# metric-names

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## Purpose

Exports the stable constant objects `METRIC_NAMES` and `ATTRIBUTE_KEYS` that define every OTel metric name and span attribute key used across `@suaveplan/events-metrics`. Centralising these names prevents typos, enables IDE completion, and makes it easy to audit the full observability surface of the package.

These constants are the single source of truth consumed by both the instrumentation code and the tests that assert metric names are correct.

## Features

- `METRIC_NAMES` — all five OTel metric names: dispatch total, listener error total, dispatch latency histogram, queue depth gauge, active subscribers gauge
- `ATTRIBUTE_KEYS` — all four OTel attribute keys: event name, event category, listener ID, bus ID
- Both objects use `as const` for full literal-type narrowing

## Usage: Basic Example

```ts
import { METRIC_NAMES, ATTRIBUTE_KEYS } from "@suaveplan/events-metrics";

console.log(METRIC_NAMES.DISPATCH_TOTAL);   // "suaveplan.events.dispatch.total"
console.log(ATTRIBUTE_KEYS.EVENT_NAME);      // "event.name"
```

## Usage: Advanced Example

```ts
import { METRIC_NAMES, ATTRIBUTE_KEYS } from "@suaveplan/events-metrics";
import { metrics } from "@opentelemetry/api";

const meter = metrics.getMeter("my-app");
const counter = meter.createCounter(METRIC_NAMES.DISPATCH_TOTAL);
counter.add(1, { [ATTRIBUTE_KEYS.EVENT_NAME]: "user.created" });
```

## API Reference

### `METRIC_NAMES`

| Key | Value |
|---|---|
| `DISPATCH_TOTAL` | `"suaveplan.events.dispatch.total"` |
| `LISTENER_ERROR_TOTAL` | `"suaveplan.events.listener.error.total"` |
| `DISPATCH_LATENCY_MS` | `"suaveplan.events.dispatch.latency_ms"` |
| `QUEUE_DEPTH` | `"suaveplan.events.queue.depth"` |
| `ACTIVE_SUBSCRIBERS` | `"suaveplan.events.subscribers.active"` |

### `ATTRIBUTE_KEYS`

| Key | Value |
|---|---|
| `EVENT_NAME` | `"event.name"` |
| `EVENT_CATEGORY` | `"event.category"` |
| `LISTENER_ID` | `"listener.id"` |
| `BUS_ID` | `"bus.id"` |

## Implementation Notes

The constants are defined in `src/constants/index.ts` and re-exported from this module to follow the package structure convention. Consumers should import from `@suaveplan/events-metrics` (the root barrel) rather than the internal path to benefit from tree-shaking and future path changes.