Display active tracks in OTel metrics (#1085)

* Add track, feed and transceiver spans under call span

src/otel/OTelCallAbstractMediaStreamSpan.ts

@@ -0,0 +1,62 @@
+import opentelemetry, { Span } from "@opentelemetry/api";
+import { TrackStats } from "matrix-js-sdk/src/webrtc/stats/statsReport";
+
+import { ElementCallOpenTelemetry } from "./otel";
+import { OTelCallMediaStreamTrackSpan } from "./OTelCallMediaStreamTrackSpan";
+
+type TrackId = string;
+
+export abstract class OTelCallAbstractMediaStreamSpan {
+  protected readonly trackSpans = new Map<
+    TrackId,
+    OTelCallMediaStreamTrackSpan
+  >();
+  public readonly span;
+
+  public constructor(
+    readonly oTel: ElementCallOpenTelemetry,
+    readonly callSpan: Span,
+    protected readonly type: string
+  ) {
+    const ctx = opentelemetry.trace.setSpan(
+      opentelemetry.context.active(),
+      callSpan
+    );
+    const options = {
+      links: [
+        {
+          context: callSpan.spanContext(),
+        },
+      ],
+    };
+    this.span = oTel.tracer.startSpan(this.type, options, ctx);
+  }
+
+  protected upsertTrackSpans(tracks: TrackStats[]) {
+    let prvTracks: TrackId[] = [...this.trackSpans.keys()];
+    tracks.forEach((t) => {
+      if (!this.trackSpans.has(t.id)) {
+        this.trackSpans.set(
+          t.id,
+          new OTelCallMediaStreamTrackSpan(this.oTel, this.span, t)
+        );
+      }
+      this.trackSpans.get(t.id)?.update(t);
+      prvTracks = prvTracks.filter((prvTrackId) => prvTrackId !== t.id);
+    });
+
+    prvTracks.forEach((prvTrackId) => {
+      this.trackSpans.get(prvTrackId)?.end();
+      this.trackSpans.delete(prvTrackId);
+    });
+  }
+
+  public abstract update(data: Object): void;
+
+  public end(): void {
+    this.trackSpans.forEach((tSpan) => {
+      tSpan.end();
+    });
+    this.span.end();
+  }
+}