4. Донцов Роман Алексеевич. 613

src/part1/constants.py

@@ -19,20 +19,24 @@
 # 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
+TIMESTAMP_MS_MAX: Final[int] = 2**TIMESTAMP_BITS - 1
+NODE_ID_MAX: Final[int] = 2**NODE_ID_BITS - 1
+SEQUENCE_ID_MAX: Final[int] = 2**SEQUENCE_ID_BITS - 1
 
 # Здесь можно добавить собственные вспомогательные константы
 # (например, сдвиги полей при сборке идентификатора).
+
+TIMESTAMP_SHIFT: Final[int] = SEQUENCE_ID_BITS + NODE_ID_BITS
+
+NODE_ID_SHIFT: Final[int] = SEQUENCE_ID_BITS

src/part1/snowflake.py

@@ -1,114 +1,59 @@
-"""Twitter Snowflake identifier generator.
+#!/usr/bin/env python3
 
-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).
+import time
 
-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,
+    NODE_ID_SHIFT,
+    SEQUENCE_ID_BITS,
     SEQUENCE_ID_MAX,
     TIMESTAMP_MS_MAX,
+    TIMESTAMP_SHIFT,
 )
 
 
 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 int(time.time() * 1000) - 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
+    return (snowflake_id >> (TIMESTAMP_SHIFT)) + 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
+    mask = (1 << NODE_ID_BITS) - 1
+    return (snowflake_id >> NODE_ID_SHIFT) & mask
 
 
 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
+    mask = (1 << SEQUENCE_ID_BITS) - 1
+    return snowflake_id & mask
 
 
 def generate_snowflake_id(
     sequence_id: int,
     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
+
+    current_millis = read_current_millis(epoch_ms)
+
+    if not (0 <= current_millis <= TIMESTAMP_MS_MAX):
+        print("overflows")
+        return None
+    return (
+        (current_millis << (TIMESTAMP_SHIFT))
+        | (node_id << NODE_ID_SHIFT)
+        | (sequence_id)
+    )

src/part2/cart.py

@@ -1,18 +1,10 @@
-"""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``.
-"""
+# Shopping-cart operations layered on top of the product store.
 
+import sys
 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 +16,17 @@
 
 # TODO: задайте позиции полей внутри кортежа CartLine
 LINE_PRODUCT_ID_INDEX: Final = 0
-LINE_QUANTITY_INDEX: Final = 0
+LINE_QUANTITY_INDEX: Final = 1
+
+
+def find_cart_line(
+    cart: list[CartLine], product_id: int
+) -> tuple[int, CartLine] | None:
+    # Вспомогательная функция для поиска строки в корзине и её индекса.
+    for i, line in enumerate(cart):
+        if line[LINE_PRODUCT_ID_INDEX] == product_id:
+            return i, line
+    return None
 
 
 def add_to_cart(
@@ -33,28 +35,33 @@ 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. Поиск товара на складе
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
+    # 2. Проверка доступного количества
+    available = product[QUANTITY_INDEX]
+    if available < quantity:
+        print(
+            f"not enough stock for product {product_id}: "
+            f"{available} available, {quantity} requested",
+            file=sys.stdout,
+        )
+        return None
+    # 3. Обновление склада
+    new_fields = (product[NAME_INDEX], product[PRICE_INDEX], available - quantity)
+    update_product(storage, product_id, new_fields)
+    # 4. Обновление корзины
+    cart_search = find_cart_line(cart, product_id)
+    if cart_search:
+        idx, old_line = cart_search
+        new_line: CartLine = (product_id, old_line[LINE_QUANTITY_INDEX] + quantity)
+        cart[idx] = new_line
+    else:
+        new_line = (product_id, quantity)
+        cart.append(new_line)
+    return new_line
 
 
 def remove_from_cart(
@@ -63,27 +70,36 @@ 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. Поиск строки в корзине
+    cart_search = find_cart_line(cart, product_id)
+    if not cart_search:
+        print(f"product {product_id} is not in the cart", file=sys.stdout)
+        return None
+
+    idx, line = cart_search
+    in_cart = line[LINE_QUANTITY_INDEX]
+    # 2. Проверка количества в корзине
+    if in_cart < quantity:
+        print(
+            f"cart holds only {in_cart} unit(s) of product {product_id}, "
+            f"cannot remove {quantity}",
+            file=sys.stdout,
+        )
+        return None
+    # 3. Проверка существования товара на складе
+    product = read_product(storage, product_id)
+    if product is None:
+        return None
+    # 4. Обновление склада и корзины
+    available = product[QUANTITY_INDEX]
+    new_fields = (product[NAME_INDEX], product[PRICE_INDEX], available + quantity)
+    update_product(storage, product_id, new_fields)
+    remaining_quantity = in_cart - quantity
+    if remaining_quantity == 0:
+        cart.pop(idx)
+        return (product_id, 0)
+    else:
+        new_line: CartLine = (product_id, remaining_quantity)
+        cart[idx] = new_line
+        return new_line