1. Безымянный Сергей Андреевич. 613

Solve Task 2/cart.py

@@ -0,0 +1,99 @@
+from typing import Final
+from crud import (
+    read_product,
+    update_product,
+)
+from storage import (
+    QUANTITY_INDEX,
+    NAME_INDEX,
+    PRICE_INDEX,
+    Product)
+
+CartLine = tuple[int, int]
+LINE_PRODUCT_ID_INDEX: Final = 0
+LINE_QUANTITY_INDEX: Final = 1
+
+
+def find_cart_line(cart: list[CartLine],
+                   product_id: int,) -> CartLine | None:
+    for line in cart:
+        if line[LINE_PRODUCT_ID_INDEX] == product_id:
+            return line
+    print(f"Product {product_id} is not in the cart/")
+    return None
+
+
+def add_to_cart(storage: list[Product],
+                cart: list[CartLine],
+                product_id: int,
+                quantity: int) -> CartLine | None:
+    product = read_product(storage, product_id)
+    if product is None:
+        return product
+    storage_quantity = product[QUANTITY_INDEX]
+    if storage_quantity < quantity:
+        print(f"Not enough stock for product {product_id}: "
+              f"{storage_quantity} available, "
+              f"{quantity} requested.")
+        return None
+
+    new_field = (
+        product[NAME_INDEX],
+        product[PRICE_INDEX],
+        storage_quantity - quantity
+    )
+    update_product(storage, product_id, new_field)
+
+    for index, line in enumerate(cart):
+        if line[LINE_PRODUCT_ID_INDEX] == product_id:
+            new_line: CartLine = (
+                product_id,
+                line[LINE_QUANTITY_INDEX] + quantity
+            )
+            cart[index] = new_line
+            return new_line
+    new_line: CartLine = (product_id, quantity)
+    cart.append(new_line)
+    return new_line
+
+
+def remove_from_cart(storage: list[Product],
+                     cart: list[CartLine],
+                     product_id: int,
+                     quantity: int) -> CartLine | None:
+    cart_line = find_cart_line(cart, product_id)
+    product = read_product(storage, product_id)
+    if cart_line is None:
+        return cart_line
+    if cart_line[LINE_QUANTITY_INDEX] < quantity:
+        print(f"Cart holds only {cart_line[LINE_QUANTITY_INDEX]} "
+              f"unit(s) of product {product_id}, cannot remove {quantity}.")
+        return None
+    if product is None:
+        return None
+    new_quantity = product[QUANTITY_INDEX] + quantity
+    new_fields = (
+        product[NAME_INDEX],
+        product[PRICE_INDEX],
+        new_quantity,
+        )
+    update_product(
+        storage,
+        product_id,
+        new_fields,
+    )
+    new_line: CartLine = (
+        product_id,
+        cart_line[LINE_QUANTITY_INDEX] - quantity,
+    )
+    new_line: CartLine = (
+            product_id,
+            cart_line[LINE_QUANTITY_INDEX]-quantity
+        )
+    if new_line[LINE_QUANTITY_INDEX] == 0:
+        cart.remove(cart_line)
+        return new_line
+    for index, line in enumerate(cart):
+        if line == cart_line:
+            cart[index] = new_line
+            return new_line

Solve Task 2/crud.py

@@ -0,0 +1,65 @@
+from decimal import Decimal
+from storage import (
+    PRODUCT_ID_MIN,
+    PRODUCT_ID_INDEX,
+    NAME_INDEX,
+    Product,
+)
+from utils import normalize_price
+
+
+def create_product(storage: list[Product],
+                   fields: tuple[str, Decimal, int]) -> int | None:
+    product_name, product_price, product_quantity = fields
+    for product in storage:
+        if product_name == product[NAME_INDEX]:
+            print(f"Product name {product_name} is already taken.")
+            return None
+    product_id = generate_product_id(storage)
+    storage.append((
+        product_id,
+        product_name,
+        normalize_price(product_price),
+        product_quantity
+    ))
+    return product_id
+
+
+def generate_product_id(storage: list[Product]) -> int:
+    if not storage:
+        return PRODUCT_ID_MIN
+    MAX_INDEX = max(product[PRODUCT_ID_INDEX] for product in storage)
+    return MAX_INDEX + 1
+
+
+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(
+    storage: list[Product],
+    product_id: int,
+    fields: tuple[str, Decimal, int],
+) -> Product | None:
+    for index, product in enumerate(storage):
+        if product[PRODUCT_ID_INDEX] == product_id:
+            new_name, new_price, new_quantity = fields
+            norm_price = normalize_price(new_price)
+            NEW_PRODUCT = (product_id, new_name, norm_price, new_quantity)
+            storage[index] = NEW_PRODUCT
+            return NEW_PRODUCT
+    print(f"No product with id {product_id}")
+    return None
+
+
+def delete_product(storage: list[Product], product_id: int) -> int | None:
+    for index, product in enumerate(storage):
+        if product[PRODUCT_ID_INDEX] == product_id:
+            storage.pop(index)
+            return product_id
+    print(f"No product with id {product_id}.")
+    return None

Solve Task 2/storage.py

@@ -0,0 +1,11 @@
+from decimal import Decimal
+from typing import Final
+
+Product = tuple[int, str, Decimal, int]
+
+PRODUCT_ID_INDEX: Final[int] = 0
+NAME_INDEX: Final[int] = 1
+PRICE_INDEX: Final[int] = 2
+QUANTITY_INDEX: Final[int] = 3
+
+PRODUCT_ID_MIN: Final[int] = 1

Solve Task 2/utils.py

@@ -0,0 +1,9 @@
+from typing import Final
+from decimal import Decimal, ROUND_HALF_UP
+
+PRICE_PRECISION: Final[int] = 2
+PRICE_STEP: Final = Decimal(1).scaleb(-PRICE_PRECISION)
+
+
+def normalize_price(price: Decimal) -> Decimal:
+    return price.quantize(PRICE_STEP, rounding=ROUND_HALF_UP)

src/part1/constants.py

@@ -1,38 +1,12 @@
-"""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).
+from time import time
+
+
+CURRENT_EPOCH_MS: int = int(time() * 1000)
+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

src/part1/snowflake.py

@@ -1,114 +1,44 @@
-"""Twitter Snowflake identifier generator.
-
-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
-    EPOCH_MS_DEFAULT,
-    NODE_ID_DEFAULT,
-    NODE_ID_MAX,
-    SEQUENCE_ID_MAX,
-    TIMESTAMP_MS_MAX,
-)
+from .constants import *
 
 
 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
-
-
-def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
-    """Read the timestamp field out of a Snowflake identifier.
+    return CURRENT_EPOCH_MS - epoch_ms
 
-    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
+def generate_snowflake_id(
+    sequence_id: int, node_id: int = NODE_ID_DEFAULT, epoch_ms: int = EPOCH_MS_DEFAULT
+) -> int | None:
+    if not (0 <= node_id <= NODE_ID_MAX):
+        print(f"node_id must be in [0 ; {NODE_ID_MAX}]")
+        return None
 
+    if not (0 <= sequence_id <= SEQUENCE_ID_MAX):
+        print(f"sequence_id must be in [0 ; {SEQUENCE_ID_MAX}]")
+        return None
 
-def decode_node_id(snowflake_id: int) -> int:
-    """Read the node identifier field out of a Snowflake identifier.
+    timestamp_ms = read_current_millis(epoch_ms)
 
-    Args:
-        snowflake_id: An identifier produced by :func:`generate_snowflake_id`.
+    if timestamp_ms > TIMESTAMP_MS_MAX:
+        print("Timestamp overflows")
+        return None
 
-    Returns:
-        The node identifier packed into ``snowflake_id``, in the range
-        ``[0, NODE_ID_MAX]``.
-    """
-    # TODO: реализуйте функцию
-    return 0
+    snowflake_id: int = (
+        (timestamp_ms << (NODE_ID_BITS + SEQUENCE_ID_BITS))
+        | (node_id << SEQUENCE_ID_BITS)
+        | sequence_id
+    )
+    return snowflake_id
 
 
 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.
-
-    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.
+def decode_node_id(snowflake_id: int) -> int:
+    return (snowflake_id >> SEQUENCE_ID_BITS) & NODE_ID_MAX
 
-    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
+def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
+    return (
+        (snowflake_id >> NODE_ID_BITS + SEQUENCE_ID_BITS) & TIMESTAMP_MS_MAX
+    ) + epoch_ms