enhance chat functionality with infinite scrolling and message retrieval improvements

src/app/app.config.ts

@@ -1,5 +1,5 @@
 import { ApplicationConfig, provideZoneChangeDetection } from '@angular/core';
-import { provideRouter } from '@angular/router';
+import { provideRouter, withInMemoryScrolling } from '@angular/router';
 
 import { routes } from './app.routes';
 import { provideHttpClient } from '@angular/common/http';
@@ -10,7 +10,10 @@ import { provideMarkdown } from 'ngx-markdown';
 export const appConfig: ApplicationConfig = {
   providers: [
     provideZoneChangeDetection({ eventCoalescing: true }),
-    provideRouter(routes),
+    provideRouter(routes, withInMemoryScrolling({
+      anchorScrolling: "enabled",
+      scrollPositionRestoration: 'top'
+    })),
     provideHttpClient(),
     provideAnimations(),
     provideToastr({

src/app/chat/chat/chat.component.html

@@ -18,7 +18,7 @@
   <mat-drawer-content>
     <app-toolbar (sidebar)="drawer.toggle()" />
 
-    <app-feed #feed
+    <app-feed #feed (outOfMessages)="this.GetMoreMessages()"
       [messages]="(this.channels && this.channels.length) != 0 ? this.channels[this.selectedChannel].messages : []"></app-feed>
 
     <app-message-bar

src/app/chat/chat/chat.component.ts

@@ -41,7 +41,7 @@ export class ChatComponent implements OnInit {
 
   private getMessages(): void {
     this.channels.forEach((channelObj, i) => {
-      this.chatService.GetMessages(channelObj.channel.id).subscribe({
+      this.chatService.GetMessageStream(channelObj.channel.id).subscribe({
         next: message => {
           channelObj.messages.push(message);
           this.feed.ScrollEventHandler();
@@ -56,6 +56,18 @@ export class ChatComponent implements OnInit {
     });
   }
 
+  public GetMoreMessages(): void {
+    this.chatService.GetMessages(this.channels[this.selectedChannel].channel.id, this.channels[this.selectedChannel].messages[0]?.time ?? new Date())
+      .subscribe({
+        next: messages => {
+          let lastMessage = this.channels[this.selectedChannel].messages[0];
+          this.channels[this.selectedChannel].messages.unshift(...messages);
+          this.feed.ScrollToMessage(lastMessage.channel_id, lastMessage.id);
+        },
+        error: () => this.toastrService.error("Failed to fetch older messages.", "Error")
+      });
+  }
+
   public GetChannelList(): Channel[] {
     return this.channels.map(c => c.channel);
   }

src/app/chat/chat/feed/feed.component.html

@@ -1,3 +1 @@
-<div #scrollable id="scrollable">
 <app-message *ngFor="let message of this.messages" [message]="message" />
-</div>

src/app/chat/chat/feed/feed.component.ts

@@ -1,4 +1,4 @@
-import { AfterViewInit, Component, DoCheck, ElementRef, EventEmitter, Input, IterableDiffer, IterableDiffers, Output } from '@angular/core';
+import { AfterViewInit, Component, DoCheck, ElementRef, EventEmitter, HostListener, Input, IterableDiffer, IterableDiffers, Output, QueryList, ViewChildren } from '@angular/core';
 import { Message } from '../../../models/message';
 
 @Component({
@@ -9,6 +9,7 @@ import { Message } from '../../../models/message';
 })
 export class FeedComponent implements AfterViewInit {
   @Input('messages') public messages?: Message[];
+  @Output('outOfMessages') public outOfMessages: EventEmitter<void> = new EventEmitter<void>();
 
   constructor(private element: ElementRef<HTMLElement>) { }
 
@@ -21,11 +22,38 @@ export class FeedComponent implements AfterViewInit {
     return Math.abs(element.scrollHeight - element.clientHeight - element.scrollTop) <= 100;
   }
 
+  private isAtTop(): boolean {
+    let element = this.element.nativeElement;
+    return element.scrollTop == 0;
+  }
+
   private scrollToBottom(): void {
     setTimeout(() => this.element.nativeElement.scrollTop = this.element.nativeElement.scrollHeight, 100);
   }
 
+  // handles scroll to bottom events from the chat component when a new message arrives
   public ScrollEventHandler(): void {
     if (this.isAtBottom()) this.scrollToBottom();
   }
+
+  @HostListener('scroll')
+  private detectOutOfMessages(): void {
+    if (this.isAtTop()) {
+      this.outOfMessages.emit();
+    }
+  }
+
+  public ScrollToMessage(channelID: number, messageID: number): void {
+    setTimeout(() => {
+      let id = `#c${channelID}m${messageID}`;
+
+      let target = this.element.nativeElement.querySelector(id) as HTMLDivElement | null;
+      if (!target) return;
+
+      this.element.nativeElement.scrollTo({
+        top: target.offsetTop - target.offsetHeight,
+        behavior: "instant"
+      });
+    }, 100);
+  }
 }

src/app/chat/chat/feed/message/message.component.html

@@ -1,4 +1,4 @@
-<div class="message-container">
+<div [id]="`c${message.channel_id}m${message.id}`" class="message-container">
   <app-profile-picture [username]="this.message.sender_name" />
 
   <div class="message-inner-container">

src/app/services/chat.service.ts

@@ -37,10 +37,9 @@ export class ChatService {
       );
   }
 
-  public GetMessages(channelID: number): Observable<Message> {
+  public GetMessages(channelID: number, from: Date, limit: number = 10): Observable<Message[]> {
-    let url = `${environment.apiBase}/chat/messages/${channelID}`;
+    let url = `${environment.apiBase}/chat/messages/${channelID}?limit=${limit}&from=${from.toISOString()}`;
-    let messages: Observable<Message[]> =
+    return this.http.get<GetMessagesResponse>(url, { withCredentials: true })
-      this.http.get<GetMessagesResponse>(url, { withCredentials: true })
       .pipe(
         map(response => {
           if (response.error) {
@@ -53,20 +52,37 @@ export class ChatService {
 
           throw new Error("bad API response, missing messages with no error");
         }),
+        // HttpClient doesn't parse Date objects by default
+        map(msgs => {
+          return msgs.map(msg => {
+            if (typeof msg.time == 'string')
+              msg.time = new Date(msg.time);
+
+            return msg;
+          })
+        }),
         catchError(error => throwError(() => new Error(error.error.message)))
       );
+  }
 
-    url = `${environment.apiBase}/chat/subscribe/${channelID}`;
+  public GetMessageStream(channelID: number, historyLimit: number = 10): Observable<Message> {
+    let messages: Observable<Message[]> = this.GetMessages(channelID, new Date(), historyLimit);
+
+    let url = `${environment.apiBase}/chat/subscribe/${channelID}`;
     let socket = webSocket<Message>(url);
 
     return merge(
-      messages.pipe(mergeMap(msgArray => from(msgArray))),
+      messages
-      socket.asObservable())
+        .pipe(mergeMap(msgArray => from(msgArray))),
+      socket.asObservable()
         .pipe(map(msg => {
           // HttpClient doesn't parse Date objects by default
+          if (typeof msg.time == 'string')
             msg.time = new Date(msg.time);
+
           return msg;
-      }));
+        }))
+    );
   }
 
   public SendMessage(channel: number, content: string): Observable<SendMessageResponse> {