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

func init() {
	registerCollector(statUserIndexesSubsystem, defaultDisabled, NewPGStatUserIndexesCollector)
}

type PGStatUserIndexesCollector struct {
	log log.Logger
}

const statUserIndexesSubsystem = "stat_user_indexes"

func NewPGStatUserIndexesCollector(config collectorConfig) (Collector, error) {
	return &PGStatUserIndexesCollector{log: config.logger}, nil
}

var (
	statUserIndexesIdxScan = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, statUserIndexesSubsystem, "idx_scans_total"),
		"Number of index scans initiated on this index",
		[]string{"schemaname", "relname", "indexrelname"},
		prometheus.Labels{},
	)
	statUserIndexesIdxTupRead = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, statUserIndexesSubsystem, "idx_tup_reads_total"),
		"Number of index entries returned by scans on this index",
		[]string{"schemaname", "relname", "indexrelname"},
		prometheus.Labels{},
	)
	statUserIndexesIdxTupFetch = prometheus.NewDesc(
		prometheus.BuildFQName(namespace, statUserIndexesSubsystem, "idx_tup_fetches_total"),
		"Number of live table rows fetched by simple index scans using this index",
		[]string{"schemaname", "relname", "indexrelname"},
		prometheus.Labels{},
	)

	statUserIndexesQuery = `
	SELECT
		schemaname,
		relname,
		indexrelname,
		idx_scan,
		idx_tup_read,
		idx_tup_fetch
	FROM pg_stat_user_indexes
	`
)

func (c *PGStatUserIndexesCollector) Update(ctx context.Context, instance *instance, ch chan<- prometheus.Metric) error {
	db := instance.getDB()
	rows, err := db.QueryContext(ctx,
		statUserIndexesQuery)

	if err != nil {
		return err
	}
	defer rows.Close()
	for rows.Next() {
		var schemaname, relname, indexrelname sql.NullString
		var idxScan, idxTupRead, idxTupFetch sql.NullFloat64

		if err := rows.Scan(&schemaname, &relname, &indexrelname, &idxScan, &idxTupRead, &idxTupFetch); err != nil {
			return err
		}
		if !schemaname.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because schemaname is not valid")
			continue
		}
		if !relname.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because relname is not valid")
			continue
		}
		if !indexrelname.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because indexrelname is not valid")
			continue
		}
		labels := []string{schemaname.String, relname.String, indexrelname.String}

		if !idxScan.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because idx_scan is not valid")
			continue
		}
		if !idxTupRead.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because idx_tup_read is not valid")
			continue
		}
		if !idxTupFetch.Valid {
			level.Debug(c.log).Log("msg", "Skipping stats on index because idx_tup_fetch is not valid")
			continue
		}

		idxScanMetric := idxScan.Float64
		ch <- prometheus.MustNewConstMetric(
			statUserIndexesIdxScan,
			prometheus.CounterValue,
			idxScanMetric,
			labels...,
		)

		idxTupReadMetric := idxTupRead.Float64
		ch <- prometheus.MustNewConstMetric(
			statUserIndexesIdxTupRead,
			prometheus.CounterValue,
			idxTupReadMetric,
			labels...,
		)

		idxTupFetchMetric := idxTupFetch.Float64
		ch <- prometheus.MustNewConstMetric(
			statUserIndexesIdxTupFetch,
			prometheus.CounterValue,
			idxTupFetchMetric,
			labels...,
		)
	}
	if err := rows.Err(); err != nil {
		return err
	}
	return nil
}