// Copyright 2023 The Prometheus Authors
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package collector

import (
	"context"
	"database/sql"

	"github.com/go-kit/log"
	"github.com/prometheus/client_golang/prometheus"
)

func init() {
	registerCollector("replication_slot", defaultEnabled, NewPGReplicationSlotCollector)
}

type PGReplicationSlotCollector struct {
	log log.Logger
}

func NewPGReplicationSlotCollector(logger log.Logger) (Collector, error) {
	return &PGReplicationSlotCollector{log: logger}, nil
}

var pgReplicationSlot = map[string]*prometheus.Desc{
	"current_wal_lsn": prometheus.NewDesc(
		"pg_replication_slot_current_wal_lsn",
		"current wal lsn value",
		[]string{"slot_name"}, nil,
	),
	"confirmed_flush_lsn": prometheus.NewDesc(
		"pg_replication_slot_confirmed_flush_lsn",
		"last lsn confirmed flushed to the replication slot",
		[]string{"slot_name"}, nil,
	),
	"is_active": prometheus.NewDesc(
		"pg_replication_slot_is_active",
		"last lsn confirmed flushed to the replication slot",
		[]string{"slot_name"}, nil,
	),
}

func (PGReplicationSlotCollector) Update(ctx context.Context, db *sql.DB, ch chan<- prometheus.Metric) error {
	rows, err := db.QueryContext(ctx,
		`SELECT
			slot_name,
			pg_current_wal_lsn() - '0/0' AS current_wal_lsn,
			coalesce(confirmed_flush_lsn, '0/0') - '0/0',
			active
		FROM
			pg_replication_slots;`)
	if err != nil {
		return err
	}
	defer rows.Close()

	for rows.Next() {
		var slot_name string
		var wal_lsn int64
		var flush_lsn int64
		var is_active int
		if err := rows.Scan(&slot_name, &wal_lsn, &flush_lsn, &is_active); err != nil {
			return err
		}

		ch <- prometheus.MustNewConstMetric(
			pgReplicationSlot["current_wal_lsn"],
			prometheus.GaugeValue, float64(wal_lsn), slot_name,
		)
		if (is_active == 1) {
			ch <- prometheus.MustNewConstMetric(
				pgReplicationSlot["confirmed_flush_lsn"],
				prometheus.GaugeValue, float64(flush_lsn), slot_name,
			)
		}
		ch <- prometheus.MustNewConstMetric(
			pgReplicationSlot["is_active"],
			prometheus.GaugeValue, int(flush_lsn), slot_name,
		)
	}
	if err := rows.Err(); err != nil {
		return err
	}
	return nil
}