package oidc

import (
	"bytes"
	"net/http"
	"net/url"
	"strings"

	"github.com/coreos/go-oidc/v3/oidc"
	"github.com/dchest/uniuri"
	"github.com/gorilla/sessions"
	"github.com/pkg/errors"
	"gitlab.com/wpetit/goweb/logger"
	"golang.org/x/oauth2"
)

const (
	sessionKeyAccessToken          = "access-token"
	sessionKeyRefreshToken         = "refresh-token"
	sessionKeyTokenExpiry          = "token-expiry"
	sessionKeyIDToken              = "id-token"
	sessionKeyPostLoginRedirectURL = "post-login-redirect-url"
	sessionKeyLoginState           = "login-state"
	sessionKeyLoginNonce           = "login-nonce"
)

var (
	ErrLoginRequired = errors.New("login required")
)

type Client struct {
	httpClient *http.Client
	oauth2     *oauth2.Config
	provider   *oidc.Provider
	verifier   *oidc.IDTokenVerifier
	authParams map[string]string
}

func (c *Client) Verifier() *oidc.IDTokenVerifier {
	return c.verifier
}

func (c *Client) Provider() *oidc.Provider {
	return c.provider
}

func (c *Client) Authenticate(w http.ResponseWriter, r *http.Request, sess *sessions.Session, postLoginRedirectURL string) (*oidc.IDToken, error) {
	idToken, err := c.getIDToken(r, sess)
	if err != nil {
		logger.Warn(r.Context(), "could not retrieve idtoken", logger.CapturedE(errors.WithStack(err)))

		c.login(w, r, sess, postLoginRedirectURL)

		return nil, errors.WithStack(ErrLoginRequired)
	}

	return idToken, nil
}

func (c *Client) login(w http.ResponseWriter, r *http.Request, sess *sessions.Session, postLoginRedirectURL string) {
	ctx := r.Context()

	state := uniuri.New()
	nonce := uniuri.New()

	sess.Values[sessionKeyLoginState] = state
	sess.Values[sessionKeyLoginNonce] = nonce
	sess.Values[sessionKeyPostLoginRedirectURL] = postLoginRedirectURL

	if err := sess.Save(r, w); err != nil {
		logger.Error(ctx, "could not save session", logger.CapturedE(errors.WithStack(err)))
		http.Error(w, http.StatusText(http.StatusInternalServerError), http.StatusInternalServerError)

		return
	}

	authCodeOptions := []oauth2.AuthCodeOption{}
	authCodeOptions = append(authCodeOptions, oidc.Nonce(nonce))

	for key, val := range c.authParams {
		authCodeOptions = append(authCodeOptions, oauth2.SetAuthURLParam(key, val))
	}

	authCodeURL := c.oauth2.AuthCodeURL(
		state,
		authCodeOptions...,
	)

	http.Redirect(w, r, authCodeURL, http.StatusFound)
}

func (c *Client) HandleCallback(w http.ResponseWriter, r *http.Request, sess *sessions.Session) error {
	token, _, rawIDToken, err := c.validate(r, sess)
	if err != nil {
		return errors.Wrap(err, "could not validate oidc token")
	}

	sess.Values[sessionKeyIDToken] = rawIDToken
	sess.Values[sessionKeyAccessToken] = token.AccessToken
	sess.Values[sessionKeyRefreshToken] = token.RefreshToken
	sess.Values[sessionKeyTokenExpiry] = token.Expiry.UTC().Unix()

	if err := sess.Save(r, w); err != nil {
		return errors.WithStack(err)
	}

	rawPostLoginRedirectURL, exists := sess.Values[sessionKeyPostLoginRedirectURL]
	if !exists {
		return errors.Wrap(err, "could not find post login redirect url")
	}

	postLoginRedirectURL, ok := rawPostLoginRedirectURL.(string)
	if !ok {
		return errors.Wrapf(err, "unexpected value '%v' for post login redirect url", rawPostLoginRedirectURL)
	}

	http.Redirect(w, r, postLoginRedirectURL, http.StatusTemporaryRedirect)

	return nil
}

func (c *Client) HandleLogout(w http.ResponseWriter, r *http.Request, sess *sessions.Session, postLogoutRedirectURL string) error {
	state := uniuri.New()
	sess.Values[sessionKeyLoginState] = state

	ctx := r.Context()

	rawIDToken, err := c.getRawIDToken(sess)
	if err != nil {
		logger.Error(ctx, "could not retrieve raw id token", logger.CapturedE(errors.WithStack(err)))
	}

	sess.Values[sessionKeyIDToken] = nil
	sess.Values[sessionKeyAccessToken] = nil
	sess.Values[sessionKeyRefreshToken] = nil
	sess.Values[sessionKeyTokenExpiry] = nil
	sess.Options.MaxAge = -1

	if err := sess.Save(r, w); err != nil {
		return errors.Wrap(err, "could not save session")
	}

	if rawIDToken == "" {
		http.Redirect(w, r, postLogoutRedirectURL, http.StatusFound)
		return nil
	}

	sessionEndURL, err := c.sessionEndURL(rawIDToken, state, postLogoutRedirectURL)
	if err != nil {
		return errors.Wrap(err, "could not retrieve session end url")
	}

	if sessionEndURL != "" {
		http.Redirect(w, r, sessionEndURL, http.StatusFound)
	} else {
		http.Redirect(w, r, postLogoutRedirectURL, http.StatusFound)
	}

	return nil
}

func (c *Client) sessionEndURL(idTokenHint, state, postLogoutRedirectURL string) (string, error) {
	sessionEndEndpoint := &struct {
		URL string `json:"end_session_endpoint"`
	}{}

	if err := c.provider.Claims(&sessionEndEndpoint); err != nil {
		return "", errors.Wrap(err, "could not unmarshal claims")
	}

	if sessionEndEndpoint.URL == "" {
		return "", nil
	}

	var buf bytes.Buffer
	buf.WriteString(sessionEndEndpoint.URL)

	v := url.Values{}

	if idTokenHint != "" {
		v.Set("id_token_hint", idTokenHint)
	}

	if postLogoutRedirectURL != "" {
		v.Set("post_logout_redirect_uri", postLogoutRedirectURL)
	}

	if state != "" {
		v.Set("state", state)
	}

	if strings.Contains(sessionEndEndpoint.URL, "?") {
		buf.WriteByte('&')
	} else {
		buf.WriteByte('?')
	}

	buf.WriteString(v.Encode())

	return buf.String(), nil
}

func (c *Client) validate(r *http.Request, sess *sessions.Session) (*oauth2.Token, *oidc.IDToken, string, error) {
	ctx := r.Context()
	ctx = oidc.ClientContext(ctx, c.httpClient)

	rawStoredState := sess.Values[sessionKeyLoginState]
	receivedState := r.URL.Query().Get("state")

	storedState, ok := rawStoredState.(string)
	if !ok {
		return nil, nil, "", errors.New("could not find state in session")
	}

	if receivedState != storedState {
		return nil, nil, "", errors.New("state mismatch")
	}

	code := r.URL.Query().Get("code")

	token, err := c.oauth2.Exchange(ctx, code)
	if err != nil {
		return nil, nil, "", errors.Wrap(err, "could not exchange token")
	}

	rawIDToken, ok := token.Extra("id_token").(string)
	if !ok {
		return nil, nil, "", errors.New("could not find id token")
	}

	idToken, err := c.verifier.Verify(ctx, rawIDToken)
	if err != nil {
		return nil, nil, "", errors.Wrap(err, "could not verify id token")
	}

	return token, idToken, rawIDToken, nil
}

func (c *Client) getRawIDToken(sess *sessions.Session) (string, error) {
	rawIDToken, ok := sess.Values[sessionKeyIDToken].(string)
	if !ok || rawIDToken == "" {
		return "", errors.New("id token not found")
	}

	return rawIDToken, nil
}

func (c *Client) getIDToken(r *http.Request, sess *sessions.Session) (*oidc.IDToken, error) {
	rawIDToken, err := c.getRawIDToken(sess)
	if err != nil {
		return nil, errors.Wrap(err, "could not retrieve raw idtoken")
	}

	idToken, err := c.verifier.Verify(r.Context(), rawIDToken)
	if err != nil {
		return nil, errors.Wrap(err, "could not verify id token")
	}

	return idToken, nil
}

func NewClient(funcs ...ClientOptionFunc) *Client {
	opts := NewClientOptions(funcs...)

	oauth2 := &oauth2.Config{
		ClientID:     opts.ClientID,
		ClientSecret: opts.ClientSecret,
		Endpoint:     opts.Provider.Endpoint(),
		RedirectURL:  opts.RedirectURL,
		Scopes:       opts.Scopes,
	}

	verifier := opts.Provider.Verifier(&oidc.Config{
		ClientID:        opts.ClientID,
		SkipIssuerCheck: opts.SkipIssuerCheck,
	})

	return &Client{
		oauth2:     oauth2,
		provider:   opts.Provider,
		verifier:   verifier,
		authParams: opts.AuthParams,
		httpClient: opts.HTTPClient,
	}
}