// Copyright 2018 The Prometheus Authors
// Licensed 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 testutil

import (
	"bytes"
	"fmt"
	"io"
	"reflect"

	"github.com/prometheus/common/expfmt"

	dto "github.com/prometheus/client_model/go"

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

// CollectAndCompare registers the provided Collector with a newly created
// pedantic Registry. It then does the same as GatherAndCompare, gathering the
// metrics from the pedantic Registry.
func CollectAndCompare(c prometheus.Collector, expected io.Reader, metricNames ...string) error {
	reg := prometheus.NewPedanticRegistry()
	if err := reg.Register(c); err != nil {
		return fmt.Errorf("registering collector failed: %s", err)
	}
	return GatherAndCompare(reg, expected, metricNames...)
}

// GatherAndCompare gathers all metrics from the provided Gatherer and compares
// it to an expected output read from the provided Reader in the Prometheus text
// exposition format. If any metricNames are provided, only metrics with those
// names are compared.
func GatherAndCompare(g prometheus.Gatherer, expected io.Reader, metricNames ...string) error {
	metrics, err := g.Gather()
	if err != nil {
		return fmt.Errorf("gathering metrics failed: %s", err)
	}
	if metricNames != nil {
		metrics = filterMetrics(metrics, metricNames)
	}
	var tp expfmt.TextParser
	expectedMetrics, err := tp.TextToMetricFamilies(expected)
	if err != nil {
		return fmt.Errorf("parsing expected metrics failed: %s", err)
	}

	if !reflect.DeepEqual(metrics, internal.NormalizeMetricFamilies(expectedMetrics)) {
		// Encode the gathered output to the readable text format for comparison.
		var buf1 bytes.Buffer
		enc := expfmt.NewEncoder(&buf1, expfmt.FmtText)
		for _, mf := range metrics {
			if err := enc.Encode(mf); err != nil {
				return fmt.Errorf("encoding result failed: %s", err)
			}
		}
		// Encode normalized expected metrics again to generate them in the same ordering
		// the registry does to spot differences more easily.
		var buf2 bytes.Buffer
		enc = expfmt.NewEncoder(&buf2, expfmt.FmtText)
		for _, mf := range internal.NormalizeMetricFamilies(expectedMetrics) {
			if err := enc.Encode(mf); err != nil {
				return fmt.Errorf("encoding result failed: %s", err)
			}
		}

		return fmt.Errorf(`
metric output does not match expectation; want:

%s

got:

%s
`, buf2.String(), buf1.String())
	}
	return nil
}

func filterMetrics(metrics []*dto.MetricFamily, names []string) []*dto.MetricFamily {
	var filtered []*dto.MetricFamily
	for _, m := range metrics {
		for _, name := range names {
			if m.GetName() == name {
				filtered = append(filtered, m)
				break
			}
		}
	}
	return filtered
}