4. Банад Михаил Вячеславович. 614

src/part1/constants.py

@@ -1,38 +1,10 @@
-"""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
-
-# Node identifier used when the caller does not supply one.
-NODE_ID_DEFAULT: Final[int] = 0
-
-# Width of each field, in bits.
-TIMESTAMP_BITS: Final[int] = 0
-NODE_ID_BITS: Final[int] = 0
-SEQUENCE_ID_BITS: Final[int] = 0
-
-# 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).
+EPOCH_MS_DEFAULT: int = 1288834974657
+NODE_ID_DEFAULT: int = 1
+TIMESTAMP_BITS: int = 41
+NODE_ID_BITS: int = 10
+SEQUENCE_ID_BITS: int = 12
+TIMESTAMP_MS_MAX: int = 2**TIMESTAMP_BITS - 1
+NODE_ID_MAX: int = 2**NODE_ID_BITS - 1
+SEQUENCE_ID_MAX: int = 2**SEQUENCE_ID_BITS - 1
+NODE_ID_SHIFT: int = SEQUENCE_ID_BITS
+TIMESTAMP_SHIFT: int = SEQUENCE_ID_BITS + NODE_ID_BITS

src/part1/snowflake.py

@@ -1,114 +1,52 @@
-"""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_DEFAULT,
     NODE_ID_MAX,
+    NODE_ID_SHIFT,
     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(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 int(snowflake_id // (2**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
+def decode_node_id(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
+    return int(
+        (
+            snowflake_id
+            - (
+                (decode_timestamp_ms(snowflake_id, epoch_ms) - epoch_ms)
+                * 2**TIMESTAMP_SHIFT
+            )
+        )
+        // (2**NODE_ID_SHIFT)
+    )
 
 
 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 int(snowflake_id - ((snowflake_id // 2**NODE_ID_SHIFT) * (2**NODE_ID_SHIFT)))
 
 
 def generate_snowflake_id(
-    sequence_id: int,
-    node_id: int = NODE_ID_DEFAULT,
-    epoch_ms: int = EPOCH_MS_DEFAULT,
+    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
+    current_millis = read_current_millis(epoch_ms)
+    if current_millis < 0 or current_millis > TIMESTAMP_MS_MAX:
+        raise ValueError("Превышен максимальный лимит времени")
+    if node_id < 0 or node_id > NODE_ID_MAX:
+        raise ValueError("Node Id выходит за допустимые пределы")
+    if sequence_id < 0 or sequence_id > SEQUENCE_ID_MAX:
+        raise ValueError("Sequence Id выходит за допустимые пределы")
+    return int(
+        (current_millis * (2**TIMESTAMP_SHIFT))
+        + (node_id * (2**NODE_ID_SHIFT) + sequence_id)
+    )

src/part4/cart.py

@@ -1,18 +1,4 @@
-"""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 .storage import QUANTITY_KEY, Product
 
 
 def add_to_cart(
@@ -22,32 +8,20 @@ def add_to_cart(
     product_id: str,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        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.
+    available = storage[product_id][QUANTITY_KEY]
+    if available < quantity:
+        print(
+            f"not enough stock for product {product_id}: {available} available, {quantity} requested"
+        )
+        return None
 
-    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.
-
-    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
+    storage[product_id][QUANTITY_KEY] -= quantity
+    cart[product_id] = cart.get(product_id, 0) + quantity
+    return cart[product_id]
 
 
 def remove_from_cart(
@@ -57,31 +31,24 @@ def remove_from_cart(
     product_id: str,
     quantity: int,
 ) -> int | None:
-    """Move ``quantity`` units of ``product_id`` from ``cart`` back to the store.
-
-    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.
-
-    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.
-
-    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
+    if product_id not in cart:
+        print(f"product {product_id} is not in the cart")
+        return None
+
+    in_cart = cart[product_id]
+    if in_cart < quantity:
+        print(
+            f"cart holds only {in_cart} unit(s) of product {product_id}, cannot remove {quantity}"
+        )
+        return None
+
+    if product_id not in storage:
+        print(f"no product with id {product_id}")
+        return None
+
+    storage[product_id][QUANTITY_KEY] += quantity
+    cart[product_id] -= quantity
+    remaining = cart[product_id]
+    if remaining == 0:
+        del cart[product_id]
+    return remaining