Improve error messages (#533)

cgt_calc/currency_converter.py

@@ -90,8 +90,15 @@ def _query_hmrc_api(self, date: datetime.date) -> None:
                 "https://www.trade-tariff.service.gov.uk/api/v2/"
                 f"exchange_rates/files/monthly_xml_{month_str}.xml"
             )
-
-        response = self.session.get(url, timeout=10)
+        try:
+            response = self.session.get(url, timeout=10)
+        except Exception as err:
+            msg = f"Error while fetching HMRC exchange rates for the month {month_str} "
+            msg += f"from the following url: {url}.\n"
+            msg += "Either try again or if you're sure about the rates you can "
+            msg += f"add them manually in {self.exchange_rates_file}.\n"
+            msg += f"The error was: {err}\n"
+            raise ParsingError(url, msg) from err
 
         if not response.ok:
             raise ParsingError(

cgt_calc/main.py

@@ -194,6 +194,7 @@ def convert_to_hmrc_transactions(
         portfolio: dict[str, Decimal] = {}
         acquisition_list: HmrcTransactionLog = {}
         disposal_list: HmrcTransactionLog = {}
+        balance_history: list[Decimal] = []
 
         for i, transaction in enumerate(transactions):
             new_balance = balance[(transaction.broker, transaction.currency)]
@@ -257,11 +258,19 @@ def convert_to_hmrc_transactions(
                 raise InvalidTransactionError(
                     transaction, f"Action not processed({transaction.action})"
                 )
+            balance_history.append(new_balance)
             if self.balance_check and new_balance < 0:
                 msg = f"Reached a negative balance({new_balance})"
                 msg += f" for broker {transaction.broker} ({transaction.currency})"
                 msg += " after processing the following transactions:\n"
-                msg += "\n".join(map(str, transactions[: i + 1]))
+                msg += "\n".join(
+                    [
+                        f"{trx}\nBalance after transaction={balance_after}"
+                        for trx, balance_after in zip(
+                            transactions[: i + 1], balance_history
+                        )
+                    ]
+                )
                 raise CalculationError(msg)
             balance[(transaction.broker, transaction.currency)] = new_balance
         print("First pass completed")