package appview

import (
	"context"
	"time"

	"github.com/prometheus/client_golang/prometheus"
	"provenance/internal/storage"
)

const metricsDBTimeout = time.Second

type databaseMetrics struct {
	store                                        storage.Store
	bytes, wal, connections, inUse, waits, error *prometheus.Desc
}

func newDatabaseMetrics(store storage.Store) *databaseMetrics {
	desc := func(name, help string) *prometheus.Desc { return prometheus.NewDesc(name, help, nil, nil) }
	return &databaseMetrics{store: store,
		bytes:       desc("provenance_database_allocated_bytes", "SQLite allocated page bytes, excluding WAL and caches."),
		wal:         desc("provenance_database_wal_bytes", "Current SQLite WAL file size."),
		connections: desc("provenance_database_connections", "Open database connections."),
		inUse:       desc("provenance_database_connections_in_use", "Database connections currently in use."),
		waits:       desc("provenance_database_connection_waits_total", "Database connection waits since process start."),
		error:       desc("provenance_database_scrape_error", "One when database allocation statistics cannot be read."),
	}
}

func (m *databaseMetrics) Describe(ch chan<- *prometheus.Desc) {
	for _, desc := range []*prometheus.Desc{m.bytes, m.wal, m.connections, m.inUse, m.waits, m.error} {
		ch <- desc
	}
}

func (m *databaseMetrics) Collect(ch chan<- prometheus.Metric) {
	ctx, cancel := context.WithTimeout(context.Background(), metricsDBTimeout)
	defer cancel()
	stats, err := m.store.DatabaseStats(ctx)
	if err != nil {
		ch <- prometheus.MustNewConstMetric(m.error, prometheus.GaugeValue, 1)
		return
	}
	ch <- prometheus.MustNewConstMetric(m.error, prometheus.GaugeValue, 0)
	ch <- prometheus.MustNewConstMetric(m.bytes, prometheus.GaugeValue, float64(stats.AllocatedBytes))
	ch <- prometheus.MustNewConstMetric(m.wal, prometheus.GaugeValue, float64(stats.WALBytes))
	ch <- prometheus.MustNewConstMetric(m.connections, prometheus.GaugeValue, float64(stats.Connections))
	ch <- prometheus.MustNewConstMetric(m.inUse, prometheus.GaugeValue, float64(stats.InUse))
	ch <- prometheus.MustNewConstMetric(m.waits, prometheus.CounterValue, float64(stats.Waits))
}