package handlers

import (
	"context"
	"net/http"

	"git.haelnorr.com/h/golib/cookies"
	"git.haelnorr.com/h/golib/hws"
	"git.haelnorr.com/h/golib/hwsauth"
	"github.com/pkg/errors"
	"github.com/uptrace/bun"

	"git.haelnorr.com/h/oslstats/internal/config"
	"git.haelnorr.com/h/oslstats/internal/db"
	"git.haelnorr.com/h/oslstats/internal/discord"
	"git.haelnorr.com/h/oslstats/internal/store"
	"git.haelnorr.com/h/oslstats/internal/throw"
	"git.haelnorr.com/h/oslstats/pkg/oauth"
)

func Callback(
	s *hws.Server,
	auth *hwsauth.Authenticator[*db.User, bun.Tx],
	conn *bun.DB,
	cfg *config.Config,
	store *store.Store,
	discordAPI *discord.APIClient,
) http.Handler {
	return http.HandlerFunc(
		func(w http.ResponseWriter, r *http.Request) {
			attempts, exceeded, track := store.TrackRedirect(r, "/callback", 5)

			if exceeded {
				err := track.Error(attempts)
				store.ClearRedirectTrack(r, "/callback")
				throw.BadRequest(s, w, r, "Too many redirects. Please try logging in again.", err)
				return
			}

			state := r.URL.Query().Get("state")
			code := r.URL.Query().Get("code")
			if state == "" && code == "" {
				http.Redirect(w, r, "/", http.StatusBadRequest)
				return
			}
			data, err := verifyState(cfg.OAuth, w, r, state)
			if err != nil {
				if vsErr, ok := err.(*verifyStateError); ok {
					if vsErr.IsCookieError() {
						throw.Unauthorized(s, w, r, "OAuth session not found or expired", err)
					} else {
						throw.ForbiddenSecurity(s, w, r, "OAuth state verification failed", err)
					}
				} else {
					throw.ForbiddenSecurity(s, w, r, "OAuth state verification failed", err)
				}
				return
			}
			store.ClearRedirectTrack(r, "/callback")

			switch data {
			case "login":
				var redirect func()
				if ok := db.WithWriteTx(s, w, r, conn, func(ctx context.Context, tx bun.Tx) (bool, error) {
					redirect, err = login(ctx, auth, tx, cfg, w, r, code, store, discordAPI)
					if err != nil {
						throw.InternalServiceError(s, w, r, "OAuth login failed", err)
						return false, nil
					}
					return true, nil
				}); !ok {
					return
				}
				redirect()
				return
			}
		},
	)
}

type verifyStateError struct {
	err         error
	cookieError bool
}

func (e *verifyStateError) Error() string {
	return e.err.Error()
}

func (e *verifyStateError) IsCookieError() bool {
	return e.cookieError
}

func verifyState(
	cfg *oauth.Config,
	w http.ResponseWriter,
	r *http.Request,
	state string,
) (string, error) {
	if r == nil {
		return "", errors.New("request cannot be nil")
	}
	if state == "" {
		return "", errors.New("state param field is empty")
	}

	uak, err := oauth.GetStateCookie(r)
	if err != nil {
		return "", &verifyStateError{
			err:         errors.Wrap(err, "oauth.GetStateCookie"),
			cookieError: true,
		}
	}

	data, err := oauth.VerifyState(cfg, state, uak)
	if err != nil {
		return "", &verifyStateError{
			err:         errors.Wrap(err, "oauth.VerifyState"),
			cookieError: false,
		}
	}

	oauth.DeleteStateCookie(w)
	return data, nil
}

func login(
	ctx context.Context,
	auth *hwsauth.Authenticator[*db.User, bun.Tx],
	tx bun.Tx,
	cfg *config.Config,
	w http.ResponseWriter,
	r *http.Request,
	code string,
	store *store.Store,
	discordAPI *discord.APIClient,
) (func(), error) {
	token, err := discordAPI.AuthorizeWithCode(code)
	if err != nil {
		return nil, errors.Wrap(err, "discordAPI.AuthorizeWithCode")
	}
	session, err := discord.NewOAuthSession(token)
	if err != nil {
		return nil, errors.Wrap(err, "discord.NewOAuthSession")
	}
	discorduser, err := session.GetUser()
	if err != nil {
		return nil, errors.Wrap(err, "session.GetUser")
	}

	user, err := db.GetUserByDiscordID(ctx, tx, discorduser.ID)
	if err != nil {
		return nil, errors.Wrap(err, "db.GetUserByDiscordID")
	}
	var redirect string
	if user == nil {
		sessionID, err := store.CreateRegistrationSession(discorduser, token)
		if err != nil {
			return nil, errors.Wrap(err, "store.CreateRegistrationSession")
		}
		http.SetCookie(w, &http.Cookie{
			Name:     "registration_session",
			Path:     "/",
			Value:    sessionID,
			MaxAge:   300, // 5 minutes
			HttpOnly: true,
			Secure:   cfg.HWSAuth.SSL,
			SameSite: http.SameSiteLaxMode,
		})
		redirect = "/register"
	} else {
		err = user.UpdateDiscordToken(ctx, tx, token)
		if err != nil {
			return nil, errors.Wrap(err, "user.UpdateDiscordToken")
		}

		// Check if user should be granted admin role (environment-based)
		if shouldGrantAdmin(user, cfg.RBAC) {
			err := ensureUserHasAdminRole(ctx, tx, user)
			if err != nil {
				return nil, errors.Wrap(err, "ensureUserHasAdminRole")
			}
		}

		err := auth.Login(w, r, user, true)
		if err != nil {
			return nil, errors.Wrap(err, "auth.Login")
		}
		redirect = cookies.CheckPageFrom(w, r)
	}
	return func() {
		http.Redirect(w, r, redirect, http.StatusSeeOther)
	}, nil
}