// Licensed to the LF AI & Data foundation under one
// or more contributor license agreements. See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership. The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License. You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package cache

import (
	"github.com/prometheus/client_golang/prometheus"
)

// WIP: this function is a showcase of how to use prometheus, do not use it in production.
func PrometheusCacheMonitor[K comparable, V any](c Cache[K, V], namespace, subsystem string) {
	hitRate := prometheus.NewGaugeFunc(
		prometheus.GaugeOpts{
			Namespace: namespace,
			Subsystem: subsystem,
			Name:      "cache_hitrate",
			Help:      "hit rate equals hitcount / (hitcount + misscount)",
		},
		func() float64 {
			hit := float64(c.Stats().HitCount.Load())
			miss := float64(c.Stats().MissCount.Load())
			return hit / (hit + miss)
		})
	// TODO: adding more metrics.
	prometheus.MustRegister(hitRate)
}
