// Copyright 2016 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 discovery

import (
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/go-kit/kit/log"
	"github.com/go-kit/kit/log/level"

	sd_config "github.com/prometheus/prometheus/discovery/config"
	"github.com/prometheus/prometheus/discovery/targetgroup"

	"github.com/prometheus/prometheus/discovery/azure"
	"github.com/prometheus/prometheus/discovery/consul"
	"github.com/prometheus/prometheus/discovery/dns"
	"github.com/prometheus/prometheus/discovery/ec2"
	"github.com/prometheus/prometheus/discovery/file"
	"github.com/prometheus/prometheus/discovery/gce"
	"github.com/prometheus/prometheus/discovery/kubernetes"
	"github.com/prometheus/prometheus/discovery/marathon"
	"github.com/prometheus/prometheus/discovery/openstack"
	"github.com/prometheus/prometheus/discovery/triton"
	"github.com/prometheus/prometheus/discovery/zookeeper"
)

// Discoverer provides information about target groups. It maintains a set
// of sources from which TargetGroups can originate. Whenever a discovery provider
// detects a potential change, it sends the TargetGroup through its channel.
//
// Discoverer does not know if an actual change happened.
// It does guarantee that it sends the new TargetGroup whenever a change happens.
//
// Discoverers should initially send a full set of all discoverable TargetGroups.
type Discoverer interface {
	// Run hands a channel to the discovery provider(consul,dns etc) through which it can send
	// updated target groups.
	// Must returns if the context gets canceled. It should not close the update
	// channel on returning.
	Run(ctx context.Context, up chan<- []*targetgroup.Group)
}

type poolKey struct {
	setName  string
	provider string
}

// NewManager is the Discovery Manager constructor
func NewManager(logger log.Logger) *Manager {
	return &Manager{
		logger:         logger,
		syncCh:         make(chan map[string][]*targetgroup.Group),
		targets:        make(map[poolKey]map[string]*targetgroup.Group),
		discoverCancel: []context.CancelFunc{},
		ctx:            context.Background(),
	}
}

// Manager maintains a set of discovery providers and sends each update to a map channel.
// Targets are grouped by the target set name.
type Manager struct {
	logger         log.Logger
	mtx            sync.RWMutex
	ctx            context.Context
	discoverCancel []context.CancelFunc
	// Some Discoverers(eg. k8s) send only the updates for a given target group
	// so we use map[tg.Source]*targetgroup.Group to know which group to update.
	targets map[poolKey]map[string]*targetgroup.Group
	// The sync channels sends the updates in map[targetSetName] where targetSetName is the job value from the scrape config.
	syncCh chan map[string][]*targetgroup.Group
	// True if updates were received in the last 5 seconds.
	recentlyUpdated bool
	// Protects recentlyUpdated.
	recentlyUpdatedMtx sync.Mutex
}

// Run starts the background processing
func (m *Manager) Run(ctx context.Context) error {
	m.ctx = ctx
	for {
		select {
		case <-ctx.Done():
			m.cancelDiscoverers()
			return ctx.Err()
		}
	}
}

// SyncCh returns a read only channel used by all Discoverers to send target updates.
func (m *Manager) SyncCh() <-chan map[string][]*targetgroup.Group {
	return m.syncCh
}

// ApplyConfig removes all running discovery providers and starts new ones using the provided config.
func (m *Manager) ApplyConfig(cfg map[string]sd_config.ServiceDiscoveryConfig) error {
	m.mtx.Lock()
	defer m.mtx.Unlock()

	m.cancelDiscoverers()
	for name, scfg := range cfg {
		for provName, prov := range m.providersFromConfig(scfg) {
			m.startProvider(m.ctx, poolKey{setName: name, provider: provName}, prov)
		}
	}

	return nil
}

func (m *Manager) startProvider(ctx context.Context, poolKey poolKey, worker Discoverer) {
	ctx, cancel := context.WithCancel(ctx)
	updates := make(chan []*targetgroup.Group)

	m.discoverCancel = append(m.discoverCancel, cancel)

	go worker.Run(ctx, updates)
	go m.runProvider(ctx, poolKey, updates)
	go m.runUpdater(ctx)
}

func (m *Manager) runProvider(ctx context.Context, poolKey poolKey, updates chan []*targetgroup.Group) {
	for {
		select {
		case <-ctx.Done():
			return
		case tgs, ok := <-updates:
			// Handle the case that a target provider exits and closes the channel
			// before the context is done.
			if !ok {
				return
			}
			m.updateGroup(poolKey, tgs)
			m.recentlyUpdatedMtx.Lock()
			m.recentlyUpdated = true
			m.recentlyUpdatedMtx.Unlock()
		}
	}
}

func (m *Manager) runUpdater(ctx context.Context) {
	ticker := time.NewTicker(5 * time.Second)
	defer ticker.Stop()

	for {
		select {
		case <-ctx.Done():
			return
		case <-ticker.C:
			m.recentlyUpdatedMtx.Lock()
			if m.recentlyUpdated {
				m.syncCh <- m.allGroups()
				m.recentlyUpdated = false
			}
			m.recentlyUpdatedMtx.Unlock()
		}
	}
}

func (m *Manager) cancelDiscoverers() {
	for _, c := range m.discoverCancel {
		c()
	}
	m.targets = make(map[poolKey]map[string]*targetgroup.Group)
	m.discoverCancel = nil
}

func (m *Manager) updateGroup(poolKey poolKey, tgs []*targetgroup.Group) {
	m.mtx.Lock()
	defer m.mtx.Unlock()

	for _, tg := range tgs {
		if tg != nil { // Some Discoverers send nil target group so need to check for it to avoid panics.
			if _, ok := m.targets[poolKey]; !ok {
				m.targets[poolKey] = make(map[string]*targetgroup.Group)
			}
			m.targets[poolKey][tg.Source] = tg
		}
	}
}

func (m *Manager) allGroups() map[string][]*targetgroup.Group {
	m.mtx.Lock()
	defer m.mtx.Unlock()

	tSets := map[string][]*targetgroup.Group{}
	for pkey, tsets := range m.targets {
		for _, tg := range tsets {
			// Even if the target group 'tg' is empty we still need to send it to the 'Scrape manager'
			// to signal that it needs to stop all scrape loops for this target set.
			tSets[pkey.setName] = append(tSets[pkey.setName], tg)
		}
	}
	return tSets
}

func (m *Manager) providersFromConfig(cfg sd_config.ServiceDiscoveryConfig) map[string]Discoverer {
	providers := map[string]Discoverer{}

	app := func(mech string, i int, tp Discoverer) {
		providers[fmt.Sprintf("%s/%d", mech, i)] = tp
	}

	for i, c := range cfg.DNSSDConfigs {
		app("dns", i, dns.NewDiscovery(*c, log.With(m.logger, "discovery", "dns")))
	}
	for i, c := range cfg.FileSDConfigs {
		app("file", i, file.NewDiscovery(c, log.With(m.logger, "discovery", "file")))
	}
	for i, c := range cfg.ConsulSDConfigs {
		k, err := consul.NewDiscovery(c, log.With(m.logger, "discovery", "consul"))
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot create Consul discovery", "err", err)
			continue
		}
		app("consul", i, k)
	}
	for i, c := range cfg.MarathonSDConfigs {
		t, err := marathon.NewDiscovery(*c, log.With(m.logger, "discovery", "marathon"))
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot create Marathon discovery", "err", err)
			continue
		}
		app("marathon", i, t)
	}
	for i, c := range cfg.KubernetesSDConfigs {
		k, err := kubernetes.New(log.With(m.logger, "discovery", "k8s"), c)
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot create Kubernetes discovery", "err", err)
			continue
		}
		app("kubernetes", i, k)
	}
	for i, c := range cfg.ServersetSDConfigs {
		app("serverset", i, zookeeper.NewServersetDiscovery(c, log.With(m.logger, "discovery", "zookeeper")))
	}
	for i, c := range cfg.NerveSDConfigs {
		app("nerve", i, zookeeper.NewNerveDiscovery(c, log.With(m.logger, "discovery", "nerve")))
	}
	for i, c := range cfg.EC2SDConfigs {
		app("ec2", i, ec2.NewDiscovery(c, log.With(m.logger, "discovery", "ec2")))
	}
	for i, c := range cfg.OpenstackSDConfigs {
		openstackd, err := openstack.NewDiscovery(c, log.With(m.logger, "discovery", "openstack"))
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot initialize OpenStack discovery", "err", err)
			continue
		}
		app("openstack", i, openstackd)
	}

	for i, c := range cfg.GCESDConfigs {
		gced, err := gce.NewDiscovery(*c, log.With(m.logger, "discovery", "gce"))
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot initialize GCE discovery", "err", err)
			continue
		}
		app("gce", i, gced)
	}
	for i, c := range cfg.AzureSDConfigs {
		app("azure", i, azure.NewDiscovery(c, log.With(m.logger, "discovery", "azure")))
	}
	for i, c := range cfg.TritonSDConfigs {
		t, err := triton.New(log.With(m.logger, "discovery", "trition"), c)
		if err != nil {
			level.Error(m.logger).Log("msg", "Cannot create Triton discovery", "err", err)
			continue
		}
		app("triton", i, t)
	}
	if len(cfg.StaticConfigs) > 0 {
		app("static", 0, NewStaticProvider(cfg.StaticConfigs))
	}

	return providers
}

// StaticProvider holds a list of target groups that never change.
type StaticProvider struct {
	TargetGroups []*targetgroup.Group
}

// NewStaticProvider returns a StaticProvider configured with the given
// target groups.
func NewStaticProvider(groups []*targetgroup.Group) *StaticProvider {
	for i, tg := range groups {
		tg.Source = fmt.Sprintf("%d", i)
	}
	return &StaticProvider{groups}
}

// Run implements the Worker interface.
func (sd *StaticProvider) Run(ctx context.Context, ch chan<- []*targetgroup.Group) {
	// We still have to consider that the consumer exits right away in which case
	// the context will be canceled.
	select {
	case ch <- sd.TargetGroups:
	case <-ctx.Done():
	}
	close(ch)
}