/**
 * A helper type to generate dot-prefixed keys.
 */
type DotPrefix<T extends string> = T extends '' ? '' : `.${T}`;

/**
 * Recursively generates all possible dot-notation paths for a nested object type.
 */
type Path<T> = (T extends object ?
    { [K in keyof T]: `${K}${DotPrefix<Path<T[K]>>}` }[keyof T] :
    ''
) extends infer P ? P : never;

interface UserSettings {
    theme: 'dark' | 'light';
    language: string;
    notifications: {
        email: boolean;
        sms: boolean;
        push: {
            enabled: boolean;
            frequency: 'daily' | 'weekly';
        };
    };
    profile: {
        firstName: string;
        lastName: string;
    };
    preferences?: {
        privacy: boolean;
    };
}

type UserSettingPaths = Path<UserSettings>;
/*
type UserSettingPaths = "theme" | "language" | "notifications" | "profile" | "preferences" | "notifications.email" | "notifications.sms" | "notifications.push" | "profile.firstName" | "profile.lastName" | "preferences.privacy" | "notifications.push.enabled" | "notifications.push.frequency"
*/

// Example Usage:
function getSetting<T, K extends Path<T>>(obj: T, path: K): any {
    const parts = path.split('.');
    let current: any = obj;
    for (const part of parts) {
        if (current === undefined || current === null) return undefined;
        current = current[part];
    }
    return current;
}

const settings: UserSettings = {
    theme: 'dark',
    language: 'en',
    notifications: {
        email: true,
        sms: false,
        push: { enabled: true, frequency: 'daily' }
    },
    profile: { firstName: 'John', lastName: 'Doe' }
};

const theme = getSetting(settings, 'theme'); // string: 'dark'
const emailNotifications = getSetting(settings, 'notifications.email'); // boolean: true
const pushFrequency = getSetting(settings, 'notifications.push.frequency'); // 'daily' | 'weekly': 'daily'
// const invalidPath = getSetting(settings, 'notifications.foo'); // Type Error!

// This utility is extremely useful for form libraries, i18n key management,
// and safe access to nested properties without string literals errors.