package imgcache

import (
	"fmt"

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

// registerCounters makes the cache's counters and registers them on
// metricsRegistry. The counters are kept in memory, so adding to one waits
// for nothing and makes no database call. It fails when metricsRegistry
// already holds counters of the same names.
func (c *Cache) registerCounters(metricsRegistry prometheus.Registerer) error {
	c.cacheHits = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_hits_total",
		Help: "Image requests served from the cache.",
	})
	c.cacheMisses = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_cache_misses_total",
		Help: "Image requests not served from the cache.",
	})
	c.upstreamFetches = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_upstream_fetches_total",
		Help: "Fetches of a source image from upstream that read any bytes.",
	})
	c.upstreamFetchBytes = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_upstream_fetch_bytes_total",
		Help: "Bytes read from upstream by fetches of source images.",
	})
	c.transforms = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "pixa_transforms_total",
		Help: "Images the image processor transformed.",
	})

	for _, counter := range []prometheus.Counter{
		c.cacheHits, c.cacheMisses, c.upstreamFetches, c.upstreamFetchBytes, c.transforms,
	} {
		err := metricsRegistry.Register(counter)
		if err != nil {
			return fmt.Errorf("failed to register the cache's counters: %w", err)
		}
	}

	return nil
}