/*
 Copyright 2020, 2021 Jan Dittberner


 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 handlers

import (
	"bytes"
	"context"
	"errors"
	"fmt"
	"html/template"
	"net/http"
	"strconv"
	"time"

	"git.cacert.org/oidc_idp/ui"
	"github.com/gorilla/csrf"
	"github.com/nicksnyder/go-i18n/v2/i18n"
	"github.com/ory/hydra-client-go/client/admin"
	"github.com/ory/hydra-client-go/models"
	log "github.com/sirupsen/logrus"

	"git.cacert.org/oidc_idp/services"
)

type acrType string

const (
	ClientCertificate acrType = "cert" // client certificate login
	// ClientCertificateOTP   acrType = "cert+otp"
	// ClientCertificateToken acrType = "cert+token"
)

type templateName string

const (
	CertificateLogin            templateName = "cert"
	NoEmailsInClientCertificate              = "no_emails"
)

type loginHandler struct {
	adminClient    *admin.Client
	bundle         *i18n.Bundle
	context        context.Context
	logger         *log.Logger
	templates      map[templateName]*template.Template
	messageCatalog *services.MessageCatalog
}

func (h *loginHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	var err error
	challenge := r.URL.Query().Get("login_challenge")
	h.logger.Debugf("received login challenge %s\n", challenge)
	accept := r.Header.Get("Accept-Language")
	localizer := i18n.NewLocalizer(h.bundle, accept)

	certEmails := h.getEmailAddressesFromClientCertificate(r)

	if certEmails == nil {
		h.renderNoEmailsInClientCertificate(w, localizer)
		return
	}

	switch r.Method {
	case http.MethodGet:
		loginRequest, err := h.adminClient.GetLoginRequest(admin.NewGetLoginRequestParams().WithLoginChallenge(challenge))
		if err != nil {
			h.logger.Warnf("could not get login request for challenge %s: %v", challenge, err)

			var e *admin.GetLoginRequestGone
			if errors.As(err, &e) {
				w.Header().Set("Location", *e.GetPayload().RedirectTo)
				w.WriteHeader(http.StatusGone)
				return
			}
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}
		h.renderRequestForClientCert(w, r, certEmails, localizer, loginRequest)
		break
	case http.MethodPost:
		if r.FormValue("use-identity") != "accept" {
			h.rejectLogin(w, challenge, localizer)
			return
		}

		var userId string
		// perform certificate auth
		h.logger.Infof("would perform certificate authentication with: %+v", certEmails)
		userId, err = h.performCertificateLogin(certEmails, r)
		if err != nil {
			http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
			return
		}

		// finish login and redirect to target
		loginRequest, err := h.adminClient.AcceptLoginRequest(
			admin.NewAcceptLoginRequestParams().WithLoginChallenge(challenge).WithBody(
				&models.AcceptLoginRequest{
					Acr:         string(ClientCertificate),
					Remember:    true,
					RememberFor: 0,
					Subject:     &userId,
				}).WithTimeout(time.Second * 10))
		if err != nil {
			h.logger.Errorf("error getting login request: %#v", err)
			var errorDetails *ErrorDetails
			switch v := err.(type) {
			case *admin.AcceptLoginRequestNotFound:
				payload := v.GetPayload()
				errorDetails = &ErrorDetails{
					ErrorMessage: payload.Error,
					ErrorDetails: []string{payload.ErrorDescription},
				}
				if v.Payload.StatusCode != 0 {
					errorDetails.ErrorCode = strconv.Itoa(int(payload.StatusCode))
				}
				break
			default:
				errorDetails = &ErrorDetails{
					ErrorMessage: "could not accept login",
					ErrorDetails: []string{err.Error()},
				}
			}
			GetErrorBucket(r).AddError(errorDetails)
			return
		}
		w.Header().Add("Location", *loginRequest.GetPayload().RedirectTo)
		w.WriteHeader(http.StatusFound)
	default:
		http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)
		return
	}
}

func (h *loginHandler) rejectLogin(w http.ResponseWriter, challenge string, localizer *i18n.Localizer) {
	rejectLoginRequest, err := h.adminClient.RejectLoginRequest(admin.NewRejectLoginRequestParams().WithLoginChallenge(challenge).WithBody(
		&models.RejectRequest{
			ErrorDescription: h.messageCatalog.LookupMessage("LoginDeniedByUser", nil, localizer),
			ErrorHint:        h.messageCatalog.LookupMessage("HintChooseAnIdentityForAuthentication", nil, localizer),
			StatusCode:       http.StatusForbidden,
		},
	).WithTimeout(time.Second * 10))
	if err != nil {
		h.logger.Errorf("error getting reject login request: %#v", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
	w.Header().Set("Location", *rejectLoginRequest.GetPayload().RedirectTo)
	w.WriteHeader(http.StatusFound)
}

func (h *loginHandler) getEmailAddressesFromClientCertificate(r *http.Request) []string {
	if r.TLS != nil && r.TLS.PeerCertificates != nil && len(r.TLS.PeerCertificates) > 0 {
		firstCert := r.TLS.PeerCertificates[0]
		for _, email := range firstCert.EmailAddresses {
			h.logger.Infof("authenticated with a client certificate for email address %s", email)
		}
		return firstCert.EmailAddresses
	}
	return nil
}

func (h *loginHandler) renderRequestForClientCert(w http.ResponseWriter, r *http.Request, emails []string, localizer *i18n.Localizer, loginRequest *admin.GetLoginRequestOK) {
	trans := func(label string) string {
		return h.messageCatalog.LookupMessage(label, nil, localizer)
	}

	rendered := bytes.NewBuffer(make([]byte, 0))
	err := h.templates[CertificateLogin].Lookup("base").Execute(rendered, map[string]interface{}{
		"Title":          trans("LoginTitle"),
		csrf.TemplateTag: csrf.TemplateField(r),
		"IntroText": template.HTML(h.messageCatalog.LookupMessage(
			"CertLoginIntroText",
			map[string]interface{}{"ClientName": loginRequest.GetPayload().Client.ClientName},
			localizer,
		)),
		"EmailChoiceText": h.messageCatalog.LookupMessagePlural("EmailChoiceText", nil, localizer, len(emails)),
		"emails":          emails,
		"RequestText":     trans("CertLoginRequestText"),
		"AcceptLabel":     trans("LabelAcceptCertLogin"),
		"RejectLabel":     trans("LabelRejectCertLogin"),
	})
	if err != nil {
		h.logger.Error(err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
	w.Header().Add("Pragma", "no-cache")
	w.Header().Set("Cache-Control", "no-cache, no-store, must-revalidate")
	_, _ = w.Write(rendered.Bytes())
}

func (h *loginHandler) performCertificateLogin(emails []string, r *http.Request) (string, error) {
	requestedEmail := r.PostFormValue("email")
	for _, email := range emails {
		if email == requestedEmail {
			return email, nil
		}
	}
	return "", fmt.Errorf("no user found")
}

func (h *loginHandler) renderNoEmailsInClientCertificate(w http.ResponseWriter, localizer *i18n.Localizer) {
	trans := func(label string) string {
		return h.messageCatalog.LookupMessage(label, nil, localizer)
	}

	err := h.templates[NoEmailsInClientCertificate].Lookup("base").Execute(w, map[string]interface{}{
		"Title":       trans("NoEmailsInClientCertificateTitle"),
		"Explanation": trans("NoEmailsInClientCertificateExplanation"),
	})
	if err != nil {
		h.logger.Error(err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
		return
	}
}

func NewLoginHandler(ctx context.Context, logger *log.Logger) (*loginHandler, error) {
	return &loginHandler{
		adminClient: ctx.Value(CtxAdminClient).(*admin.Client),
		bundle:      services.GetI18nBundle(ctx),
		context:     ctx,
		logger:      logger,
		templates: map[templateName]*template.Template{
			CertificateLogin: template.Must(template.ParseFS(
				ui.Templates,
				"templates/base.gohtml",
				"templates/client_certificate.gohtml",
			)),
			NoEmailsInClientCertificate: template.Must(template.ParseFS(
				ui.Templates,
				"templates/base.gohtml",
				"templates/no_email_in_client_certificate.gohtml",
			)),
		},
		messageCatalog: services.GetMessageCatalog(ctx),
	}, nil
}