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Switch FX rates to Frankfurter

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This commit is contained in:
Edward Betts 2026-06-20 17:40:12 +01:00
parent a369c44ae9
commit fc82cf280a
2 changed files with 184 additions and 12 deletions
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132
agenda/fx.py
View file

@ -11,6 +11,7 @@ import httpx
DEFAULT_FX_CACHE_TTL_HOURS = 24
DEFAULT_FX_FAILURE_RETRY_HOURS = 24
FRANKFURTER_CACHE_PREFIX = "frankfurter"
async def get_gbpusd(config: flask.config.Config) -> Decimal:
@ -57,13 +58,47 @@ def read_cached_rates(
with open(filename) as file:
data = json.load(file, parse_float=Decimal)
quotes = data.get("quotes")
if not isinstance(quotes, dict):
frankfurter_rates = _frankfurter_rates(data, currencies)
if frankfurter_rates:
return frankfurter_rates
if isinstance(data, list):
return {}
return {
cur: Decimal(quotes[f"GBP{cur}"]) for cur in currencies if f"GBP{cur}" in quotes
}
if not isinstance(data, dict):
return {}
rates = data.get("rates")
if isinstance(rates, dict):
return {cur: Decimal(rates[cur]) for cur in currencies if cur in rates}
quotes = data.get("quotes")
if isinstance(quotes, dict):
return {
cur: Decimal(quotes[f"GBP{cur}"])
for cur in currencies
if f"GBP{cur}" in quotes
}
return {}
def _frankfurter_rates(data: typing.Any, currencies: list[str]) -> dict[str, Decimal]:
"""Extract rates from Frankfurter's response format."""
if not isinstance(data, list):
return {}
rates: dict[str, Decimal] = {}
for item in data:
if not isinstance(item, dict):
continue
quote = item.get("quote")
rate = item.get("rate")
if isinstance(quote, str) and quote in currencies and rate is not None:
rates[quote] = Decimal(rate)
return rates
def _fx_cache_datetime(filename: str) -> datetime:
@ -93,8 +128,12 @@ def _latest_file(
return max(matching_files) if matching_files else None
def get_rates(config: flask.config.Config) -> dict[str, Decimal]:
"""Get current values of exchange rates for a list of currencies against GBP."""
def get_rates_exchangerate_host(config: flask.config.Config) -> dict[str, Decimal]:
"""Get exchange rates from exchangerate.host.
Kept as a fallback implementation in case we decide to switch back from
Frankfurter.
"""
currencies = config["CURRENCIES"]
access_key = config["EXCHANGERATE_ACCESS_KEY"]
data_dir = config["DATA_DIR"]
@ -160,3 +199,82 @@ def get_rates(config: flask.config.Config) -> dict[str, Decimal]:
for cur in currencies
if f"GBP{cur}" in data["quotes"]
}
def get_rates(config: flask.config.Config) -> dict[str, Decimal]:
"""Get current values of exchange rates for a list of currencies against GBP."""
currencies = config["CURRENCIES"]
data_dir = config["DATA_DIR"]
cache_ttl_hours = int(config.get("FX_CACHE_TTL_HOURS", DEFAULT_FX_CACHE_TTL_HOURS))
failure_retry_hours = int(
config.get("FX_FAILURE_RETRY_HOURS", DEFAULT_FX_FAILURE_RETRY_HOURS)
)
now = datetime.now()
now_str = now.strftime("%Y-%m-%d_%H:%M")
fx_dir = os.path.join(data_dir, "fx")
os.makedirs(fx_dir, exist_ok=True) # Ensure the directory exists
currency_string = ",".join(sorted(currencies))
legacy_file_suffix = f"{currency_string}_to_GBP.json"
frankfurter_file_suffix = f"{FRANKFURTER_CACHE_PREFIX}_{legacy_file_suffix}"
existing_data = os.listdir(fx_dir)
valid_cache_files = [
f
for f in existing_data
if f.endswith(legacy_file_suffix) or f.endswith(frankfurter_file_suffix)
]
attempt_files = [f for f in existing_data if f.endswith(frankfurter_file_suffix)]
latest_attempt = _latest_file(fx_dir, attempt_files, currencies, valid_only=False)
latest_source_valid = _latest_file(
fx_dir, attempt_files, currencies, valid_only=True
)
latest_valid = _latest_file(fx_dir, valid_cache_files, currencies, valid_only=True)
latest_valid_path = (
os.path.join(fx_dir, latest_valid) if latest_valid is not None else None
)
if config["OFFLINE_MODE"]:
return read_cached_rates(latest_valid_path, currencies)
if latest_source_valid is not None:
recent = _fx_cache_datetime(latest_source_valid)
delta = now - recent
if delta < timedelta(hours=cache_ttl_hours):
return read_cached_rates(
os.path.join(fx_dir, latest_source_valid), currencies
)
if latest_attempt is not None:
recent_attempt = _fx_cache_datetime(latest_attempt)
attempt_delta = now - recent_attempt
if attempt_delta < timedelta(hours=failure_retry_hours):
return read_cached_rates(latest_valid_path, currencies)
url = "https://api.frankfurter.dev/v2/rates"
params = {"base": "GBP", "quotes": currency_string}
filename = f"{now_str}_{frankfurter_file_suffix}"
try:
with httpx.Client() as client:
response = client.get(url, params=params, timeout=10)
except (httpx.ConnectError, httpx.ReadTimeout):
return read_cached_rates(latest_valid_path, currencies)
try:
data = json.loads(response.text, parse_float=Decimal)
except json.decoder.JSONDecodeError:
return read_cached_rates(latest_valid_path, currencies)
frankfurter_rates = _frankfurter_rates(data, currencies)
if not frankfurter_rates:
with open(os.path.join(fx_dir, filename), "w") as file:
file.write(response.text)
return read_cached_rates(latest_valid_path, currencies)
with open(os.path.join(fx_dir, filename), "w") as file:
file.write(response.text)
return frankfurter_rates

64
tests/test_fx.py
View file

@ -19,7 +19,7 @@ class TestReadCachedRates:
assert result == {}
def test_read_cached_rates_valid_file(self) -> None:
"""Test reading valid cached rates file."""
"""Test reading valid exchangerate.host cached rates file."""
currencies = ["USD", "EUR", "JPY"]
data = {
"quotes": {
@ -46,6 +46,37 @@ class TestReadCachedRates:
finally:
os.unlink(filepath)
def test_read_cached_rates_frankfurter_file(self) -> None:
"""Test reading valid Frankfurter cached rates file."""
currencies = ["USD", "EUR", "JPY"]
data = [
{"date": "2026-06-20", "base": "GBP", "quote": "USD", "rate": 1.25},
{"date": "2026-06-20", "base": "GBP", "quote": "EUR", "rate": 1.15},
{"date": "2026-06-20", "base": "GBP", "quote": "JPY", "rate": 150.0},
{
"date": "2026-06-20",
"base": "GBP",
"quote": "CAD",
"rate": 1.70,
}, # Not requested
]
with tempfile.NamedTemporaryFile(mode="w", suffix=".json", delete=False) as f:
json.dump(data, f)
filepath = f.name
try:
result = read_cached_rates(filepath, currencies)
assert len(result) == 3
assert result["USD"] == Decimal("1.25")
assert result["EUR"] == Decimal("1.15")
assert result["JPY"] == Decimal("150.0")
assert "CAD" not in result # Not requested
finally:
os.unlink(filepath)
def test_read_cached_rates_missing_currencies(self) -> None:
"""Test with some currencies missing from data."""
currencies = ["USD", "EUR", "CHF"] # CHF not in data
@ -158,8 +189,8 @@ class TestReadCachedRates:
os.unlink(filepath)
def test_get_rates_uses_older_valid_cache_when_latest_attempt_is_usage_limit() -> None:
"""A usage-limit API response should not replace usable cached rates."""
def test_get_rates_ignores_old_usage_limit_attempt_when_using_frankfurter() -> None:
"""An old provider usage-limit response should not block Frankfurter refreshes."""
with tempfile.TemporaryDirectory() as temp_dir:
fx_dir = os.path.join(temp_dir, "fx")
os.mkdir(fx_dir)
@ -200,8 +231,31 @@ def test_get_rates_uses_older_valid_cache_when_latest_attempt_is_usage_limit() -
) as mock_client:
mock_datetime.now.return_value = datetime(2026, 6, 20, 12, 35)
mock_datetime.strptime.side_effect = datetime.strptime
mock_response = (
mock_client.return_value.__enter__.return_value.get.return_value
)
mock_response.text = json.dumps(
[
{
"date": "2026-06-20",
"base": "GBP",
"quote": "EUR",
"rate": 1.16,
},
{
"date": "2026-06-20",
"base": "GBP",
"quote": "USD",
"rate": 1.26,
},
]
)
result = get_rates(config)
assert result == {"USD": Decimal("1.25"), "EUR": Decimal("1.15")}
mock_client.assert_not_called()
assert result == {"USD": Decimal("1.26"), "EUR": Decimal("1.16")}
mock_client.return_value.__enter__.return_value.get.assert_called_once_with(
"https://api.frankfurter.dev/v2/rates",
params={"base": "GBP", "quotes": "EUR,USD"},
timeout=10,
)