// Copyright 2013 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 httputil

import (
	"crypto/tls"
	"crypto/x509"
	"fmt"
	"io/ioutil"
	"net/http"
	"strings"
	"time"

	"github.com/mwitkow/go-conntrack"
	config_util "github.com/prometheus/common/config"
)

// NewClient returns a http.Client using the specified http.RoundTripper.
func newClient(rt http.RoundTripper) *http.Client {
	return &http.Client{Transport: rt}
}

// NewClientFromConfig returns a new HTTP client configured for the
// given config.HTTPClientConfig. The name is used as go-conntrack metric label.
func NewClientFromConfig(cfg config_util.HTTPClientConfig, name string) (*http.Client, error) {
	rt, err := NewRoundTripperFromConfig(cfg, name)
	if err != nil {
		return nil, err
	}
	return newClient(rt), nil
}

// NewRoundTripperFromConfig returns a new HTTP RoundTripper configured for the
// given config.HTTPClientConfig. The name is used as go-conntrack metric label.
func NewRoundTripperFromConfig(cfg config_util.HTTPClientConfig, name string) (http.RoundTripper, error) {
	tlsConfig, err := NewTLSConfig(cfg.TLSConfig)
	if err != nil {
		return nil, err
	}
	// The only timeout we care about is the configured scrape timeout.
	// It is applied on request. So we leave out any timings here.
	var rt http.RoundTripper = &http.Transport{
		Proxy:               http.ProxyURL(cfg.ProxyURL.URL),
		MaxIdleConns:        20000,
		MaxIdleConnsPerHost: 1000, // see https://github.com/golang/go/issues/13801
		DisableKeepAlives:   false,
		TLSClientConfig:     tlsConfig,
		DisableCompression:  true,
		// 5 minutes is typically above the maximum sane scrape interval. So we can
		// use keepalive for all configurations.
		IdleConnTimeout: 5 * time.Minute,
		DialContext: conntrack.NewDialContextFunc(
			conntrack.DialWithTracing(),
			conntrack.DialWithName(name),
		),
	}

	// If a bearer token is provided, create a round tripper that will set the
	// Authorization header correctly on each request.
	if len(cfg.BearerToken) > 0 {
		rt = NewBearerAuthRoundTripper(string(cfg.BearerToken), rt)
	} else if len(cfg.BearerTokenFile) > 0 {
		rt = NewBearerAuthFileRoundTripper(cfg.BearerTokenFile, rt)
	}

	if cfg.BasicAuth != nil {
		rt = NewBasicAuthRoundTripper(cfg.BasicAuth.Username, string(cfg.BasicAuth.Password), rt)
	}

	// Return a new configured RoundTripper.
	return rt, nil
}

type bearerAuthRoundTripper struct {
	bearerToken string
	rt          http.RoundTripper
}

// NewBearerAuthRoundTripper adds the provided bearer token to a request unless the authorization
// header has already been set.
func NewBearerAuthRoundTripper(bearer string, rt http.RoundTripper) http.RoundTripper {
	return &bearerAuthRoundTripper{bearer, rt}
}

func (rt *bearerAuthRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	if len(req.Header.Get("Authorization")) == 0 {
		req = cloneRequest(req)
		req.Header.Set("Authorization", "Bearer "+rt.bearerToken)
	}

	return rt.rt.RoundTrip(req)
}

type bearerAuthFileRoundTripper struct {
	bearerFile string
	rt         http.RoundTripper
}

// NewBearerAuthFileRoundTripper adds the bearer token read from the provided file to a request unless
// the authorization header has already been set. This file is read for every request.
func NewBearerAuthFileRoundTripper(bearerFile string, rt http.RoundTripper) http.RoundTripper {
	return &bearerAuthFileRoundTripper{bearerFile, rt}
}

func (rt *bearerAuthFileRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	if len(req.Header.Get("Authorization")) == 0 {
		b, err := ioutil.ReadFile(rt.bearerFile)
		if err != nil {
			return nil, fmt.Errorf("unable to read bearer token file %s: %s", rt.bearerFile, err)
		}
		bearerToken := strings.TrimSpace(string(b))

		req = cloneRequest(req)
		req.Header.Set("Authorization", "Bearer "+bearerToken)
	}

	return rt.rt.RoundTrip(req)
}

type basicAuthRoundTripper struct {
	username string
	password string
	rt       http.RoundTripper
}

// NewBasicAuthRoundTripper will apply a BASIC auth authorization header to a request unless it has
// already been set.
func NewBasicAuthRoundTripper(username, password string, rt http.RoundTripper) http.RoundTripper {
	return &basicAuthRoundTripper{username, password, rt}
}

func (rt *basicAuthRoundTripper) RoundTrip(req *http.Request) (*http.Response, error) {
	if len(req.Header.Get("Authorization")) != 0 {
		return rt.rt.RoundTrip(req)
	}
	req = cloneRequest(req)
	req.SetBasicAuth(rt.username, rt.password)
	return rt.rt.RoundTrip(req)
}

// cloneRequest returns a clone of the provided *http.Request.
// The clone is a shallow copy of the struct and its Header map.
func cloneRequest(r *http.Request) *http.Request {
	// Shallow copy of the struct.
	r2 := new(http.Request)
	*r2 = *r
	// Deep copy of the Header.
	r2.Header = make(http.Header)
	for k, s := range r.Header {
		r2.Header[k] = s
	}
	return r2
}

// NewTLSConfig creates a new tls.Config from the given config_util.TLSConfig.
func NewTLSConfig(cfg config_util.TLSConfig) (*tls.Config, error) {
	tlsConfig := &tls.Config{InsecureSkipVerify: cfg.InsecureSkipVerify}

	// If a CA cert is provided then let's read it in so we can validate the
	// scrape target's certificate properly.
	if len(cfg.CAFile) > 0 {
		caCertPool := x509.NewCertPool()
		// Load CA cert.
		caCert, err := ioutil.ReadFile(cfg.CAFile)
		if err != nil {
			return nil, fmt.Errorf("unable to use specified CA cert %s: %s", cfg.CAFile, err)
		}
		caCertPool.AppendCertsFromPEM(caCert)
		tlsConfig.RootCAs = caCertPool
	}

	if len(cfg.ServerName) > 0 {
		tlsConfig.ServerName = cfg.ServerName
	}
	// If a client cert & key is provided then configure TLS config accordingly.
	if len(cfg.CertFile) > 0 && len(cfg.KeyFile) > 0 {
		cert, err := tls.LoadX509KeyPair(cfg.CertFile, cfg.KeyFile)
		if err != nil {
			return nil, fmt.Errorf("unable to use specified client cert (%s) & key (%s): %s", cfg.CertFile, cfg.KeyFile, err)
		}
		tlsConfig.Certificates = []tls.Certificate{cert}
	}
	tlsConfig.BuildNameToCertificate()

	return tlsConfig, nil
}