observe-server/common/prometheus/gauge.go

package prometheus

import (
	"context"
	"fmt"
	"strings"
	"sync"
	"time"

	"github.com/prometheus/common/model"
)

type Gauge struct {
	wg            *sync.WaitGroup
	name          string
	labels        map[string]string
	rangeSelector string
	baseTime      time.Time
	minutes       int64
}

func NewGauge(wg *sync.WaitGroup, name string, labels map[string]string, ts time.Time, mins int64) Gauge {
	rangeSelector := fmt.Sprintf("%dm", mins)
	return Gauge{
		wg:            wg,
		name:          name,
		labels:        labels,
		rangeSelector: rangeSelector,
		baseTime:      ts,
		minutes:       mins,
	}
}

func (g Gauge) makeMetricNameLabels(name string) string {
	labelList := make([]string, 0, len(g.labels))
	for key, val := range g.labels {
		labelList = append(labelList, fmt.Sprintf("%s='%s'", key, val))
	}
	return fmt.Sprintf("%s{%s}", name, strings.Join(labelList, ","))
}

func (g Gauge) Max(res *float64) error {
	defer g.wg.Done()
	nameLabels := g.makeMetricNameLabels(g.name)
	query := fmt.Sprintf("max(max_over_time(%s[%s]))", nameLabels, g.rangeSelector)
	result, _, err := PromeApi().Query(context.Background(), query, g.baseTime)
	if err != nil {
		return err
	}
	for _, sample := range result.(model.Vector) {
		*res = float64(sample.Value)
	}
	return nil
}