CREATE TYPE "PaymentMethod" AS ENUM (
    'pay_u',
    'payment_on_the_spot'
    );

CREATE TYPE "ShoppingCartState" AS ENUM (
    'active',
    'closed'
    );

CREATE TYPE "QuantityUnit" AS ENUM (
    'g',
    'dkg',
    'kg',
    'piece'
    );

CREATE TABLE shopping_carts
(
    id             serial                                                             NOT NULL,
    buyer_id       integer                                                            NOT NULL,
    payment_method "PaymentMethod"     DEFAULT 'payment_on_the_spot'::"PaymentMethod" NOT NULL,
    state          "ShoppingCartState" DEFAULT 'active'::"ShoppingCartState"          NOT NULL,
    checkout_notes text
);

CREATE TABLE shopping_cart_items
(
    id                 serial            NOT NULL,
    product_variant_id integer           NOT NULL,
    product_id         integer           NOT NULL,
    shopping_cart_id   integer,
    quantity           integer DEFAULT 0 NOT NULL,
    quantity_unit      "QuantityUnit"    NOT NULL,
    CONSTRAINT positive_quantity CHECK ((quantity >= 0))
);