package server

import (
	"bytes"
	"context"
	"crypto/sha256"
	"errors"
	"io/ioutil"
	"strings"
	"time"

	"forge.cadoles.com/wpetit/go-http-peering/crypto"

	peering "forge.cadoles.com/wpetit/go-http-peering"
	jwt "github.com/dgrijalva/jwt-go"

	"net/http"
)

const (
	AuthorizationType            = "Bearer"
	KeyPeerID         ContextKey = "peerID"
)

var (
	ErrInvalidClaims   = errors.New("invalid claims")
	ErrInvalidChecksum = errors.New("invalid checksum")
	ErrNotPeered       = errors.New("not peered")
)

type ContextKey string

func Authenticate(store peering.Store, funcs ...OptionFunc) func(http.Handler) http.Handler {
	options := createOptions(funcs...)
	logger := options.Logger

	middleware := func(next http.Handler) http.Handler {
		fn := func(w http.ResponseWriter, r *http.Request) {
			authorization := r.Header.Get("Authorization")

			if authorization == "" {
				sendError(w, http.StatusUnauthorized)
				return
			}

			parts := strings.SplitN(authorization, " ", 2)

			if len(parts) != 2 || parts[0] != AuthorizationType {
				sendError(w, http.StatusUnauthorized)
				return
			}

			token, err := jwt.ParseWithClaims(parts[1], &peering.PeerClaims{}, func(token *jwt.Token) (interface{}, error) {
				claims, ok := token.Claims.(*peering.PeerClaims)
				if !ok {
					return nil, ErrInvalidClaims
				}
				peerID := peering.PeerID(claims.Issuer)
				peer, err := store.Get(peerID)
				if err != nil {
					return nil, err
				}
				if peer.Status == peering.StatusRejected {
					return nil, ErrPeerRejected
				}
				if peer.Status != peering.StatusPeered {
					return nil, ErrNotPeered
				}
				publicKey, err := crypto.DecodePEMToPublicKey(peer.PublicKey)
				if err != nil {
					return nil, err
				}
				return publicKey, nil
			})
			if err != nil || !token.Valid {
				logger.Printf("[ERROR] %s", err)
				if err == ErrPeerRejected {
					sendError(w, http.StatusForbidden)
				} else {
					sendError(w, http.StatusUnauthorized)
				}
				return
			}

			claims, ok := token.Claims.(*peering.PeerClaims)
			if !ok {
				logger.Printf("[ERROR] %s", ErrInvalidClaims)
				sendError(w, http.StatusUnauthorized)
				return
			}

			body, err := ioutil.ReadAll(r.Body)
			if err != nil {
				logger.Printf("[ERROR] %s", err)
				sendError(w, http.StatusInternalServerError)
				return
			}

			if err := r.Body.Close(); err != nil {
				logger.Printf("[ERROR] %s", err)
				sendError(w, http.StatusInternalServerError)
				return
			}

			match, err := compareChecksum(body, claims.BodySum)
			if err != nil {
				logger.Printf("[ERROR] %s", err)
				sendError(w, http.StatusUnauthorized)
				return
			}

			if !match {
				logger.Printf("[ERROR] %s", ErrInvalidChecksum)
				sendError(w, http.StatusBadRequest)
				return
			}

			peerID := peering.PeerID(claims.Issuer)

			if err := store.UpdateLastContact(peerID, r.RemoteAddr, time.Now()); err != nil {
				logger.Printf("[ERROR] %s", err)
				sendError(w, http.StatusInternalServerError)
				return
			}

			ctx := context.WithValue(r.Context(), KeyPeerID, peerID)
			r = r.WithContext(ctx)
			r.Body = ioutil.NopCloser(bytes.NewBuffer(body))

			next.ServeHTTP(w, r)

		}
		return http.HandlerFunc(fn)
	}
	return middleware
}

func GetPeerID(r *http.Request) (peering.PeerID, error) {
	peerID, ok := r.Context().Value(KeyPeerID).(peering.PeerID)
	if !ok {
		return "", ErrUnauthorized
	}
	return peerID, nil
}

func sendError(w http.ResponseWriter, status int) {
	http.Error(w, http.StatusText(status), status)
}

func compareChecksum(body []byte, sum []byte) (bool, error) {
	sha := sha256.New()
	_, err := sha.Write(body)
	if err != nil {
		return false, err
	}
	return bytes.Equal(sum, sha.Sum(nil)), nil
}