Fastify amplitude decorator (#61)

* Amplitude fastify decorator

* doc changes

README.md

@@ -155,7 +155,7 @@ To add this plugin to your Fastify instance, register it with the following conf
 * `apiUsageTracking` (optional): You can use this callback to generate an event that will automatically be sent for tracking API usage. Non-specification of this feature will lead to disabling of API tracking.
 * `plugins` (optional): This feature allows you to expand the plugin's functionality, from altering event properties to relaying to third-party APIs. To learn more, visit [this link](https://www.docs.developers.amplitude.com/data/sdks/typescript-node/#plugins).
 
-While `apiUsageTracking` can be configured for automatic tracking of API usage, the `amplitudeTrack` method allows you to send events to Amplitude whenever necessary.
+The plugin decorates your Fastify instance with a `Amplitude`, which you can inject and use the `track` method on it to send events whenever you need
 
 > 📘 To ensure optimal functionality with this plugin, you may need to incorporate Amplitude types into your development dependencies.
 > ```

lib/index.ts

@@ -31,7 +31,7 @@ export type { PublicHealthcheckPluginOptions, HealthCheck } from './plugins/publ
 
 export {
   amplitudePlugin,
-  amplitudeTrack,
+  Amplitude,
   type AmplitudeConfig,
   type CreateApiTrackingEventFn,
 } from './plugins/amplitudePlugin'

lib/plugins/amplitudePlugin.spec.ts

@@ -3,7 +3,7 @@ import type { BaseEvent, EnrichmentPlugin, Result, Event } from '@amplitude/anal
 import type { FastifyInstance } from 'fastify'
 import fastify from 'fastify'
 
-import { amplitudePlugin, amplitudeTrack } from './amplitudePlugin'
+import { amplitudePlugin } from './amplitudePlugin'
 
 describe('amplitudePlugin', () => {
   let app: FastifyInstance
@@ -57,7 +57,7 @@ describe('amplitudePlugin', () => {
     })
 
     // When
-    const result = await amplitudeTrack({ event_type: 'event not tracked' }).promise
+    const result = await app.amplitude.track({ event_type: 'event not tracked' }).promise
 
     // Then
     expect(result).toBeNull()
@@ -81,7 +81,7 @@ describe('amplitudePlugin', () => {
 
     // When
     const event: BaseEvent = { event_type: 'event tracked' }
-    const response = await amplitudeTrack(event).promise
+    const response = await app.amplitude.track(event).promise
 
     // Then
     expect(response).toBe(trackResponse)

lib/plugins/amplitudePlugin.ts

@@ -14,14 +14,19 @@ import type {
 } from 'fastify'
 import fp from 'fastify-plugin'
 
-let pluginConfig: AmplitudeConfig | null = null
+declare module 'fastify' {
+  interface FastifyInstance {
+    amplitude: Amplitude
+  }
+}
 
 async function plugin(
   fastify: FastifyInstance,
   config: AmplitudeConfig,
   next: (err?: Error) => void,
 ) {
-  pluginConfig = config
+  const amplitudeInstance = new Amplitude(config.isEnabled)
+  fastify.decorate('amplitude', amplitudeInstance)
 
   if (!config.isEnabled) {
     return next()
@@ -34,7 +39,7 @@ async function plugin(
   await init(config.apiKey, config.options).promise
 
   if (config.apiUsageTracking) {
-    enableApiUsageTracking(fastify, config.apiUsageTracking)
+    enableApiUsageTracking(fastify, amplitudeInstance, config.apiUsageTracking)
   }
   if (config.plugins) {
     // @ts-expect-error
@@ -46,14 +51,15 @@ async function plugin(
 
 function enableApiUsageTracking(
   fastify: FastifyInstance,
+  amplitude: Amplitude,
   eventCreationFn: CreateApiTrackingEventFn,
 ) {
   fastify.addHook(
     'onResponse',
     (req: FastifyRequest, res: FastifyReply, done: HookHandlerDoneFunction) => {
       const event = eventCreationFn(req, res)
       if (event) {
-        amplitudeTrack(event)
+        amplitude.track(event)
       }
       return done()
     },
@@ -114,12 +120,21 @@ export const amplitudePlugin = fp<AmplitudeConfig>(plugin, {
   name: 'amplitude-plugin',
 })
 
-/**
- * Sends the given event to Amplitude
- *
- * @param event Event to send to amplitude. Please check
- * [this](https://amplitude.github.io/Amplitude-TypeScript/interfaces/_amplitude_analytics_node.Types.BaseEvent.html)
- * to get more info about the BaseEvent type
- */
-export const amplitudeTrack = (event: BaseEvent): AmplitudeReturn<Result | null> =>
-  pluginConfig?.isEnabled ? track(event) : { promise: Promise.resolve(null) }
+export class Amplitude {
+  private readonly isEnabled: boolean
+
+  constructor(isEnabled: boolean) {
+    this.isEnabled = isEnabled
+  }
+
+  /**
+   * Sends the given event to Amplitude
+   *
+   * @param event Event to send to amplitude. Please check
+   * [this](https://amplitude.github.io/Amplitude-TypeScript/interfaces/_amplitude_analytics_node.Types.BaseEvent.html)
+   * to get more info about the BaseEvent type
+   */
+  public track(event: BaseEvent): AmplitudeReturn<Result | null> {
+    return this.isEnabled ? track(event) : { promise: Promise.resolve(null) }
+  }
+}