feat(desktop): show download progress and diagnostics on splash (#3273)

fluxer_desktop/src/main/ModuleDownloadRate.ts

@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: AGPL-3.0-or-later
+
+const RATE_SMOOTHING_WINDOW_MS = 3000;
+const RATE_MIN_SAMPLE_MS = 200;
+
+export class ModuleDownloadRate {
+	private lastBytes: number | null = null;
+	private lastAt = 0;
+	private rate: number | null = null;
+
+	public reset(): void {
+		this.lastBytes = null;
+		this.lastAt = 0;
+		this.rate = null;
+	}
+
+	public sample(bytes: number, at: number): number | null {
+		if (this.lastBytes == null || bytes < this.lastBytes) {
+			this.lastBytes = bytes;
+			this.lastAt = at;
+			this.rate = null;
+			return null;
+		}
+		const elapsed = at - this.lastAt;
+		if (elapsed < RATE_MIN_SAMPLE_MS) {
+			return this.rate;
+		}
+		const instant = ((bytes - this.lastBytes) * 1000) / elapsed;
+		const weight = 1 - Math.exp(-elapsed / RATE_SMOOTHING_WINDOW_MS);
+		this.rate = this.rate == null ? instant : this.rate + (instant - this.rate) * weight;
+		this.lastBytes = bytes;
+		this.lastAt = at;
+		return this.rate;
+	}
+}