1 files changed, 133 insertions, 0 deletions
diff --git a/u/trace/metrics.ts b/u/trace/metrics.ts
new file mode 100644
index 0000000..a26ee5d
--- /dev/null
+++ b/u/trace/metrics.ts
@@ -0,0 +1,133 @@
+import {
+  isObject,
+  type ITrace,
+  type ITraceWith,
+  type Mapper,
+  type SideEffect,
+} from "@emprespresso/pengueno";
+
+export enum Unit {
+  COUNT,
+  MILLISECONDS,
+}
+
+export interface IMetric {
+  readonly count: IEmittableMetric;
+  readonly time: IEmittableMetric;
+  readonly failure: IMetric;
+  readonly success: IMetric;
+  readonly _isIMetric: true;
+}
+export const isIMetric = (t: unknown): t is IMetric =>
+  isObject(t) && "_isIMetric" in t;
+
+export interface IEmittableMetric {
+  readonly name: string;
+  readonly unit: Unit;
+  withValue: Mapper<number, MetricValue>;
+}
+
+export class EmittableMetric implements IEmittableMetric {
+  constructor(public readonly name: string, public readonly unit: Unit) {
+  }
+
+  public withValue(value: number): MetricValue {
+    return {
+      name: this.name,
+      unit: this.unit,
+      _isMetricValue: true as true,
+      emissionTimestamp: Date.now(),
+      value,
+    };
+  }
+}
+
+export class Metric implements IMetric {
+  constructor(
+    public readonly count: IEmittableMetric,
+    public readonly time: IEmittableMetric,
+    public readonly failure: Metric,
+    public readonly success: Metric,
+    public readonly _isIMetric: true = true,
+  ) {}
+
+  static fromName(name: string): Metric {
+    return new Metric(
+      new EmittableMetric(`${name}.count`, Unit.COUNT),
+      new EmittableMetric(`${name}.elapsed`, Unit.MILLISECONDS),
+      Metric.fromName(`${name}.failure`),
+      Metric.fromName(`${name}.success`),
+    );
+  }
+}
+
+export interface MetricValue {
+  readonly name: string;
+  readonly unit: Unit;
+  readonly value: number;
+  readonly emissionTimestamp: number;
+  readonly _isMetricValue: true;
+}
+export const isMetricValue = (t: unknown): t is MetricValue =>
+  isObject(t) && "_isMetricValue" in t;
+
+export const isMetricsTraceSupplier = (t: unknown): t is MetricsTraceSupplier =>
+  isMetricValue(t) || isIMetric(t);
+
+export type MetricsTraceSupplier = ITraceWith<IMetric | MetricValue>;
+type MetricTracingTuple = [IMetric, Date];
+export class MetricsTrace implements ITrace<MetricsTraceSupplier> {
+  constructor(
+    private readonly metricConsumer: SideEffect<Array<MetricValue>>,
+    private readonly tracing: Array<MetricTracingTuple> = [],
+    private readonly flushed: Set<IMetric> = new Set(),
+  ) {}
+
+  public addTrace(trace: MetricsTraceSupplier) {
+    if (isMetricValue(trace) || typeof trace === "string") return this;
+    return new MetricsTrace(this.metricConsumer)._nowTracing(trace);
+  }
+
+  public trace(metric: MetricsTraceSupplier) {
+    if (typeof metric === "string") return this;
+    if (isMetricValue(metric)) {
+      this.metricConsumer([metric]);
+      return this;
+    }
+
+    const foundMetricValues = this.tracing.flatMap((
+      [tracing, startedTracing],
+    ) =>
+      [tracing, tracing.success, tracing.failure]
+        .filter((_tracing) => metric === _tracing)
+        .flatMap((metric) => [
+          this.addMetric(metric, startedTracing),
+          this.addMetric(tracing, startedTracing),
+        ])
+    ).flatMap((values) => values);
+
+    if (foundMetricValues.length === 0) {
+      return this._nowTracing(metric);
+    }
+
+    this.metricConsumer(foundMetricValues);
+    return this;
+  }
+
+  private addMetric(metric: IMetric, startedTracing: Date): Array<MetricValue> {
+    if (this.flushed.has(metric)) {
+      return [];
+    }
+
+    this.flushed.add(metric);
+    return [
+      metric.count.withValue(1.0),
+      metric.time.withValue(Date.now() - startedTracing.getTime()),
+    ];
+  }
+
+  private _nowTracing(metric: IMetric): MetricsTrace {
+    this.tracing.push([metric, new Date()]);
+    return this;
+  }
+}