/*
Copyright 2014 The Kubernetes 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 app implements a Server object for running the scheduler.
package app

import (
	"context"
	"fmt"
	"io"
	"net/http"
	"os"
	goruntime "runtime"

	utilerrors "k8s.io/apimachinery/pkg/util/errors"
	utilruntime "k8s.io/apimachinery/pkg/util/runtime"
	"k8s.io/apiserver/pkg/authentication/authenticator"
	"k8s.io/apiserver/pkg/authorization/authorizer"
	genericapifilters "k8s.io/apiserver/pkg/endpoints/filters"
	apirequest "k8s.io/apiserver/pkg/endpoints/request"
	genericfilters "k8s.io/apiserver/pkg/server/filters"
	"k8s.io/apiserver/pkg/server/healthz"
	"k8s.io/apiserver/pkg/server/mux"
	"k8s.io/apiserver/pkg/server/routes"
	"k8s.io/apiserver/pkg/util/term"
	v1core "k8s.io/client-go/kubernetes/typed/core/v1"
	"k8s.io/client-go/tools/leaderelection"
	cliflag "k8s.io/component-base/cli/flag"
	"k8s.io/component-base/cli/globalflag"
	schedulerserverconfig "k8s.io/kubernetes/cmd/kube-scheduler/app/config"
	"k8s.io/kubernetes/cmd/kube-scheduler/app/options"
	"k8s.io/kubernetes/pkg/api/legacyscheme"
	"k8s.io/kubernetes/pkg/controller"
	"k8s.io/kubernetes/pkg/scheduler"
	"k8s.io/kubernetes/pkg/scheduler/algorithmprovider"
	kubeschedulerconfig "k8s.io/kubernetes/pkg/scheduler/apis/config"
	"k8s.io/kubernetes/pkg/scheduler/metrics"
	"k8s.io/kubernetes/pkg/util/configz"
	utilflag "k8s.io/kubernetes/pkg/util/flag"
	"k8s.io/kubernetes/pkg/version"
	"k8s.io/kubernetes/pkg/version/verflag"

	"github.com/prometheus/client_golang/prometheus"
	"github.com/spf13/cobra"
	"k8s.io/klog"
)

// NewSchedulerCommand creates a *cobra.Command object with default parameters
func NewSchedulerCommand() *cobra.Command {
	opts, err := options.NewOptions()
	if err != nil {
		klog.Fatalf("unable to initialize command options: %v", err)
	}

	cmd := &cobra.Command{
		Use: "kube-scheduler",
		Long: `The Kubernetes scheduler is a policy-rich, topology-aware,
workload-specific function that significantly impacts availability, performance,
and capacity. The scheduler needs to take into account individual and collective
resource requirements, quality of service requirements, hardware/software/policy
constraints, affinity and anti-affinity specifications, data locality, inter-workload
interference, deadlines, and so on. Workload-specific requirements will be exposed
through the API as necessary.`,
		Run: func(cmd *cobra.Command, args []string) {
			if err := runCommand(cmd, args, opts); err != nil {
				fmt.Fprintf(os.Stderr, "%v\n", err)
				os.Exit(1)
			}
		},
	}
	fs := cmd.Flags()
	namedFlagSets := opts.Flags()
	verflag.AddFlags(namedFlagSets.FlagSet("global"))
	globalflag.AddGlobalFlags(namedFlagSets.FlagSet("global"), cmd.Name())
	for _, f := range namedFlagSets.FlagSets {
		fs.AddFlagSet(f)
	}

	usageFmt := "Usage:\n  %s\n"
	cols, _, _ := term.TerminalSize(cmd.OutOrStdout())
	cmd.SetUsageFunc(func(cmd *cobra.Command) error {
		fmt.Fprintf(cmd.OutOrStderr(), usageFmt, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStderr(), namedFlagSets, cols)
		return nil
	})
	cmd.SetHelpFunc(func(cmd *cobra.Command, args []string) {
		fmt.Fprintf(cmd.OutOrStdout(), "%s\n\n"+usageFmt, cmd.Long, cmd.UseLine())
		cliflag.PrintSections(cmd.OutOrStdout(), namedFlagSets, cols)
	})
	cmd.MarkFlagFilename("config", "yaml", "yml", "json")

	return cmd
}

// runCommand runs the scheduler.
func runCommand(cmd *cobra.Command, args []string, opts *options.Options) error {
	verflag.PrintAndExitIfRequested()
	utilflag.PrintFlags(cmd.Flags())

	if len(args) != 0 {
		fmt.Fprint(os.Stderr, "arguments are not supported\n")
	}

	if errs := opts.Validate(); len(errs) > 0 {
		fmt.Fprintf(os.Stderr, "%v\n", utilerrors.NewAggregate(errs))
		os.Exit(1)
	}

	if len(opts.WriteConfigTo) > 0 {
		if err := options.WriteConfigFile(opts.WriteConfigTo, &opts.ComponentConfig); err != nil {
			fmt.Fprintf(os.Stderr, "%v\n", err)
			os.Exit(1)
		}
		klog.Infof("Wrote configuration to: %s\n", opts.WriteConfigTo)
	}

	c, err := opts.Config()
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v\n", err)
		os.Exit(1)
	}

	stopCh := make(chan struct{})

	// Get the completed config
	cc := c.Complete()

	// To help debugging, immediately log version
	klog.Infof("Version: %+v", version.Get())

	// Apply algorithms based on feature gates.
	// TODO: make configurable?
	algorithmprovider.ApplyFeatureGates()

	// Configz registration.
	if cz, err := configz.New("componentconfig"); err == nil {
		cz.Set(cc.ComponentConfig)
	} else {
		return fmt.Errorf("unable to register configz: %s", err)
	}

	return Run(cc, stopCh)
}

// Run executes the scheduler based on the given configuration. It only return on error or when stopCh is closed.
func Run(cc schedulerserverconfig.CompletedConfig, stopCh <-chan struct{}) error {
	// To help debugging, immediately log version
	klog.V(1).Infof("Starting Kubernetes Scheduler version %+v", version.Get())

	// Create the scheduler.
	sched, err := scheduler.New(cc.Client,
		cc.InformerFactory.Core().V1().Nodes(),
		cc.PodInformer,
		cc.InformerFactory.Core().V1().PersistentVolumes(),
		cc.InformerFactory.Core().V1().PersistentVolumeClaims(),
		cc.InformerFactory.Core().V1().ReplicationControllers(),
		cc.InformerFactory.Apps().V1().ReplicaSets(),
		cc.InformerFactory.Apps().V1().StatefulSets(),
		cc.InformerFactory.Core().V1().Services(),
		cc.InformerFactory.Policy().V1beta1().PodDisruptionBudgets(),
		cc.InformerFactory.Storage().V1().StorageClasses(),
		cc.Recorder,
		cc.ComponentConfig.AlgorithmSource,
		stopCh,
		scheduler.WithName(cc.ComponentConfig.SchedulerName),
		scheduler.WithHardPodAffinitySymmetricWeight(cc.ComponentConfig.HardPodAffinitySymmetricWeight),
		scheduler.WithPreemptionDisabled(cc.ComponentConfig.DisablePreemption),
		scheduler.WithPercentageOfNodesToScore(cc.ComponentConfig.PercentageOfNodesToScore),
		scheduler.WithBindTimeoutSeconds(*cc.ComponentConfig.BindTimeoutSeconds))
	if err != nil {
		return err
	}

	// Prepare the event broadcaster.
	if cc.Broadcaster != nil && cc.EventClient != nil {
		cc.Broadcaster.StartLogging(klog.V(6).Infof)
		cc.Broadcaster.StartRecordingToSink(&v1core.EventSinkImpl{Interface: cc.EventClient.Events("")})
	}

	// Setup healthz checks.
	var checks []healthz.HealthzChecker
	if cc.ComponentConfig.LeaderElection.LeaderElect {
		checks = append(checks, cc.LeaderElection.WatchDog)
	}

	// Start up the healthz server.
	if cc.InsecureServing != nil {
		separateMetrics := cc.InsecureMetricsServing != nil
		handler := buildHandlerChain(newHealthzHandler(&cc.ComponentConfig, separateMetrics, checks...), nil, nil)
		if err := cc.InsecureServing.Serve(handler, 0, stopCh); err != nil {
			return fmt.Errorf("failed to start healthz server: %v", err)
		}
	}
	if cc.InsecureMetricsServing != nil {
		handler := buildHandlerChain(newMetricsHandler(&cc.ComponentConfig), nil, nil)
		if err := cc.InsecureMetricsServing.Serve(handler, 0, stopCh); err != nil {
			return fmt.Errorf("failed to start metrics server: %v", err)
		}
	}
	if cc.SecureServing != nil {
		handler := buildHandlerChain(newHealthzHandler(&cc.ComponentConfig, false, checks...), cc.Authentication.Authenticator, cc.Authorization.Authorizer)
		// TODO: handle stoppedCh returned by c.SecureServing.Serve
		if _, err := cc.SecureServing.Serve(handler, 0, stopCh); err != nil {
			// fail early for secure handlers, removing the old error loop from above
			return fmt.Errorf("failed to start secure server: %v", err)
		}
	}

	// Start all informers.
	go cc.PodInformer.Informer().Run(stopCh)
	cc.InformerFactory.Start(stopCh)

	// Wait for all caches to sync before scheduling.
	cc.InformerFactory.WaitForCacheSync(stopCh)
	controller.WaitForCacheSync("scheduler", stopCh, cc.PodInformer.Informer().HasSynced)

	// Prepare a reusable runCommand function.
	run := func(ctx context.Context) {
		sched.Run()
		<-ctx.Done()
	}

	ctx, cancel := context.WithCancel(context.TODO()) // TODO once Run() accepts a context, it should be used here
	defer cancel()

	go func() {
		select {
		case <-stopCh:
			cancel()
		case <-ctx.Done():
		}
	}()

	// If leader election is enabled, runCommand via LeaderElector until done and exit.
	if cc.LeaderElection != nil {
		cc.LeaderElection.Callbacks = leaderelection.LeaderCallbacks{
			OnStartedLeading: run,
			OnStoppedLeading: func() {
				utilruntime.HandleError(fmt.Errorf("lost master"))
			},
		}
		leaderElector, err := leaderelection.NewLeaderElector(*cc.LeaderElection)
		if err != nil {
			return fmt.Errorf("couldn't create leader elector: %v", err)
		}

		leaderElector.Run(ctx)

		return fmt.Errorf("lost lease")
	}

	// Leader election is disabled, so runCommand inline until done.
	run(ctx)
	return fmt.Errorf("finished without leader elect")
}

// buildHandlerChain wraps the given handler with the standard filters.
func buildHandlerChain(handler http.Handler, authn authenticator.Request, authz authorizer.Authorizer) http.Handler {
	requestInfoResolver := &apirequest.RequestInfoFactory{}
	failedHandler := genericapifilters.Unauthorized(legacyscheme.Codecs, false)

	handler = genericapifilters.WithRequestInfo(handler, requestInfoResolver)
	handler = genericapifilters.WithAuthorization(handler, authz, legacyscheme.Codecs)
	handler = genericapifilters.WithAuthentication(handler, authn, failedHandler, nil)
	handler = genericapifilters.WithRequestInfo(handler, requestInfoResolver)
	handler = genericfilters.WithPanicRecovery(handler)

	return handler
}

func installMetricHandler(pathRecorderMux *mux.PathRecorderMux) {
	configz.InstallHandler(pathRecorderMux)
	defaultMetricsHandler := prometheus.Handler().ServeHTTP
	pathRecorderMux.HandleFunc("/metrics", func(w http.ResponseWriter, req *http.Request) {
		if req.Method == "DELETE" {
			metrics.Reset()
			io.WriteString(w, "metrics reset\n")
			return
		}
		defaultMetricsHandler(w, req)
	})
}

// newMetricsHandler builds a metrics server from the config.
func newMetricsHandler(config *kubeschedulerconfig.KubeSchedulerConfiguration) http.Handler {
	pathRecorderMux := mux.NewPathRecorderMux("kube-scheduler")
	installMetricHandler(pathRecorderMux)
	if config.EnableProfiling {
		routes.Profiling{}.Install(pathRecorderMux)
		if config.EnableContentionProfiling {
			goruntime.SetBlockProfileRate(1)
		}
	}
	return pathRecorderMux
}

// newHealthzHandler creates a healthz server from the config, and will also
// embed the metrics handler if the healthz and metrics address configurations
// are the same.
func newHealthzHandler(config *kubeschedulerconfig.KubeSchedulerConfiguration, separateMetrics bool, checks ...healthz.HealthzChecker) http.Handler {
	pathRecorderMux := mux.NewPathRecorderMux("kube-scheduler")
	healthz.InstallHandler(pathRecorderMux, checks...)
	if !separateMetrics {
		installMetricHandler(pathRecorderMux)
	}
	if config.EnableProfiling {
		routes.Profiling{}.Install(pathRecorderMux)
		if config.EnableContentionProfiling {
			goruntime.SetBlockProfileRate(1)
		}
	}
	return pathRecorderMux
}