1. Устинов Семён Михайлович. 614

src/part1/TASK.md

@@ -7,7 +7,7 @@
 Начнём с фундамента: у каждой записи должен быть уникальный идентификатор.
 
 Казалось бы, можно просто нумеровать записи 1, 2, 3, … Пока хранилище живёт на
-одной машине, так и происходит. Но реальные системы почти всегда распределены:
+одной машине, так и происходит. Но реальные системы почти  всегда распределены:
 записи создаются на десятках серверов одновременно. Тогда возникают проблемы:
 
 - единый счётчик становится «бутылочным горлышком»: каждому серверу приходится

src/part1/__init__.py

@@ -1 +0,0 @@
-"""Homework 3: a Twitter Snowflake identifier generator and its bit layout."""

src/part1/constants.py

@@ -1,38 +1,13 @@
-"""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: Final[int] = 1288834974657
+NODE_ID_DEFAULT: Final[int] = 1
+TIMESTAMP_BITS: Final[int] = 41
+NODE_ID_BITS: Final[int] = 10
+SEQUENCE_ID_BITS: Final[int] = 12
+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
+NODE_ID_SHIFT: Final[int] = SEQUENCE_ID_BITS
+TIMESTAMP_SHIFT: Final[int] = SEQUENCE_ID_BITS + NODE_ID_BITS

src/part1/snowflake.py

@@ -1,114 +1,49 @@
-"""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 time.time_ns() // 1000000 - 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_ms = snowflake_id >> TIMESTAMP_SHIFT
+    return stored_ms + 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 >> NODE_ID_SHIFT) & 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(
     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.
+    if not (0 <= node_id <= NODE_ID_MAX):
+        print(f"node_id must be in [0, {NODE_ID_MAX}], got {node_id}")
+        return None
 
-    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.
+    if not (0 <= sequence_id <= SEQUENCE_ID_MAX):
+        print(f"sequence_id must be in [0, {SEQUENCE_ID_MAX}], got {sequence_id}")
+        return None
 
-    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).
+    elapsed_ms = read_current_millis(epoch_ms)
+    if elapsed_ms > TIMESTAMP_MS_MAX:
+        print(f"timestamp overflows: {elapsed_ms} > {TIMESTAMP_MS_MAX}")
+        return None
 
-    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
+    return (elapsed_ms << TIMESTAMP_SHIFT) | (node_id << NODE_ID_SHIFT) | sequence_id

src/part2/cart.py

@@ -11,20 +11,17 @@
 
 from typing import Final
 
-from .crud import read_product, update_product  # noqa: F401
-from .storage import (  # noqa: F401
-    NAME_INDEX,
-    PRICE_INDEX,
-    QUANTITY_INDEX,
+from .crud import read_product, update_product
+from .storage import (
     Product,
 )
 
 
 type CartLine = tuple[int, int]
 
 # TODO: задайте позиции полей внутри кортежа CartLine
-LINE_PRODUCT_ID_INDEX: Final = 0
-LINE_QUANTITY_INDEX: Final = 0
+LINE_PRODUCT_ID_INDEX: Final[int] = 0
+LINE_QUANTITY_INDEX: Final[int] = 1
 
 
 def add_to_cart(
@@ -53,8 +50,30 @@ def add_to_cart(
         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)
+    product = read_product(storage, product_id)
+    if not product:
+        return None
+
+    _, name, price, stock_quantity = product
+    if stock_quantity < quantity:
+        print(
+            f"Not enough stock for product {product_id}: "
+            f"{stock_quantity} available, {quantity} requested"
+        )
+        return None
+
+    update_product(storage, product_id, (name, price, stock_quantity - quantity))
+
+    for i in range(len(cart)):
+        if cart[i][LINE_PRODUCT_ID_INDEX] == product_id:
+            cart_quantity = cart[i][LINE_QUANTITY_INDEX]
+            new_line = (product_id, cart_quantity + quantity)
+            cart[i] = new_line
+            return new_line
+
+    new_line = (product_id, quantity)
+    cart.append(new_line)
+    return new_line
 
 
 def remove_from_cart(
@@ -85,5 +104,34 @@ def remove_from_cart(
         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)
+    for i in range(len(cart)):
+        if cart[i][LINE_PRODUCT_ID_INDEX] == product_id:
+            cart_quantity = cart[i][LINE_QUANTITY_INDEX]
+            if quantity > cart_quantity:
+                print(
+                    f"Cart holds only {cart_quantity} units of product {product_id}, "
+                    f"cannot remove {quantity}"
+                )
+                return None
+
+            product = read_product(storage, product_id)
+            if not product:
+                return None
+
+            _, name, price, stock_quantity = product
+            update_product(
+                storage,
+                product_id,
+                (name, price, stock_quantity + quantity),
+            )
+
+            remaining_quantity = cart_quantity - quantity
+            if remaining_quantity == 0:
+                del cart[i]
+                return (product_id, 0)
+
+            cart[i] = (product_id, remaining_quantity)
+            return cart[i]
+
+    print(f"Product {product_id} is not in the cart")
+    return None

src/part2/crud.py

@@ -14,13 +14,13 @@
 
 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:
@@ -34,8 +34,14 @@ def generate_product_id(storage: list[Product]) -> int:
         :data:`~src.part2.storage.PRODUCT_ID_MIN` when ``storage`` is
         empty.
     """
-    # TODO: реализуйте функцию
-    return 0
+    if not storage:
+        return PRODUCT_ID_MIN
+
+    max_id = 0
+    for product in storage:
+        current_id = int(product[PRODUCT_ID_INDEX])
+        max_id = max(current_id, max_id)
+    return max_id + 1
 
 
 def create_product(
@@ -56,24 +62,34 @@ def create_product(
         ``storage`` is left unchanged and a message naming the clashing
         name is printed.
     """
-    # TODO: реализуйте функцию
-    return 0
+    name, price, quantity = fields
+    for product in storage:
+        if product[NAME_INDEX] == name:
+            print(f"Product name '{name}' is already taken")
+            return None
+
+    new_id = generate_product_id(storage)
+    normalized_price = normalize_price(price)
+    storage.append((new_id, name, normalized_price, quantity))
+    return new_id
 
 
 def read_product(storage: list[Product], product_id: int) -> Product | None:
     """Return the product stored under ``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
-    return (0, "", Decimal(0), 0)
+    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(
@@ -99,8 +115,15 @@ def update_product(
         ``None`` when no product carries that identifier (``storage`` is
         left unchanged and a message is printed).
     """
-    # TODO: реализуйте функцию
-    return (0, "", Decimal(0), 0)
+    name, price, quantity = fields
+    normalized_price = normalize_price(price)
+    for i in range(len(storage)):
+        if storage[i][PRODUCT_ID_INDEX] == product_id:
+            updated_product = (product_id, name, normalized_price, quantity)
+            storage[i] = updated_product
+            return updated_product
+    print(f"No product with id {product_id}")
+    return None
 
 
 def delete_product(storage: list[Product], product_id: int) -> int | None:
@@ -116,5 +139,9 @@ def delete_product(storage: list[Product], product_id: int) -> int | None:
         product carried that identifier (``storage`` is left unchanged and
         a message is printed).
     """
-    # TODO: реализуйте функцию
-    return 0
+    for i in range(len(storage)):
+        if storage[i][PRODUCT_ID_INDEX] == product_id:
+            del storage[i]
+            return product_id
+    print(f"No product with id {product_id}")
+    return None