package metrics

import (
	"context"
	"errors"
	"net/http"
	"time"

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

type Metrics struct {
	Registry *prometheus.Registry

	CheckRuns        *prometheus.CounterVec
	CheckSkipped     *prometheus.CounterVec
	CheckDuration    *prometheus.HistogramVec
	CheckStatus      *prometheus.GaugeVec
	CheckExitCode    *prometheus.GaugeVec
	CheckLastRun     *prometheus.GaugeVec
	CheckLastSuccess *prometheus.GaugeVec
	CheckInterval    *prometheus.GaugeVec
	ChecksConfigured prometheus.Gauge
	SpoolDepth       prometheus.Gauge
	SpoolBytes       prometheus.Gauge
	SendAttempts     *prometheus.CounterVec
	SendFailures     *prometheus.CounterVec
	EventsAccepted   prometheus.Counter
	EventsDedup      prometheus.Counter
	LastHeartbeat    prometheus.Gauge
	BuildInfo        *prometheus.GaugeVec
}

// StatusCode maps a CheckResultEvent status string to a numeric gauge value.
func StatusCode(status string) float64 {
	switch status {
	case "ok":
		return 0
	case "warning":
		return 1
	case "critical":
		return 2
	default:
		return 3
	}
}

func New() *Metrics {
	reg := prometheus.NewRegistry()
	m := &Metrics{Registry: reg}
	m.CheckRuns = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "monlet_agent_check_runs_total",
		Help: "Number of check runs by id and status.",
	}, []string{"check_id", "status"})
	m.CheckSkipped = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "monlet_agent_check_skipped_total",
		Help: "Number of ticks skipped due to overlap.",
	}, []string{"check_id"})
	m.CheckDuration = prometheus.NewHistogramVec(prometheus.HistogramOpts{
		Name:    "monlet_agent_check_duration_seconds",
		Help:    "Check execution duration.",
		Buckets: prometheus.DefBuckets,
	}, []string{"check_id"})
	m.SpoolDepth = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "monlet_agent_spool_events",
		Help: "Current spool depth in events.",
	})
	m.SpoolBytes = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "monlet_agent_spool_bytes",
		Help: "Current spool size in bytes.",
	})
	m.SendAttempts = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "monlet_agent_send_attempts_total",
		Help: "Outbound send attempts by kind.",
	}, []string{"kind"})
	m.SendFailures = prometheus.NewCounterVec(prometheus.CounterOpts{
		Name: "monlet_agent_send_failures_total",
		Help: "Outbound send failures by kind.",
	}, []string{"kind"})
	m.EventsAccepted = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "monlet_agent_events_accepted_total",
		Help: "Events accepted by the server.",
	})
	m.EventsDedup = prometheus.NewCounter(prometheus.CounterOpts{
		Name: "monlet_agent_events_deduplicated_total",
		Help: "Events the server reported as duplicates.",
	})
	m.CheckStatus = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_check_status",
		Help: "Last observed status per check: 0=ok,1=warning,2=critical,3=unknown.",
	}, []string{"check_id"})
	m.CheckExitCode = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_check_exit_code",
		Help: "Last exit code per check.",
	}, []string{"check_id"})
	m.CheckLastRun = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_check_last_run_timestamp_seconds",
		Help: "Unix timestamp of the last completed run per check.",
	}, []string{"check_id"})
	m.CheckLastSuccess = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_check_last_success_timestamp_seconds",
		Help: "Unix timestamp of the last ok run per check.",
	}, []string{"check_id"})
	m.CheckInterval = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_check_interval_seconds",
		Help: "Configured interval per check.",
	}, []string{"check_id"})
	m.ChecksConfigured = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "monlet_agent_checks_configured",
		Help: "Number of checks configured.",
	})
	m.LastHeartbeat = prometheus.NewGauge(prometheus.GaugeOpts{
		Name: "monlet_agent_last_heartbeat_timestamp_seconds",
		Help: "Unix timestamp of the last successful heartbeat ack.",
	})
	m.BuildInfo = prometheus.NewGaugeVec(prometheus.GaugeOpts{
		Name: "monlet_agent_build_info",
		Help: "Constant 1 with build labels.",
	}, []string{"version", "mode"})
	reg.MustRegister(m.CheckRuns, m.CheckSkipped, m.CheckDuration,
		m.CheckStatus, m.CheckExitCode, m.CheckLastRun, m.CheckLastSuccess,
		m.CheckInterval, m.ChecksConfigured,
		m.SpoolDepth, m.SpoolBytes,
		m.SendAttempts, m.SendFailures,
		m.EventsAccepted, m.EventsDedup,
		m.LastHeartbeat, m.BuildInfo)
	return m
}

// Serve blocks until ctx is done; the listener is closed on shutdown.
func (m *Metrics) Serve(ctx context.Context, addr string) error {
	mux := http.NewServeMux()
	mux.Handle("/metrics", promhttp.HandlerFor(m.Registry, promhttp.HandlerOpts{}))
	srv := &http.Server{Addr: addr, Handler: mux, ReadHeaderTimeout: 5 * time.Second}

	errCh := make(chan error, 1)
	go func() { errCh <- srv.ListenAndServe() }()

	select {
	case <-ctx.Done():
		shutCtx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
		defer cancel()
		_ = srv.Shutdown(shutCtx)
		return nil
	case err := <-errCh:
		if errors.Is(err, http.ErrServerClosed) {
			return nil
		}
		return err
	}
}