// Licensed to Elasticsearch B.V. under one or more contributor
// license agreements. See the NOTICE file distributed with
// this work for additional information regarding copyright
// ownership. Elasticsearch B.V. licenses this file to you 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 statement

import (
	"context"

	"github.com/pkg/errors"

	"github.com/elastic/beats/v7/metricbeat/mb"
	"github.com/elastic/beats/v7/metricbeat/module/postgresql"
)

// init registers the MetricSet with the central registry as soon as the program
// starts. The New function will be called later to instantiate an instance of
// the MetricSet for each host defined in the module's configuration. After the
// MetricSet has been created then Fetch will begin to be called periodically.
func init() {
	mb.Registry.MustAddMetricSet("postgresql", "statement", New,
		mb.WithHostParser(postgresql.ParseURL),
	)
}

// MetricSet holds any configuration or state information. It must implement
// the mb.MetricSet interface. And this is best achieved by embedding
// mb.BaseMetricSet because it implements all of the required mb.MetricSet
// interface methods except for Fetch.
type MetricSet struct {
	*postgresql.MetricSet
}

// New creates a new instance of the MetricSet. New is responsible for unpacking
// any MetricSet specific configuration options if there are any.
func New(base mb.BaseMetricSet) (mb.MetricSet, error) {
	ms, err := postgresql.NewMetricSet(base)
	if err != nil {
		return nil, err
	}
	return &MetricSet{MetricSet: ms}, nil
}

// Fetch methods implements the data gathering and data conversion to the right
// format. It publishes the event which is then forwarded to the output. In case
// of an error set the Error field of mb.Event or simply call report.Error().
func (m *MetricSet) Fetch(reporter mb.ReporterV2) error {
	ctx := context.Background()
	results, err := m.QueryStats(ctx, "SELECT * FROM pg_stat_statements")
	if err != nil {
		return errors.Wrap(err, "QueryStats")
	}

	for _, result := range results {
		data, _ := schema.Apply(result)
		// Older versions of PostgreSQL had the execution time in `*_time` fields
		// instead of `*_exec_time`, keep compatibility with them.
		if _, ok := result["total_time"]; ok {
			execTimes, _ := schemaOldTime.Apply(result)
			data.DeepUpdate(execTimes)
		}
		reporter.Event(mb.Event{
			MetricSetFields: data,
		})
	}

	return nil
}
