/*
Copyright 2016 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 main

import (
	"flag"
	"fmt"
	"net/http"
	"net/url"
	"os"
	"time"

	"github.com/golang/glog"
	basecmd "github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/cmd"
	"github.com/kubernetes-incubator/custom-metrics-apiserver/pkg/provider"
	"k8s.io/apimachinery/pkg/util/wait"
	"k8s.io/apiserver/pkg/util/logs"
	"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"
)

type PrometheusAdapter struct {
	basecmd.AdapterBase

	// 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
	// MetricsRelistInterval is the interval at which to relist the set of available metrics
	MetricsRelistInterval time.Duration
}

func (cmd *PrometheusAdapter) makePromClient() (prom.Client, error) {
	baseURL, err := url.Parse(cmd.PrometheusURL)
	if err != nil {
		return nil, fmt.Errorf("invalid Prometheus URL %q: %v", baseURL, err)
	}
	promHTTPClient, err := makeHTTPClient(cmd.PrometheusAuthInCluster, cmd.PrometheusAuthConf)
	if err != nil {
		return nil, err
	}
	genericPromClient := prom.NewGenericAPIClient(promHTTPClient, baseURL)
	instrumentedGenericPromClient := mprom.InstrumentGenericAPIClient(genericPromClient, baseURL.String())
	return prom.NewClientForAPI(instrumentedGenericPromClient), nil
}

func (cmd *PrometheusAdapter) addFlags() {
	cmd.Flags().StringVar(&cmd.PrometheusURL, "prometheus-url", cmd.PrometheusURL,
		"URL for connecting to Prometheus.")
	cmd.Flags().BoolVar(&cmd.PrometheusAuthInCluster, "prometheus-auth-incluster", cmd.PrometheusAuthInCluster,
		"use auth details from the in-cluster kubeconfig when connecting to prometheus.")
	cmd.Flags().StringVar(&cmd.PrometheusAuthConf, "prometheus-auth-config", cmd.PrometheusAuthConf,
		"kubeconfig file used to configure auth when connecting to Prometheus.")
	cmd.Flags().StringVar(&cmd.AdapterConfigFile, "config", cmd.AdapterConfigFile,
		"Configuration file containing details of how to transform between Prometheus metrics "+
			"and custom metrics API resources")
	cmd.Flags().DurationVar(&cmd.MetricsRelistInterval, "metrics-relist-interval", cmd.MetricsRelistInterval, ""+
		"interval at which to re-list the set of all available metrics from Prometheus")
}

func (cmd *PrometheusAdapter) makeProvider(stopCh <-chan struct{}) (provider.CustomMetricsProvider, error) {
	// load metrics discovery configuration
	if cmd.AdapterConfigFile == "" {
		return nil, fmt.Errorf("no metrics discovery configuration file specified (make sure to use --config)")
	}
	metricsConfig, err := adaptercfg.FromFile(cmd.AdapterConfigFile)
	if err != nil {
		return nil, fmt.Errorf("unable to load metrics discovery configuration: %v", err)
	}

	// make the prometheus client
	promClient, err := cmd.makePromClient()
	if err != nil {
		return nil, fmt.Errorf("unable to construct Prometheus client: %v", err)
	}

	// grab the mapper and dynamic client
	mapper, err := cmd.RESTMapper()
	if err != nil {
		return nil, fmt.Errorf("unable to construct RESTMapper: %v", err)
	}
	dynClient, err := cmd.DynamicClient()
	if err != nil {
		return nil, fmt.Errorf("unable to construct Kubernetes client: %v", err)
	}

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

	// construct the provider and start it
	cmProvider, runner := cmprov.NewPrometheusProvider(mapper, dynClient, promClient, namers, cmd.MetricsRelistInterval)
	runner.RunUntil(stopCh)

	return cmProvider, nil
}

func main() {
	logs.InitLogs()
	defer logs.FlushLogs()

	// set up flags
	cmd := &PrometheusAdapter{
		PrometheusURL:         "https://localhost",
		MetricsRelistInterval: 10 * time.Minute,
	}
	cmd.addFlags()
	cmd.Flags().AddGoFlagSet(flag.CommandLine) // make sure we get the glog flags
	cmd.Flags().Parse(os.Args)

	// construct the provider
	cmProvider, err := cmd.makeProvider(wait.NeverStop)
	if err != nil {
		glog.Fatalf("unable to construct custom metrics provider: %v", err)
	}

	// attach the provider to the server and run it
	cmd.WithCustomMetrics(cmProvider)
	if err := cmd.Run(wait.NeverStop); err != nil {
		glog.Fatalf("unable to run custom metrics adapter: %v", err)
	}
}

// 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
}