add documentation to readme and sample ExampleCollector.php

src/ExampleCollector.php

@@ -0,0 +1,60 @@
+<?php
+
+namespace Superbalist\LaravelPrometheusExporter;
+
+use Prometheus\Gauge;
+
+class ExampleCollector implements CollectorInterface
+{
+    /**
+     * @var Gauge
+     */
+    protected $usersRegisteredGauge;
+
+    /**
+     * Return the name of the collector.
+     *
+     * @return string
+     */
+    public function getName()
+    {
+        return 'users';
+    }
+
+    /**
+     * Register all metrics associated with the collector.
+     *
+     * The metrics needs to be registered on the exporter object.
+     * eg:
+     * ```php
+     * $exporter->registerCounter('search_requests_total', 'The total number of search requests.');
+     * ```
+     *
+     * @param PrometheusExporter $exporter
+     */
+    public function registerMetrics(PrometheusExporter $exporter)
+    {
+        $this->usersRegisteredGauge = $exporter->registerGauge(
+            'users_registered_total',
+            'The total number of registered users.',
+            ['group']
+        );
+    }
+
+    /**
+     * Collect metrics data, if need be, before exporting.
+     *
+     * As an example, this may be used to perform time consuming database queries and set the value of a counter
+     * or gauge.
+     */
+    public function collect()
+    {
+        // retrieve the total number of staff users registered
+        // eg: $totalUsers = Users::where('group', 'staff')->count();
+        $this->usersRegisteredGauge->set(36, ['staff']);
+
+        // retrieve the total number of regular users registered
+        // eg: $totalUsers = Users::where('group', 'regular')->count();
+        $this->usersRegisteredGauge->set(192, ['regular']);
+    }
+}