veridian/app/composables/useAuth.ts

import type { BetterAuthClientOptions, InferSessionFromClient, InferUserFromClient, User } from 'better-auth/client';
import { twoFactorClient } from 'better-auth/client/plugins';
import { createAuthClient } from 'better-auth/vue';
import { Err, Ok, type Result } from '~~/types/result';
import { assert } from '~~/utils/assert';

export enum AuthError {
    NotAuthenticated = 'NOT_AUTHENTICATED',
    SignInFailed = 'SIGN_IN_FAILED',
    SignUpFailed = 'SIGN_UP_FAILED',
    SignOutFailed = 'SIGN_OUT_FAILED',
    UpdateFailed = 'UPDATE_FAILED',
    NetworkError = 'NETWORK_ERROR',
}

export type AuthUser = InferUserFromClient<BetterAuthClientOptions> & {
    twoFactorEnabled?: boolean | null;
};

type sessionData = {
    session: InferSessionFromClient<BetterAuthClientOptions> | null;
    user: AuthUser | null;
};

// Signing in either finishes right away, or stops at the second factor when
// the account has two-factor authentication turned on.
export type SignInResult =
    | { twoFactorRequired: false; user: User; token: string }
    | { twoFactorRequired: true };

export const useAuth = () => {
    const authClient = createAuthClient({
        plugins: [twoFactorClient()],
    });
    const session = useState<InferSessionFromClient<BetterAuthClientOptions> | null>('auth:session', () => null);
    const user = useState<AuthUser | null>('auth:user', () => null);
    const sessionFetching = import.meta.server ? ref(false) : useState('auth:sessionFetching', () => false);

    let sessionPromise: Promise<Result<sessionData, AuthError>> | null = null;

    const fetchSession = async (): Promise<Result<sessionData, AuthError>> => {
        if (sessionPromise) {
            console.log('already fetching session');
            return sessionPromise;
        }

        sessionFetching.value = true;
        const { promise, resolve } = Promise.withResolvers<Result<sessionData, AuthError>>();
        sessionPromise = promise;
        let data: {
            session: InferSessionFromClient<BetterAuthClientOptions>;
            user: AuthUser;
        } | null = null;

        try {
            if (import.meta.server) {
                data =
                    (
                        await useFetch<{
                            session: InferSessionFromClient<BetterAuthClientOptions>;
                            user: AuthUser;
                        }>('/api/auth/get-session')
                    ).data.value ?? null;
            } else {
                data = (await authClient.getSession()).data;
            }

            session.value = data?.session || null;
            user.value = data?.user || null;
            resolve(Ok({ session: data?.session || null, user: data?.user || null }));
        } catch (error) {
            console.error('Failed to fetch session:', error);
            resolve(Err(AuthError.NetworkError));
        } finally {
            sessionFetching.value = false;
        }

        return sessionPromise;
    };

    if (import.meta.client) {
        authClient.$store.listen('$sessionSignal', async (signal) => {
            if (!signal) return;
            await fetchSession();
        });
    }

    const signIn = async (
        email: string,
        password: string
    ): Promise<Result<SignInResult, { error: AuthError, data?: any }>> => {
        sessionFetching.value = true;

        try {
            const { data, error } = await authClient.signIn.email({
                email,
                password,
            });

            if (error) {
                console.error('Sign in failed:', error);
                return Err({ error: AuthError.SignInFailed, data: error });
            }

            if (!data) {
                return Err({ error: AuthError.SignInFailed });
            }

            // no session exists yet, verifyTwoFactor() finishes the sign in
            if ('twoFactorRedirect' in data && data.twoFactorRedirect) {
                return Ok({ twoFactorRequired: true });
            }

            user.value = data.user;

            clearNuxtData();

            return Ok({ twoFactorRequired: false, user: data.user, token: data.token });
        } catch (err) {
            console.error('Sign in error:', err);
            return Err({ error: AuthError.NetworkError });
        } finally {
            sessionFetching.value = false;
        }
    };

    const verifyTwoFactor = async (
        code: string,
        options: { backupCode?: boolean; trustDevice?: boolean } = {}
    ): Promise<Result<{ user: User; token: string }, { error: AuthError, data?: any }>> => {
        sessionFetching.value = true;

        try {
            const body = { code, trustDevice: options.trustDevice ?? false };
            const { data, error } = options.backupCode
                ? await authClient.twoFactor.verifyBackupCode(body)
                : await authClient.twoFactor.verifyTotp(body);

            if (error) {
                return Err({ error: AuthError.SignInFailed, data: error });
            }

            if (!data || !data.token) {
                return Err({ error: AuthError.SignInFailed });
            }

            user.value = data.user as AuthUser;

            clearNuxtData();

            return Ok({ user: data.user as User, token: data.token });
        } catch (err) {
            console.error('Two-factor verification error:', err);
            return Err({ error: AuthError.NetworkError });
        } finally {
            sessionFetching.value = false;
        }
    };

    const signUp = async (
        email: string,
        password: string,
        name: string
    ): Promise<Result<{ user: User; token: string }, { error: AuthError, data?: any }>> => {
        sessionFetching.value = true;

        try {
            const { data, error } = await authClient.signUp.email({
                email,
                password,
                name,
            });

            if (error) {
                console.error('Sign up failed:', error);
                return Err({ error: AuthError.SignUpFailed, data: error });
            }

            if (!data || !data.token) {
                return Err({ error: AuthError.SignUpFailed });
            }

            user.value = data.user;

            clearNuxtData();

            return Ok({ user: data.user, token: data.token });
        } catch (err) {
            console.error('Sign up error:', err);
            return Err({ error: AuthError.NetworkError });
        } finally {
            sessionFetching.value = false;
        }
    };

    const signOut = async (): Promise<Result<void, AuthError>> => {
        sessionFetching.value = true;

        try {
            const { error } = await authClient.signOut();

            if (error) {
                console.error('Sign out failed:', error);
                return Err(AuthError.SignOutFailed);
            }

            user.value = null;
            session.value = null;

            clearNuxtData();

            return Ok(undefined);
        } catch (err) {
            console.error('Sign out error:', err);
            return Err(AuthError.NetworkError);
        } finally {
            sessionFetching.value = false;
        }
    };

    const updateProfile = async (
        updates: { name?: string; image?: string | null }
    ): Promise<Result<void, AuthError>> => {
        try {
            const { error } = await authClient.updateUser(updates);

            if (error) {
                console.error('Profile update failed:', error);
                return Err(AuthError.UpdateFailed);
            }

            if (user.value) {
                user.value = { ...user.value, ...updates };
            }

            return Ok(undefined);
        } catch (err) {
            console.error('Profile update error:', err);
            return Err(AuthError.NetworkError);
        }
    };

    return {
        client: authClient,
        session,
        user,
        loggedIn: computed(() => !!session.value),
        signIn,
        verifyTwoFactor,
        signUp,
        signOut,
        updateProfile,
        fetchSession,
    };
};