package oidc

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

	"github.com/coreos/go-oidc/v3/oidc"
	"github.com/dchest/uniuri"
	"github.com/pkg/errors"
	"gitlab.com/wpetit/goweb/middleware/container"
	"gitlab.com/wpetit/goweb/service/session"
	"golang.org/x/oauth2"
)

type Client struct {
	oauth2    *oauth2.Config
	provider  *oidc.Provider
	verifier  *oidc.IDTokenVerifier
	acrValues string
}

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

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

func (c *Client) Login(w http.ResponseWriter, r *http.Request) {
	ctn := container.Must(r.Context())

	sess, err := session.Must(ctn).Get(w, r)
	if err != nil {
		panic(errors.Wrap(err, "could not retrieve session"))
	}

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

	sess.Set(SessionOIDCStateKey, state)
	sess.Set(SessionOIDCNonceKey, nonce)

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

	authCodeOptions := []oauth2.AuthCodeOption{}
	authCodeOptions = append(authCodeOptions, oidc.Nonce(nonce))
	if c.acrValues != "" {
		authCodeOptions = append(authCodeOptions, oauth2.SetAuthURLParam("acr_values", c.acrValues))
	}

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

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

func (c *Client) Logout(w http.ResponseWriter, r *http.Request, postLogoutRedirectURL string) {
	rawIDToken, err := RawIDToken(w, r)
	if err != nil {
		panic(errors.Wrap(err, "could not retrieve raw id token"))
	}

	ctn := container.Must(r.Context())

	sess, err := session.Must(ctn).Get(w, r)
	if err != nil {
		panic(errors.Wrap(err, "could not retrieve session"))
	}

	state := uniuri.New()

	sess.Set(SessionOIDCStateKey, state)
	sess.Unset(SessionIDTokenKey)

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

	sessionEndURL, err := c.sessionEndURL(rawIDToken, state, postLogoutRedirectURL)
	if err != nil {
		panic(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)
	}
}

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(w http.ResponseWriter, r *http.Request) (*oidc.IDToken, string, error) {
	ctx := r.Context()
	ctn := container.Must(ctx)

	sess, err := session.Must(ctn).Get(w, r)
	if err != nil {
		return nil, "", errors.Wrap(err, "could not retrieve session")
	}

	rawStoredState := sess.Get(SessionOIDCStateKey)
	receivedState := r.URL.Query().Get("state")

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

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

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

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

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

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

	return idToken, rawIDToken, nil
}

func NewClient(opts ...OptionFunc) *Client {
	opt := fromDefault(opts...)

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

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

	return &Client{oauth2, opt.Provider, verifier, opt.AcrValues}
}