2. Васильев Егор Евгеньевич. 613

src/part1/constants.py

@@ -19,20 +19,20 @@
 # 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).

src/part1/snowflake.py

@@ -13,12 +13,14 @@
 :func:`decode_node_id` and :func:`decode_sequence_id`.
 """
 
-import time  # noqa: F401
+import time
 
-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_MS_MAX,
 )
@@ -35,7 +37,8 @@ def read_current_millis(epoch_ms: int) -> int:
         negative if ``epoch_ms`` lies in the future.
     """
     # TODO: реализуйте функцию
-    return 0
+    now_ms = int(time.time() * 1000)
+    return now_ms - epoch_ms
 
 
 def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) -> int:
@@ -50,8 +53,8 @@ def decode_timestamp_ms(snowflake_id: int, epoch_ms: int = EPOCH_MS_DEFAULT) ->
         The absolute Unix time in milliseconds at which the identifier was
         generated.
     """
-    # TODO: реализуйте функцию
-    return 0
+    snowflake_id_time = snowflake_id >> (NODE_ID_BITS + SEQUENCE_ID_BITS)
+    return snowflake_id_time + epoch_ms
 
 
 def decode_node_id(snowflake_id: int) -> int:
@@ -65,7 +68,9 @@ def decode_node_id(snowflake_id: int) -> int:
         ``[0, NODE_ID_MAX]``.
     """
     # TODO: реализуйте функцию
-    return 0
+    snowflake_id_knot = snowflake_id >> SEQUENCE_ID_BITS
+    snowflake_id_knot = snowflake_id_knot & NODE_ID_MAX
+    return snowflake_id_knot
 
 
 def decode_sequence_id(snowflake_id: int) -> int:
@@ -79,7 +84,7 @@ def decode_sequence_id(snowflake_id: int) -> int:
         the range ``[0, SEQUENCE_ID_MAX]``.
     """
     # TODO: реализуйте функцию
-    return 0
+    return snowflake_id & SEQUENCE_ID_MAX
 
 
 def generate_snowflake_id(
@@ -111,4 +116,17 @@ def generate_snowflake_id(
         cases an explanatory message is printed to stdout first.
     """
     # TODO: реализуйте функцию
-    return 0
+    if node_id < 0 or node_id > NODE_ID_MAX:
+        print(f"node_id must be in [0, {NODE_ID_MAX}], got {node_id}")
+        return None
+    if sequence_id < 0 or sequence_id > SEQUENCE_ID_MAX:
+        print(f"sequence_id must be in [0, {SEQUENCE_ID_MAX}], got {sequence_id}")
+        return None
+    time_ms = read_current_millis(epoch_ms)
+    if time_ms > TIMESTAMP_MS_MAX:
+        print("overflows")
+        return None
+    snowflake_id = sequence_id
+    snowflake_id |= node_id << SEQUENCE_ID_BITS
+    snowflake_id |= time_ms << (NODE_ID_BITS + SEQUENCE_ID_BITS)
+    return snowflake_id

src/part2/cart.py

@@ -1,20 +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``.
-"""
-
 from typing import Final
 
 from .crud import read_product, update_product  # noqa: F401
 from .storage import (  # noqa: F401
     NAME_INDEX,
     PRICE_INDEX,
+    PRODUCT_ID_INDEX,
     QUANTITY_INDEX,
     Product,
 )
@@ -24,37 +14,65 @@
 
 # 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(
-    storage: list[Product],
+def change_cart_quantity(
     cart: list[CartLine],
     product_id: int,
     quantity: int,
 ) -> CartLine | None:
-    """Move ``quantity`` units of ``product_id`` from the store into ``cart``.
+    for i, cart_i in enumerate(cart):
+        if cart_i[LINE_PRODUCT_ID_INDEX] == product_id:
+            if cart_i[LINE_QUANTITY_INDEX] + quantity == 0:
+                del cart[i]
+                return (product_id, 0)
+            cart[i] = (cart_i[0], cart_i[1] + quantity)
+            return cart[i]
+    return None
 
-    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)
+def add_to_cart(
+    storage: list[Product],
+    cart: list[CartLine],
+    product_id: int,
+    quantity: int,
+) -> CartLine | None:
+    product_new = read_product(storage, product_id)
+    if product_new is None:
+        return None
+    if product_new[QUANTITY_INDEX] < quantity:
+        print(
+            f"not enough stock for product {product_id}: {product_new[QUANTITY_INDEX]} available, {quantity} requested"
+        )
+        return None
+    index = next(
+        (i for i, p in enumerate(storage) if p[PRODUCT_ID_INDEX] == product_id), None
+    )
+    if index is None:
+        return None
+    storage[index] = (
+        product_new[0],
+        product_new[1],
+        product_new[2],
+        product_new[3] - quantity,
+    )
+    change = change_cart_quantity(cart, product_id, quantity)
+    if change is None:
+        cart.append((product_id, quantity))
+        return (product_id, quantity)
+    else:
+        return change
+
+
+def find_cart_line(
+    cart: list[CartLine],
+    product_id: int,
+) -> CartLine | None:
+    for cart_i in cart:
+        if cart_i[LINE_PRODUCT_ID_INDEX] == product_id:
+            return cart_i
+    return None
 
 
 def remove_from_cart(
@@ -63,27 +81,27 @@ 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)
+    cart_find = find_cart_line(cart, product_id)
+    if cart_find is None:
+        print(f"product {product_id} is not in the cart")
+        return None
+    if cart_find[LINE_QUANTITY_INDEX] < quantity:
+        print(
+            f"cart holds only {cart_find[LINE_QUANTITY_INDEX]} unit(s) of product {product_id}, cannot remove {quantity}"
+        )
+        return None
+    product_new = read_product(storage, product_id)
+    if product_new == None:
+        return None
+    index = next(
+        (i for i, p in enumerate(storage) if p[PRODUCT_ID_INDEX] == product_id), None
+    )
+    if index is None:
+        return None
+    storage[index] = (
+        product_new[0],
+        product_new[1],
+        product_new[2],
+        product_new[3] + quantity,
+    )
+    return change_cart_quantity(cart, product_id, -quantity)