/*
Copyright 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"
	"context"
	"fmt"
	"html/template"
	"io"
	"log/slog"
	"net/http"

	"github.com/gorilla/csrf"
	"github.com/nicksnyder/go-i18n/v2/i18n"
	client "github.com/ory/hydra-client-go/v2"

	"code.cacert.org/cacert/oidc-idp/internal/services"
)

type acrType string

const (
	// ClientCertificate represents a client certificate login
	ClientCertificate acrType = "urn:cacert:1fa:cert"
	// ClientCertificateOTP   acrType = "urn:cacert:2fa:cert+otp"
	// ClientCertificateToken acrType = "urn:cacert:2fa:cert+token"
)

type contextKey int

const (
	ctxKeyMessage contextKey = iota
)

type LoginHandler struct {
	logger      *slog.Logger
	trans       *services.I18NService
	adminClient client.OAuth2API
	templates   TemplateCache
}

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
	}

	localizer := getLocalizer(h.trans, r)

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

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

		return
	}

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

	certFullName, certEmails := getDataFromClientCert(h.logger, r)

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

		return
	}

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

func (h *LoginHandler) handleGet(
	w http.ResponseWriter,
	r *http.Request,
	challenge string,
	certEmails []string,
	localizer *i18n.Localizer,
) {
	oAuth2LoginRequest, response, err := h.adminClient.GetOAuth2LoginRequest(
		r.Context(),
	).LoginChallenge(challenge).Execute()
	if err != nil {
		h.logger.Warn(
			"could not get login request for challenge",
			"error", err, "challenge", challenge,
		)

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

		return
	}

	usableEmails := certEmails

	defer func() { _ = response.Body.Close() }()

	h.logger.Debug(
		"got response for GetOAuth2LoginRequest",
		"response", response.Status, "login_request", oAuth2LoginRequest,
	)

	if subject, ok := oAuth2LoginRequest.GetSubjectOk(); ok && *subject != "" {
		h.logger.Info("oauth2LoginRequest expects subject", "subject", *subject)

		subjectInCert := false

		for _, email := range certEmails {
			if *subject == email {
				subjectInCert = true
				break
			}
		}

		if !subjectInCert {
			h.rejectLoginMissingSubject(w, r, challenge, localizer, *subject)

			return
		}

		usableEmails = []string{*subject}
	}

	h.renderRequestForClientCert(w, r, usableEmails, localizer, oAuth2LoginRequest)
}

type FlashMessage struct {
	Type    string
	Message string
}

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

		return
	}

	if r.FormValue("email") == "" {
		h.handleGet(w, r.WithContext(context.WithValue(
			r.Context(),
			ctxKeyMessage,
			FlashMessage{
				Type:    "warning",
				Message: h.trans.LookupMessage("NoEmailAddressSelected", nil, localizer),
			},
		)), challenge, certEmails, localizer)

		return
	}

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

	userID, err := h.performCertificateLogin(certEmails, r)
	if err != nil {
		h.logger.Error("could not perform certificate login", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	session, err := GetSession(r)
	if err != nil {
		h.logger.Error("could not perform certificate login", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	session.Values[services.SessionFullName] = certFullName
	session.Values[services.SessionEmail] = userID
	session.Options.HttpOnly = true
	session.Options.Secure = true

	if err = session.Save(r, w); err != nil {
		h.logger.Error("could not save session", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	// finish login and redirect to target
	acceptRequest := client.NewAcceptOAuth2LoginRequest(userID)
	acceptRequest.SetRemember(true)
	acceptRequest.SetRememberFor(0)
	acceptRequest.SetAcr(string(ClientCertificate))

	loginRequest, response, err := h.adminClient.AcceptOAuth2LoginRequest(
		r.Context(),
	).LoginChallenge(challenge).AcceptOAuth2LoginRequest(*acceptRequest).Execute()
	if err != nil {
		h.logger.Error("error getting login request", "error", err)

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

		return
	}

	defer func() { _ = response.Body.Close() }()

	h.logger.Debug("got response for AcceptOAuth2LoginRequest",
		"response", response.Status, "accept_login_request", loginRequest,
	)

	if h.logger.Enabled(r.Context(), slog.LevelDebug) {
		if rb, err := io.ReadAll(response.Body); err == nil {
			h.logger.Debug("response body from Hydra", "response_body", rb)
		}
	}

	w.Header().Add("Location", loginRequest.GetRedirectTo())
	w.WriteHeader(http.StatusFound)
}

func (h *LoginHandler) rejectLogin(
	w http.ResponseWriter,
	r *http.Request,
	challenge string,
	localizer *i18n.Localizer,
) {
	rejectRequest := client.NewRejectOAuth2RequestWithDefaults()
	rejectRequest.SetErrorDescription(h.trans.LookupMessage("LoginDeniedByUser", nil, localizer))
	rejectRequest.SetErrorHint(h.trans.LookupMessage("HintChooseAnIdentityForAuthentication", nil, localizer))
	rejectRequest.SetStatusCode(http.StatusForbidden)

	rejectLoginRequest, response, err := h.adminClient.RejectOAuth2LoginRequest(
		r.Context(),
	).LoginChallenge(challenge).RejectOAuth2Request(*rejectRequest).Execute()
	if err != nil {
		h.logger.Error("error sending reject login request", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	defer func() { _ = response.Body.Close() }()

	h.logger.DebugContext(
		r.Context(),
		"got response for RejectOAuth2LoginRequest",
		"response", response.Status, "reject_login_request", rejectLoginRequest,
	)

	w.Header().Set("Location", rejectLoginRequest.GetRedirectTo())
	w.WriteHeader(http.StatusFound)
}

func (h *LoginHandler) rejectLoginMissingSubject(w http.ResponseWriter, r *http.Request, challenge string, localizer *i18n.Localizer, subject string) {
	rejectRequest := client.NewRejectOAuth2RequestWithDefaults()
	rejectRequest.SetErrorDescription(h.trans.LookupMessage("LoginDeniedSubjectMissing", map[string]interface{}{"Subject": subject}, localizer))
	rejectRequest.SetErrorHint(h.trans.LookupMessage("HintChooseDifferentClientCertificate", nil, localizer))
	rejectRequest.SetStatusCode(http.StatusForbidden)

	rejectLoginRequest, response, err := h.adminClient.RejectOAuth2LoginRequest(r.Context()).LoginChallenge(challenge).RejectOAuth2Request(*rejectRequest).Execute()
	if err != nil {
		h.logger.Error("error sending reject login request", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	defer func() { _ = response.Body.Close() }()

	h.logger.DebugContext(
		r.Context(),
		"got response for RejectOAuth2LoginRequest",
		"response", response.Status, "reject_login_request", rejectLoginRequest,
	)

	w.Header().Set("Location", rejectLoginRequest.GetRedirectTo())
	w.WriteHeader(http.StatusFound)
}

func (h *LoginHandler) renderRequestForClientCert(
	w http.ResponseWriter,
	r *http.Request,
	emails []string,
	localizer *i18n.Localizer,
	loginRequest *client.OAuth2LoginRequest,
) {
	msg := h.trans.LookupMessage
	msgPlural := h.trans.LookupMessagePlural
	msgMarkdown := h.trans.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.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),
		"FlashMessage":    r.Context().Value(ctxKeyMessage),
	})
	if err != nil {
		h.logger.Error("template rendering failed", "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) renderNoChallengeInRequest(w http.ResponseWriter, localizer *i18n.Localizer) {
	err := h.templates[NoChallengeInRequest].Lookup("base").Execute(w, map[string]interface{}{
		"Title": h.trans.LookupMessage("NoChallengeInRequestTitle", nil, localizer),
		"Explanation": template.HTML(h.trans.LookupMarkdownMessage( //nolint:gosec
			"NoChallengeInRequestExplanation",
			nil,
			localizer,
		)),
	})
	if err != nil {
		h.logger.Error("template rendering failed", "error", err)
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}
}

func NewLoginHandler(
	logger *slog.Logger, tc TemplateCache, trans *services.I18NService, adminClient client.OAuth2API,
) *LoginHandler {
	return &LoginHandler{
		logger:      logger,
		trans:       trans,
		adminClient: adminClient,
		templates:   tc,
	}
}