false;
+    }
+
     async fill() {
         if (!this._loading && !this._entry.edgeReached) {
             this._loading = true;

src/domain/session/room/timeline/tiles/ITile.ts

@@ -0,0 +1,44 @@
+import {UpdateAction} from "../UpdateAction.js";
+import {BaseEntry} from "../../../../../matrix/room/timeline/entries/BaseEntry";
+import {BaseEventEntry} from "../../../../../matrix/room/timeline/entries/BaseEventEntry";
+import {IDisposable} from "../../../../../utils/Disposables";
+
+export type EmitUpdateFn = (tile: ITile<BaseEntry>, props: any) => void
+
+export enum TileShape {
+    Message = "message",
+    MessageStatus = "message-status",
+    Announcement = "announcement",
+    File = "file",
+    Gap = "gap",
+    Image = "image",
+    Location = "location",
+    MissingAttachment = "missing-attachment",
+    Redacted = "redacted",
+    Video = "video",
+    DateHeader = "date-header"
+}
+
+// TODO: should we imply inheriting from view model here?
+export interface ITile<E extends BaseEntry = BaseEntry> extends IDisposable {
+    setUpdateEmit(emitUpdate: EmitUpdateFn): void;
+    get upperEntry(): E;
+    get lowerEntry(): E;
+    compare(tile: ITile<BaseEntry>): number;
+    compareEntry(entry: BaseEntry): number;
+    // update received for already included (falls within sort keys) entry
+    updateEntry(entry: BaseEntry, param: any): UpdateAction;
+    // return whether the tile should be removed
+    // as SimpleTile only has one entry, the tile should be removed
+    removeEntry(entry: BaseEntry): boolean
+    // SimpleTile can only contain 1 entry
+    tryIncludeEntry(): boolean;
+    // let item know it has a new sibling
+    updatePreviousSibling(prev: ITile<BaseEntry> | undefined): void;
+    // let item know it has a new sibling
+    updateNextSibling(next: ITile<BaseEntry> | undefined): void;
+    notifyVisible(): void;
+    get needsDateSeparator(): boolean;
+    createDateSeparator(): ITile<BaseEntry> | undefined;
+    get shape(): TileShape;
+}

src/domain/session/room/timeline/tiles/SimpleTile.js

@@ -15,13 +15,17 @@ limitations under the License.
 */
 
 import {UpdateAction} from "../UpdateAction.js";
+import {TileShape} from "./ITile";
 import {ViewModel} from "../../../../ViewModel";
 import {SendStatus} from "../../../../../matrix/room/sending/PendingEvent.js";
+import {DateTile} from "./DateTile";
 
 export class SimpleTile extends ViewModel {
     constructor(entry, options) {
         super(options);
         this._entry = entry;
+        this._date = this._entry.timestamp ? new Date(this._entry.timestamp) : undefined;
+        this._needsDateSeparator = false;
         this._emitUpdate = undefined;
     }
     // view model props for all subclasses
@@ -37,8 +41,22 @@ export class SimpleTile extends ViewModel {
         return false;
     }
 
-    get hasDateSeparator() {
-        return false;
+    get needsDateSeparator() {
+        return this._needsDateSeparator;
+    }
+
+    createDateSeparator() {
+        return new DateTile(this, this.childOptions({}));
+    }
+
+    _updateDateSeparator(prev) {
+        if (prev && prev._date && this._date) {
+            this._needsDateSeparator = prev._date.getFullYear() !== this._date.getFullYear() ||
+                prev._date.getMonth() !== this._date.getMonth() ||
+                prev._date.getDate() !== this._date.getDate();
+        } else {
+            this._needsDateSeparator = !!this._date;
+        }
     }
 
     get id() {
@@ -123,8 +141,10 @@ export class SimpleTile extends ViewModel {
         return false;
     }
     // let item know it has a new sibling
-    updatePreviousSibling(/*prev*/) {
-
+    updatePreviousSibling(prev) {
+        if (prev?.shape !== TileShape.DateHeader) {
+            this._updateDateSeparator(prev);
+        }
     }
 
     // let item know it has a new sibling
@@ -160,3 +180,65 @@ export class SimpleTile extends ViewModel {
         return this._options.timeline.me;
     }
 }
+
+import { EventEntry } from "../../../../../matrix/room/timeline/entries/EventEntry.js";
+
+export function tests() {
+    return {
+        "needsDateSeparator is false when previous sibling is for same date": assert => {
+            const fridayEntry = new EventEntry({
+                event: {
+                    origin_server_ts: 1669376446222,
+                    type: "m.room.message",
+                    content: {}
+                }
+            }, undefined);
+            const thursdayEntry = new EventEntry({
+                event: {
+                    origin_server_ts: fridayEntry.timestamp - (60 * 60 * 8 * 1000),
+                    type: "m.room.message",
+                    content: {}
+                }
+            }, undefined);
+            const fridayTile = new SimpleTile(fridayEntry, {});
+            const thursdayTile = new SimpleTile(thursdayEntry, {});
+            assert.equal(fridayTile.needsDateSeparator, false);
+            fridayTile.updatePreviousSibling(thursdayTile);
+            assert.equal(fridayTile.needsDateSeparator, false);
+        },
+        "needsDateSeparator is true when previous sibling is for different date": assert => {
+            const fridayEntry = new EventEntry({
+                event: {
+                    origin_server_ts: 1669376446222,
+                    type: "m.room.message",
+                    content: {}
+                }
+            }, undefined);
+            const thursdayEntry = new EventEntry({
+                event: {
+                    origin_server_ts: fridayEntry.timestamp - (60 * 60 * 24 * 1000),
+                    type: "m.room.message",
+                    content: {}
+                }
+            }, undefined);
+            const fridayTile = new SimpleTile(fridayEntry, {});
+            const thursdayTile = new SimpleTile(thursdayEntry, {});
+            assert.equal(fridayTile.needsDateSeparator, false);
+            fridayTile.updatePreviousSibling(thursdayTile);
+            assert.equal(fridayTile.needsDateSeparator, true);
+        },
+        "needsDateSeparator is true when previous sibling is undefined": assert => {
+            const fridayEntry = new EventEntry({
+                event: {
+                    origin_server_ts: 1669376446222,
+                    type: "m.room.message",
+                    content: {}
+                }
+            }, undefined);
+            const fridayTile = new SimpleTile(fridayEntry, {});
+            assert.equal(fridayTile.needsDateSeparator, false);
+            fridayTile.updatePreviousSibling(undefined);
+            assert.equal(fridayTile.needsDateSeparator, true);
+        },
+    }
+}

src/domain/session/room/timeline/tiles/index.ts

@@ -27,7 +27,7 @@ import {EncryptedEventTile} from "./EncryptedEventTile.js";
 import {EncryptionEnabledTile} from "./EncryptionEnabledTile.js";
 import {MissingAttachmentTile} from "./MissingAttachmentTile.js";
 
-import type {SimpleTile} from "./SimpleTile.js";
+import type {ITile, TileShape} from "./ITile";
 import type {Room} from "../../../../../matrix/room/Room";
 import type {Timeline} from "../../../../../matrix/room/timeline/Timeline";
 import type {FragmentBoundaryEntry} from "../../../../../matrix/room/timeline/entries/FragmentBoundaryEntry";
@@ -42,7 +42,7 @@ export type Options = ViewModelOptions & {
     timeline: Timeline
     tileClassForEntry: TileClassForEntryFn;
 };
-export type TileConstructor = new (entry: TimelineEntry, options: Options) => SimpleTile;
+export type TileConstructor = new (entry: TimelineEntry, options: Options) => ITile;
 
 export function tileClassForEntry(entry: TimelineEntry): TileConstructor | undefined {
     if (entry.isGap) {

src/platform/types/types.ts

@@ -16,7 +16,7 @@ limitations under the License.
 
 import type {RequestResult} from "../web/dom/request/fetch.js";
 import type {RequestBody} from "../../matrix/net/common";
-import type {ILogItem} from "../../logging/types";
+import type { BaseObservableValue } from "../../observable/ObservableValue";
 
 export interface IRequestOptions {
     uploadProgress?: (loadedBytes: number) => void;
@@ -43,3 +43,9 @@ export type File = {
     readonly name: string;
     readonly blob: IBlobHandle;
 }
+
+export interface ITimeFormatter {
+    formatTime(date: Date): string;
+    formatRelativeDate(date: Date): string;
+    formatMachineReadableDate(date: Date): string;
+}

src/platform/web/Platform.js

@@ -39,6 +39,7 @@ import {Disposables} from "../../utils/Disposables";
 import {parseHTML} from "./parsehtml.js";
 import {handleAvatarError} from "./ui/avatar";
 import {ThemeLoader} from "./theming/ThemeLoader";
+import {TimeFormatter} from "./dom/TimeFormatter";
 
 function addScript(src) {
     return new Promise(function (resolve, reject) {
@@ -139,6 +140,7 @@ export class Platform {
         this._createLogger(options?.development);
         this.history = new History();
         this.onlineStatus = new OnlineStatus();
+        this.timeFormatter = new TimeFormatter();
         this._serviceWorkerHandler = null;
         if (assetPaths.serviceWorker && "serviceWorker" in navigator) {
             this._serviceWorkerHandler = new ServiceWorkerHandler();

src/platform/web/dom/TimeFormatter.ts

@@ -0,0 +1,83 @@
+/*
+Copyright 2022 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import type { ITimeFormatter } from "../../types/types";
+import {Clock} from "./Clock";
+
+enum TimeScope {
+    Minute = 60 * 1000,
+    Day = 24 * 60 * 60 * 1000,
+}
+
+export class TimeFormatter implements ITimeFormatter {
+
+    private todayMidnight: Date;
+    private relativeDayFormatter: Intl.RelativeTimeFormat;
+    private weekdayFormatter: Intl.DateTimeFormat;
+    private currentYearFormatter: Intl.DateTimeFormat;
+    private otherYearFormatter: Intl.DateTimeFormat;
+    private timeFormatter: Intl.DateTimeFormat;
+
+    constructor(private clock: Clock) {
+        // don't use the clock time here as the DOM relative formatters don't support setting the reference date anyway
+        this.todayMidnight = new Date();
+        this.todayMidnight.setHours(0, 0, 0, 0);
+        this.relativeDayFormatter = new Intl.RelativeTimeFormat(undefined, {numeric: "auto"});
+        this.weekdayFormatter = new Intl.DateTimeFormat(undefined, {weekday: 'long'});
+        this.currentYearFormatter = new Intl.DateTimeFormat(undefined, {
+            weekday: 'long',
+            month: 'long',
+            day: 'numeric'
+        });
+        this.otherYearFormatter = new Intl.DateTimeFormat(undefined, {
+            weekday: 'long',
+            year: 'numeric',
+            month: 'long',
+            day: 'numeric'
+        });
+        this.timeFormatter = new Intl.DateTimeFormat(undefined, {hour: "numeric", minute: "2-digit"});
+    }
+    
+    formatTime(date: Date): string {
+        return this.timeFormatter.format(date);
+    }
+
+    formatMachineReadableDate(date: Date): string {
+        return `${date.getFullYear()}-${date.getMonth() + 1}-${date.getDate()}`;    
+    }
+
+    formatRelativeDate(date: Date): string {
+        let daysDiff = Math.floor((date.getTime() - this.todayMidnight.getTime()) / TimeScope.Day);
+        console.log("formatRelativeDate daysDiff", daysDiff, date);
+        if (daysDiff >= -1 && daysDiff <= 1) {
+            // Tomorrow, Today, Yesterday
+            return capitalizeFirstLetter(this.relativeDayFormatter.format(daysDiff, "day"));
+        } else if (daysDiff > -7 && daysDiff < 0) {
+            // Wednesday
+            return this.weekdayFormatter.format(date);
+        } else if (this.todayMidnight.getFullYear() === date.getFullYear()) {
+            // Friday, November 6
+            return this.currentYearFormatter.format(date);
+        } else {
+            // Friday, November 5, 2021
+            return this.otherYearFormatter.format(date);
+        }
+    }
+}
+
+function capitalizeFirstLetter(str: string) {
+    return str.slice(0, 1).toLocaleUpperCase() + str.slice(1);
+}

src/platform/web/ui/css/themes/element/timeline.css

@@ -422,3 +422,22 @@ only loads when the top comes into view*/
 .GapView.isAtTop {
     padding: 52px 20px 12px 20px;
 }
+
+.DateHeader {
+    font-weight: bold;
+    font-size: 1.5rem;
+    position: sticky;
+    top: 5px;
+}
+
+.DateHeader time {
+    margin: 0 auto;
+    padding: 12px 4px;
+    width: 250px;
+    padding: 12px;
+    display: block;
+    color: var(--light-text-color);
+    background-color: var(--background-color-primary);
+    border-radius: 8px;
+    text-align: center;
+  }

src/platform/web/ui/session/room/common.ts

@@ -22,31 +22,34 @@ import {LocationView} from "./timeline/LocationView.js";
 import {MissingAttachmentView} from "./timeline/MissingAttachmentView.js";
 import {AnnouncementView} from "./timeline/AnnouncementView.js";
 import {RedactedView} from "./timeline/RedactedView.js";
-import {SimpleTile} from "../../../../../domain/session/room/timeline/tiles/SimpleTile.js";
+import {ITile, TileShape} from "../../../../../domain/session/room/timeline/tiles/ITile.js";
 import {GapView} from "./timeline/GapView.js";
+import {DateHeaderView} from "./timeline/DateHeaderView";
 import type {TileViewConstructor, ViewClassForEntryFn} from "./TimelineView";
 
-export function viewClassForTile(vm: SimpleTile): TileViewConstructor {
+export function viewClassForTile(vm: ITile): TileViewConstructor {
     switch (vm.shape) {
-        case "gap":
+        case TileShape.Gap:
             return GapView;
-        case "announcement":
+        case TileShape.Announcement:
             return AnnouncementView;
-        case "message":
-        case "message-status":
+        case TileShape.Message:
+        case TileShape.MessageStatus:
             return TextMessageView;
-        case "image":
+        case TileShape.Image:
             return ImageView;
-        case "video":
+        case TileShape.Video:
             return VideoView;
-        case "file":
+        case TileShape.File:
             return FileView;
-        case "location":
+        case TileShape.Location:
             return LocationView;
-        case "missing-attachment":
+        case TileShape.MissingAttachment:
             return MissingAttachmentView;
-        case "redacted":
+        case TileShape.Redacted:
             return RedactedView;
+        case TileShape.DateHeader:
+            return DateHeaderView;
         default:
             throw new Error(`Tiles of shape "${vm.shape}" are not supported, check the tileClassForEntry function in the view model`);
     }

src/platform/web/ui/session/room/timeline/BaseMediaView.js

@@ -34,7 +34,7 @@ export class BaseMediaView extends BaseMessageView {
         const children = [
             t.div({className: "spacer", style: spacerStyle}),
             this.renderMedia(t, vm),
-            t.time(vm.date + " " + vm.time),
+            t.time(vm.time),
         ];
         const status = t.div({
             className: {

src/platform/web/ui/session/room/timeline/DateHeaderView.ts

@@ -0,0 +1,33 @@
+/*
+Copyright 2020 Bruno Windels <bruno@windels.cloud>
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {TemplateView} from "../../../general/TemplateView";
+import {spinner} from "../../../common.js";
+import type {DateTile} from "../../../../../../domain/session/room/timeline/tiles/DateTile";
+
+export class DateHeaderView extends TemplateView<DateTile> {
+    // ignore other argument
+    constructor(vm) {
+        super(vm);
+    }
+
+    render(t, vm) {
+        return t.h2({className: "DateHeader"}, t.time({dateTime: vm.machineReadableDate}, vm.relativeDate));
+    }
+
+    /* This is called by the parent ListView, which just has 1 listener for the whole list */
+    onClick() {}
+}

src/platform/web/ui/session/room/timeline/FileView.js

@@ -24,7 +24,7 @@ export class FileView extends BaseMessageView {
         } else {
             children.push(
                 t.button({className: "link", onClick: () => vm.download()}, vm => vm.label),
-                t.time(vm.date + " " + vm.time)
+                t.time(vm.time)
             );
         }
         return t.p({className: "Timeline_messageBody statusMessage"}, children);

src/platform/web/ui/session/room/timeline/LocationView.js

@@ -21,7 +21,7 @@ export class LocationView extends BaseMessageView {
         return t.p({className: "Timeline_messageBody statusMessage"}, [
             t.span(vm.label),
             t.a({className: "Timeline_locationLink", href: vm.mapsLink, target: "_blank", rel: "noopener"}, vm.i18n`Open in maps`),
-            t.time(vm.date + " " + vm.time)
+            t.time(vm.time)
         ]);
     }
 }

src/platform/web/ui/session/room/timeline/TextMessageView.js

@@ -20,7 +20,7 @@ import {ReplyPreviewError, ReplyPreviewView} from "./ReplyPreviewView.js";
 
 export class TextMessageView extends BaseMessageView {
     renderMessageBody(t, vm) {
-        const time = t.time({className: {hidden: !vm.date}}, vm.date + " " + vm.time);
+        const time = t.time({className: {hidden: !vm.time}}, vm.time);
         const container = t.div({
             className: {
                 "Timeline_messageBody": true,