package metrics

import (
	"github.com/jackc/pgx/v5/pgxpool"
	"github.com/prometheus/client_golang/prometheus"
)

// poolCollector reports the database connection pool's statistics on every scrape.
type poolCollector struct {
	pool *pgxpool.Pool

	acquiredConns        *prometheus.Desc
	idleConns            *prometheus.Desc
	totalConns           *prometheus.Desc
	maxConns             *prometheus.Desc
	acquires             *prometheus.Desc
	acquireWait          *prometheus.Desc
	emptyAcquires        *prometheus.Desc
	canceledAcquires     *prometheus.Desc
	newConns             *prometheus.Desc
	maxLifetimeDestroyed *prometheus.Desc
	maxIdleDestroyed     *prometheus.Desc
}

// NewPoolCollector returns a collector for the musicserver_db_pool_* metrics of pool.
// Register it once, for example with prometheus.MustRegister.
func NewPoolCollector(pool *pgxpool.Pool) prometheus.Collector {
	desc := func(name, help string) *prometheus.Desc {
		return prometheus.NewDesc("musicserver_db_pool_"+name, help, nil, nil)
	}
	return &poolCollector{
		pool:                 pool,
		acquiredConns:        desc("acquired_conns", "Connections in use."),
		idleConns:            desc("idle_conns", "Idle connections."),
		totalConns:           desc("total_conns", "Open connections, in use, idle and being opened."),
		maxConns:             desc("max_conns", "Most connections the pool opens."),
		acquires:             desc("acquires_total", "Connections handed out."),
		acquireWait:          desc("acquire_wait_seconds_total", "Total time spent waiting for a connection."),
		emptyAcquires:        desc("empty_acquires_total", "Acquires that had to wait because no connection was idle."),
		canceledAcquires:     desc("canceled_acquires_total", "Acquires canceled while waiting, for example by a timeout."),
		newConns:             desc("new_conns_total", "Connections opened."),
		maxLifetimeDestroyed: desc("max_lifetime_destroyed_total", "Connections closed for reaching their maximum lifetime."),
		maxIdleDestroyed:     desc("max_idle_destroyed_total", "Connections closed for being idle too long."),
	}
}

func (c *poolCollector) Describe(ch chan<- *prometheus.Desc) {
	prometheus.DescribeByCollect(c, ch)
}

func (c *poolCollector) Collect(ch chan<- prometheus.Metric) {
	s := c.pool.Stat()
	gauge := func(d *prometheus.Desc, v float64) {
		ch <- prometheus.MustNewConstMetric(d, prometheus.GaugeValue, v)
	}
	counter := func(d *prometheus.Desc, v float64) {
		ch <- prometheus.MustNewConstMetric(d, prometheus.CounterValue, v)
	}
	gauge(c.acquiredConns, float64(s.AcquiredConns()))
	gauge(c.idleConns, float64(s.IdleConns()))
	gauge(c.totalConns, float64(s.TotalConns()))
	gauge(c.maxConns, float64(s.MaxConns()))
	counter(c.acquires, float64(s.AcquireCount()))
	counter(c.acquireWait, s.AcquireDuration().Seconds())
	counter(c.emptyAcquires, float64(s.EmptyAcquireCount()))
	counter(c.canceledAcquires, float64(s.CanceledAcquireCount()))
	counter(c.newConns, float64(s.NewConnsCount()))
	counter(c.maxLifetimeDestroyed, float64(s.MaxLifetimeDestroyCount()))
	counter(c.maxIdleDestroyed, float64(s.MaxIdleDestroyCount()))
}