chore(exporter): rework exporter to fix wrong histogram usage and cache metric data

internal/exporter/exporter.go

@@ -0,0 +1,61 @@
+package exporter
+
+import (
+	"net/http"
+
+	"git.ar21.de/yolokube/country-geo-locations/internal/cache"
+	"git.ar21.de/yolokube/country-geo-locations/internal/cmd"
+	"git.ar21.de/yolokube/country-geo-locations/internal/database"
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+)
+
+type Exporter struct {
+	config   *cmd.AppSettings
+	cache    *cache.Cache
+	database *database.Database
+	metrics  *Metrics
+}
+
+func NewExporter(config *cmd.AppSettings, c *cache.Cache, db *database.Database) *Exporter {
+	exporter := &Exporter{
+		config:   config,
+		cache:    c,
+		database: db,
+	}
+
+	exporter.metrics = NewMetrics(exporter)
+	return exporter
+}
+
+func (e *Exporter) Collect() {
+	e.metrics.collectCacheTTLMetric()
+	e.metrics.collectCurrentlyCachedMetric()
+	e.metrics.collectDatabaseReadyMetric()
+	e.metrics.collectDatabaseTimestampMetric()
+}
+
+func (e *Exporter) Middleware() func(next http.Handler) http.Handler {
+	return Middleware{
+		metrics: e.metrics,
+	}.handler
+}
+
+func (e *Exporter) Start() error {
+	prometheus.MustRegister(
+		e.metrics.metricCacheTTL,
+		e.metrics.metricCurrentlyCached,
+		e.metrics.metricDatabaseTimestamp,
+		e.metrics.metricDatabaseReady,
+		e.metrics.metricRequestsTotal,
+		e.metrics.metricRequestLatency,
+	)
+
+	server := &http.Server{
+		Addr:              e.config.ExporterAddress,
+		Handler:           promhttp.Handler(),
+		ReadHeaderTimeout: e.config.ReadHeaderTimeout,
+	}
+
+	return server.ListenAndServe()
+}