/*
** Zabbix
** Copyright 2001-2024 Zabbix SIA
**
** 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 plugin

import (
	"context"
	"errors"

	"github.com/jackc/pgx/v4"
	"golang.zabbix.com/sdk/zbxerr"
)

// connectionsHandler executes select from pg_stat_activity command and returns JSON if all is OK or nil otherwise.
func connectionsHandler(ctx context.Context, conn PostgresClient,
	_ string, _ map[string]string, _ ...string) (interface{}, error) {
	var connectionsJSON string

	query := `SELECT row_to_json(T)
	FROM (
		SELECT
			sum(CASE WHEN state = 'active' THEN 1 ELSE 0 END) AS active,
			sum(CASE WHEN state = 'idle' THEN 1 ELSE 0 END) AS idle,
			sum(CASE WHEN state = 'idle in transaction' THEN 1 ELSE 0 END) AS idle_in_transaction,
			sum(CASE WHEN state = 'idle in transaction (aborted)' THEN 1 ELSE 0 END) AS idle_in_transaction_aborted,
			sum(CASE WHEN state = 'fastpath function call' THEN 1 ELSE 0 END) AS fastpath_function_call,
			sum(CASE WHEN state = 'disabled' THEN 1 ELSE 0 END) AS disabled,
			count(*) AS total,
			count(*)*100/(SELECT current_setting('max_connections')::int) AS total_pct,
			sum(CASE WHEN wait_event IS NOT NULL THEN 1 ELSE 0 END) AS waiting,
			(SELECT count(*) FROM pg_prepared_xacts) AS prepared
		FROM pg_stat_activity WHERE datid IS NOT NULL AND state IS NOT NULL) T;`

	row, err := conn.QueryRow(ctx, query)
	if err != nil {
		return nil, zbxerr.ErrorCannotFetchData.Wrap(err)
	}

	err = row.Scan(&connectionsJSON)
	if err != nil {
		if errors.Is(err, pgx.ErrNoRows) {
			return nil, zbxerr.ErrorEmptyResult.Wrap(err)
		}

		return nil, zbxerr.ErrorCannotFetchData.Wrap(err)
	}

	return connectionsJSON, nil
}