feat: add an api to prune messages from the end

src/channel_state.ts

@@ -152,6 +152,15 @@ export class ChannelState {
     );
   }
 
+  pruneOldest(maxMessages: number) {
+    const currentIndex = this.messageSets.findIndex((s) => s.isCurrent);
+    if (this.messageSets[currentIndex].isLatest) {
+      const newMessages = this.messageSets[currentIndex].messages;
+      this.messageSets[currentIndex].messages = newMessages.slice(-maxMessages);
+      this.messageSets[currentIndex].pagination.hasPrev = true;
+    }
+  }
+
   /**
    * addMessageSorted - Add a message to the state
    *
@@ -821,7 +830,7 @@ export class ChannelState {
         messages: [],
         isLatest: true,
         isCurrent: true,
-        pagination: DEFAULT_MESSAGE_SET_PAGINATION,
+        pagination: { ...DEFAULT_MESSAGE_SET_PAGINATION },
       },
     ];
   }
@@ -1017,7 +1026,7 @@ export class ChannelState {
                 messages: [],
                 isCurrent: false,
                 isLatest: false,
-                pagination: DEFAULT_MESSAGE_SET_PAGINATION,
+                pagination: { ...DEFAULT_MESSAGE_SET_PAGINATION },
               });
               targetMessageSetIndex = this.messageSets.length - 1;
             } else {
@@ -1026,7 +1035,7 @@ export class ChannelState {
                 messages: [],
                 isCurrent: false,
                 isLatest,
-                pagination: DEFAULT_MESSAGE_SET_PAGINATION, // fixme: it is problematic decide about pagination without having data
+                pagination: { ...DEFAULT_MESSAGE_SET_PAGINATION }, // fixme: it is problematic decide about pagination without having data
               });
               if (isLatest) {
                 this.messageSets.slice(1).forEach((set) => {

src/constants.ts

@@ -1,10 +1,13 @@
 export const DEFAULT_QUERY_CHANNELS_MESSAGE_LIST_PAGE_SIZE = 25;
 export const DEFAULT_QUERY_CHANNEL_MESSAGE_LIST_PAGE_SIZE = 100;
-export const DEFAULT_MESSAGE_SET_PAGINATION = { hasNext: false, hasPrev: false };
+export const DEFAULT_MESSAGE_SET_PAGINATION = Object.freeze({
+  hasNext: false,
+  hasPrev: false,
+});
 export const DEFAULT_UPLOAD_SIZE_LIMIT_BYTES = 100 * 1024 * 1024; // 100 MB
 export const API_MAX_FILES_ALLOWED_PER_MESSAGE = 10;
 export const MAX_CHANNEL_MEMBER_COUNT_IN_CHANNEL_QUERY = 100;
-export const RESERVED_UPDATED_MESSAGE_FIELDS = {
+export const RESERVED_UPDATED_MESSAGE_FIELDS = Object.freeze({
   // Dates should not be converted back to ISO strings as JS looses precision on them (milliseconds)
   created_at: true,
   deleted_at: true,
@@ -25,7 +28,7 @@ export const RESERVED_UPDATED_MESSAGE_FIELDS = {
   html: true,
   __html: true,
   user: true,
-} as const;
-export const LOCAL_MESSAGE_FIELDS = { error: true } as const;
+});
+export const LOCAL_MESSAGE_FIELDS = Object.freeze({ error: true });
 export const DEFAULT_QUERY_CHANNELS_RETRY_COUNT = 3;
 export const DEFAULT_QUERY_CHANNELS_MS_BETWEEN_RETRIES = 1000; // 1 second

test/unit/channel_state.test.js

@@ -910,6 +910,87 @@ describe('ChannelState addMessagesSorted', function () {
 	});
 });
 
+describe('ChannelState message pruning', () => {
+	let channelState;
+	let initialMessages = [];
+
+	beforeEach(() => {
+		channelState = new ChannelState();
+		initialMessages = Array.from({ length: 10 }, () =>
+			generateMsg({ date: toISOString(100) }),
+		);
+		channelState.addMessagesSorted(initialMessages);
+	});
+
+	it('should prune messages from the end when we are in the latest set', () => {
+		expect(channelState.messageSets.length).to.be.equal(1);
+		expect(channelState.messageSets[0].isLatest).to.be.equal(true);
+		expect(channelState.messageSets[0].isCurrent).to.be.equal(true);
+		expect(channelState.messages.length).to.be.equal(10);
+		expect(channelState.messagePagination.hasPrev).to.be.equal(false);
+
+		const previousHasNext = channelState.messagePagination.hasNext;
+
+		channelState.pruneOldest(5);
+
+		expect(channelState.messageSets.length).to.be.equal(1);
+		expect(channelState.messages.length).to.be.equal(5);
+		expect(channelState.messagePagination.hasPrev).to.be.equal(true);
+		expect(channelState.messagePagination.hasNext).to.be.equal(previousHasNext);
+	});
+
+	it('should do nothing if the current message set is not also the latest', () => {
+		expect(channelState.messageSets.length).to.be.equal(1);
+
+		channelState.messageSets[0].isLatest = false;
+
+		expect(channelState.messages.length).to.be.equal(10);
+		expect(channelState.messagePagination.hasPrev).to.be.equal(false);
+
+		channelState.pruneOldest(5);
+
+		expect(channelState.messages.length).to.be.equal(10);
+		expect(channelState.messagePagination.hasPrev).to.be.equal(false);
+	});
+
+	it('should prune the correct messageSet', () => {
+		channelState.addMessagesSorted(
+			Array.from({ length: 10 }, () => generateMsg({ date: toISOString(50) })),
+			false,
+			true,
+			true,
+			'new',
+		);
+
+		expect(channelState.messageSets.length).to.be.equal(2);
+
+		channelState.pruneOldest(5);
+
+		const currentMessageSet = channelState.messageSets.find((ms) => ms.isCurrent);
+		const otherMessageSet = channelState.messageSets.find((ms) => !ms.isCurrent);
+
+		expect(currentMessageSet.messages.length).to.be.equal(5);
+		expect(currentMessageSet.pagination.hasPrev).to.be.equal(true);
+		expect(channelState.messages).to.be.equal(currentMessageSet.messages);
+
+		expect(otherMessageSet.messages.length).to.be.equal(10);
+		expect(otherMessageSet.pagination.hasPrev).to.be.equal(false);
+	});
+
+	it('should correctly apply pruning', () => {
+		channelState.pruneOldest(5);
+
+		expect(channelState.messages.length).to.be.equal(5);
+		for (const message of initialMessages.slice(-5)) {
+			expect(channelState.messages.some((m) => m.id === message.id)).to.be.equal(true);
+		}
+
+		for (const message of initialMessages.slice(0, 5)) {
+			expect(channelState.messages.some((m) => m.id === message.id)).to.be.equal(false);
+		}
+	});
+});
+
 describe('ChannelState reactions', () => {
 	const message = generateMsg();
 	let state;