package exporter

import (
	"log"

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

const (
	namespace      string = "country_geo_locations"
	cacheSubsystem string = "cache"
	dbSubsystem    string = "db"

	metricNameCacheTTL          string = "ttl"
	metricNameCurrentlyCached   string = "currently_cached"
	metricNameDatabaseTimestamp string = "timestamp"
	metricNameDatabaseReady     string = "ready"
	metricNameRequestsTotal     string = "requests_total"
	metricNameRequestLatency    string = "request_latency"
)

type Metrics struct {
	exporter *Exporter

	metricCacheTTL          prometheus.Gauge
	metricCurrentlyCached   prometheus.Gauge
	metricDatabaseTimestamp *prometheus.GaugeVec
	metricDatabaseReady     prometheus.Gauge
	metricRequestsTotal     prometheus.Counter
	metricRequestLatency    prometheus.Histogram
}

func NewMetrics(e *Exporter) *Metrics {
	return &Metrics{
		exporter: e,
		metricCacheTTL: prometheus.NewGauge(
			prometheus.GaugeOpts{
				Namespace: namespace,
				Subsystem: cacheSubsystem,
				Name:      metricNameCacheTTL,
				Help:      "Duration for cached requests",
			},
		),
		metricCurrentlyCached: prometheus.NewGauge(
			prometheus.GaugeOpts{
				Namespace: namespace,
				Subsystem: cacheSubsystem,
				Name:      metricNameCurrentlyCached,
				Help:      "Number of cached entries",
			},
		),
		metricDatabaseTimestamp: prometheus.NewGaugeVec(
			prometheus.GaugeOpts{
				Namespace: namespace,
				Subsystem: dbSubsystem,
				Name:      metricNameDatabaseTimestamp,
				Help:      "Timestamp of the CSV file",
			},
			[]string{metricNameDatabaseTimestamp},
		),
		metricDatabaseReady: prometheus.NewGauge(
			prometheus.GaugeOpts{
				Namespace: namespace,
				Subsystem: dbSubsystem,
				Name:      metricNameDatabaseReady,
				Help:      "Ready status of the database",
			},
		),
		metricRequestsTotal: prometheus.NewCounter(
			prometheus.CounterOpts{
				Namespace: namespace,
				Name:      metricNameRequestsTotal,
				Help:      "Counter for total requests",
			},
		),
		metricRequestLatency: prometheus.NewHistogram(
			prometheus.HistogramOpts{
				Namespace: namespace,
				Name:      metricNameRequestLatency,
				Help:      "Latency statistics for requests",
				Buckets:   prometheus.ExponentialBuckets(0.000001, 1.5, 40),
			},
		),
	}
}

func (m *Metrics) collectCacheTTLMetric() {
	m.metricCacheTTL.Set(m.exporter.config.CacheTTL.Seconds())
}

func (m *Metrics) collectCurrentlyCachedMetric() {
	m.metricCurrentlyCached.Set(float64(m.exporter.cache.Count()))
}

func (m *Metrics) collectDatabaseTimestampMetric() {
	timestamp, err := m.exporter.database.Timestamp()
	if err != nil {
		log.Printf("failed to read file timestamp: %v", err)
		return
	}

	m.metricDatabaseTimestamp.WithLabelValues(timestamp.String()).Set(float64(timestamp.Unix()))
}

func (m *Metrics) collectDatabaseReadyMetric() {
	var dbReady float64
	if m.exporter.database.IsReady() {
		dbReady = 1
	}

	m.metricDatabaseReady.Set(dbReady)
}