type Mutable<T> = {
    -readonly [P in keyof T]: T[P];
};

type DeepMutable<T> = T extends object ? {
    -readonly [P in keyof T]: DeepMutable<T[P]>;
} : T;

interface Product {
    readonly id: string;
    readonly name: string;
    details: {
        readonly sku: string;
        price: number;
    };
    tags: readonly string[];
}

type ModifiableProduct = Mutable<Product>;
// type ModifiableProduct = { id: string; name: string; details: { readonly sku: string; price: number; }; tags: readonly string[]; }
// Only top-level readonly removed

type FullyModifiableProduct = DeepMutable<Product>;
/*
type FullyModifiableProduct = {
    id: string;
    name: string;
    details: {
        sku: string;
        price: number;
    };
    tags: string[];
}
*/

const product: Readonly<Product> = {
    id: 'p123',
    name: 'Laptop',
    details: { sku: 'LTP-XYZ', price: 1200 },
    tags: ['electronics', 'computers']
};

// product.id = 'p456'; // Error: Cannot assign to 'id' because it is a read-only property.

const modifiableProduct: FullyModifiableProduct = product as FullyModifiableProduct;
modifiableProduct.id = 'p456'; // OK
modifiableProduct.details.sku = 'LTP-ABC'; // OK
modifiableProduct.tags.push('sale'); // OK