From 21fa8d0a3c4b90a0ca2b69a9c2c41d8c51f58429 Mon Sep 17 00:00:00 2001
From: "Jonathan D. Rhyne" <jonathan@pspdfkit.com>
Date: Mon, 26 Jan 2026 20:28:21 -0500
Subject: [PATCH] feat(report): add latency percentiles

Include p50/p95/min/max latency metrics in benchmark reports and clarify notes.
---
 src/commands/report.ts | 41 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 39 insertions(+), 2 deletions(-)

diff --git a/src/commands/report.ts b/src/commands/report.ts
index f206877..6b2a942 100644
--- a/src/commands/report.ts
+++ b/src/commands/report.ts
@@ -17,6 +17,7 @@ type BenchmarkResults = {
   }>;
   summary?: {
     avgLatencyMs?: number;
+    errorCount?: number;
   };
   warnings?: string[];
 };
@@ -71,6 +72,20 @@ const ensureOutputPath = async (filePath: string): Promise<void> => {
 const isFiniteNumber = (value: unknown): value is number =>
   typeof value === "number" && Number.isFinite(value);
 
+const percentile = (values: number[], p: number): number | undefined => {
+  if (values.length === 0) {
+    return undefined;
+  }
+  const sorted = [...values].sort((a, b) => a - b);
+  const index = (sorted.length - 1) * p;
+  const lower = Math.floor(index);
+  const upper = Math.ceil(index);
+  if (lower === upper) {
+    return sorted[lower];
+  }
+  return sorted[lower] + (sorted[upper] - sorted[lower]) * (index - lower);
+};
+
 export const registerReportCommand = (program: Command) => {
   program
     .command("report")
@@ -111,8 +126,25 @@ export const registerReportCommand = (program: Command) => {
             : isFiniteNumber(parsed.summary?.avgLatencyMs)
               ? parsed.summary?.avgLatencyMs
               : undefined;
+        const p50Latency = percentile(latencies, 0.5);
+        const p95Latency = percentile(latencies, 0.95);
+        const minLatency = latencies.length > 0 ? Math.min(...latencies) : undefined;
+        const maxLatency = latencies.length > 0 ? Math.max(...latencies) : undefined;
         const avgLatencyText =
           typeof avgLatency === "number" ? avgLatency.toFixed(2) : "N/A";
+        const p50LatencyText =
+          typeof p50Latency === "number" ? p50Latency.toFixed(2) : "N/A";
+        const p95LatencyText =
+          typeof p95Latency === "number" ? p95Latency.toFixed(2) : "N/A";
+        const minLatencyText =
+          typeof minLatency === "number" ? minLatency.toFixed(2) : "N/A";
+        const maxLatencyText =
+          typeof maxLatency === "number" ? maxLatency.toFixed(2) : "N/A";
+        const errorCount = isFiniteNumber(parsed.summary?.errorCount)
+          ? parsed.summary?.errorCount
+          : undefined;
+        const errorCountText =
+          typeof errorCount === "number" ? String(errorCount) : "N/A";
 
         const status = parsed.status ? parsed.status : "unknown";
         const warnings = Array.isArray(parsed.warnings) ? parsed.warnings : [];
@@ -124,13 +156,18 @@ export const registerReportCommand = (program: Command) => {
           `- Suite: ${suite}`,
           `- Runs: ${runCount}`,
           `- Avg latency (ms): ${avgLatencyText}`,
+          `- p50 latency (ms): ${p50LatencyText}`,
+          `- p95 latency (ms): ${p95LatencyText}`,
+          `- Min latency (ms): ${minLatencyText}`,
+          `- Max latency (ms): ${maxLatencyText}`,
+          `- Errors: ${errorCountText}`,
           "",
           warnings.length > 0 ? "## Warnings" : "",
           ...warnings.map((warning) => `- ${warning}`),
           warnings.length > 0 ? "" : "",
           "## Notes",
-          "- If this report is marked as stub, replace placeholder metrics with real benchmark output.",
-          "- Re-run `dws benchmark --suite <name>` after integrating the DWS API.",
+          "- Generated from a single results file; combine baseline/deterministic reports externally if needed.",
+          "- Re-run `dws benchmark --suite <name>` after environment changes to keep results current.",
           "",
         ].filter((line) => line !== "");