// Copyright 2015 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 consul

import (
	"fmt"
	"strconv"
	"strings"
	"time"

	consul "github.com/hashicorp/consul/api"
	"github.com/prometheus/common/log"
	"github.com/prometheus/common/model"
	"golang.org/x/net/context"

	"github.com/prometheus/prometheus/config"
)

const (
	watchTimeout  = 30 * time.Second
	retryInterval = 15 * time.Second

	// addressLabel is the name for the label containing a target's address.
	addressLabel = model.MetaLabelPrefix + "consul_address"
	// nodeLabel is the name for the label containing a target's node name.
	nodeLabel = model.MetaLabelPrefix + "consul_node"
	// tagsLabel is the name of the label containing the tags assigned to the target.
	tagsLabel = model.MetaLabelPrefix + "consul_tags"
	// serviceLabel is the name of the label containing the service name.
	serviceLabel = model.MetaLabelPrefix + "consul_service"
	// serviceAddressLabel is the name of the label containing the (optional) service address.
	serviceAddressLabel = model.MetaLabelPrefix + "consul_service_address"
	//servicePortLabel is the name of the label containing the service port.
	servicePortLabel = model.MetaLabelPrefix + "consul_service_port"
	// datacenterLabel is the name of the label containing the datacenter ID.
	datacenterLabel = model.MetaLabelPrefix + "consul_dc"
	// serviceIDLabel is the name of the label containing the service ID.
	serviceIDLabel = model.MetaLabelPrefix + "consul_service_id"
)

// Discovery retrieves target information from a Consul server
// and updates them via watches.
type Discovery struct {
	client           *consul.Client
	clientConf       *consul.Config
	clientDatacenter string
	tagSeparator     string
	watchedServices  []string // Set of services which will be discovered.
}

// NewDiscovery returns a new Discovery for the given config.
func NewDiscovery(conf *config.ConsulSDConfig) (*Discovery, error) {
	clientConf := &consul.Config{
		Address:    conf.Server,
		Scheme:     conf.Scheme,
		Datacenter: conf.Datacenter,
		Token:      conf.Token,
		HttpAuth: &consul.HttpBasicAuth{
			Username: conf.Username,
			Password: conf.Password,
		},
	}
	client, err := consul.NewClient(clientConf)
	if err != nil {
		return nil, err
	}
	cd := &Discovery{
		client:          client,
		clientConf:      clientConf,
		tagSeparator:    conf.TagSeparator,
		watchedServices: conf.Services,
	}
	// If the datacenter isn't set in the clientConf, let's get it from the local Consul agent
	// (Consul default is to use local node's datacenter if one isn't given for a query).
	if clientConf.Datacenter == "" {
		info, err := client.Agent().Self()
		if err != nil {
			return nil, err
		}
		cd.clientDatacenter = info["Config"]["Datacenter"].(string)
	} else {
		cd.clientDatacenter = clientConf.Datacenter
	}
	return cd, nil
}

// shouldWatch returns whether the service of the given name should be watched.
func (cd *Discovery) shouldWatch(name string) bool {
	// If there's no fixed set of watched services, we watch everything.
	if len(cd.watchedServices) == 0 {
		return true
	}
	for _, sn := range cd.watchedServices {
		if sn == name {
			return true
		}
	}
	return false
}

// Run implements the TargetProvider interface.
func (cd *Discovery) Run(ctx context.Context, ch chan<- []*config.TargetGroup) {
	defer close(ch)

	// Watched services and their cancelation functions.
	services := map[string]func(){}

	var lastIndex uint64
	for {
		catalog := cd.client.Catalog()
		srvs, meta, err := catalog.Services(&consul.QueryOptions{
			WaitIndex: lastIndex,
			WaitTime:  watchTimeout,
		})

		// We have to check the context at least once. The checks during channel sends
		// do not guarantee that.
		select {
		case <-ctx.Done():
			return
		default:
		}

		if err != nil {
			log.Errorf("Error refreshing service list: %s", err)
			time.Sleep(retryInterval)
			continue
		}
		// If the index equals the previous one, the watch timed out with no update.
		if meta.LastIndex == lastIndex {
			continue
		}
		lastIndex = meta.LastIndex

		// Check for new services.
		for name := range srvs {
			if !cd.shouldWatch(name) {
				continue
			}
			if _, ok := services[name]; ok {
				continue // We are already watching the service.
			}

			srv := &consulService{
				client: cd.client,
				name:   name,
				labels: model.LabelSet{
					serviceLabel:    model.LabelValue(name),
					datacenterLabel: model.LabelValue(cd.clientDatacenter),
				},
				tagSeparator: cd.tagSeparator,
			}

			wctx, cancel := context.WithCancel(ctx)
			go srv.watch(wctx, ch)

			services[name] = cancel
		}

		// Check for removed services.
		for name, cancel := range services {
			if _, ok := srvs[name]; !ok {
				// Call the watch cancelation function.
				cancel()
				delete(services, name)

				// Send clearing target group.
				select {
				case <-ctx.Done():
					return
				case ch <- []*config.TargetGroup{{Source: name}}:
				}
			}
		}
	}
}

// consulService contains data belonging to the same service.
type consulService struct {
	name         string
	labels       model.LabelSet
	client       *consul.Client
	tagSeparator string
}

func (srv *consulService) watch(ctx context.Context, ch chan<- []*config.TargetGroup) {
	catalog := srv.client.Catalog()

	lastIndex := uint64(0)
	for {
		nodes, meta, err := catalog.Service(srv.name, "", &consul.QueryOptions{
			WaitIndex: lastIndex,
			WaitTime:  watchTimeout,
		})
		// Check the context before potentially falling in a continue-loop.
		select {
		case <-ctx.Done():
			return
		default:
			// Continue.
		}

		if err != nil {
			log.Errorf("Error refreshing service %s: %s", srv.name, err)
			time.Sleep(retryInterval)
			continue
		}
		// If the index equals the previous one, the watch timed out with no update.
		if meta.LastIndex == lastIndex {
			continue
		}
		lastIndex = meta.LastIndex

		tgroup := config.TargetGroup{
			Source:  srv.name,
			Labels:  srv.labels,
			Targets: make([]model.LabelSet, 0, len(nodes)),
		}

		for _, node := range nodes {

			// We surround the separated list with the separator as well. This way regular expressions
			// in relabeling rules don't have to consider tag positions.
			var tags = srv.tagSeparator + strings.Join(node.ServiceTags, srv.tagSeparator) + srv.tagSeparator

			// If the service address is not empty it should be used instead of the node address
			// since the service may be registered remotely through a different node
			var addr string
			if node.ServiceAddress != "" {
				addr = fmt.Sprintf("%s:%d", node.ServiceAddress, node.ServicePort)
			} else {
				addr = fmt.Sprintf("%s:%d", node.Address, node.ServicePort)
			}

			tgroup.Targets = append(tgroup.Targets, model.LabelSet{
				model.AddressLabel:  model.LabelValue(addr),
				addressLabel:        model.LabelValue(node.Address),
				nodeLabel:           model.LabelValue(node.Node),
				tagsLabel:           model.LabelValue(tags),
				serviceAddressLabel: model.LabelValue(node.ServiceAddress),
				servicePortLabel:    model.LabelValue(strconv.Itoa(node.ServicePort)),
				serviceIDLabel:      model.LabelValue(node.ServiceID),
			})
		}
		// Check context twice to ensure we always catch cancelation.
		select {
		case <-ctx.Done():
			return
		default:
		}
		select {
		case <-ctx.Done():
			return
		case ch <- []*config.TargetGroup{&tgroup}:
		}
	}
}