package main

import (
	"bytes"
	"crypto/tls"
	"crypto/x509"
	"encoding/json"
	"errors"
	"fmt"
	"io/ioutil"
	"log"
	"net"
	"net/http"
	"net/url"
	"os"
	"strings"
	"time"

	"github.com/ericchiang/oidc"
	"github.com/spf13/cobra"
	"golang.org/x/net/context"
	"golang.org/x/oauth2"
)

type app struct {
	clientID     string
	clientSecret string
	redirectURI  string

	verifier *oidc.IDTokenVerifier
	provider *oidc.Provider

	ctx    context.Context
	cancel context.CancelFunc
}

// return an HTTP client which trusts the provided root CAs.
func httpClientForRootCAs(rootCAs string) (*http.Client, error) {
	tlsConfig := tls.Config{RootCAs: x509.NewCertPool()}
	rootCABytes, err := ioutil.ReadFile(rootCAs)
	if err != nil {
		return nil, fmt.Errorf("failed to read root-ca: %v", err)
	}
	if !tlsConfig.RootCAs.AppendCertsFromPEM(rootCABytes) {
		return nil, fmt.Errorf("no certs found in root CA file %q", rootCAs)
	}
	return &http.Client{
		Transport: &http.Transport{
			TLSClientConfig: &tlsConfig,
			Proxy:           http.ProxyFromEnvironment,
			Dial: (&net.Dialer{
				Timeout:   30 * time.Second,
				KeepAlive: 30 * time.Second,
			}).Dial,
			TLSHandshakeTimeout:   10 * time.Second,
			ExpectContinueTimeout: 1 * time.Second,
		},
	}, nil
}

func cmd() *cobra.Command {
	var (
		a         app
		issuerURL string
		listen    string
		tlsCert   string
		tlsKey    string
		rootCAs   string
	)
	c := cobra.Command{
		Use:   "example-app",
		Short: "An example OpenID Connect client",
		Long:  "",
		RunE: func(cmd *cobra.Command, args []string) error {
			if len(args) != 0 {
				return errors.New("surplus arguments provided")
			}

			u, err := url.Parse(a.redirectURI)
			if err != nil {
				return fmt.Errorf("parse redirect-uri: %v", err)
			}
			listenURL, err := url.Parse(listen)
			if err != nil {
				return fmt.Errorf("parse listen address: %v", err)
			}

			a.ctx, a.cancel = context.WithCancel(context.Background())

			if rootCAs != "" {
				client, err := httpClientForRootCAs(rootCAs)
				if err != nil {
					return err
				}

				// This sets the OAuth2 client and oidc client.
				a.ctx = context.WithValue(a.ctx, oauth2.HTTPClient, &client)
			}

			// TODO(ericchiang): Retry with backoff
			provider, err := oidc.NewProvider(a.ctx, issuerURL)
			if err != nil {
				return fmt.Errorf("Failed to query provider %q: %v", issuerURL, err)
			}
			a.provider = provider
			a.verifier = provider.NewVerifier(a.ctx, oidc.VerifyAudience(a.clientID))

			http.HandleFunc("/", a.handleIndex)
			http.HandleFunc("/login", a.handleLogin)
			http.HandleFunc(u.Path, a.handleCallback)

			switch listenURL.Scheme {
			case "http":
				log.Printf("listening on %s", listen)
				return http.ListenAndServe(listenURL.Host, nil)
			case "https":
				log.Printf("listening on %s", listen)
				return http.ListenAndServeTLS(listenURL.Host, tlsCert, tlsKey, nil)
			default:
				return fmt.Errorf("listen address %q is not using http or https", listen)
			}
		},
	}
	c.Flags().StringVar(&a.clientID, "client-id", "example-app", "OAuth2 client ID of this application.")
	c.Flags().StringVar(&a.clientSecret, "client-secret", "ZXhhbXBsZS1hcHAtc2VjcmV0", "OAuth2 client secret of this application.")
	c.Flags().StringVar(&a.redirectURI, "redirect-uri", "http://127.0.0.1:5555/callback", "Callback URL for OAuth2 responses.")
	c.Flags().StringVar(&issuerURL, "issuer", "http://127.0.0.1:5556", "URL of the OpenID Connect issuer.")
	c.Flags().StringVar(&listen, "listen", "http://127.0.0.1:5555", "HTTP(S) address to listen at.")
	c.Flags().StringVar(&tlsCert, "tls-cert", "", "X509 cert file to present when serving HTTPS.")
	c.Flags().StringVar(&tlsKey, "tls-key", "", "Private key for the HTTPS cert.")
	c.Flags().StringVar(&rootCAs, "issuer-root-ca", "", "Root certificate authorities for the issuer. Defaults to host certs.")
	return &c
}

func main() {
	if err := cmd().Execute(); err != nil {
		fmt.Fprintf(os.Stderr, "error: %v\n", err)
		os.Exit(2)
	}
}

func (a *app) handleIndex(w http.ResponseWriter, r *http.Request) {
	renderIndex(w)
}

func (a *app) oauth2Config(scopes []string) *oauth2.Config {
	return &oauth2.Config{
		ClientID:     a.clientID,
		ClientSecret: a.clientSecret,
		Endpoint:     a.provider.Endpoint(),
		Scopes:       scopes,
		RedirectURL:  a.redirectURI,
	}
}

func (a *app) handleLogin(w http.ResponseWriter, r *http.Request) {
	var scopes []string
	if extraScopes := r.FormValue("extra_scopes"); extraScopes != "" {
		scopes = strings.Split(extraScopes, " ")
	}
	var clients []string
	if crossClients := r.FormValue("cross_client"); crossClients != "" {
		clients = strings.Split(crossClients, " ")
	}
	for _, client := range clients {
		scopes = append(scopes, "audience:server:client_id:"+client)
	}

	// TODO(ericchiang): Determine if provider does not support "offline_access" or has
	// some other mechanism for requesting refresh tokens.
	scopes = append(scopes, "openid", "profile", "email", "offline_access")
	http.Redirect(w, r, a.oauth2Config(scopes).AuthCodeURL(""), http.StatusSeeOther)
}

func (a *app) handleCallback(w http.ResponseWriter, r *http.Request) {
	if errMsg := r.FormValue("error"); errMsg != "" {
		http.Error(w, errMsg+": "+r.FormValue("error_description"), http.StatusBadRequest)
		return
	}

	code := r.FormValue("code")
	refresh := r.FormValue("refresh_token")
	var (
		err   error
		token *oauth2.Token
	)
	oauth2Config := a.oauth2Config(nil)
	switch {
	case code != "":
		token, err = oauth2Config.Exchange(a.ctx, code)
	case refresh != "":
		t := &oauth2.Token{
			RefreshToken: refresh,
			Expiry:       time.Now().Add(-time.Hour),
		}
		token, err = oauth2Config.TokenSource(a.ctx, t).Token()
	default:
		http.Error(w, "no code in request", http.StatusBadRequest)
		return
	}

	if err != nil {
		http.Error(w, fmt.Sprintf("failed to get token: %v", err), http.StatusInternalServerError)
		return
	}

	rawIDToken, ok := token.Extra("id_token").(string)
	if !ok {
		http.Error(w, "no id_token in token response", http.StatusInternalServerError)
		return
	}

	idToken, err := a.verifier.Verify(rawIDToken)
	if err != nil {
		http.Error(w, fmt.Sprintf("Failed to verify ID token: %v", err), http.StatusInternalServerError)
		return
	}
	var claims json.RawMessage
	idToken.Claims(&claims)

	buff := new(bytes.Buffer)
	json.Indent(buff, []byte(claims), "", "  ")

	renderToken(w, a.redirectURI, rawIDToken, token.RefreshToken, buff.Bytes())
}