diff --git a/chart/function/create_chart.py b/chart/function/create_chart.py
index 4431ec7..7bf9eb9 100644
--- a/chart/function/create_chart.py
+++ b/chart/function/create_chart.py
@@ -13,99 +13,98 @@ from function.gen_unique_name import generate_unique_name
 from database.server import create_pool
 
 async def create_chart(
-        from_currency: str,
-        conv_currency: str,
-        start_date: str,
-        end_date: str
+		from_currency: str,
+		conv_currency: str,
+		start_date: str,
+		end_date: str
 ) -> (str, None):
-    """
-    Generates a line chart of currency rates for a given date range.
+	"""
+	Generates a line chart of currency rates for a given date range.
 
-    The chart shows the exchange rate trend between `from_currency` and
-    `conv_currency` within the specified `start_date` and `end_date` range.
-    The generated chart is saved as a PNG file, and the function returns the
-    file name. If data is invalid or insufficient, the function returns `None`.
+	The chart shows the exchange rate trend between `from_currency` and
+	`conv_currency` within the specified `start_date` and `end_date` range.
+	The generated chart is saved as a PNG file, and the function returns the
+	file name. If data is invalid or insufficient, the function returns `None`.
 
-    Args:
-        from_currency (str): The base currency (e.g., "USD").
-        conv_currency (str): The target currency (e.g., "EUR").
-        start_date (str): The start date in the format 'YYYY-MM-DD'.
-        end_date (str): The end date in the format 'YYYY-MM-DD'.
+	Args:
+		from_currency (str): The base currency (e.g., "USD").
+		conv_currency (str): The target currency (e.g., "EUR").
+		start_date (str): The start date in the format 'YYYY-MM-DD'.
+		end_date (str): The end date in the format 'YYYY-MM-DD'.
 
-    Returns:
-        str | None: The name of the saved chart file, or `None` if the operation fails.
-    """
-    pool = await create_pool()
+	Returns:
+		str | None: The name of the saved chart file, or `None` if the operation fails.
+	"""
+	pool = await create_pool()
 
-    if not validate_date(start_date) or not validate_date(end_date):
-        return None
+	if not validate_date(start_date) or not validate_date(end_date):
+		return None
 
-    start_date_obj = datetime.strptime(start_date, '%Y-%m-%d').date()
-    end_date_obj = datetime.strptime(end_date, '%Y-%m-%d').date()
+	start_date_obj = datetime.strptime(start_date, '%Y-%m-%d').date()
+	end_date_obj = datetime.strptime(end_date, '%Y-%m-%d').date()
 
-    async with pool.acquire() as conn:
-        data = await conn.fetch(
-            'SELECT date, rate FROM currency '
-            'WHERE (date BETWEEN $1 AND $2) ' +
+	async with pool.acquire() as conn:
+		data = await conn.fetch(
+			'SELECT date, rate FROM currency '
+			'WHERE (date BETWEEN $1 AND $2) ' +
 			'AND from_currency = $3 AND conv_currency = $4 ORDER BY date',
-            start_date_obj,
-            end_date_obj,
-            from_currency.upper(),
-            conv_currency.upper()
-        )
+			start_date_obj,
+			end_date_obj,
+			from_currency.upper(),
+			conv_currency.upper()
+		)
 
-    if not data or len(data) <= 1:
-        return None
+	if not data or len(data) <= 1:
+		return None
 
-    date, rate = [], []
+	date, rate = [], []
 
-    for row in data:
-        parsed_date = datetime.strptime(row['data'], '%Y-%m-%d%H:%M:%S.%fZ').date()
-        date.append(parsed_date)
-        rate.append(row['rate'])
+	for row in data:
+		parsed_date = datetime.strptime(row['data'], '%Y-%m-%d%H:%M:%S.%fZ').date()
+		date.append(parsed_date)
+		rate.append(row['rate'])
 
-    spline = make_interp_spline(range(len(date)), rate, k=2)
-    x = np.arange(len(date))
+	spline = make_interp_spline(range(len(date)), rate, k=2)
+	x = np.arange(len(date))
 
-    newx_2 = np.linspace(0, len(date) - 1, 200)
-    newy_2 = spline_2(newx_2)
-    fig, ax = plt.subplot(figsize=(15, 6))
+	newx_2 = np.linspace(0, len(date) - 1, 200)
+	newy_2 = spline_2(newx_2)
+	fig, ax = plt.subplot(figsize=(15, 6))
 
-    for label in (ax.get_xticklabels() + ax.get_yticklabels()):
-        label.set_fontsize(10)
+	for label in (ax.get_xticklabels() + ax.get_yticklabels()):
+		label.set_fontsize(10)
 
-    ax.set_xtick(np.linspace(0, len(date) - 1, 10))
-    ax.set_xticklabels(
-        [
-            date[int(i)].strftime('%Y-%m-%d') 
-            for i in np.linspace(0, len(date) - 1, 10).astype(int)
-        ]
-        )
+	ax.set_xtick(np.linspace(0, len(date) - 1, 10))
+	ax.set_xticklabels(
+		[
+			date[int(i)].strftime('%Y-%m-%d') 
+			for i in np.linspace(0, len(date) - 1, 10).astype(int)
+		]
+		)
 
-    name = await generate_unique_name(
-        f'{from_currency.upper()}_{conv_currency.upper()}',
-        datetime.now()
-    )
+	name = await generate_unique_name(
+		f'{from_currency.upper()}_{conv_currency.upper()}',
+		datetime.now()
+	)
 
-    plt.plot(newx_2, newy_2)
-    plt.savefig(f'../charts/{name}.png')
-    fig.clear()
+	plt.savefig(f'../charts/{name}.png')
+	fig.clear()
 
-    return name
+	return name
 
 
 def validate_date(date_str: str) -> bool:
-    """
-    Validates whether the provided string is a valid date in the format 'YYYY-MM-DD'.
+	"""
+	Validates whether the provided string is a valid date in the format 'YYYY-MM-DD'.
 
-    Args:
-        date_str (str): The date string to validate.
+	Args:
+		date_str (str): The date string to validate.
 
-    Returns:
-        bool: `True` if the string is a valid date, `False` otherwise.
-    """
-    try:
-        datetime.strptime(date_str, '%Y-%m-%d')
-        return True
-    except ValueError:
-        return False
+	Returns:
+		bool: `True` if the string is a valid date, `False` otherwise.
+	"""
+	try:
+		datetime.strptime(date_str, '%Y-%m-%d')
+		return True
+	except ValueError:
+		return False