// This is Free Software under GNU Affero General Public License v >= 3.0
// without warranty, see README.md and license for details.
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// License-Filename: LICENSES/AGPL-3.0.txt
//
// Copyright (C) 2018 by via donau
//   – Österreichische Wasserstraßen-Gesellschaft mbH
// Software engineering by Intevation GmbH
//
// Author(s):
//  * Sascha L. Teichmann <sascha.teichmann@intevation.de>

package geoserver

import (
	"container/list"
	"log"
	"net"
	"net/url"
	"sync"
	"time"
)

var (
	confQueue     = list.New()
	confQueueCond = sync.NewCond(new(sync.Mutex))
)

func init() {
	go asyncConfigure()
}

func asyncConfigure() {
	for {
		var fn func() error
		confQueueCond.L.Lock()
		for confQueue.Len() == 0 {
			confQueueCond.Wait()
		}
		fn = confQueue.Remove(confQueue.Front()).(func() error)
		confQueueCond.L.Unlock()
		if err := reconfigure(fn); err != nil {
			log.Printf("warn: configure GeoServer failed: %v\n", err)
		}
	}
}

func reconfigure(fn func() error) error {
	log.Println("info: configure GeoServer...")
	const (
		maxTries = 10
		sleep    = time.Second * 5
	)
	var err error
	for try := 1; try <= maxTries; try++ {
		if err = fn(); err == nil {
			break
		}
		if try < maxTries {
			if uerr, ok := err.(*url.Error); ok {
				if oerr, ok := uerr.Err.(*net.OpError); ok && oerr.Op == "dial" {
					log.Printf("warn: failed attempt %d of %d to configure GeoServer. "+
						"Will try again in %s...\n", try, maxTries, sleep)
					time.Sleep(sleep)
					continue
				}
			}
		}
		break
	}
	return err
}

// Reconfigure adds a function to a queue of functions to update
// the GeoServer async. The functions are run again a number
// of times if network errors apppear indicating that the
// GeoServer is down.
func Reconfigure(fn func() error) {
	confQueueCond.L.Lock()
	defer confQueueCond.L.Unlock()
	confQueue.PushBack(fn)
	confQueueCond.Signal()
}