// Package github implements OAuth2 support for github.com
package github

import (
	"crypto/rand"
	"encoding/hex"
	"encoding/json"
	"io/ioutil"
	"net/http"
	"net/url"

	"github.com/google/go-github/github"
	"github.com/matrix-org/go-neb/database"
	"github.com/matrix-org/go-neb/services/github/client"
	"github.com/matrix-org/go-neb/types"
	log "github.com/sirupsen/logrus"
)

// RealmType of the Github Realm
const RealmType = "github"

// Realm can handle OAuth processes with github.com
//
// Example request:
//  {
//      "ClientSecret": "YOUR_CLIENT_SECRET",
//      "ClientID": "YOUR_CLIENT_ID"
//  }
type Realm struct {
	id          string
	redirectURL string

	// The client secret for this Github application.
	ClientSecret string
	// The client ID for this Github application.
	ClientID string
	// Optional. The URL to redirect the client to after authentication.
	StarterLink string
}

// Session represents an authenticated github session
type Session struct {
	id      string
	userID  string
	realmID string

	// AccessToken is the github access token for the user
	AccessToken string
	// Scopes are the set of *ALLOWED* scopes (which may not be the same as the requested scopes)
	Scopes string
	// Optional. The client-supplied URL to redirect them to after the auth process is complete.
	ClientsRedirectURL string
}

// AuthRequest is a request for authenticating with github.com
type AuthRequest struct {
	// Optional. The URL to redirect to after authentication.
	RedirectURL string
}

// AuthResponse is a response to an AuthRequest.
type AuthResponse struct {
	// The URL to visit to perform OAuth on github.com
	URL string
}

// Authenticated returns true if the user has completed the auth process
func (s *Session) Authenticated() bool {
	return s.AccessToken != ""
}

// Info returns a list of possible repositories that this session can integrate with.
func (s *Session) Info() interface{} {
	logger := log.WithFields(log.Fields{
		"user_id":  s.userID,
		"realm_id": s.realmID,
	})
	cli := client.New(s.AccessToken)
	var repos []client.TrimmedRepository

	opts := &github.RepositoryListOptions{
		Type: "all",
		ListOptions: github.ListOptions{
			PerPage: 100,
		},
	}
	for {
		// query for a list of possible projects
		rs, resp, err := cli.Repositories.List("", opts)
		if err != nil {
			logger.WithError(err).Print("Failed to query github projects on github.com")
			return nil
		}

		for _, r := range rs {
			repos = append(repos, client.TrimRepository(r))
		}

		if resp.NextPage == 0 {
			break
		}
		opts.ListOptions.Page = resp.NextPage
		logger.Print("Session.Info() Next => ", resp.NextPage)
	}
	logger.Print("Session.Info() Returning ", len(repos), " repos")

	return struct {
		Repos []client.TrimmedRepository
	}{repos}
}

// UserID returns the user_id who authorised with Github
func (s *Session) UserID() string {
	return s.userID
}

// RealmID returns the realm ID of the realm which performed the authentication
func (s *Session) RealmID() string {
	return s.realmID
}

// ID returns the session ID
func (s *Session) ID() string {
	return s.id
}

// ID returns the realm ID
func (r *Realm) ID() string {
	return r.id
}

// Type is github
func (r *Realm) Type() string {
	return RealmType
}

// Init does nothing.
func (r *Realm) Init() error {
	return nil
}

// Register does nothing.
func (r *Realm) Register() error {
	return nil
}

// RequestAuthSession generates an OAuth2 URL for this user to auth with github via.
// The request body is of type "github.AuthRequest". The response is of type "github.AuthResponse".
//
// Request example:
//   {
//       "RedirectURL": "https://optional-url.com/to/redirect/to/after/auth"
//   }
//
// Response example:
//   {
//       "URL": "https://github.com/login/oauth/authorize?client_id=abcdef&client_secret=acascacac...."
//   }
func (r *Realm) RequestAuthSession(userID string, req json.RawMessage) interface{} {
	state, err := randomString(10)
	if err != nil {
		log.WithError(err).Print("Failed to generate state param")
		return nil
	}

	u, _ := url.Parse("https://github.com/login/oauth/authorize")
	q := u.Query()
	q.Set("client_id", r.ClientID)
	q.Set("client_secret", r.ClientSecret)
	q.Set("state", state)
	q.Set("redirect_uri", r.redirectURL)
	q.Set("scope", "admin:repo_hook,admin:org_hook,repo")
	u.RawQuery = q.Encode()
	session := &Session{
		id:      state, // key off the state for redirects
		userID:  userID,
		realmID: r.ID(),
	}

	// check if they supplied a redirect URL
	var reqBody AuthRequest
	if err = json.Unmarshal(req, &reqBody); err != nil {
		log.WithError(err).Print("Failed to decode request body")
		return nil
	}
	session.ClientsRedirectURL = reqBody.RedirectURL
	log.WithFields(log.Fields{
		"clients_redirect_url": session.ClientsRedirectURL,
		"redirect_url":         u.String(),
	}).Print("RequestAuthSession: Performing redirect")

	_, err = database.GetServiceDB().StoreAuthSession(session)
	if err != nil {
		log.WithError(err).Print("Failed to store new auth session")
		return nil
	}

	return &AuthResponse{u.String()}
}

// OnReceiveRedirect processes OAuth redirect requests from Github
func (r *Realm) OnReceiveRedirect(w http.ResponseWriter, req *http.Request) {
	// parse out params from the request
	code := req.URL.Query().Get("code")
	state := req.URL.Query().Get("state")
	logger := log.WithFields(log.Fields{
		"state": state,
	})
	logger.WithField("code", code).Print("GithubRealm: OnReceiveRedirect")
	if code == "" || state == "" {
		failWith(logger, w, 400, "code and state are required", nil)
		return
	}
	// load the session (we keyed off the state param)
	session, err := database.GetServiceDB().LoadAuthSessionByID(r.ID(), state)
	if err != nil {
		// most likely cause
		failWith(logger, w, 400, "Provided ?state= param is not recognised.", err)
		return
	}
	ghSession, ok := session.(*Session)
	if !ok {
		failWith(logger, w, 500, "Unexpected session found.", nil)
		return
	}
	logger.WithField("user_id", ghSession.UserID()).Print("Mapped redirect to user")

	if ghSession.AccessToken != "" && ghSession.Scopes != "" {
		r.redirectOr(w, 400, "You have already authenticated with Github", logger, ghSession)
		return
	}

	// exchange code for access_token
	res, err := http.PostForm("https://github.com/login/oauth/access_token",
		url.Values{"client_id": {r.ClientID}, "client_secret": {r.ClientSecret}, "code": {code}})
	if err != nil {
		failWith(logger, w, 502, "Failed to exchange code for token", err)
		return
	}
	defer res.Body.Close()
	body, err := ioutil.ReadAll(res.Body)
	if err != nil {
		failWith(logger, w, 502, "Failed to read token response", err)
		return
	}
	vals, err := url.ParseQuery(string(body))
	if err != nil {
		failWith(logger, w, 502, "Failed to parse token response", err)
		return
	}

	// update database and return
	ghSession.AccessToken = vals.Get("access_token")
	ghSession.Scopes = vals.Get("scope")
	logger.WithField("scope", ghSession.Scopes).Print("Scopes granted.")
	_, err = database.GetServiceDB().StoreAuthSession(ghSession)
	if err != nil {
		failWith(logger, w, 500, "Failed to persist session", err)
		return
	}
	r.redirectOr(
		w, 200, "You have successfully linked your Github account to "+ghSession.UserID(), logger, ghSession,
	)
}

func (r *Realm) redirectOr(w http.ResponseWriter, code int, msg string, logger *log.Entry, ghSession *Session) {
	if ghSession.ClientsRedirectURL != "" {
		w.Header().Set("Location", ghSession.ClientsRedirectURL)
		w.WriteHeader(302)
		// technically don't need a body but *shrug*
		w.Write([]byte(ghSession.ClientsRedirectURL))
	} else {
		failWith(logger, w, code, msg, nil)
	}
}

// AuthSession returns a Github Session for this user
func (r *Realm) AuthSession(id, userID, realmID string) types.AuthSession {
	return &Session{
		id:      id,
		userID:  userID,
		realmID: realmID,
	}
}

func failWith(logger *log.Entry, w http.ResponseWriter, code int, msg string, err error) {
	logger.WithError(err).Print(msg)
	w.WriteHeader(code)
	w.Write([]byte(msg))
}

// Generate a cryptographically secure pseudorandom string with the given number of bytes (length).
// Returns a hex string of the bytes.
func randomString(length int) (string, error) {
	b := make([]byte, length)
	_, err := rand.Read(b)
	if err != nil {
		return "", err
	}
	return hex.EncodeToString(b), nil
}

func init() {
	types.RegisterAuthRealm(func(realmID, redirectURL string) types.AuthRealm {
		return &Realm{id: realmID, redirectURL: redirectURL}
	})
}