/*
Copyright 2017 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

import (
	"fmt"
	"io"
	"net/http"
	"net/url"
	"time"

	"github.com/spf13/cobra"
	"k8s.io/client-go/discovery"
	"k8s.io/client-go/dynamic"
	"k8s.io/client-go/rest"
	"k8s.io/client-go/tools/clientcmd"

	prom "github.com/directxman12/k8s-prometheus-adapter/pkg/client"
	mprom "github.com/directxman12/k8s-prometheus-adapter/pkg/client/metrics"
	adaptercfg "github.com/directxman12/k8s-prometheus-adapter/pkg/config"
	cmprov "github.com/directxman12/k8s-prometheus-adapter/pkg/custom-provider"
	"github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/cmd/server"
	"github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/dynamicmapper"
)

// NewCommandStartPrometheusAdapterServer provides a CLI handler for 'start master' command
func NewCommandStartPrometheusAdapterServer(out, errOut io.Writer, stopCh <-chan struct{}) *cobra.Command {
	baseOpts := server.NewCustomMetricsAdapterServerOptions(out, errOut)
	o := PrometheusAdapterServerOptions{
		CustomMetricsAdapterServerOptions: baseOpts,
		MetricsRelistInterval:             10 * time.Minute,
		PrometheusURL:                     "https://localhost",
	}

	cmd := &cobra.Command{
		Short: "Launch the custom metrics API adapter server",
		Long:  "Launch the custom metrics API adapter server",
		RunE: func(c *cobra.Command, args []string) error {
			if err := o.Complete(); err != nil {
				return err
			}
			if err := o.Validate(args); err != nil {
				return err
			}
			if err := o.RunCustomMetricsAdapterServer(stopCh); err != nil {
				return err
			}
			return nil
		},
	}

	flags := cmd.Flags()
	o.SecureServing.AddFlags(flags)
	o.Authentication.AddFlags(flags)
	o.Authorization.AddFlags(flags)
	o.Features.AddFlags(flags)

	flags.StringVar(&o.RemoteKubeConfigFile, "lister-kubeconfig", o.RemoteKubeConfigFile, ""+
		"kubeconfig file pointing at the 'core' kubernetes server with enough rights to list "+
		"any described objets")
	flags.DurationVar(&o.MetricsRelistInterval, "metrics-relist-interval", o.MetricsRelistInterval, ""+
		"interval at which to re-list the set of all available metrics from Prometheus")
	flags.DurationVar(&o.DiscoveryInterval, "discovery-interval", o.DiscoveryInterval, ""+
		"interval at which to refresh API discovery information")
	flags.StringVar(&o.PrometheusURL, "prometheus-url", o.PrometheusURL,
		"URL for connecting to Prometheus.")
	flags.BoolVar(&o.PrometheusAuthInCluster, "prometheus-auth-incluster", o.PrometheusAuthInCluster,
		"use auth details from the in-cluster kubeconfig when connecting to prometheus.")
	flags.StringVar(&o.PrometheusAuthConf, "prometheus-auth-config", o.PrometheusAuthConf,
		"kubeconfig file used to configure auth when connecting to Prometheus.")
	flags.StringVar(&o.AdapterConfigFile, "config", o.AdapterConfigFile,
		"Configuration file containing details of how to transform between Prometheus metrics "+
			"and custom metrics API resources")

	cmd.MarkFlagRequired("config")

	return cmd
}

// makeHTTPClient constructs an HTTP for connecting with the given auth options.
func makeHTTPClient(inClusterAuth bool, kubeConfigPath string) (*http.Client, error) {
	// make sure we're not trying to use two different sources of auth
	if inClusterAuth && kubeConfigPath != "" {
		return nil, fmt.Errorf("may not use both in-cluster auth and an explicit kubeconfig at the same time")
	}

	// return the default client if we're using no auth
	if !inClusterAuth && kubeConfigPath == "" {
		return http.DefaultClient, nil
	}

	var authConf *rest.Config
	if kubeConfigPath != "" {
		var err error
		loadingRules := &clientcmd.ClientConfigLoadingRules{ExplicitPath: kubeConfigPath}
		loader := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loadingRules, &clientcmd.ConfigOverrides{})
		authConf, err = loader.ClientConfig()
		if err != nil {
			return nil, fmt.Errorf("unable to construct  auth configuration from %q for connecting to Prometheus: %v", kubeConfigPath, err)
		}
	} else {
		var err error
		authConf, err = rest.InClusterConfig()
		if err != nil {
			return nil, fmt.Errorf("unable to construct in-cluster auth configuration for connecting to Prometheus: %v", err)
		}
	}
	tr, err := rest.TransportFor(authConf)
	if err != nil {
		return nil, fmt.Errorf("unable to construct client transport for connecting to Prometheus: %v", err)
	}
	return &http.Client{Transport: tr}, nil
}

func (o PrometheusAdapterServerOptions) RunCustomMetricsAdapterServer(stopCh <-chan struct{}) error {
	if o.AdapterConfigFile == "" {
		return fmt.Errorf("no discovery configuration file specified")
	}

	metricsConfig, err := adaptercfg.FromFile(o.AdapterConfigFile)
	if err != nil {
		return fmt.Errorf("unable to load metrics discovery configuration: %v", err)
	}

	config, err := o.Config()
	if err != nil {
		return err
	}

	config.GenericConfig.EnableMetrics = true

	var clientConfig *rest.Config
	if len(o.RemoteKubeConfigFile) > 0 {
		loadingRules := &clientcmd.ClientConfigLoadingRules{ExplicitPath: o.RemoteKubeConfigFile}
		loader := clientcmd.NewNonInteractiveDeferredLoadingClientConfig(loadingRules, &clientcmd.ConfigOverrides{})

		clientConfig, err = loader.ClientConfig()
	} else {
		clientConfig, err = rest.InClusterConfig()
	}
	if err != nil {
		return fmt.Errorf("unable to construct lister client config to initialize provider: %v", err)
	}

	discoveryClient, err := discovery.NewDiscoveryClientForConfig(clientConfig)
	if err != nil {
		return fmt.Errorf("unable to construct discovery client for dynamic client: %v", err)
	}

	dynamicMapper, err := dynamicmapper.NewRESTMapper(discoveryClient, o.DiscoveryInterval)
	if err != nil {
		return fmt.Errorf("unable to construct dynamic discovery mapper: %v", err)
	}

	dynamicClient, err := dynamic.NewForConfig(clientConfig)
	if err != nil {
		return fmt.Errorf("unable to construct lister client to initialize provider: %v", err)
	}

	// TODO: actually configure this client (strip query vars, etc)
	baseURL, err := url.Parse(o.PrometheusURL)
	if err != nil {
		return fmt.Errorf("invalid Prometheus URL %q: %v", baseURL, err)
	}
	promHTTPClient, err := makeHTTPClient(o.PrometheusAuthInCluster, o.PrometheusAuthConf)
	if err != nil {
		return err
	}
	genericPromClient := prom.NewGenericAPIClient(promHTTPClient, baseURL)
	instrumentedGenericPromClient := mprom.InstrumentGenericAPIClient(genericPromClient, baseURL.String())
	promClient := prom.NewClientForAPI(instrumentedGenericPromClient)

	namers, err := cmprov.NamersFromConfig(metricsConfig, dynamicMapper)
	if err != nil {
		return fmt.Errorf("unable to construct naming scheme from metrics rules: %v", err)
	}

	cmProvider, runner := cmprov.NewPrometheusProvider(dynamicMapper, dynamicClient, promClient, namers, o.MetricsRelistInterval)
	runner.RunUntil(stopCh)

	server, err := config.Complete().New("prometheus-custom-metrics-adapter", cmProvider, nil)
	if err != nil {
		return err
	}
	return server.GenericAPIServer.PrepareRun().Run(stopCh)
}

type PrometheusAdapterServerOptions struct {
	*server.CustomMetricsAdapterServerOptions

	// RemoteKubeConfigFile is the config used to list pods from the master API server
	RemoteKubeConfigFile string
	// MetricsRelistInterval is the interval at which to relist the set of available metrics
	MetricsRelistInterval time.Duration
	// DiscoveryInterval is the interval at which discovery information is refreshed
	DiscoveryInterval time.Duration
	// PrometheusURL is the URL describing how to connect to Prometheus.  Query parameters configure connection options.
	PrometheusURL string
	// PrometheusAuthInCluster enables using the auth details from the in-cluster kubeconfig to connect to Prometheus
	PrometheusAuthInCluster bool
	// PrometheusAuthConf is the kubeconfig file that contains auth details used to connect to Prometheus
	PrometheusAuthConf string
	// AdapterConfigFile points to the file containing the metrics discovery configuration.
	AdapterConfigFile string
}
