package prometheus

import (
	"context"
	"errors"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"net/url"
	"sync"
	"time"

	"github.com/influxdata/telegraf"
	"github.com/influxdata/telegraf/internal"
	"github.com/influxdata/telegraf/internal/tls"
	"github.com/influxdata/telegraf/plugins/inputs"
)

const acceptHeader = `application/vnd.google.protobuf;proto=io.prometheus.client.MetricFamily;encoding=delimited;q=0.7,text/plain;version=0.0.4;q=0.3`

type Prometheus struct {
	// An array of urls to scrape metrics from.
	URLs []string `toml:"urls"`

	// An array of Kubernetes services to scrape metrics from.
	KubernetesServices []string

	// Location of kubernetes config file
	KubeConfig string

	// Bearer Token authorization file path
	BearerToken string `toml:"bearer_token"`

	ResponseTimeout internal.Duration `toml:"response_timeout"`

	tls.ClientConfig

	client *http.Client

	// Should we scrape Kubernetes services for prometheus annotations
	MonitorPods    bool `toml:"monitor_kubernetes_pods"`
	lock           sync.Mutex
	kubernetesPods []URLAndAddress
	cancel         context.CancelFunc
	wg             sync.WaitGroup
}

var sampleConfig = `
  ## An array of urls to scrape metrics from.
  urls = ["http://localhost:9100/metrics"]

  ## An array of Kubernetes services to scrape metrics from.
  # kubernetes_services = ["http://my-service-dns.my-namespace:9100/metrics"]

  ## Kubernetes config file to create client from.
  # kube_config = "/path/to/kubernetes.config"

  ## Scrape Kubernetes pods for the following prometheus annotations:
  ## - prometheus.io/scrape: Enable scraping for this pod
  ## - prometheus.io/scheme: If the metrics endpoint is secured then you will need to
  ##     set this to 'https' & most likely set the tls config.
  ## - prometheus.io/path: If the metrics path is not /metrics, define it with this annotation.
  ## - prometheus.io/port: If port is not 9102 use this annotation
  # monitor_kubernetes_pods = true

  ## Use bearer token for authorization
  # bearer_token = /path/to/bearer/token

  ## Specify timeout duration for slower prometheus clients (default is 3s)
  # response_timeout = "3s"

  ## Optional TLS Config
  # tls_ca = /path/to/cafile
  # tls_cert = /path/to/certfile
  # tls_key = /path/to/keyfile
  ## Use TLS but skip chain & host verification
  # insecure_skip_verify = false
`

func (p *Prometheus) SampleConfig() string {
	return sampleConfig
}

func (p *Prometheus) Description() string {
	return "Read metrics from one or many prometheus clients"
}

var ErrProtocolError = errors.New("prometheus protocol error")

func (p *Prometheus) AddressToURL(u *url.URL, address string) *url.URL {
	host := address
	if u.Port() != "" {
		host = address + ":" + u.Port()
	}
	reconstructedURL := &url.URL{
		Scheme:     u.Scheme,
		Opaque:     u.Opaque,
		User:       u.User,
		Path:       u.Path,
		RawPath:    u.RawPath,
		ForceQuery: u.ForceQuery,
		RawQuery:   u.RawQuery,
		Fragment:   u.Fragment,
		Host:       host,
	}
	return reconstructedURL
}

type URLAndAddress struct {
	OriginalURL *url.URL
	URL         *url.URL
	Address     string
	Tags        map[string]string
}

func (p *Prometheus) GetAllURLs() ([]URLAndAddress, error) {
	allURLs := make([]URLAndAddress, 0)
	for _, u := range p.URLs {
		URL, err := url.Parse(u)
		if err != nil {
			log.Printf("prometheus: Could not parse %s, skipping it. Error: %s", u, err.Error())
			continue
		}

		allURLs = append(allURLs, URLAndAddress{URL: URL, OriginalURL: URL})
	}
	p.lock.Lock()
	defer p.lock.Unlock()
	// loop through all pods scraped via the prometheus annotation on the pods
	allURLs = append(allURLs, p.kubernetesPods...)

	for _, service := range p.KubernetesServices {
		URL, err := url.Parse(service)
		if err != nil {
			return nil, err
		}

		resolvedAddresses, err := net.LookupHost(URL.Hostname())
		if err != nil {
			log.Printf("prometheus: Could not resolve %s, skipping it. Error: %s", URL.Host, err.Error())
			continue
		}
		for _, resolved := range resolvedAddresses {
			serviceURL := p.AddressToURL(URL, resolved)
			allURLs = append(allURLs, URLAndAddress{URL: serviceURL, Address: resolved, OriginalURL: URL})
		}
	}
	return allURLs, nil
}

// Reads stats from all configured servers accumulates stats.
// Returns one of the errors encountered while gather stats (if any).
func (p *Prometheus) Gather(acc telegraf.Accumulator) error {
	if p.client == nil {
		client, err := p.createHTTPClient()
		if err != nil {
			return err
		}
		p.client = client
	}

	var wg sync.WaitGroup

	allURLs, err := p.GetAllURLs()
	if err != nil {
		return err
	}
	for _, URL := range allURLs {
		wg.Add(1)
		go func(serviceURL URLAndAddress) {
			defer wg.Done()
			acc.AddError(p.gatherURL(serviceURL, acc))
		}(URL)
	}

	wg.Wait()

	return nil
}

func (p *Prometheus) createHTTPClient() (*http.Client, error) {
	tlsCfg, err := p.ClientConfig.TLSConfig()
	if err != nil {
		return nil, err
	}

	client := &http.Client{
		Transport: &http.Transport{
			TLSClientConfig:   tlsCfg,
			DisableKeepAlives: true,
		},
		Timeout: p.ResponseTimeout.Duration,
	}

	return client, nil
}

func (p *Prometheus) gatherURL(u URLAndAddress, acc telegraf.Accumulator) error {
	var req *http.Request
	var err error
	var uClient *http.Client
	if u.URL.Scheme == "unix" {
		path := u.URL.Query().Get("path")
		if path == "" {
			path = "/metrics"
		}
		req, err = http.NewRequest("GET", "http://localhost"+path, nil)

		// ignore error because it's been handled before getting here
		tlsCfg, _ := p.ClientConfig.TLSConfig()
		uClient = &http.Client{
			Transport: &http.Transport{
				TLSClientConfig:   tlsCfg,
				DisableKeepAlives: true,
				Dial: func(network, addr string) (net.Conn, error) {
					c, err := net.Dial("unix", u.URL.Path)
					return c, err
				},
			},
			Timeout: p.ResponseTimeout.Duration,
		}
	} else {
		if u.URL.Path == "" {
			u.URL.Path = "/metrics"
		}
		req, err = http.NewRequest("GET", u.URL.String(), nil)
	}

	req.Header.Add("Accept", acceptHeader)

	var token []byte
	if p.BearerToken != "" {
		token, err = ioutil.ReadFile(p.BearerToken)
		if err != nil {
			return err
		}
		req.Header.Set("Authorization", "Bearer "+string(token))
	}

	var resp *http.Response
	if u.URL.Scheme != "unix" {
		resp, err = p.client.Do(req)
	} else {
		resp, err = uClient.Do(req)
	}
	if err != nil {
		return fmt.Errorf("error making HTTP request to %s: %s", u.URL, err)
	}
	defer resp.Body.Close()

	if resp.StatusCode != http.StatusOK {
		return fmt.Errorf("%s returned HTTP status %s", u.URL, resp.Status)
	}

	body, err := ioutil.ReadAll(resp.Body)
	if err != nil {
		return fmt.Errorf("error reading body: %s", err)
	}

	metrics, err := Parse(body, resp.Header)
	if err != nil {
		return fmt.Errorf("error reading metrics for %s: %s",
			u.URL, err)
	}

	for _, metric := range metrics {
		tags := metric.Tags()
		// strip user and password from URL
		u.OriginalURL.User = nil
		tags["url"] = u.OriginalURL.String()
		if u.Address != "" {
			tags["address"] = u.Address
		}
		for k, v := range u.Tags {
			tags[k] = v
		}

		switch metric.Type() {
		case telegraf.Counter:
			acc.AddCounter(metric.Name(), metric.Fields(), tags, metric.Time())
		case telegraf.Gauge:
			acc.AddGauge(metric.Name(), metric.Fields(), tags, metric.Time())
		case telegraf.Summary:
			acc.AddSummary(metric.Name(), metric.Fields(), tags, metric.Time())
		case telegraf.Histogram:
			acc.AddHistogram(metric.Name(), metric.Fields(), tags, metric.Time())
		default:
			acc.AddFields(metric.Name(), metric.Fields(), tags, metric.Time())
		}
	}

	return nil
}

// Start will start the Kubernetes scraping if enabled in the configuration
func (p *Prometheus) Start(a telegraf.Accumulator) error {
	if p.MonitorPods {
		var ctx context.Context
		ctx, p.cancel = context.WithCancel(context.Background())
		return p.start(ctx)
	}
	return nil
}

func (p *Prometheus) Stop() {
	p.cancel()
	p.wg.Wait()
}

func init() {
	inputs.Add("prometheus", func() telegraf.Input {
		return &Prometheus{ResponseTimeout: internal.Duration{Duration: time.Second * 3}}
	})
}