Fix new message do not appear sometimes (#185)

Signed-off-by: Ajay Bura <ajbura@gmail.com>

src/app/organisms/room/EventLimit.js

@@ -0,0 +1,39 @@
+class EventLimit {
+  constructor() {
+    this._from = 0;
+
+    this.SMALLEST_EVT_HEIGHT = 32;
+    this.PAGES_COUNT = 4;
+  }
+
+  get maxEvents() {
+    return Math.round(document.body.clientHeight / this.SMALLEST_EVT_HEIGHT) * this.PAGES_COUNT;
+  }
+
+  get from() {
+    return this._from;
+  }
+
+  get end() {
+    return this._from + this.maxEvents;
+  }
+
+  setMaxEvents(maxEvents) {
+    this.maxEvents = maxEvents;
+  }
+
+  setFrom(from) {
+    this._from = from < 0 ? 0 : from;
+  }
+
+  paginate(backwards, limit, timelineLength) {
+    this._from = backwards ? this._from - limit : this._from + limit;
+
+    if (!backwards && this.end > timelineLength) {
+      this._from = timelineLength - this.maxEvents;
+    }
+    if (this._from < 0) this._from = 0;
+  }
+}
+
+export default EventLimit;