/*
   Copyright 2014 CoreOS, Inc.

   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 proxy

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

const (
	// amount of time an endpoint will be held in a failed
	// state before being reconsidered for proxied requests
	endpointFailureWait = 5 * time.Second

	// how often the proxy will attempt to refresh its set of endpoints
	refreshEndpoints = 30 * time.Second
)

func newDirector(urlsFunc GetProxyURLs) *director {
	d := &director{
		uf: urlsFunc,
	}
	d.refresh()
	go func() {
		for {
			select {
			case <-time.After(refreshEndpoints):
				d.refresh()
			}
		}
	}()
	return d
}

type director struct {
	sync.Mutex
	ep []*endpoint
	uf GetProxyURLs
}

func (d *director) refresh() {
	urls := d.uf()
	d.Lock()
	defer d.Unlock()
	var endpoints []*endpoint
	for _, u := range urls {
		uu, err := url.Parse(u)
		if err != nil {
			log.Printf("proxy: upstream URL invalid: %v", err)
			continue
		}
		endpoints = append(endpoints, newEndpoint(*uu))
	}
	d.ep = endpoints
}

func (d *director) endpoints() []*endpoint {
	d.Lock()
	defer d.Unlock()
	filtered := make([]*endpoint, 0)
	for _, ep := range d.ep {
		if ep.Available {
			filtered = append(filtered, ep)
		}
	}

	return filtered
}

func newEndpoint(u url.URL) *endpoint {
	ep := endpoint{
		URL:       u,
		Available: true,
		failFunc:  timedUnavailabilityFunc(endpointFailureWait),
	}

	return &ep
}

type endpoint struct {
	sync.Mutex

	URL       url.URL
	Available bool

	failFunc func(ep *endpoint)
}

func (ep *endpoint) Failed() {
	ep.Lock()
	if !ep.Available {
		ep.Unlock()
		return
	}

	ep.Available = false
	ep.Unlock()

	log.Printf("proxy: marked endpoint %s unavailable", ep.URL.String())

	if ep.failFunc == nil {
		log.Printf("proxy: no failFunc defined, endpoint %s will be unavailable forever.", ep.URL.String())
		return
	}

	ep.failFunc(ep)
}

func timedUnavailabilityFunc(wait time.Duration) func(*endpoint) {
	return func(ep *endpoint) {
		time.AfterFunc(wait, func() {
			ep.Available = true
			log.Printf("proxy: marked endpoint %s available", ep.URL.String())
		})
	}
}