diff --git a/pyproject.toml b/pyproject.toml
index 06fbe913..342512a4 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -9,6 +9,7 @@ dependencies = []
 [dependency-groups]
 dev = [
     "mypy==2.3.1",
+    "pytest>=9.1.1",
     "ruff==0.16.8",
 ]
 
diff --git a/src/part1/constants.py b/src/part1/constants.py
index 9abfbba2..9205c47d 100644
--- a/src/part1/constants.py
+++ b/src/part1/constants.py
@@ -1,38 +1,18 @@
-"""Bit layout and default epoch for the Twitter Snowflake ID generator.
-
-A Snowflake identifier is a 63-bit positive integer packed as follows, from
-the most significant bit downwards:
-
-    1 bit   unused sign bit, always zero
-    41 bits milliseconds elapsed since a custom epoch
-    10 bits node identifier
-    12 bits per-millisecond sequence counter
-
-The shift and mask constants should be derived from the bit widths so that
-changing a width keeps everything else consistent.
-"""
-
 from typing import Final
 
 
-# TODO: замените заглушки (0) на корректные значения, см. TASK.md.
-# Все константы, зависящие от ёмкостей *_BITS, должны вычисляться из них.
-
 # Twitter's original Snowflake epoch: 2010-11-04 01:42:54.657 UTC.
-EPOCH_MS_DEFAULT: Final[int] = 0
+EPOCH_MS_DEFAULT: Final[int] = 1288834974657
 
 # Node identifier used when the caller does not supply one.
-NODE_ID_DEFAULT: Final[int] = 0
+NODE_ID_DEFAULT: Final[int] = 1
 
 # Width of each field, in bits.
-TIMESTAMP_BITS: Final[int] = 0
-NODE_ID_BITS: Final[int] = 0
-SEQUENCE_ID_BITS: Final[int] = 0
+TIMESTAMP_BITS: Final[int] = 41
+NODE_ID_BITS: Final[int] = 10
+SEQUENCE_ID_BITS: Final[int] = 12
 
 # Largest value each field can hold.
-TIMESTAMP_MS_MAX: Final[int] = 0
-NODE_ID_MAX: Final[int] = 0
-SEQUENCE_ID_MAX: Final[int] = 0
-
-# Здесь можно добавить собственные вспомогательные константы
-# (например, сдвиги полей при сборке идентификатора).
+TIMESTAMP_MS_MAX: Final[int] = (1 << TIMESTAMP_BITS) - 1
+NODE_ID_MAX: Final[int] = (1 << NODE_ID_BITS) - 1
+SEQUENCE_ID_MAX: Final[int] = (1 << SEQUENCE_ID_BITS) - 1
diff --git a/src/part1/snowflake.py b/src/part1/snowflake.py
index d3abf050..73cded6c 100644
--- a/src/part1/snowflake.py
+++ b/src/part1/snowflake.py
@@ -1,85 +1,32 @@
-"""Twitter Snowflake identifier generator.
+import time
 
-Snowflake produces roughly time-ordered 64-bit integer identifiers without
-coordination between nodes. Each identifier packs the milliseconds elapsed
-since a custom epoch, a node identifier and a per-millisecond sequence counter
-into a single 63-bit positive integer (see ``constants`` for the layout).
-
-The public entry point is :func:`generate_snowflake_id`. It is stateless: the
-caller passes the sequence counter on every call and is responsible for
-advancing it within a millisecond and resetting it when the clock ticks over.
-
-Each packed field can be read back on its own with :func:`decode_timestamp_ms`,
-:func:`decode_node_id` and :func:`decode_sequence_id`.
-"""
-
-import time  # noqa: F401
-
-from .constants import (  # noqa: F401
+from .constants import (
     EPOCH_MS_DEFAULT,
+    NODE_ID_BITS,
     NODE_ID_DEFAULT,
     NODE_ID_MAX,
+    SEQUENCE_ID_BITS,
     SEQUENCE_ID_MAX,
+    TIMESTAMP_BITS,
     TIMESTAMP_MS_MAX,
 )
 
 
 def read_current_millis(epoch_ms: int) -> int:
-    """Read the number of milliseconds elapsed since the custom epoch.
-
-    Args:
-        epoch_ms: The custom epoch expressed as Unix milliseconds.
-
-    Returns:
-        The count of whole milliseconds between ``epoch_ms`` and now. May be
-        negative if ``epoch_ms`` lies in the future.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return time.time_ns() // 10**6 - epoch_ms
 
 
 def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
-    """Read the timestamp field out of a Snowflake identifier.
-
-    Args:
-        snowflake_id: An identifier produced against the same epoch.
-        epoch_ms: The epoch the identifier was generated against. Defaults to
-            the original Twitter epoch (2010-11-04 01:42:54.657 UTC).
-
-    Returns:
-        The absolute Unix time in milliseconds at which the identifier was
-        generated.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    stored_time = snowflake_id >> (NODE_ID_BITS + SEQUENCE_ID_BITS)
+    return stored_time + epoch_ms
 
 
 def decode_node_id(snowflake_id: int) -> int:
-    """Read the node identifier field out of a Snowflake identifier.
-
-    Args:
-        snowflake_id: An identifier produced by :func:`generate_snowflake_id`.
-
-    Returns:
-        The node identifier packed into ``snowflake_id``, in the range
-        ``[0, NODE_ID_MAX]``.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return (snowflake_id >> SEQUENCE_ID_BITS) & NODE_ID_MAX
 
 
 def decode_sequence_id(snowflake_id: int) -> int:
-    """Read the sequence counter field out of a Snowflake identifier.
-
-    Args:
-        snowflake_id: An identifier produced by :func:`generate_snowflake_id`.
-
-    Returns:
-        The per-millisecond sequence counter packed into ``snowflake_id``, in
-        the range ``[0, SEQUENCE_ID_MAX]``.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    return snowflake_id & SEQUENCE_ID_MAX
 
 
 def generate_snowflake_id(
@@ -87,28 +34,26 @@ def generate_snowflake_id(
     node_id: int = NODE_ID_DEFAULT,
     epoch_ms: int = EPOCH_MS_DEFAULT,
 ) -> int | None:
-    """Build and return a Snowflake identifier for the current millisecond.
-
-    The function is stateless: the caller passes the per-millisecond sequence
-    counter explicitly. It is the caller's responsibility to increment
-    ``sequence_id`` for identifiers minted within the same millisecond and to
-    reset it once the clock advances.
-
-    Args:
-        sequence_id: The per-millisecond sequence counter, in the range
-            ``[0, SEQUENCE_ID_MAX]``.
-        node_id: The identifier of this node, in the range ``[0, NODE_ID_MAX]``.
-            Optional; defaults to ``NODE_ID_DEFAULT``.
-        epoch_ms: The start of the epoch as Unix milliseconds. Optional;
-            defaults to the original Twitter epoch (2010-11-04 01:42:54.657
-            UTC).
 
-    Returns:
-        The Snowflake identifier as a positive 63-bit integer, or ``None`` if
-        ``node_id`` is outside ``[0, NODE_ID_MAX]``, ``sequence_id`` is outside
-        ``[0, SEQUENCE_ID_MAX]``, or the elapsed time no longer fits in the
-        timestamp field (roughly 69 years after ``epoch_ms``). In each of those
-        cases an explanatory message is printed to stdout first.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    if not (0 <= node_id <= NODE_ID_MAX):
+        print(f"node_id must be in [0, {NODE_ID_MAX}], got {node_id}")
+        return None
+
+    if not (0 <= sequence_id <= SEQUENCE_ID_MAX):
+        print(f"sequence_id must be in [0, {SEQUENCE_ID_MAX}], got {sequence_id}")
+        return None
+
+    timestamp_ms = read_current_millis(epoch_ms)
+    if not (0 <= timestamp_ms <= TIMESTAMP_MS_MAX):
+        print(
+            f"timestamp_ms value is overflows {TIMESTAMP_BITS} bits:"
+            f"{timestamp_ms} > {TIMESTAMP_MS_MAX}"
+        )
+        return None
+
+    snowflake_id = (
+        (timestamp_ms << (NODE_ID_BITS + SEQUENCE_ID_BITS))
+        | (node_id << SEQUENCE_ID_BITS)
+        | sequence_id
+    )
+    return snowflake_id
diff --git a/src/part2/cart.py b/src/part2/cart.py
index 063f9aea..cf0e4e96 100644
--- a/src/part2/cart.py
+++ b/src/part2/cart.py
@@ -1,18 +1,7 @@
-"""Shopping-cart operations layered on top of the product store.
-
-The cart is a plain list of tuples, one :data:`CartLine` --
-``(product_id, quantity)`` -- per distinct product. Moving units between the
-store and the cart keeps the two sides in balance: :func:`add_to_cart` takes
-units out of stock, :func:`remove_from_cart` puts them back.
-
-Like the CRUD layer, the failure path never raises -- the operation prints
-an explanatory message to stdout and returns ``None``.
-"""
-
 from typing import Final
 
-from .crud import read_product, update_product  # noqa: F401
-from .storage import (  # noqa: F401
+from .crud import read_product, update_product
+from .storage import (
     NAME_INDEX,
     PRICE_INDEX,
     QUANTITY_INDEX,
@@ -24,7 +13,7 @@
 
 # TODO: задайте позиции полей внутри кортежа CartLine
 LINE_PRODUCT_ID_INDEX: Final = 0
-LINE_QUANTITY_INDEX: Final = 0
+LINE_QUANTITY_INDEX: Final = 1
 
 
 def add_to_cart(
@@ -33,28 +22,41 @@ def add_to_cart(
     product_id: int,
     quantity: int,
 ) -> CartLine | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
-
-    The product is looked up in ``storage``. If it is missing, a message is
-    printed (by :func:`~src.part2.crud.read_product`) and nothing
-    changes. If the store holds fewer units than requested, an explanatory
-    message is printed and nothing changes. Otherwise the store record is
-    decremented by ``quantity`` and the cart line for ``product_id`` gains
-    ``quantity`` units -- a new line is created when the cart had none.
-
-    Args:
-        storage: The product store to draw stock from; modified in place on
-            success.
-        cart: The cart to add the units to; modified in place on success.
-        product_id: The identifier of the product to add.
-        quantity: Number of units to move into the cart.
-
-    Returns:
-        The cart line for ``product_id`` after the addition, or ``None``
-        when the product is unknown or the store cannot cover the request.
-    """
-    # TODO: реализуйте функцию
-    return (0, 0)
+    """Move ``quantity`` units of ``product_id`` from the store into ``cart``."""
+    # 1. Ищем товар. read_product сам напечатает сообщение, если не нашёл.
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
+
+    product_name = product[NAME_INDEX]
+    product_price = product[PRICE_INDEX]
+    product_quantity = product[QUANTITY_INDEX]
+
+    # 2. Проверяем остаток
+    if product_quantity < quantity:
+        print(
+            f"not enough stock for product {product_id}: "
+            f"{product_quantity} available, {quantity} requested"
+        )
+        return None
+
+    # 3. Списываем со склада
+    update_product(
+        storage,
+        product_id,
+        (product_name, product_price, product_quantity - quantity),
+    )
+
+    # 4. Обновляем строку корзины или создаём новую
+    for i, line in enumerate(cart):
+        if line[LINE_PRODUCT_ID_INDEX] == product_id:
+            new_line = (product_id, line[LINE_QUANTITY_INDEX] + quantity)
+            cart[i] = new_line
+            return new_line
+
+    new_line = (product_id, quantity)
+    cart.append(new_line)
+    return new_line
 
 
 def remove_from_cart(
@@ -63,27 +65,50 @@ def remove_from_cart(
     product_id: int,
     quantity: int,
 ) -> CartLine | None:
-    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store.
-
-    The cart line for ``product_id`` is looked up. If there is none, a
-    message is printed and nothing changes. If the line holds fewer units
-    than requested, an explanatory message is printed and nothing changes.
-    Otherwise the cart line loses ``quantity`` units -- the line is dropped
-    when it reaches zero -- and the store record gains ``quantity`` units
-    back.
-
-    Args:
-        storage: The product store to return stock to; modified in place on
-            success.
-        cart: The cart to take the units from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-        quantity: Number of units to move back into the store.
-
-    Returns:
-        The cart line for ``product_id`` after the removal (a quantity of
-        zero means the line was dropped), or ``None`` when the cart has no
-        line for the product or holds too few units.
-    """
-    # TODO: реализуйте функцию
-    return (0, 0)
+    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store."""
+    # 1. Ищем строку корзины
+    line_index = None
+    for i, line in enumerate(cart):
+        if line[LINE_PRODUCT_ID_INDEX] == product_id:
+            line_index = i
+            break
+
+    if line_index is None:
+        print(f"product {product_id} is not in the cart")
+        return None
+
+    # 2. Проверяем, хватает ли единиц в строке
+    line_quantity = cart[line_index][LINE_QUANTITY_INDEX]
+    if line_quantity < quantity:
+        print(
+            f"not enough units of product {product_id} in cart: "
+            f"{line_quantity} available, {quantity} requested"
+        )
+        return None
+
+    # 3. Находим товар на складе, чтобы вернуть ему единицы
+    product = read_product(storage, product_id)
+    if product is None:
+        print(f"product {product_id} is missing from the store")
+        return None
+
+    product_name = product[NAME_INDEX]
+    product_price = product[PRICE_INDEX]
+    product_quantity = product[QUANTITY_INDEX]
+
+    # 4. Возвращаем единицы на склад
+    update_product(
+        storage,
+        product_id,
+        (product_name, product_price, product_quantity + quantity),
+    )
+
+    # 5. Уменьшаем строку; если стало 0 — удаляем
+    remaining = line_quantity - quantity
+    if remaining == 0:
+        del cart[line_index]
+        return (product_id, 0)
+
+    new_line = (product_id, remaining)
+    cart[line_index] = new_line
+    return new_line
diff --git a/src/part2/crud.py b/src/part2/crud.py
index d026cbcb..919f0a39 100644
--- a/src/part2/crud.py
+++ b/src/part2/crud.py
@@ -1,79 +1,46 @@
-"""Create/read/update/delete operations over the in-memory product store.
-
-Every operation takes the store -- a list of
-:data:`~src.part2.storage.Product` tuples -- as its first argument and
-works on it in place. The failure path never raises: the operation prints
-an explanatory message to stdout and returns ``None``.
-
-The identifier of a new product is derived from the store itself
-(:func:`generate_product_id`): one past the greatest identifier in use, or
-:data:`~src.part2.storage.PRODUCT_ID_MIN` when the store is empty.
-Product names are kept unique -- :func:`create_product` refuses a name that
-is already taken.
-"""
-
 from decimal import Decimal
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_INDEX,
     PRODUCT_ID_INDEX,
     PRODUCT_ID_MIN,
     Product,
 )
-from .utils import normalize_price  # noqa: F401
+from .utils import normalize_price
 
 
 def generate_product_id(storage: list[Product]) -> int:
-    """Choose the identifier for the next product added to ``storage``.
-
-    Args:
-        storage: The product store to inspect.
-
-    Returns:
-        One past the greatest identifier currently held in ``storage``, or
-        :data:`~src.part2.storage.PRODUCT_ID_MIN` when ``storage`` is
-        empty.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    if not storage:
+        return PRODUCT_ID_MIN
+    return max(product[PRODUCT_ID_INDEX] for product in storage) + 1
 
 
 def create_product(
     storage: list[Product], fields: tuple[str, Decimal, int]
 ) -> int | None:
-    """Append a new product to ``storage`` and return its new identifier.
 
-    Args:
-        storage: The product store to append to; modified in place on
-            success.
-        fields: A ``(name, price, quantity)`` tuple describing the product.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
+    name, price, quantity = fields
 
-    Returns:
-        The identifier generated for the new product, or ``None`` when a
-        product with the same name already exists. In the ``None`` case
-        ``storage`` is left unchanged and a message naming the clashing
-        name is printed.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    if any(product[NAME_INDEX] == name for product in storage):
+        print(f"product name {name} is already taken.")
+        return None
 
+    new_product_id = generate_product_id(storage)
 
-def read_product(storage: list[Product], product_id: int) -> Product | None:
-    """Return the product stored under ``product_id``.
+    normalized_price = normalize_price(price)
 
-    Args:
-        storage: The product store to search.
-        product_id: The identifier to look up.
+    new_product = (new_product_id, name, normalized_price, quantity)
+    storage.append(new_product)
+    return new_product_id
 
-    Returns:
-        The matching ``(product_id, name, price, quantity)`` record, or
-        ``None`` when no product carries that identifier (a message is
-        printed in that case).
-    """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+
+def read_product(storage: list[Product], product_id: int) -> Product | None:
+
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            return product
+    print(f"no product with id {product_id}")
+    return None
 
 
 def update_product(
@@ -81,40 +48,25 @@ def update_product(
     product_id: int,
     fields: tuple[str, Decimal, int],
 ) -> Product | None:
-    """Overwrite the fields of the product stored under ``product_id``.
+    name, price, quantity = fields
+    normalized_price = normalize_price(price)
 
-    The identifier itself is preserved; only ``name``, ``price`` and
-    ``quantity`` are replaced.
+    for i, product in enumerate(storage):
+        if product[PRODUCT_ID_INDEX] == product_id:
+            updated = (product_id, name, normalized_price, quantity)
+            storage[i] = updated
+            return updated
 
-    Args:
-        storage: The product store to modify; the matching record is
-            replaced in place on success.
-        product_id: The identifier of the product to change.
-        fields: A ``(name, price, quantity)`` tuple with the new values.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
-
-    Returns:
-        The updated ``(product_id, name, price, quantity)`` record, or
-        ``None`` when no product carries that identifier (``storage`` is
-        left unchanged and a message is printed).
-    """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+    print(f"no product with id {product_id}")
+    return None
 
 
 def delete_product(storage: list[Product], product_id: int) -> int | None:
-    """Remove the product stored under ``product_id`` from ``storage``.
-
-    Args:
-        storage: The product store to remove from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-
-    Returns:
-        ``product_id`` when a product was removed, or ``None`` when no
-        product carried that identifier (``storage`` is left unchanged and
-        a message is printed).
-    """
-    # TODO: реализуйте функцию
-    return 0
+
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            storage.remove(product)
+            return product_id
+
+    print(f"no product with id {product_id}")
+    return None
diff --git a/src/part2/storage.py b/src/part2/storage.py
index b63d5fc7..81651a75 100644
--- a/src/part2/storage.py
+++ b/src/part2/storage.py
@@ -1,34 +1,12 @@
-"""In-memory product store for the shop CRUD exercise.
-
-The store is deliberately primitive: a plain list of tuples, with no
-persistence, no indexing and no schema enforcement. Each element is a
-:data:`Product` record -- a ``(product_id, name, price, quantity)`` tuple
-where:
-
-* ``product_id`` -- unique positive integer key, assigned by the create
-  operation in :mod:`src.part2.crud`;
-* ``name`` -- human-readable product name, unique across the store;
-* ``price`` -- price of a single unit, held as a :class:`~decimal.Decimal`
-  amount rounded to a fixed number of decimal places (see
-  :func:`src.part2.utils.normalize_price`) so that money is never
-  subject to binary floating-point error;
-* ``quantity`` -- number of units currently in stock.
-
-Field positions are exposed as ``*_INDEX`` constants so callers never
-hard-code tuple offsets.
-"""
-
 from decimal import Decimal
 from typing import Final
 
 
 type Product = tuple[int, str, Decimal, int]
 
-# TODO: задайте позиции полей внутри кортежа Product
 PRODUCT_ID_INDEX: Final = 0
-NAME_INDEX: Final = 0
-PRICE_INDEX: Final = 0
-QUANTITY_INDEX: Final = 0
+NAME_INDEX: Final = 1
+PRICE_INDEX: Final = 2
+QUANTITY_INDEX: Final = 3
 
-# TODO: задайте идентификатор первого товара в пустом хранилище
-PRODUCT_ID_MIN: Final[int] = 0
+PRODUCT_ID_MIN: Final[int] = 1
diff --git a/src/part2/utils.py b/src/part2/utils.py
index 11bd7a76..b03ba2bd 100644
--- a/src/part2/utils.py
+++ b/src/part2/utils.py
@@ -1,29 +1,10 @@
-"""Standalone helpers shared by the part2 storage and CRUD modules.
-
-For now this is limited to money handling: :func:`normalize_price` rounds a
-raw :class:`~decimal.Decimal` amount to the fixed number of fractional
-digits (:data:`PRICE_PRECISION`) that every stored price uses, keeping
-currency values free of binary floating-point error.
-"""
-
-from decimal import ROUND_HALF_UP, Decimal  # noqa: F401
+from decimal import ROUND_HALF_UP, Decimal
 from typing import Final
 
 
-# TODO: задайте число знаков после запятой и шаг квантования
-PRICE_PRECISION: Final[int] = 0
-PRICE_STEP: Final = Decimal(0)
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final = Decimal(1).scaleb(-PRICE_PRECISION)
 
 
 def normalize_price(price: Decimal) -> Decimal:
-    """Round a price to the precision every stored record uses.
-
-    Args:
-        price: The raw price amount.
-
-    Returns:
-        ``price`` quantised to :data:`PRICE_PRECISION` fractional digits,
-        with halves rounded up.
-    """
-    # TODO: реализуйте функцию
-    return Decimal(0)
+    return Decimal(price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP))
diff --git a/src/part3/crud.py b/src/part3/crud.py
index 68811d7e..765c594d 100644
--- a/src/part3/crud.py
+++ b/src/part3/crud.py
@@ -1,87 +1,49 @@
-"""Create/read/update/delete operations over the in-memory product store.
-
-Every operation takes the store -- a list of
-:data:`~src.part3.storage.Product` tuples -- as its first argument and
-works on it in place. The failure path never raises: the operation prints
-an explanatory message to stdout and returns ``None``.
-
-The identifier of a new product is derived from the store itself
-(:func:`generate_product_id`): one past the greatest identifier in use, or
-:data:`~src.part3.storage.PRODUCT_ID_MIN` when the store is empty.
-
-Every product name that reaches the store is passed through
-:func:`~src.part3.utils.normalize_product_name` first. A name that
-normalises to an empty string is rejected -- the operation prints a
-message and changes nothing. Names are also kept unique --
-:func:`create_product` refuses a normalised name that is already taken,
-and :func:`update_product` refuses one that is already taken by another
-product.
-"""
-
 from decimal import Decimal
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_INDEX,
     PRODUCT_ID_INDEX,
     PRODUCT_ID_MIN,
     Product,
 )
-from .utils import normalize_price, normalize_product_name  # noqa: F401
+from .utils import normalize_price, normalize_product_name
 
 
 def generate_product_id(storage: list[Product]) -> int:
-    """Choose the identifier for the next product added to ``storage``.
-
-    Args:
-        storage: The product store to inspect.
-
-    Returns:
-        One past the greatest identifier currently held in ``storage``, or
-        :data:`~src.part3.storage.PRODUCT_ID_MIN` when ``storage`` is
-        empty.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 2)
-    return 0
+    if not storage:
+        return PRODUCT_ID_MIN
+    return max(product[PRODUCT_ID_INDEX] for product in storage) + 1
 
 
 def create_product(
     storage: list[Product], fields: tuple[str, Decimal, int]
 ) -> int | None:
-    """Append a new product to ``storage`` and return its new identifier.
-
-    Args:
-        storage: The product store to append to; modified in place on
-            success.
-        fields: A ``(name, price, quantity)`` tuple describing the product.
-            ``name`` is normalised (surrounding whitespace stripped,
-            lower-cased) before it is stored or compared. ``price`` is a
-            :class:`~decimal.Decimal` amount and is rounded to the stored
-            money precision before it is saved.
-
-    Returns:
-        The identifier generated for the new product, or ``None`` when
-        ``name`` is blank once normalised or a product with the same
-        normalised name already exists. In the ``None`` case ``storage``
-        is left unchanged and an explanatory message is printed.
-    """
-    # TODO: реализуйте функцию
-    return 0
 
+    name, price, quantity = fields
+    name = normalize_product_name(name)
 
-def read_product(storage: list[Product], product_id: int) -> Product | None:
-    """Return the product stored under ``product_id``.
+    if not name:
+        print("product name must not be blank")
+        return None
+
+    if any(product[NAME_INDEX] == name for product in storage):
+        print(f"product name '{name}' is already taken")
+        return None
+
+    new_product_id = generate_product_id(storage)
+    normalized_price = normalize_price(price)
+
+    new_product = (new_product_id, name, normalized_price, quantity)
+    storage.append(new_product)
+    return new_product_id
 
-    Args:
-        storage: The product store to search.
-        product_id: The identifier to look up.
 
-    Returns:
-        The matching ``(product_id, name, price, quantity)`` record, or
-        ``None`` when no product carries that identifier (a message is
-        printed in that case).
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 2)
-    return (0, "", Decimal(0), 0)
+def read_product(storage: list[Product], product_id: int) -> Product | None:
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            return product
+    print(f"no product with id {product_id}")
+    return None
 
 
 def update_product(
@@ -89,43 +51,38 @@ def update_product(
     product_id: int,
     fields: tuple[str, Decimal, int],
 ) -> Product | None:
-    """Overwrite the fields of the product stored under ``product_id``.
-
-    The identifier itself is preserved; only ``name``, ``price`` and
-    ``quantity`` are replaced.
-
-    Args:
-        storage: The product store to modify; the matching record is
-            replaced in place on success.
-        product_id: The identifier of the product to change.
-        fields: A ``(name, price, quantity)`` tuple with the new values.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
-
-    Returns:
-        The updated ``(product_id, name, price, quantity)`` record, or
-        ``None`` when ``name`` is blank once normalised, no product
-        carries that identifier, or the normalised name is already taken
-        by another product. In every ``None`` case ``storage`` is left
-        unchanged and an explanatory message is printed. Renaming a
-        product to its own current name is allowed.
-    """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+    name, price, quantity = fields
+    normalized_name = normalize_product_name(name)
+    normalized_price = normalize_price(price)
+
+    if not normalized_name:
+        print("product name must not be blank")
+        return None
+
+    for product in storage:
+        if (
+            product[NAME_INDEX] == normalized_name
+            and product[PRODUCT_ID_INDEX] != product_id
+        ):
+            print(f"product name '{normalized_name}' is already taken")
+            return None
+
+    for i, product in enumerate(storage):
+        if product[PRODUCT_ID_INDEX] == product_id:
+            updated = (product_id, normalized_name, normalized_price, quantity)
+            storage[i] = updated
+            return updated
+
+    print(f"no product with id {product_id}")
+    return None
 
 
 def delete_product(storage: list[Product], product_id: int) -> int | None:
-    """Remove the product stored under ``product_id`` from ``storage``.
-
-    Args:
-        storage: The product store to remove from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-
-    Returns:
-        ``product_id`` when a product was removed, or ``None`` when no
-        product carried that identifier (``storage`` is left unchanged and
-        a message is printed).
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 2)
-    return 0
+
+    for product in storage:
+        if product[PRODUCT_ID_INDEX] == product_id:
+            storage.remove(product)
+            return product_id
+
+    print(f"no product with id {product_id}")
+    return None
diff --git a/src/part3/run_admin.py b/src/part3/run_admin.py
index c5feeb0b..f35e09c6 100644
--- a/src/part3/run_admin.py
+++ b/src/part3/run_admin.py
@@ -1,107 +1,80 @@
-"""Interactive admin console for the part3 in-memory product store.
-
-Running this module starts a read-eval-print loop over a single product
-store that lives in memory for the lifetime of the process. Every line
-typed at the prompt is stripped of surrounding whitespace and matched
-against the set of known commands:
-
-* ``help`` -- print the list of commands and what each one does;
-* ``exit`` -- leave the loop and end the program;
-* ``show`` -- print the whole store as a text table;
-* ``create <name...> <price> <quantity>`` -- add a product;
-* ``read <id>`` -- print one product;
-* ``update <id> <name...> <price> <quantity>`` -- overwrite a product;
-* ``delete <id>`` -- remove a product.
-
-For ``create`` and ``update`` the price and quantity are always the last
-two words of the line; everything between the verb (and, for ``update``,
-the id) and those two words is joined with single spaces into the
-product name, so a multi-word name such as ``Gibson SG Junior`` needs no
-quoting.
-
-The four CRUD commands forward to :mod:`src.part3.crud`; whatever
-that call returns is printed unless it is ``None``. A line whose first
-word is not a known verb, or that carries the wrong number of arguments
-for its verb, prints an "is not a command" notice. A line that names a
-command correctly but whose id, price or quantity argument will not
-parse prints a distinct "arguments are invalid" notice. Either way the
-store is left untouched and the loop keeps running; only ``exit`` stops
-it.
-"""
-
-from decimal import Decimal, InvalidOperation  # noqa: F401
+from decimal import Decimal, InvalidOperation
 from typing import Final
 
-from .crud import (  # noqa: F401
+from .crud import (
     create_product,
     delete_product,
     read_product,
     update_product,
 )
 from .storage import Product
-from .utils import get_storage_str_representation  # noqa: F401
-
-
-# TODO: задайте приглашение и текст справки
-PROMPT: Final[str] = ""
-HELP_TEXT: Final[str] = ""
+from .utils import get_storage_str_representation
+
+
+PROMPT: Final[str] = "admin> "
+HELP_TEXT: Final[str] = (
+    "Available commands:\n"
+    "  help                                       show this message\n"
+    "  exit                                       leave the console\n"
+    "  show                                       print the whole store as a table\n"
+    "  create <name...> <price> <quantity>        add a product, print its new id\n"
+    "  read <id>                                  print the product with that id\n"
+    "  update <id> <name...> <price> <quantity>   overwrite that product's fields\n"
+    "  delete <id>                                remove the product with that id\n"
+    "\n"
+    "For create and update the price and quantity are the last two words of the\n"
+    "line; everything before them is the product name, so it may contain spaces\n"
+    '(for example "Gibson SG Junior") and needs no quoting.'
+)
 
 
 def show_help() -> None:
-    """Print the command reference to stdout.
-
-    The text is the module-level :data:`HELP_TEXT` constant, printed as
-    is: a heading, one line per command with a short description, and a
-    note on how multi-word names are parsed.
-    """
-    # TODO: реализуйте функцию
+    print(HELP_TEXT)
 
 
 def print_result(result: object) -> None:
-    """Print a CRUD result to stdout unless it is ``None``.
-
-    Args:
-        result: The value returned by a CRUD operation. ``None`` means the
-            operation already reported its own failure, so nothing is
-            printed in that case.
-    """
-    # TODO: реализуйте функцию
+    if result is not None:
+        print(result)
 
 
 def run_command(storage: list[Product], line: str) -> bool:
-    """Parse one console line and carry out the command it names.
-
-    Args:
-        storage: The product store shared across the session; mutated in
-            place by the ``create``, ``update`` and ``delete`` commands.
-        line: One line of console input, already stripped of surrounding
-            whitespace.
-
-    Returns:
-        ``True`` to keep the read-eval-print loop running, or ``False``
-        once the ``exit`` command has been seen. A line that is not a
-        known command prints a notice and still returns ``True``.
-
-    Raises:
-        ValueError: If an id or quantity argument of a CRUD command does
-            not parse as a base-10 integer.
-        decimal.InvalidOperation: If the price argument of ``create`` or
-            ``update`` does not parse as a decimal number.
-    """
-    # TODO: реализуйте функцию
-    return False
+    commands = line.split()
+
+    match commands:
+        case ["help"]:
+            show_help()
+            return True
+        case ["exit"]:
+            return False
+        case ["show"]:
+            print_result(get_storage_str_representation(storage))
+            return True
+        case ["read", product_id]:
+            print_result(read_product(storage, int(product_id)))
+            return True
+        case ["delete", product_id]:
+            print_result(delete_product(storage, int(product_id)))
+            return True
+        case ["update", product_id, *args] if len(args) >= 3:
+            name = " ".join(args[:-2])
+            price = Decimal(args[-2])
+            quantity = int(args[-1])
+            print_result(
+                update_product(storage, int(product_id), (name, price, quantity))
+            )
+            return True
+        case ["create", *args] if len(args) >= 3:
+            name = " ".join(args[:-2])
+            price = Decimal(args[-2])
+            quantity = int(args[-1])
+            print_result(create_product(storage, (name, price, quantity)))
+            return True
+        case _:
+            print(f"{line!r} is not a command")
+            return True
 
 
 def main() -> None:
-    """Run the admin console until the ``exit`` command is entered.
-
-    A single product store is created empty and kept in memory for the
-    whole session. Each iteration reads one line from stdin, strips its
-    surrounding whitespace and hands it to :func:`run_command`. A line
-    that names a command but whose id, price or quantity argument does
-    not parse is caught here and reported without stopping the loop; only
-    ``exit`` ends it.
-    """
     storage: list[Product] = []
     running = True
 
diff --git a/src/part3/storage.py b/src/part3/storage.py
index c5e34be5..81651a75 100644
--- a/src/part3/storage.py
+++ b/src/part3/storage.py
@@ -1,35 +1,12 @@
-"""In-memory product store for the shop CRUD exercise.
-
-The store is deliberately primitive: a plain list of tuples, with no
-persistence, no indexing and no schema enforcement. Each element is a
-:data:`Product` record -- a ``(product_id, name, price, quantity)`` tuple
-where:
-
-* ``product_id`` -- unique positive integer key, assigned by the create
-  operation in :mod:`src.part3.crud`;
-* ``name`` -- human-readable product name, unique across the store;
-* ``price`` -- price of a single unit, held as a :class:`~decimal.Decimal`
-  amount rounded to a fixed number of decimal places (see
-  :func:`src.part3.utils.normalize_price`) so that money is never
-  subject to binary floating-point error;
-* ``quantity`` -- number of units currently in stock.
-
-Field positions are exposed as ``*_INDEX`` constants so callers never
-hard-code tuple offsets.
-"""
-
 from decimal import Decimal
 from typing import Final
 
 
 type Product = tuple[int, str, Decimal, int]
 
-# TODO: задайте позиции полей внутри кортежа Product (используйте своё решение
-# части 2)
 PRODUCT_ID_INDEX: Final = 0
-NAME_INDEX: Final = 0
-PRICE_INDEX: Final = 0
-QUANTITY_INDEX: Final = 0
+NAME_INDEX: Final = 1
+PRICE_INDEX: Final = 2
+QUANTITY_INDEX: Final = 3
 
-# TODO: задайте идентификатор первого товара в пустом хранилище
-PRODUCT_ID_MIN: Final[int] = 0
+PRODUCT_ID_MIN: Final[int] = 1
diff --git a/src/part3/utils.py b/src/part3/utils.py
index 318ded0b..f7717194 100644
--- a/src/part3/utils.py
+++ b/src/part3/utils.py
@@ -1,95 +1,48 @@
-"""Standalone helpers shared by the part3 storage and CRUD modules.
-
-Normalisation:
-
-* :func:`normalize_price` rounds a raw :class:`~decimal.Decimal` amount to
-  the fixed number of fractional digits (:data:`PRICE_PRECISION`) that
-  every stored price uses, keeping currency values free of binary
-  floating-point error.
-* :func:`normalize_product_name` strips surrounding whitespace from a
-  product name, collapses every internal run of whitespace to a single
-  space and lower-cases it, giving every stored name a single canonical
-  form.
-
-Presentation:
-
-* :func:`get_storage_str_representation` renders the whole store as a
-  text table meant to be printed to a terminal; each column is sized to
-  the longest value it holds in that particular call.
-"""
-
-from decimal import ROUND_HALF_UP, Decimal  # noqa: F401
+from decimal import ROUND_HALF_UP, Decimal
 from typing import Final
 
-from .storage import Product
+from .storage import NAME_INDEX, PRICE_INDEX, PRODUCT_ID_INDEX, QUANTITY_INDEX, Product
 
 
-# Number of fractional digits every stored price is rounded to.
-# Quantisation step derived from PRICE_PRECISION, e.g. Decimal("0.01").
-# TODO: задайте число знаков после запятой и шаг квантования (используйте своё
-# решение части 2)
-PRICE_PRECISION: Final[int] = 0
-PRICE_STEP: Final = Decimal(0)
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final = Decimal(1).scaleb(-PRICE_PRECISION)
 
-# Column headers of the table produced by get_storage_str_representation,
-# left to right. The width of each column is not fixed here -- it is
-# measured per call from the data (see the function).
-# TODO: задайте заголовки столбцов таблицы
-TABLE_HEADERS: Final[tuple[str, ...]] = ()
+TABLE_HEADERS: Final[tuple[str, ...]] = ("ID", "name", "price", "quantity")
 
 
 def normalize_price(price: Decimal) -> Decimal:
-    """Round a price to the precision every stored record uses.
-
-    Args:
-        price: The raw price amount.
-
-    Returns:
-        ``price`` quantised to :data:`PRICE_PRECISION` fractional digits,
-        with halves rounded up.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 2)
-    return Decimal(0)
+    return Decimal(price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP))
 
 
 def normalize_product_name(name: str) -> str:
-    """Reduce a product name to the canonical form the store keeps.
+    return " ".join(name.lower().split())
 
-    Args:
-        name: The raw product name.
 
-    Returns:
-        ``name`` with every leading and trailing whitespace character
-        removed, every internal run of whitespace (spaces, tabs and the
-        like) collapsed to a single space, and the rest lower-cased. For
-        example ``"abc    def\tghi\tjkl"`` becomes ``"abc def ghi jkl"``.
-        The result is an empty string when ``name`` holds nothing but
-        whitespace.
-    """
-    # TODO: реализуйте функцию
-    return ""
+def rowing_product(product: Product) -> tuple[str, ...]:
+    return (
+        str(product[PRODUCT_ID_INDEX]),
+        product[NAME_INDEX],
+        str(product[PRICE_INDEX]),
+        str(product[QUANTITY_INDEX]),
+    )
 
 
-# TODO: при необходимости добавьте свои вспомогательные функции
+def drawing_row(cells: tuple[str, ...], widths: tuple[int, ...]) -> str:
+    new_row = tuple(cell.ljust(width) for cell, width in zip(cells, widths))
+    return "| " + " | ".join(new_row) + " |"
 
 
 def get_storage_str_representation(storage: list[Product]) -> str:
-    """Render the product store as a text table with data-sized columns.
-
-    The table has the columns named by :data:`TABLE_HEADERS` -- id, name,
-    price and quantity. Each column is made exactly as wide as the longest
-    value it carries in this call (its header counted), so the columns
-    line up when the string is printed to a terminal and no value is ever
-    truncated.
-
-    Args:
-        storage: The product store to render.
-
-    Returns:
-        A multi-line string: a header row, a dashed separator row, then
-        one row per product in ``storage`` in list order. When ``storage``
-        is empty only the header and separator rows are returned, sized to
-        the header labels.
-    """
-    # TODO: реализуйте функцию
-    return ""
+    rows = [TABLE_HEADERS] + [rowing_product(product) for product in storage]
+
+    widths_of_string = tuple(
+        max(len(row[i]) for row in rows) for i in range(len(TABLE_HEADERS))
+    )
+
+    header = drawing_row(TABLE_HEADERS, widths_of_string)
+    sep_line = "|" + "|".join("-" * (width + 2) for width in widths_of_string) + "|"
+
+    lines = [drawing_row(row, widths_of_string) for row in rows[1:]]
+    table = "\n".join([header, sep_line] + lines)
+
+    return table
diff --git a/src/part4/cart.py b/src/part4/cart.py
index aed9bb72..0cb02a86 100644
--- a/src/part4/cart.py
+++ b/src/part4/cart.py
@@ -1,18 +1,11 @@
-"""Shopping-cart operations layered on top of the product store.
-
-The cart is a plain dictionary mapping each product identifier to the
-number of units of that product in the cart. Moving units between the
-store and the cart keeps the two sides in balance: :func:`add_to_cart` takes
-units out of stock, :func:`remove_from_cart` puts them back.
-
-Like the CRUD layer, the failure path never raises -- the operation prints
-an explanatory message to stdout and returns ``None``.
-"""
-
-from .storage import Product
-
-
-# TODO: при необходимости добавьте свои вспомогательные функции
+from .crud import (
+    read_product,
+    update_product,
+)
+from .storage import (
+    QUANTITY_KEY,
+    Product,
+)
 
 
 def add_to_cart(
@@ -22,32 +15,33 @@ def add_to_cart(
     product_id: str,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
+    # 1. Ищем товар. read_product сам напечатает сообщение, если не нашёл
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
 
-    The product is looked up in ``storage``. If it is missing, a message is
-    printed and nothing changes. If the store holds fewer units than
-    requested, an explanatory message is printed and nothing changes.
-    Otherwise the store record is decremented by ``quantity`` and the cart
-    gains ``quantity`` units of ``product_id`` -- the product is added when
-    the cart had none of it.
+    product_quantity = product[QUANTITY_KEY]
 
-    Args:
-        storage: The product store to draw stock from; modified in place on
-            success.
-        product_names: The normalised names in ``storage``; a
-            quantity-only change never renames a product, so it is left
-            unchanged here.
-        cart: The cart to add the units to; modified in place on success.
-        product_id: The identifier of the product to add.
-        quantity: Number of units to move into the cart.
+    # 2. Проверяем остаток
+    if product_quantity < quantity:
+        print(
+            f"not enough stock for product {product_id}: "
+            f"{product_quantity} available, {quantity} requested"
+        )
+        return None
 
-    Returns:
-        The quantity of ``product_id`` in the cart after the addition, or
-        ``None`` when the product is unknown or the store cannot cover the
-        request.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    # 3. Списываем со склада
+    update_product(
+        storage,
+        product_names,
+        product_id,
+        {QUANTITY_KEY: product_quantity - quantity},
+    )
+
+    # 4. Добавляем quantity единиц в корзину
+    remaining = cart.get(product_id, 0) + quantity
+    cart[product_id] = remaining
+    return remaining
 
 
 def remove_from_cart(
@@ -57,31 +51,40 @@ def remove_from_cart(
     product_id: str,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store.
+    # 1. Есть ли товар в корзине
+    if product_id not in cart:
+        print(f"product {product_id} is not in the cart")
+        return None
+
+    cart_quantity_now = cart[product_id]
+
+    # 2. Достаточно ли quantity в корзине
+    if cart_quantity_now < quantity:
+        print(
+            f"cart holds only {cart_quantity_now} unit(s) of product "
+            f"{product_id}, cannot remove {quantity}"
+        )
+        return None
+
+    # 3. Есть ли товар в хранилище
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
+
+    product_quantity = product[QUANTITY_KEY]
 
-    If the cart holds no units of ``product_id``, a message is printed and
-    nothing changes. If it holds fewer units than requested, an explanatory
-    message is printed and nothing changes. If the product is missing from
-    ``storage``, a message is printed and nothing changes. Otherwise the cart loses
-    ``quantity`` units of the product -- the product is dropped from the
-    cart when its quantity reaches zero -- and the store record gains
-    ``quantity`` units back.
+    # Возвращаем на склад
+    update_product(
+        storage,
+        product_names,
+        product_id,
+        {QUANTITY_KEY: product_quantity + quantity},
+    )
 
-    Args:
-        storage: The product store to return stock to; modified in place on
-            success.
-        product_names: The normalised names in ``storage``; a
-            quantity-only change never renames a product, so it is left
-            unchanged here.
-        cart: The cart to take the units from; modified in place on
-            success.
-        product_id: The identifier of the product to remove.
-        quantity: Number of units to move back into the store.
+    remaining = cart_quantity_now - quantity
+    if remaining == 0:
+        del cart[product_id]
+        return 0
 
-    Returns:
-        The quantity of ``product_id`` left in the cart after the removal
-        (zero means the product was dropped from the cart), or ``None`` when
-        the cart does not hold the product or holds too few units.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    cart[product_id] = remaining
+    return remaining
diff --git a/src/part4/crud.py b/src/part4/crud.py
index 471eff00..21ed2ad5 100644
--- a/src/part4/crud.py
+++ b/src/part4/crud.py
@@ -1,48 +1,17 @@
-"""Create/read/update/delete operations over the in-memory product store.
-
-Every operation takes the store -- a dictionary mapping product id to its
-:data:`~src.part4.storage.Product` record -- as its first argument and
-works on it in place. ``create_product``, ``update_product`` and
-``delete_product`` additionally take ``product_names``, the ``set[str]``
-of normalised names currently in ``storage`` (see
-:mod:`src.part4.storage`), and keep it in sync with ``storage`` on
-every successful call. The failure path never raises: the operation
-prints an explanatory message to stdout and returns ``None``.
-
-The identifier of a new product is a freshly generated UUID string
-(:func:`generate_product_id`), independent of insertion order or of any
-identifier already in ``storage``.
-
-Every product name that reaches the store is passed through
-:func:`~src.part4.utils.normalize_product_name` first. A name that
-normalises to an empty string is rejected -- the operation prints a
-message and changes nothing. Names are also kept unique --
-:func:`create_product` refuses a normalised name that is already taken,
-and :func:`update_product` refuses one that is already taken by another
-product -- via an O(1) membership test against ``product_names`` rather
-than a scan over ``storage.values()``.
-"""
-
-import uuid  # noqa: F401
+import uuid
 from typing import Any
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_KEY,
     PRICE_KEY,
     QUANTITY_KEY,
     Product,
 )
-from .utils import normalize_price, normalize_product_name  # noqa: F401
+from .utils import normalize_price, normalize_product_name
 
 
 def generate_product_id() -> str:
-    """Generate an identifier for a new product.
-
-    Returns:
-        A freshly generated UUID, stringified.
-    """
-    # TODO: реализуйте функцию
-    return ""
+    return str(uuid.uuid4())
 
 
 def create_product(
@@ -50,46 +19,34 @@ def create_product(
     product_names: set[str],
     fields: dict[str, Any],
 ) -> str | None:
-    """Add a new product to ``storage`` and return its new identifier.
-
-    Args:
-        storage: The product store to add to; modified in place on
-            success.
-        product_names: The normalised names already in ``storage``; the
-            new name is added to it in place on success.
-        fields: A dictionary with the ``name``, ``price`` and ``quantity``
-            keys (see :data:`~src.part4.storage.NAME_KEY`,
-            :data:`~src.part4.storage.PRICE_KEY` and
-            :data:`~src.part4.storage.QUANTITY_KEY`) describing the
-            product. ``name`` is normalised (surrounding whitespace
-            stripped, lower-cased) before it is stored or compared.
-            ``price`` is a :class:`~decimal.Decimal` amount and is rounded
-            to the stored money precision before it is saved.
-
-    Returns:
-        The identifier generated for the new product, or ``None`` when
-        ``name`` is blank once normalised or a product with the same
-        normalised name already exists. In the ``None`` case ``storage``
-        and ``product_names`` are left unchanged and an explanatory
-        message is printed.
-    """
-    # TODO: реализуйте функцию
-    return ""
+    normalized_name = normalize_product_name(fields[NAME_KEY])
 
+    if not normalized_name:
+        print("product name must not be blank")
+        return None
 
-def read_product(storage: dict[str, Product], product_id: str) -> Product | None:
-    """Return the product stored under ``product_id``.
+    if normalized_name in product_names:
+        print(f"product name '{normalized_name}' is already taken")
+        return None
+
+    new_product_id = generate_product_id()
+    normalized_price = normalize_price(fields[PRICE_KEY])
+    product_content = {
+        NAME_KEY: normalized_name,
+        PRICE_KEY: normalized_price,
+        QUANTITY_KEY: fields[QUANTITY_KEY],
+    }
 
-    Args:
-        storage: The product store to search.
-        product_id: The identifier to look up.
+    storage[new_product_id] = product_content
+    product_names.add(normalized_name)
+    return new_product_id
 
-    Returns:
-        The matching product record, or ``None`` when no product carries
-        that identifier (a message is printed in that case).
-    """
-    # TODO: реализуйте функцию
-    return {}
+
+def read_product(storage: dict[str, Product], product_id: str) -> Product | None:
+    if product_id in storage:
+        return storage[product_id]
+    print(f"no product with id {product_id}")
+    return None
 
 
 def update_product(
@@ -98,39 +55,44 @@ def update_product(
     product_id: str,
     fields: dict[str, Any],
 ) -> Product | None:
-    """Overwrite the fields of the product stored under ``product_id``.
-
-    The identifier itself is preserved. ``fields`` may carry any subset of
-    ``name``, ``price`` and ``quantity``; a key that is missing keeps the
-    value the product already has, so a caller can update a single field
-    without repeating the other two.
-
-    Args:
-        storage: The product store to modify; the matching record is
-            updated in place on success.
-        product_names: The normalised names already in ``storage``; on a
-            successful rename the old name is removed from it and the new
-            one added.
-        product_id: The identifier of the product to change.
-        fields: A dictionary with any of the ``name``, ``price`` and
-            ``quantity`` keys (see :data:`~src.part4.storage.NAME_KEY`,
-            :data:`~src.part4.storage.PRICE_KEY` and
-            :data:`~src.part4.storage.QUANTITY_KEY`) holding the new
-            values. ``price`` is a :class:`~decimal.Decimal` amount and is
-            rounded to the stored money precision before it is saved.
-            Mutated in place: a ``name`` or ``price`` value present in
-            ``fields`` is overwritten with its normalised form.
-
-    Returns:
-        The updated product record, or ``None`` when ``name`` is present
-        and blank once normalised, no product carries that identifier, or
-        the normalised name is already taken by another product. In every
-        ``None`` case ``storage`` and ``product_names`` are left unchanged
-        and an explanatory message is printed. Renaming a product to its
-        own current name is allowed.
-    """
-    # TODO: реализуйте функцию
-    return {}
+    # 1. Товар должен существовать
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+
+    product = storage[product_id]
+    old_name = product[NAME_KEY]
+
+    # 2-4. Нормализация и проверки для имени
+    if NAME_KEY in fields:
+        normalized_name = normalize_product_name(fields[NAME_KEY])
+        if not normalized_name:
+            print("product name must not be blank")
+            return None
+        if normalized_name != old_name and normalized_name in product_names:
+            print(f"product name '{normalized_name}' is already taken")
+            return None
+        fields[NAME_KEY] = normalized_name
+
+    # 5. Нормализация цены
+    if PRICE_KEY in fields:
+        fields[PRICE_KEY] = normalize_price(fields[PRICE_KEY])
+
+    # 6. Записываем поля в товар
+    if NAME_KEY in fields:
+        product[NAME_KEY] = fields[NAME_KEY]
+    if PRICE_KEY in fields:
+        product[PRICE_KEY] = fields[PRICE_KEY]
+    if QUANTITY_KEY in fields:
+        product[QUANTITY_KEY] = fields[QUANTITY_KEY]
+
+    # 7. Обновляем индекс при переименовании
+    current_name = product[NAME_KEY]
+    if current_name != old_name:
+        product_names.discard(old_name)
+        product_names.add(current_name)
+
+    return product
 
 
 def delete_product(
@@ -138,20 +100,11 @@ def delete_product(
     product_names: set[str],
     product_id: str,
 ) -> str | None:
-    """Remove the product stored under ``product_id`` from ``storage``.
-
-    Args:
-        storage: The product store to remove from; modified in place on
-            success.
-        product_names: The normalised names already in ``storage``; the
-            departing product's name is removed from it in place on
-            success.
-        product_id: The identifier of the product to remove.
-
-    Returns:
-        ``product_id`` when a product was removed, or ``None`` when no
-        product carried that identifier (``storage`` and ``product_names``
-        are left unchanged and a message is printed).
-    """
-    # TODO: реализуйте функцию
-    return ""
+    if product_id in storage:
+        name = storage[product_id][NAME_KEY]
+        del storage[product_id]
+        product_names.discard(name)
+        return product_id
+
+    print(f"no product with id {product_id}")
+    return None
diff --git a/src/part4/run_admin.py b/src/part4/run_admin.py
index 2247b29b..8cbca9a3 100644
--- a/src/part4/run_admin.py
+++ b/src/part4/run_admin.py
@@ -1,110 +1,95 @@
-"""Interactive admin console for the part4 in-memory product store.
-
-Running this module starts a read-eval-print loop over a single product
-store that lives in memory for the lifetime of the process. Every line
-typed at the prompt is stripped of surrounding whitespace and matched,
-with a ``match`` statement, against the set of known commands:
-
-* ``help`` -- print the list of commands and what each one does;
-* ``exit`` -- leave the loop and end the program;
-* ``show`` -- print the whole store as a text table;
-* ``create <name...> <price> <quantity>`` -- add a product;
-* ``read <id>`` -- print one product;
-* ``update <id> <name...> <price> <quantity>`` -- overwrite a product;
-* ``delete <id>`` -- remove a product.
-
-For ``create`` and ``update`` the price and quantity are always the last
-two words of the line; everything between the verb (and, for ``update``,
-the id) and those two words is joined with single spaces into the
-product name, so a multi-word name such as ``Gibson SG Junior`` needs no
-quoting.
-
-The four CRUD commands forward to :mod:`src.part4.crud`; whatever
-that call returns is printed unless it is ``None``. A line whose first
-word is not a known verb, or that carries the wrong number of arguments
-for its verb, prints an "is not a command" notice. A line that names a
-command correctly but whose price or quantity argument will not parse
-prints a distinct "arguments are invalid" notice. Either way the store
-is left untouched and the loop keeps running; only ``exit`` stops it.
-"""
-
-from decimal import Decimal, InvalidOperation  # noqa: F401
+from decimal import Decimal, InvalidOperation
 from typing import Final
 
-from .crud import (  # noqa: F401
+from .crud import (
     create_product,
     delete_product,
     read_product,
     update_product,
 )
-from .storage import NAME_KEY, PRICE_KEY, QUANTITY_KEY, Product  # noqa: F401
-from .utils import get_storage_str_representation  # noqa: F401
-
-
-# TODO: задайте приглашение и текст справки (используйте своё решение части 3)
-PROMPT: Final[str] = ""
-HELP_TEXT: Final[str] = ""
+from .storage import NAME_KEY, PRICE_KEY, QUANTITY_KEY, Product
+from .utils import get_storage_str_representation
+
+
+PROMPT: Final[str] = "admin> "
+HELP_TEXT: Final[str] = (
+    "Available commands:\n"
+    "  help                                       show this message\n"
+    "  exit                                       leave the console\n"
+    "  show                                       print the whole store as a table\n"
+    "  create <name...> <price> <quantity>        add a product, print its new id\n"
+    "  read <id>                                  print the product with that id\n"
+    "  update <id> <name...> <price> <quantity>   overwrite that product's fields\n"
+    "  delete <id>                                remove the product with that id\n"
+    "\n"
+    "For create and update the price and quantity are the last two words of the\n"
+    "line; everything before them is the product name, so it may contain spaces\n"
+    '(for example "Gibson SG Junior") and needs no quoting.'
+)
 
 
 def show_help() -> None:
-    """Print the command reference to stdout.
-
-    The text is the module-level :data:`HELP_TEXT` constant, printed as
-    is: a heading, one line per command with a short description, and a
-    note on how multi-word names are parsed.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
+    print(HELP_TEXT)
 
 
 def print_result(result: object) -> None:
-    """Print a CRUD result to stdout unless it is ``None``.
-
-    Args:
-        result: The value returned by a CRUD operation. ``None`` means the
-            operation already reported its own failure, so nothing is
-            printed in that case.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
+    if result is not None:
+        print(result)
 
 
 def run_command(
-    storage: dict[str, Product], product_names: set[str], line: str
+    storage: dict[str, Product],
+    product_names: set[str],
+    line: str,
 ) -> bool:
-    """Parse one console line and carry out the command it names.
-
-    Args:
-        storage: The product store shared across the session; mutated in
-            place by the ``create``, ``update`` and ``delete`` commands.
-        product_names: The normalised names already in ``storage``; kept
-            in sync by the ``create``, ``update`` and ``delete`` commands.
-        line: One line of console input, already stripped of surrounding
-            whitespace.
-
-    Returns:
-        ``True`` to keep the read-eval-print loop running, or ``False``
-        once the ``exit`` command has been seen. A line that is not a
-        known command prints a notice and still returns ``True``.
-
-    Raises:
-        ValueError: If the quantity argument of a CRUD command does not
-            parse as a base-10 integer.
-        decimal.InvalidOperation: If the price argument of ``create`` or
-            ``update`` does not parse as a decimal number.
-    """
-    # TODO: реализуйте функцию
-    return False
+    commands = line.split()
+
+    match commands:
+        case ["help"]:
+            show_help()
+            return True
+        case ["exit"]:
+            return False
+        case ["show"]:
+            print_result(get_storage_str_representation(storage))
+            return True
+        case ["read", product_id]:
+            print_result(read_product(storage, product_id))
+            return True
+        case ["delete", product_id]:
+            print_result(delete_product(storage, product_names, product_id))
+            return True
+        case ["update", product_id, *args] if len(args) >= 3:
+            name = " ".join(args[:-2])
+            price = Decimal(args[-2])
+            quantity = int(args[-1])
+            print_result(
+                update_product(
+                    storage,
+                    product_names,
+                    product_id,
+                    {NAME_KEY: name, PRICE_KEY: price, QUANTITY_KEY: quantity},
+                )
+            )
+            return True
+        case ["create", *args] if len(args) >= 3:
+            name = " ".join(args[:-2])
+            price = Decimal(args[-2])
+            quantity = int(args[-1])
+            print_result(
+                create_product(
+                    storage,
+                    product_names,
+                    {NAME_KEY: name, PRICE_KEY: price, QUANTITY_KEY: quantity},
+                )
+            )
+            return True
+        case _:
+            print(f"{line!r} is not a command")
+            return True
 
 
 def main() -> None:
-    """Run the admin console until the ``exit`` command is entered.
-
-    A single product store, and the set of normalised names it holds, are
-    created empty and kept in memory for the whole session. Each iteration
-    reads one line from stdin, strips its surrounding whitespace and hands
-    it to :func:`run_command`. A line that names a command but whose price
-    or quantity argument does not parse is caught here and reported
-    without stopping the loop; only ``exit`` ends it.
-    """
     storage: dict[str, Product] = {}
     product_names: set[str] = set()
     running = True
@@ -114,7 +99,6 @@ def main() -> None:
 
         try:
             running = run_command(storage, product_names, line)
-
         except (ValueError, InvalidOperation):
             print(f"{line!r} names a command but its arguments are invalid")
 
diff --git a/src/part4/storage.py b/src/part4/storage.py
index 9acedf07..fe192215 100644
--- a/src/part4/storage.py
+++ b/src/part4/storage.py
@@ -1,45 +1,8 @@
-"""In-memory product store for the shop CRUD exercise.
-
-The store is deliberately primitive: a plain dictionary, with no
-persistence and no schema enforcement. It maps a product's ``id`` -- a
-UUID string assigned by the create operation in :mod:`src.part4.crud`
--- to its :data:`Product` record -- a dictionary with the keys ``name``,
-``price`` and ``quantity`` -- where:
-
-* the ``storage`` key itself -- unique string identifier, assigned by the
-  create operation in :mod:`src.part4.crud`; it is not duplicated
-  inside the record;
-* ``name`` -- human-readable product name, unique across the store, held
-  in normalised form (see
-  :func:`src.part4.utils.normalize_product_name`);
-* ``price`` -- price of a single unit, held as a :class:`~decimal.Decimal`
-  amount rounded to a fixed number of decimal places (see
-  :func:`src.part4.utils.normalize_price`) so that money is never
-  subject to binary floating-point error;
-* ``quantity`` -- number of units currently in stock.
-
-Field names are exposed as ``*_KEY`` constants so callers never hard-code
-the dictionary keys.
-
-Every caller that mutates the store also threads along a second
-structure, a ``set[str]`` of the normalised names currently in use --
-see, for example, the ``product_names`` parameter of
-:func:`src.part4.crud.create_product`. Keeping that name index as a
-plain set passed next to ``storage``, rather than bundling the two into
-an object, lets a name-uniqueness check become an O(1) membership test
-against the set instead of a linear scan over ``storage.values()``. The
-set must always mirror the normalised names present in ``storage``; the
-functions in :mod:`src.part4.crud` keep the two in sync on every
-successful create, update and delete.
-"""
-
 from typing import Any, Final
 
 
 type Product = dict[str, Any]
 
-# Name of each field inside a Product record.
-# TODO: задайте имена полей записи
-NAME_KEY: Final = ""
-PRICE_KEY: Final = ""
-QUANTITY_KEY: Final = ""
+NAME_KEY: Final = "name"
+PRICE_KEY: Final = "price"
+QUANTITY_KEY: Final = "quantity"
diff --git a/src/part4/utils.py b/src/part4/utils.py
index d2a940ea..0234b1c0 100644
--- a/src/part4/utils.py
+++ b/src/part4/utils.py
@@ -1,27 +1,7 @@
-"""Standalone helpers shared by the part4 storage and CRUD modules.
-
-Normalisation:
-
-* :func:`normalize_price` rounds a raw :class:`~decimal.Decimal` amount to
-  the fixed number of fractional digits (:data:`PRICE_PRECISION`) that
-  every stored price uses, keeping currency values free of binary
-  floating-point error.
-* :func:`normalize_product_name` strips surrounding whitespace from a
-  product name, collapses every internal run of whitespace to a single
-  space and lower-cases it, giving every stored name a single canonical
-  form.
-
-Presentation:
-
-* :func:`get_storage_str_representation` renders the whole store as a
-  text table meant to be printed to a terminal; each column is sized to
-  the longest value it holds in that particular call.
-"""
-
-from decimal import ROUND_HALF_UP, Decimal  # noqa: F401
+from decimal import ROUND_HALF_UP, Decimal
 from typing import Final
 
-from .storage import (  # noqa: F401
+from .storage import (
     NAME_KEY,
     PRICE_KEY,
     QUANTITY_KEY,
@@ -29,72 +9,45 @@
 )
 
 
-# Number of fractional digits every stored price is rounded to.
-# Quantisation step derived from PRICE_PRECISION, e.g. Decimal("0.01").
-# TODO: задайте число знаков после запятой и шаг квантования (используйте своё
-# решение части 3)
-PRICE_PRECISION: Final[int] = 0
-PRICE_STEP: Final = Decimal(0)
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final = Decimal(1).scaleb(-PRICE_PRECISION)
 
-# Column headers of the table produced by get_storage_str_representation,
-# left to right. The width of each column is not fixed here -- it is
-# measured per call from the data (see the function).
-# TODO: задайте заголовки столбцов таблицы (используйте своё решение части 3)
-TABLE_HEADERS: Final[tuple[str, ...]] = ()
+TABLE_HEADERS: Final[tuple[str, ...]] = ("ID", "name", "price", "quantity")
 
 
 def normalize_price(price: Decimal) -> Decimal:
-    """Round a price to the precision every stored record uses.
-
-    Args:
-        price: The raw price amount.
-
-    Returns:
-        ``price`` quantised to :data:`PRICE_PRECISION` fractional digits,
-        with halves rounded up.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
-    return Decimal(0)
+    return Decimal(price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP))
 
 
 def normalize_product_name(name: str) -> str:
-    """Reduce a product name to the canonical form the store keeps.
+    return " ".join(name.lower().split())
 
-    Args:
-        name: The raw product name.
 
-    Returns:
-        ``name`` with every leading and trailing whitespace character
-        removed, every internal run of whitespace (spaces, tabs and the
-        like) collapsed to a single space, and the rest lower-cased. For
-        example ``"abc    def\tghi\tjkl"`` becomes ``"abc def ghi jkl"``.
-        The result is an empty string when ``name`` holds nothing but
-        whitespace.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
-    return ""
+def product_row(product_id: str, product: Product) -> tuple[str, ...]:
+    return (
+        product_id,
+        product[NAME_KEY],
+        str(product[PRICE_KEY]),
+        str(product[QUANTITY_KEY]),
+    )
 
 
-# TODO: при необходимости добавьте свои вспомогательные функции
+def drawing_row(cells: tuple[str, ...], widths: tuple[int, ...]) -> str:
+    new_row = tuple(cell.ljust(width) for cell, width in zip(cells, widths))
+    return "| " + " | ".join(new_row) + " |"
 
 
 def get_storage_str_representation(storage: dict[str, Product]) -> str:
-    """Render the product store as a text table with data-sized columns.
-
-    The table has the columns named by :data:`TABLE_HEADERS` -- id, name,
-    price and quantity. Each column is made exactly as wide as the longest
-    value it carries in this call (its header counted), so the columns
-    line up when the string is printed to a terminal and no value is ever
-    truncated.
-
-    Args:
-        storage: The product store to render.
-
-    Returns:
-        A multi-line string: a header row, a dashed separator row, then
-        one row per product in ``storage``, in insertion order. When
-        ``storage`` is empty only the header and separator rows are
-        returned, sized to the header labels.
-    """
-    # TODO: реализуйте функцию (используйте своё решение части 3)
-    return ""
+    rows = [TABLE_HEADERS] + [
+        product_row(product_id, product) for product_id, product in storage.items()
+    ]
+
+    widths_of_string = tuple(
+        max(len(row[i]) for row in rows) for i in range(len(TABLE_HEADERS))
+    )
+
+    header = drawing_row(TABLE_HEADERS, widths_of_string)
+    sep_line = "|" + "|".join("-" * (width + 2) for width in widths_of_string) + "|"
+
+    lines = [drawing_row(row, widths_of_string) for row in rows[1:]]
+    return "\n".join([header, sep_line] + lines)
diff --git "a/srcpart2crud.py\357\200\27245\357\200\2721" "b/srcpart2crud.py\357\200\27245\357\200\2721"
new file mode 100644
index 00000000..e69de29b
diff --git a/uv.lock b/uv.lock
index 2a56c481..b51f5004 100644
--- a/uv.lock
+++ b/uv.lock
@@ -1,5 +1,5 @@
 version = 1
-revision = 2
+revision = 3
 requires-python = ">=3.12"
 resolution-markers = [
     "python_full_version >= '3.15'",
@@ -70,6 +70,24 @@ wheels = [
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 version = "0.15.0"
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@@ -251,6 +278,7 @@ source = { virtual = "." }
 [package.dev-dependencies]
 dev = [
     { name = "mypy" },
+    { name = "pytest" },
     { name = "ruff" },
 ]
 
@@ -259,9 +287,44 @@ dev = [
 [package.metadata.requires-dev]
 dev = [
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+    { name = "pytest", specifier = ">=9.1.1" },
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