/*
 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 (
	"context"
	"encoding/json"
	"html/template"
	"net/http"
	"net/url"
	"strings"
	"time"

	commonModels "git.cacert.org/oidc_idp/models"
	"git.cacert.org/oidc_idp/ui"
	"github.com/go-playground/form/v4"
	"github.com/gorilla/csrf"
	"github.com/lestrrat-go/jwx/jwt/openid"
	"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 consentHandler struct {
	adminClient     *admin.Client
	bundle          *i18n.Bundle
	consentTemplate *template.Template
	context         context.Context
	logger          *log.Logger
	messageCatalog  *services.MessageCatalog
}

type ConsentInformation struct {
	GrantedScopes  []string `form:"scope"`
	SelectedClaims []string `form:"claims"`
	ConsentChecked bool     `form:"consent"`
}

type UserInfo struct {
	Email         string
	EmailVerified bool
	CommonName    string
}

var supportedScopes, supportedClaims map[string]*i18n.Message

const (
	ScopeOpenID        = "openid"
	ScopeOffline       = "offline"
	ScopeOfflineAccess = "offline_access"
	ScopeProfile       = "profile"
	ScopeEmail         = "email"
)

func init() {
	supportedScopes = make(map[string]*i18n.Message)
	supportedScopes[ScopeOpenID] = &i18n.Message{
		ID:    "Scope-openid-Description",
		Other: "Request information about your identity.",
	}
	supportedScopes[ScopeOffline] = &i18n.Message{
		ID:    "Scope-offline-Description",
		Other: "Keep access to your information until you revoke the permission.",
	}
	supportedScopes[ScopeOfflineAccess] = supportedScopes[ScopeOffline]
	supportedScopes[ScopeProfile] = &i18n.Message{
		ID:    "Scope-profile-Description",
		Other: "Access your user profile information (your name).",
	}
	supportedScopes[ScopeEmail] = &i18n.Message{
		ID:    "Scope-email-Description",
		Other: "Access your email address.",
	}

	supportedClaims = make(map[string]*i18n.Message)
	supportedClaims[openid.SubjectKey] = nil
	supportedClaims[openid.EmailKey] = nil
	supportedClaims[openid.EmailVerifiedKey] = nil
	supportedClaims[openid.GivenNameKey] = nil
	supportedClaims[openid.FamilyNameKey] = nil
	supportedClaims[openid.MiddleNameKey] = nil
	supportedClaims[openid.NameKey] = nil
	supportedClaims[openid.BirthdateKey] = nil
	supportedClaims[openid.ZoneinfoKey] = nil
	supportedClaims[openid.LocaleKey] = nil
}

func (i *UserInfo) GetFullName() string {
	return i.CommonName
}

func (h *consentHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	challenge := r.URL.Query().Get("consent_challenge")
	h.logger.Debugf("received consent challenge %s", challenge)
	accept := r.Header.Get("Accept-Language")
	localizer := i18n.NewLocalizer(h.bundle, accept)

	// retrieve consent information
	consentData, requestedClaims, err := h.getRequestedConsentInformation(challenge, r)
	if err != nil {
		// error is already handled in getRequestConsentInformation
		return
	}

	switch r.Method {
	case http.MethodGet:
		h.renderConsentForm(w, r, consentData, requestedClaims, err, localizer)
		break
	case http.MethodPost:
		var consentInfo ConsentInformation

		// validate input
		decoder := form.NewDecoder()
		if err := decoder.Decode(&consentInfo, r.Form); err != nil {
			h.logger.Error(err)
			http.Error(
				w,
				http.StatusText(http.StatusInternalServerError),
				http.StatusInternalServerError,
			)
			return
		}

		if consentInfo.ConsentChecked {
			sessionData, err := h.getSessionData(r, consentInfo, requestedClaims, consentData.Payload)
			if err != nil {
				h.logger.Errorf("could not get session data: %v", err)
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}

			consentRequest, err := h.adminClient.AcceptConsentRequest(
				admin.NewAcceptConsentRequestParams().WithConsentChallenge(challenge).WithBody(
					&models.AcceptConsentRequest{
						GrantAccessTokenAudience: nil,
						GrantScope:               consentInfo.GrantedScopes,
						HandledAt:                models.NullTime(time.Now()),
						Remember:                 true,
						RememberFor:              86400,
						Session:                  sessionData,
					}).WithTimeout(time.Second * 10))
			if err != nil {
				h.logger.Error(err)
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}
			w.Header().Add("Location", *consentRequest.GetPayload().RedirectTo)
			w.WriteHeader(http.StatusFound)
			return

		} else {
			consentRequest, err := h.adminClient.RejectConsentRequest(
				admin.NewRejectConsentRequestParams().WithConsentChallenge(challenge).WithBody(
					&models.RejectRequest{}))
			if err != nil {
				h.logger.Error(err)
				http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)
				return
			}
			w.Header().Add("Location", *consentRequest.GetPayload().RedirectTo)
			w.WriteHeader(http.StatusFound)
		}
	}
}

func (h *consentHandler) getRequestedConsentInformation(challenge string, r *http.Request) (
	*admin.GetConsentRequestOK,
	*commonModels.OIDCClaimsRequest,
	error,
) {
	consentData, err := h.adminClient.GetConsentRequest(
		admin.NewGetConsentRequestParams().WithConsentChallenge(challenge))
	if err != nil {
		h.logger.Errorf("error getting consent information: %v", err)
		var errorDetails *ErrorDetails
		errorDetails = &ErrorDetails{
			ErrorMessage: "could not get consent details",
			ErrorDetails: []string{http.StatusText(http.StatusInternalServerError)},
		}
		GetErrorBucket(r).AddError(errorDetails)
		return nil, nil, err
	}
	var requestedClaims commonModels.OIDCClaimsRequest
	requestUrl, err := url.Parse(consentData.Payload.RequestURL)
	if err != nil {
		h.logger.Warnf("could not parse original request URL %s: %v", consentData.Payload.RequestURL, err)
	} else {
		claimsParameter := requestUrl.Query().Get("claims")
		if claimsParameter != "" {
			decoder := json.NewDecoder(strings.NewReader(claimsParameter))
			err := decoder.Decode(&requestedClaims)
			if err != nil {
				h.logger.Warnf(
					"ignoring claims request parameter %s that could not be decoded: %v",
					claimsParameter,
					err,
				)
			}
		}
	}
	return consentData, &requestedClaims, nil
}

func (h *consentHandler) renderConsentForm(
	w http.ResponseWriter,
	r *http.Request,
	consentData *admin.GetConsentRequestOK,
	claims *commonModels.OIDCClaimsRequest,
	err error,
	localizer *i18n.Localizer,
) {
	trans := func(id string, values ...map[string]interface{}) string {
		if len(values) > 0 {
			return h.messageCatalog.LookupMessage(id, values[0], localizer)
		}
		return h.messageCatalog.LookupMessage(id, nil, localizer)
	}

	// render consent form
	client := consentData.GetPayload().Client
	err = h.consentTemplate.Lookup("base").Execute(w, map[string]interface{}{
		"Title":           trans("TitleRequestConsent"),
		csrf.TemplateTag:  csrf.TemplateField(r),
		"errors":          map[string]string{},
		"client":          client,
		"requestedScope":  h.mapRequestedScope(consentData.GetPayload().RequestedScope, localizer),
		"requestedClaims": h.mapRequestedClaims(claims, localizer),
		"LabelSubmit":     trans("LabelSubmit"),
		"LabelConsent":    trans("LabelConsent"),
		"IntroMoreInformation": template.HTML(trans("IntroConsentMoreInformation", map[string]interface{}{
			"client":     client.ClientName,
			"clientLink": client.ClientURI,
		})),
		"ClaimsInformation": template.HTML(trans("ClaimsInformation", nil)),
		"IntroConsentRequested": template.HTML(trans("IntroConsentRequested", map[string]interface{}{
			"client": client.ClientName,
		})),
	})
}

type scopeWithLabel struct {
	Name  string
	Label string
}

func (h *consentHandler) mapRequestedScope(scope models.StringSlicePipeDelimiter, localizer *i18n.Localizer) []*scopeWithLabel {
	result := make([]*scopeWithLabel, 0)
	for _, scopeName := range scope {
		if _, ok := supportedScopes[scopeName]; !ok {
			h.logger.Warnf("unsupported scope %s ignored", scopeName)
			continue
		}
		label, err := localizer.Localize(&i18n.LocalizeConfig{
			DefaultMessage: supportedScopes[scopeName],
		})
		if err != nil {
			h.logger.Warnf("could not localize label for scope %s: %v", scopeName, err)
			label = scopeName
		}
		result = append(result, &scopeWithLabel{Name: scopeName, Label: label})
	}
	return result
}

type claimWithLabel struct {
	Name      string
	Label     string
	Essential bool
}

func (h *consentHandler) mapRequestedClaims(claims *commonModels.OIDCClaimsRequest, localizer *i18n.Localizer) []*claimWithLabel {
	result := make([]*claimWithLabel, 0)
	known := make(map[string]bool)

	for _, claimElement := range []*commonModels.ClaimElement{claims.GetUserInfo(), claims.GetIDToken()} {
		if claimElement != nil {
			for k, v := range *claimElement {
				if _, ok := supportedClaims[k]; !ok {
					h.logger.Warnf("unsupported claim %s ignored", k)
					continue
				}
				label, err := localizer.Localize(&i18n.LocalizeConfig{
					DefaultMessage: supportedClaims[k],
				})
				if err != nil {
					h.logger.Warnf("could not localize label for claim %s: %v", k, err)
					label = k
				}
				if !known[k] {
					result = append(result, &claimWithLabel{
						Name:      k,
						Label:     label,
						Essential: v.IsEssential(),
					})
					known[k] = true
				}
			}
		}
	}
	return result
}

func (h *consentHandler) getSessionData(
	r *http.Request,
	info ConsentInformation,
	claims *commonModels.OIDCClaimsRequest,
	payload *models.ConsentRequest,
) (*models.ConsentRequestSession, error) {
	idTokenData := make(map[string]interface{}, 0)
	accessTokenData := make(map[string]interface{}, 0)

	userInfo := h.GetUserInfoFromClientCertificate(r, payload.Subject)

	h.fillTokenData(accessTokenData, payload.RequestedScope, claims, info, userInfo)
	h.fillTokenData(idTokenData, payload.RequestedScope, claims, info, userInfo)
	return &models.ConsentRequestSession{
		AccessToken: accessTokenData,
		IDToken:     idTokenData,
	}, nil
}

func (h *consentHandler) fillTokenData(
	m map[string]interface{},
	requestedScope models.StringSlicePipeDelimiter,
	claimsRequest *commonModels.OIDCClaimsRequest,
	consentInformation ConsentInformation,
	userInfo *UserInfo,
) {
	for _, scope := range requestedScope {
		granted := false
		for _, k := range consentInformation.GrantedScopes {
			if k == scope {
				granted = true
				break
			}
		}
		if !granted {
			continue
		}
		switch scope {
		case ScopeEmail:
			// email
			// OPTIONAL. This scope value requests access to the email and
			// email_verified Claims.
			m[openid.EmailKey] = userInfo.Email
			m[openid.EmailVerifiedKey] = userInfo.EmailVerified
			break
		case ScopeProfile:
			// profile
			// OPTIONAL. This scope value requests access to the
			// End-User's default profile Claims, which are: name,
			// family_name, given_name, middle_name, nickname,
			// preferred_username, profile, picture, website, gender,
			// birthdate, zoneinfo, locale, and updated_at.
			m[openid.NameKey] = userInfo.GetFullName()
			break
		}
	}
	if userInfoClaims := claimsRequest.GetUserInfo(); userInfoClaims != nil {
		for claimName, claim := range *userInfoClaims {
			granted := false
			for _, k := range consentInformation.SelectedClaims {
				if k == claimName {
					granted = true
					break
				}
			}
			if !granted {
				continue
			}
			if claim.WantedValue() != nil {
				m[claimName] = *claim.WantedValue()
				continue
			}
			if claim.IsEssential() {
				h.logger.Warnf(
					"handling for essential claim name %s not implemented",
					claimName,
				)
			} else {
				h.logger.Warnf(
					"handling for claim name %s not implemented",
					claimName,
				)
			}
		}
	}
}

func (h *consentHandler) GetUserInfoFromClientCertificate(r *http.Request, subject string) *UserInfo {
	if r.TLS != nil && r.TLS.PeerCertificates != nil && len(r.TLS.PeerCertificates) > 0 {
		firstCert := r.TLS.PeerCertificates[0]
		var verified bool
		for _, email := range firstCert.EmailAddresses {
			h.logger.Infof("authenticated with a client certificate for email address %s", email)
			if subject == email {
				verified = true
			}
		}

		if !verified {
			h.logger.Warnf("authentication attempt with a wrong certificate that did not contain the requested address %s", subject)
			return nil
		}

		return &UserInfo{
			Email:         subject,
			EmailVerified: verified,
			CommonName:    firstCert.Subject.CommonName,
		}
	}
	return nil
}

func NewConsentHandler(ctx context.Context, logger *log.Logger) (*consentHandler, error) {
	consentTemplate := template.Must(
		template.ParseFS(
			ui.Templates,
			"templates/base.gohtml",
			"templates/consent.gohtml",
		))

	return &consentHandler{
		adminClient:     ctx.Value(CtxAdminClient).(*admin.Client),
		bundle:          services.GetI18nBundle(ctx),
		consentTemplate: consentTemplate,
		context:         ctx,
		logger:          logger,
		messageCatalog:  services.GetMessageCatalog(ctx),
	}, nil
}