package imgcache

import (
	"testing"

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

// counterValues holds the values of the counters in counters.go.
type counterValues struct {
	hitCount           int64
	missCount          int64
	upstreamFetchCount int64
	upstreamFetchBytes int64
	transformCount     int64
}

// readCounters reads the counters in counters.go. They count for the whole
// process, and every test that serves an image adds to them, so a test that
// checks how much they rose does not call t.Parallel. Go runs the tests that
// do not call it one at a time, and the tests that do only after them.
func readCounters() counterValues {
	return counterValues{
		hitCount:           int64(testutil.ToFloat64(cacheHits)),
		missCount:          int64(testutil.ToFloat64(cacheMisses)),
		upstreamFetchCount: int64(testutil.ToFloat64(upstreamFetches)),
		upstreamFetchBytes: int64(testutil.ToFloat64(upstreamFetchBytes)),
		transformCount:     int64(testutil.ToFloat64(transforms)),
	}
}

// minus returns how much each counter rose from before to v.
func (v counterValues) minus(before counterValues) counterValues {
	return counterValues{
		hitCount:           v.hitCount - before.hitCount,
		missCount:          v.missCount - before.missCount,
		upstreamFetchCount: v.upstreamFetchCount - before.upstreamFetchCount,
		upstreamFetchBytes: v.upstreamFetchBytes - before.upstreamFetchBytes,
		transformCount:     v.transformCount - before.transformCount,
	}
}

// TestCounters_AreOnTheRegistryMetricsServes checks that the counters in
// counters.go are on Prometheus' default registry, which /metrics serves,
// under the names README.md gives them.
func TestCounters_AreOnTheRegistryMetricsServes(t *testing.T) {
	t.Parallel()

	names := []string{
		"pixa_cache_hits_total",
		"pixa_cache_misses_total",
		"pixa_upstream_fetches_total",
		"pixa_upstream_fetch_bytes_total",
		"pixa_transforms_total",
	}

	count, err := testutil.GatherAndCount(prometheus.DefaultGatherer, names...)
	if err != nil {
		t.Fatalf("testutil.GatherAndCount() error = %v", err)
	}

	if count != len(names) {
		t.Errorf("%d of the counters %v are on the default registry, want %d",
			count, names, len(names))
	}
}