package routing

import (
	"crypto/hmac"
	"crypto/sha256"
	"encoding/hex"
	"net/http"

	"github.com/matrix-org/dendrite/clientapi/jsonerror"
	"github.com/matrix-org/dendrite/setup/config"
	userapi "github.com/matrix-org/dendrite/userapi/api"
	"github.com/matrix-org/gomatrixserverlib"
	"github.com/matrix-org/util"
	"github.com/sirupsen/logrus"
)

// The data used to populate the /consent request
type constentTemplateData struct {
	User          string
	Version       string
	UserHMAC      string
	HasConsented  bool
	PublicVersion bool
}

func consent(writer http.ResponseWriter, req *http.Request, userAPI userapi.UserInternalAPI, cfg *config.ClientAPI) *util.JSONResponse {
	consentCfg := cfg.Matrix.UserConsentOptions
	internalError := jsonerror.InternalServerError()

	// The data used to populate the /consent request
	data := constentTemplateData{
		User:     req.FormValue("u"),
		Version:  req.FormValue("v"),
		UserHMAC: req.FormValue("h"),
	}
	switch req.Method {
	case http.MethodGet:
		// display the privacy policy without a form
		data.PublicVersion = data.User == "" || data.UserHMAC == "" || data.Version == ""

		// let's see if the user already consented to the current version
		if !data.PublicVersion {
			res := &userapi.QueryPolicyVersionResponse{}
			localPart, _, err := gomatrixserverlib.SplitID('@', data.User)
			if err != nil {
				logrus.WithError(err).Error("unable to print consent template")
				return &internalError
			}
			if err = userAPI.QueryPolicyVersion(req.Context(), &userapi.QueryPolicyVersionRequest{
				LocalPart: localPart,
			}, res); err != nil {
				logrus.WithError(err).Error("unable to print consent template")
				return &internalError
			}
			data.HasConsented = res.PolicyVersion == consentCfg.Version
		}

		err := consentCfg.Templates.ExecuteTemplate(writer, consentCfg.Version+".gohtml", data)
		if err != nil {
			logrus.WithError(err).Error("unable to print consent template")
			return nil
		}
		return nil
	case http.MethodPost:
		localPart, _, err := gomatrixserverlib.SplitID('@', data.User)
		if err != nil {
			logrus.WithError(err).Error("unable to split username")
			return &internalError
		}

		ok, err := validHMAC(data.User, data.UserHMAC, consentCfg.FormSecret)
		if err != nil || !ok {
			_, err = writer.Write([]byte("invalid HMAC provided"))
			if err != nil {
				return &internalError
			}
			return &internalError
		}
		if err := userAPI.PerformUpdatePolicyVersion(
			req.Context(),
			&userapi.UpdatePolicyVersionRequest{
				PolicyVersion: data.Version,
				LocalPart:     localPart,
			},
			&userapi.UpdatePolicyVersionResponse{},
		); err != nil {
			_, err = writer.Write([]byte("unable to update database"))
			if err != nil {
				logrus.WithError(err).Error("unable to write to database")
			}
			return &internalError
		}
		// display the privacy policy without a form
		data.PublicVersion = false
		data.HasConsented = true

		err = consentCfg.Templates.ExecuteTemplate(writer, consentCfg.Version+".gohtml", data)
		if err != nil {
			logrus.WithError(err).Error("unable to print consent template")
			return &internalError
		}
		return nil
	}
	return &util.JSONResponse{Code: http.StatusOK}
}

func validHMAC(username, userHMAC, secret string) (bool, error) {
	mac := hmac.New(sha256.New, []byte(secret))
	_, err := mac.Write([]byte(username))
	if err != nil {
		return false, err
	}
	expectedMAC := mac.Sum(nil)
	decoded, err := hex.DecodeString(userHMAC)
	if err != nil {
		return false, err
	}
	return hmac.Equal(decoded, expectedMAC), nil
}