package imgcache

import (
	"errors"
	"testing"

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

// counterValues holds the values of a cache's counters.
type counterValues struct {
	hitCount           int64
	missCount          int64
	upstreamFetchCount int64
	upstreamFetchBytes int64
	transformCount     int64
}

// readCounters reads cache's counters.
func readCounters(cache *Cache) counterValues {
	return counterValues{
		hitCount:           int64(testutil.ToFloat64(cache.cacheHits)),
		missCount:          int64(testutil.ToFloat64(cache.cacheMisses)),
		upstreamFetchCount: int64(testutil.ToFloat64(cache.upstreamFetches)),
		upstreamFetchBytes: int64(testutil.ToFloat64(cache.upstreamFetchBytes)),
		transformCount:     int64(testutil.ToFloat64(cache.transforms)),
	}
}

// TestNewCache_RegistersItsCountersOnItsRegistry checks that NewCache
// registers the cache's counters on the registry it is given, under the
// names README.md gives them.
func TestNewCache_RegistersItsCountersOnItsRegistry(t *testing.T) {
	t.Parallel()

	registry := prometheus.NewRegistry()

	_, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()}, registry)
	if err != nil {
		t.Fatalf("NewCache() error = %v", err)
	}

	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(registry, 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 registry, want %d",
			count, names, len(names))
	}
}

// TestNewCache_FailsWhenItsCountersCannotBeRegistered makes a second cache
// on the registry of a first. Its counters have the same names, so the
// registry refuses them, and NewCache must return that error.
func TestNewCache_FailsWhenItsCountersCannotBeRegistered(t *testing.T) {
	t.Parallel()

	registry := prometheus.NewRegistry()

	_, err := NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()}, registry)
	if err != nil {
		t.Fatalf("NewCache() of the first cache error = %v", err)
	}

	_, err = NewCache(evictionTestDB(t), CacheConfig{StateDir: t.TempDir()}, registry)
	t.Logf("NewCache() of the second cache error = %v", err)

	var alreadyRegistered prometheus.AlreadyRegisteredError
	if !errors.As(err, &alreadyRegistered) {
		t.Errorf("NewCache() of the second cache error = %v, want %T",
			err, alreadyRegistered)
	}
}