/*
Copyright 2020-2023 CAcert Inc.
SPDX-License-Identifier: Apache-2.0

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

    https://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"
	"crypto/x509"
	"errors"
	"fmt"
	"html/template"
	"net/http"
	"strconv"
	"time"

	"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"

	"code.cacert.org/cacert/oidc_idp/ui"

	"code.cacert.org/cacert/oidc_idp/internal/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 templateName = "no_emails"
	NoChallengeInRequest        templateName = "no_challenge"
)

const TimeoutTen = 10 * time.Second

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

func (h *LoginHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet && r.Method != http.MethodPost {
		http.Error(w, http.StatusText(http.StatusMethodNotAllowed), http.StatusMethodNotAllowed)

		return
	}

	accept := r.Header.Get("Accept-Language")
	localizer := i18n.NewLocalizer(h.bundle, accept)

	challenge := r.URL.Query().Get("login_challenge")

	if challenge == "" {
		h.renderNoChallengeInRequest(w, localizer)

		return
	}

	h.logger.WithField("challenge", challenge).Debug("received login challenge")

	certEmails := h.getEmailAddressesFromClientCertificate(r)

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

		return
	}

	if r.Method == http.MethodGet {
		h.handleGet(w, r, challenge, certEmails, localizer)
	} else {
		h.handlePost(w, r, challenge, certEmails, localizer)
	}
}

func (h *LoginHandler) handleGet(
	w http.ResponseWriter,
	r *http.Request,
	challenge string,
	certEmails []string,
	localizer *i18n.Localizer,
) {
	loginRequest, err := h.adminClient.GetLoginRequest(admin.NewGetLoginRequestParams().WithLoginChallenge(challenge))
	if err != nil {
		h.logger.WithError(err).WithField(
			"challenge", challenge,
		).Warn("could not get login request for challenge")

		var notFound *admin.GetLoginRequestNotFound

		if errors.As(err, &notFound) {
			w.WriteHeader(http.StatusNotFound)

			http.Error(w, notFound.GetPayload().ErrorDescription, http.StatusNotFound)

			return
		}

		var gone *admin.GetLoginRequestGone

		if errors.As(err, &gone) {
			w.Header().Set("Location", *gone.GetPayload().RedirectTo)
			w.WriteHeader(http.StatusGone)

			return
		}

		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	h.renderRequestForClientCert(w, r, certEmails, localizer, loginRequest)
}

func (h *LoginHandler) handlePost(
	w http.ResponseWriter,
	r *http.Request,
	challenge string,
	certEmails []string,
	localizer *i18n.Localizer,
) {
	if r.FormValue("use-identity") != "accept" {
		h.rejectLogin(w, challenge, localizer)

		return
	}

	// perform certificate auth
	h.logger.WithField("emails", certEmails).Info("will perform certificate authentication")

	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(TimeoutTen))
	if err != nil {
		h.logger.WithError(err).Error("error getting login request")

		h.fillAcceptLoginRequestErrorBucket(r, err)

		return
	}

	w.Header().Add("Location", *loginRequest.GetPayload().RedirectTo)
	w.WriteHeader(http.StatusFound)
}

func (h *LoginHandler) fillAcceptLoginRequestErrorBucket(r *http.Request, err error) {
	if errorBucket := GetErrorBucket(r); errorBucket != nil {
		var (
			errorDetails               *ErrorDetails
			acceptLoginRequestNotFound *admin.AcceptLoginRequestNotFound
		)

		if errors.As(err, &acceptLoginRequestNotFound) {
			payload := acceptLoginRequestNotFound.GetPayload()
			errorDetails = &ErrorDetails{
				ErrorMessage: payload.Error,
				ErrorDetails: []string{payload.ErrorDescription},
			}

			if acceptLoginRequestNotFound.Payload.StatusCode != 0 {
				errorDetails.ErrorCode = strconv.Itoa(int(payload.StatusCode))
			}
		} else {
			errorDetails = &ErrorDetails{
				ErrorMessage: "could not accept login",
				ErrorDetails: []string{err.Error()},
			}
		}

		errorBucket.AddError(errorDetails)
	}
}

func (h *LoginHandler) rejectLogin(w http.ResponseWriter, challenge string, localizer *i18n.Localizer) {
	const Ten = 10 * time.Second

	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(Ten))
	if err != nil {
		h.logger.WithError(err).Error("error getting reject login request")
		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]

		if !isClientCertificate(firstCert) {
			return nil
		}

		for _, email := range firstCert.EmailAddresses {
			h.logger.WithField(
				"email", email,
			).Info("authenticated with a client certificate for email address")
		}

		return firstCert.EmailAddresses
	}

	return nil
}

func isClientCertificate(cert *x509.Certificate) bool {
	for _, ext := range cert.ExtKeyUsage {
		if ext == x509.ExtKeyUsageClientAuth {
			return true
		}
	}

	return false
}

func (h *LoginHandler) renderRequestForClientCert(
	w http.ResponseWriter,
	r *http.Request,
	emails []string,
	localizer *i18n.Localizer,
	loginRequest *admin.GetLoginRequestOK,
) {
	msg := h.messageCatalog.LookupMessage
	msgPlural := h.messageCatalog.LookupMessagePlural
	msgMarkdown := h.messageCatalog.LookupMarkdownMessage

	rendered := bytes.NewBuffer(make([]byte, 0))

	err := h.templates[CertificateLogin].Lookup("base").Execute(rendered, map[string]interface{}{
		"Title":          msg("LoginTitle", nil, localizer),
		csrf.TemplateTag: csrf.TemplateField(r),
		"IntroText": template.HTML(msgMarkdown( //nolint:gosec
			"CertLoginIntroText",
			map[string]interface{}{"ClientName": loginRequest.GetPayload().Client.ClientName},
			localizer,
		)),
		"EmailChoiceText": msgPlural("EmailChoiceText", nil, localizer, len(emails)),
		"emails":          emails,
		"RequestText":     msg("CertLoginRequestText", nil, localizer),
		"AcceptLabel":     msg("LabelAcceptCertLogin", nil, localizer),
		"RejectLabel":     msg("LabelRejectCertLogin", nil, localizer),
	})
	if err != nil {
		h.logger.WithError(err).Error("template rendering failed")
		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) {
	msg := h.messageCatalog.LookupMessage

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

		return
	}
}

func (h *LoginHandler) renderNoChallengeInRequest(w http.ResponseWriter, localizer *i18n.Localizer) {
	err := h.templates[NoChallengeInRequest].Lookup("base").Execute(w, map[string]interface{}{
		"Title": h.messageCatalog.LookupMessage("NoChallengeInRequestTitle", nil, localizer),
		"Explanation": template.HTML(h.messageCatalog.LookupMarkdownMessage( //nolint:gosec
			"NoChallengeInRequestExplanation",
			nil,
			localizer,
		)),
	})
	if err != nil {
		h.logger.WithError(err).Error("template rendering failed")
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}
}

func NewLoginHandler(
	logger *log.Logger,
	bundle *i18n.Bundle,
	messageCatalog *services.MessageCatalog,
	adminClient admin.ClientService,
) *LoginHandler {
	return &LoginHandler{
		adminClient: adminClient,
		bundle:      bundle,
		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",
			)),
			NoChallengeInRequest: template.Must(template.ParseFS(
				ui.Templates,
				"templates/base.gohtml",
				"templates/no_challenge_in_request.gohtml",
			)),
		},
		messageCatalog: messageCatalog,
	}
}