/*
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 (
	"fmt"
	"net/http"

	"github.com/gorilla/sessions"
	"github.com/lestrrat-go/jwx/jwk"
	log "github.com/sirupsen/logrus"
	"golang.org/x/oauth2"

	"code.cacert.org/cacert/oidc-demo-app/internal/services"
)

const (
	sessionKeyAccessToken = iota
	sessionKeyRefreshToken
	sessionKeyIDToken
	sessionRedirectTarget
)

type OidcCallbackHandler struct {
	keySet       jwk.Set
	logger       *log.Logger
	oauth2Config *oauth2.Config
}

func (c *OidcCallbackHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	if r.Method != http.MethodGet {
		w.WriteHeader(http.StatusMethodNotAllowed)

		return
	}

	if r.URL.Path != "/callback" {
		http.NotFound(w, r)

		return
	}

	errorText := r.URL.Query().Get("error")
	errorDescription := r.URL.Query().Get("error_description")
	code := r.URL.Query().Get("code")

	if c.handleCallbackError(errorText, errorDescription, r) {
		return
	}

	tok, err := c.oauth2Config.Exchange(r.Context(), code)
	if err != nil {
		c.logger.WithError(err).Error("could not perform token exchange")
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	session, err := services.GetSessionStore().Get(r, "resource_session")
	if err != nil {
		c.logger.WithError(err).Error("could not get session store")
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	if err = c.storeTokens(session, tok); err != nil {
		c.logger.WithError(err).Error("could not store token in session")

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

		return
	}

	if err = session.Save(r, w); err != nil {
		c.logger.WithError(err).Error("could not save session")

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

		return
	}

	if redirectTarget, ok := session.Values[sessionRedirectTarget]; ok {
		if v, ok := redirectTarget.(string); ok {
			w.Header().Set("Location", v)
			w.WriteHeader(http.StatusFound)

			return
		}
	}

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

func (c *OidcCallbackHandler) handleCallbackError(errorText string, errorDescription string, r *http.Request) bool {
	if errorText != "" {
		errorDetails := &ErrorDetails{
			ErrorMessage: errorText,
		}

		if errorDescription != "" {
			errorDetails.ErrorDetails = []string{errorDescription}
		}

		GetErrorBucket(r).AddError(errorDetails)

		return true
	}

	return false
}

func (c *OidcCallbackHandler) storeTokens(
	session *sessions.Session,
	tok *oauth2.Token,
) error {
	session.Values[sessionKeyAccessToken] = tok.AccessToken
	session.Values[sessionKeyRefreshToken] = tok.RefreshToken

	idTokenValue := tok.Extra("id_token")

	idToken, ok := idTokenValue.(string)
	if !ok {
		return fmt.Errorf("ID token value %v is not a string", idTokenValue)
	}

	session.Values[sessionKeyIDToken] = idToken

	oidcToken, err := ParseIDToken(idToken, c.keySet)
	if err != nil {
		return fmt.Errorf("could not parse ID token: %w", err)
	}

	c.logger.WithFields(log.Fields{
		"sub":        oidcToken.Subject(),
		"aud":        oidcToken.Audience(),
		"issued_at":  oidcToken.IssuedAt(),
		"iss":        oidcToken.Issuer(),
		"not_before": oidcToken.NotBefore(),
		"exp":        oidcToken.Expiration(),
	}).Debug("receive OpenID Connect ID Token")

	return nil
}

func NewCallbackHandler(logger *log.Logger, keySet jwk.Set, oauth2Config *oauth2.Config) *OidcCallbackHandler {
	return &OidcCallbackHandler{
		keySet:       keySet,
		logger:       logger,
		oauth2Config: oauth2Config,
	}
}