package metrics

import (
	"github.com/prometheus/client_golang/prometheus"

	healthDomain "proxy-pool/internal/domain/health"
)

// DrainCollector exposes only fixed Controller Drain reasons. It never uses
// proxy, Upstream, Worker, session, routing or endpoint values as labels.
type DrainCollector struct {
	candidates *prometheus.CounterVec
	started    *prometheus.CounterVec
}

var _ healthDomain.DrainMetricsObserver = (*DrainCollector)(nil)

func NewDrainCollector(registerer prometheus.Registerer) (*DrainCollector, error) {
	if registerer == nil {
		return nil, ErrInvalidDependencies
	}
	candidates, err := registerCounterVec(registerer, prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: "proxy_pool", Subsystem: "controller", Name: "drain_candidates_total",
		Help: "Number of bounded Controller Drain candidates selected by reason.",
	}, []string{"reason"}))
	if err != nil {
		return nil, err
	}
	started, err := registerCounterVec(registerer, prometheus.NewCounterVec(prometheus.CounterOpts{
		Namespace: "proxy_pool", Subsystem: "controller", Name: "drains_started_total",
		Help: "Number of Controller Drain tickets started by reason.",
	}, []string{"reason"}))
	if err != nil {
		return nil, err
	}
	return &DrainCollector{candidates: candidates, started: started}, nil
}

func (collector *DrainCollector) ObserveDrain(reason healthDomain.DrainReason, candidates, started int) {
	if collector == nil || !validDrainReason(reason) || candidates < 0 || started < 0 || started > candidates {
		return
	}
	if candidates > 0 && collector.candidates != nil {
		collector.candidates.WithLabelValues(string(reason)).Add(float64(candidates))
	}
	if started > 0 && collector.started != nil {
		collector.started.WithLabelValues(string(reason)).Add(float64(started))
	}
}

func validDrainReason(reason healthDomain.DrainReason) bool {
	switch reason {
	case healthDomain.DrainReasonUnhealthy, healthDomain.DrainReasonUpstreamDisabled:
		return true
	default:
		return false
	}
}