package jmetrics // import "drjosh.dev/jmetrics"

import (
	"math"
	"sync"

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

type LiteGaugeSummary struct {
	mu    sync.Mutex
	min   float64
	max   float64
	sum   float64
	count int

	desc *prometheus.Desc
}

type LiteGaugeSummaryOpts struct {
	// As for usual Prometheus metrics
	Namespace, Subsystem, Name, Help string

	// As for usual Prometheus metrics
	ConstLabels prometheus.Labels
}

func NewLiteGaugeSummary(opts LiteGaugeSummaryOpts) *LiteGaugeSummary {
	varName := prometheus.BuildFQName(opts.Namespace, opts.Subsystem, opts.Name)
	s := &LiteGaugeSummary{
		min:  math.Inf(1),
		max:  math.Inf(-1),
		desc: prometheus.NewDesc(varName, opts.Help, []string{"stat"}, opts.ConstLabels),
	}
	return s
}

func (s *LiteGaugeSummary) Describe(ch chan<- *prometheus.Desc) { ch <- s.desc }

func (s *LiteGaugeSummary) Collect(ch chan<- prometheus.Metric) {
	s.mu.Lock()
	defer s.mu.Unlock()
	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, s.min, "min")
	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, s.max, "max")
	mean := s.sum
	if s.count > 0 {
		mean /= float64(s.count)
	}
	ch <- prometheus.MustNewConstMetric(s.desc, prometheus.GaugeValue, mean, "mean")
	s.min = math.Inf(1)
	s.max = math.Inf(-1)
	s.sum, s.count = 0, 0
}

func (s *LiteGaugeSummary) Observe(x float64) {
	s.mu.Lock()
	defer s.mu.Unlock()
	s.min = min(s.min, x)
	s.max = max(s.max, x)
	s.sum += x
	s.count++
}