feat(api): metrics for Spotify API http requests

This will help evaluate how much we are being rate limited, and on what
routes it happens most.

src/sources/spotify/spotify-api/metrics.axios-interceptor.ts

@@ -0,0 +1,84 @@
+import {
+  AxiosFulfilledInterceptor,
+  AxiosInterceptor,
+  AxiosResponseCustomConfig,
+} from "@narando/nest-axios-interceptor";
+import { HttpService } from "@nestjs/axios";
+import { Injectable, Logger } from "@nestjs/common";
+import { Counter, Histogram } from "@opentelemetry/api-metrics";
+import type { AxiosRequestConfig } from "axios";
+import { MetricService } from "nestjs-otel";
+import { UrlValueParserService } from "../../../open-telemetry/url-value-parser.service";
+
+const SPOTIFY_API_METRICS_CONFIG_KEY = Symbol("kSpotifyApiMetricsInterceptor");
+
+// Merging our custom properties with the base config
+interface SpotifyApiMetricsConfig extends AxiosRequestConfig {
+  [SPOTIFY_API_METRICS_CONFIG_KEY]: {
+    startTime: number;
+  };
+}
+
+@Injectable()
+export class MetricsInterceptor extends AxiosInterceptor<SpotifyApiMetricsConfig> {
+  private readonly logger = new Logger(this.constructor.name);
+  responseCounter: Counter;
+  requestHistogram: Histogram;
+
+  constructor(
+    httpService: HttpService,
+    metricService: MetricService,
+    private readonly urlValueParserService: UrlValueParserService
+  ) {
+    super(httpService);
+
+    this.responseCounter = metricService.getCounter(
+      "listory_spotify_api_http_response",
+      { description: "Total number of HTTP responses from Spotify API" }
+    );
+
+    this.requestHistogram = metricService.getHistogram(
+      "listory_spotify_api_http_request_duration_seconds",
+      {
+        description:
+          "HTTP latency value recorder in seconds for requests made to Spotify API",
+        boundaries: [0.025, 0.05, 0.1, 0.25, 0.5, 1, 2.5, 5, 10],
+      }
+    );
+  }
+
+  protected requestFulfilled(): AxiosFulfilledInterceptor<SpotifyApiMetricsConfig> {
+    return (config) => {
+      config[SPOTIFY_API_METRICS_CONFIG_KEY] = {
+        startTime: new Date().getTime(),
+      };
+
+      return config;
+    };
+  }
+
+  responseFulfilled(): AxiosFulfilledInterceptor<
+    AxiosResponseCustomConfig<SpotifyApiMetricsConfig>
+  > {
+    return (response) => {
+      const startTime =
+        response.config[SPOTIFY_API_METRICS_CONFIG_KEY].startTime;
+      const endTime = new Date().getTime();
+      const responseTimeSeconds = (endTime - startTime) / 1000;
+
+      const metricLabels = {
+        method: response.config.method.toUpperCase(),
+        status: response.status.toString(),
+        path: this.urlValueParserService.replacePathValues(
+          response.config.url,
+          "<id>"
+        ),
+      };
+
+      this.requestHistogram.record(responseTimeSeconds, metricLabels);
+      this.responseCounter.add(1, metricLabels);
+
+      return response;
+    };
+  }
+}

src/sources/spotify/spotify-api/spotify-api.module.ts

@@ -1,6 +1,7 @@
 import { HttpModule } from "@nestjs/axios";
 import { Module } from "@nestjs/common";
 import { ConfigService } from "@nestjs/config";
+import { MetricsInterceptor } from "./metrics.axios-interceptor";
 import { SpotifyApiService } from "./spotify-api.service";
 
 @Module({
@@ -13,7 +14,7 @@ import { SpotifyApiService } from "./spotify-api.service";
       inject: [ConfigService],
     }),
   ],
-  providers: [SpotifyApiService],
+  providers: [SpotifyApiService, MetricsInterceptor],
   exports: [SpotifyApiService],
 })
 export class SpotifyApiModule {}