// 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"
	"reflect"
	"sort"

	"github.com/prometheus/client_golang/prometheus"
	dto "github.com/prometheus/client_model/go"
	"github.com/prometheus/common/expfmt"
)

// GatherAndCompare retrieves all metrics exposed by a collector and compares it
// to an expected output in the Prometheus text exposition format.
// metricNames allows only comparing the given metrics. All are compared if it's nil.
func GatherAndCompare(c prometheus.Collector, expected string, metricNames ...string) error {
	reg := prometheus.NewPedanticRegistry()
	if err := reg.Register(c); err != nil {
		return fmt.Errorf("registering collector failed: %s", err)
	}
	metrics, err := reg.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(bytes.NewReader([]byte(expected)))
	if err != nil {
		return fmt.Errorf("parsing expected metrics failed: %s", err)
	}

	if !reflect.DeepEqual(metrics, normalizeMetricFamilies(expectedMetrics)) {
		// Encode the gathered output to the readbale 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 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 {
		drop := true
		for _, name := range names {
			if m.GetName() == name {
				drop = false
				break
			}
		}
		if !drop {
			filtered = append(filtered, m)
		}
	}
	return filtered
}

// The below sorting code is copied form the Prometheus client library modulo the added
// label pair sorting.
// https://github.com/prometheus/client_golang/blob/ea6e1db4cb8127eeb0b6954f7320363e5451820f/prometheus/registry.go#L642-L684

// metricSorter is a sortable slice of *dto.Metric.
type metricSorter []*dto.Metric

func (s metricSorter) Len() int {
	return len(s)
}

func (s metricSorter) Swap(i, j int) {
	s[i], s[j] = s[j], s[i]
}

func (s metricSorter) Less(i, j int) bool {
	sort.Sort(prometheus.LabelPairSorter(s[i].Label))
	sort.Sort(prometheus.LabelPairSorter(s[j].Label))

	if len(s[i].Label) != len(s[j].Label) {
		return len(s[i].Label) < len(s[j].Label)
	}

	for n, lp := range s[i].Label {
		vi := lp.GetValue()
		vj := s[j].Label[n].GetValue()
		if vi != vj {
			return vi < vj
		}
	}

	if s[i].TimestampMs == nil {
		return false
	}
	if s[j].TimestampMs == nil {
		return true
	}
	return s[i].GetTimestampMs() < s[j].GetTimestampMs()
}

// normalizeMetricFamilies returns a MetricFamily slice with empty
// MetricFamilies pruned and the remaining MetricFamilies sorted by name within
// the slice, with the contained Metrics sorted within each MetricFamily.
func normalizeMetricFamilies(metricFamiliesByName map[string]*dto.MetricFamily) []*dto.MetricFamily {
	for _, mf := range metricFamiliesByName {
		sort.Sort(metricSorter(mf.Metric))
	}
	names := make([]string, 0, len(metricFamiliesByName))
	for name, mf := range metricFamiliesByName {
		if len(mf.Metric) > 0 {
			names = append(names, name)
		}
	}
	sort.Strings(names)
	result := make([]*dto.MetricFamily, 0, len(names))
	for _, name := range names {
		result = append(result, metricFamiliesByName[name])
	}
	return result
}