feat: fake impact metrics with histograms

src/test/fixtures/fake-impact-metrics.ts

@@ -1,34 +1,68 @@
-export const fakeImpactMetricsResolver = () => ({
-    counters: new Map<string, { value: number; help: string }>(),
-    gauges: new Map<string, { value: number; help: string }>(),
+import type { IImpactMetricsResolver } from '../../lib/types/index.js';
 
-    defineCounter(name: string, help: string) {
-        this.counters.set(name, { value: 0, help });
-    },
+export const fakeImpactMetricsResolver = () => {
+    const counters = new Map<string, { value: number; help: string }>();
+    const gauges = new Map<string, { value: number; help: string }>();
+    const histograms = new Map<
+        string,
+        { count: number; sum: number; help: string; buckets: number[] }
+    >();
 
-    defineGauge(name: string, help: string) {
-        this.gauges.set(name, { value: 0, help });
-    },
+    const resolver: IImpactMetricsResolver = {
+        defineCounter(name: string, help: string) {
+            counters.set(name, { value: 0, help });
+        },
 
-    incrementCounter(name: string, value: number = 1) {
-        const counter = this.counters.get(name);
+        defineGauge(name: string, help: string) {
+            gauges.set(name, { value: 0, help });
+        },
 
-        if (!counter) {
-            return;
-        }
+        defineHistogram(name: string, help: string, buckets?: number[]) {
+            const defaultBuckets = buckets || [
+                0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10,
+            ];
+            histograms.set(name, {
+                count: 0,
+                sum: 0,
+                help,
+                buckets: defaultBuckets,
+            });
+        },
 
-        counter.value += value;
-        this.counters.set(name, counter);
-    },
+        incrementCounter(name: string, value: number = 1) {
+            const counter = counters.get(name);
 
-    updateGauge(name: string, value: number) {
-        const gauge = this.gauges.get(name);
+            if (!counter) {
+                return;
+            }
 
-        if (!gauge) {
-            return;
-        }
+            counter.value += value;
+            counters.set(name, counter);
+        },
 
-        gauge.value = value;
-        this.gauges.set(name, gauge);
-    },
-});
+        updateGauge(name: string, value: number) {
+            const gauge = gauges.get(name);
+
+            if (!gauge) {
+                return;
+            }
+
+            gauge.value = value;
+            gauges.set(name, gauge);
+        },
+
+        observeHistogram(name: string, value: number) {
+            const histogram = histograms.get(name);
+
+            if (!histogram) {
+                return;
+            }
+
+            histogram.count++;
+            histogram.sum += value;
+            histograms.set(name, histogram);
+        },
+    };
+
+    return { ...resolver, counters, gauges, histograms };
+};