cache: Add CacheWriter class.

oxrlib/cache.py

@@ -33,6 +33,10 @@ class CacheBase:
 
     def __init__(self, dir_path, **kwargs):
         self.dir_path = dir_path
+        try:
+            self.CacheFile = kwargs.pop('file_class')
+        except KeyError:
+            pass
         self.fn_patterns = {}
         self.setup(**kwargs)
 
@@ -62,3 +66,14 @@ class CacheBase:
     @_wrap_api_method
     def historical(self, date, base):
         return {'date': date.isoformat(), 'base': base}
+
+
+class WriteCacheFile(CacheFileBase):
+    ERRORS_MAP = []
+
+
+class CacheWriter(CacheBase):
+    CacheFile = WriteCacheFile
+
+    def open(self, path):
+        return self.CacheFile(path, 'w')

oxrlib/loaders.py

@@ -14,10 +14,11 @@ class ReadCacheFile(cache.CacheFileBase):
 
 
 class FileCache(cache.CacheBase):
+    CacheFile = ReadCacheFile
     ConfigurationError = errors.CacheLoaderConfigurationError
 
     def open(self, path):
-        return ReadCacheFile(path)
+        return self.CacheFile(path)
 
 
 class OXRAPIRequest:

tests/test_CacheWriter.py

@@ -0,0 +1,35 @@
+import datetime
+import io
+import pathlib
+
+import pytest
+
+from . import any_date, relpath
+import oxrlib.cache
+import oxrlib.errors
+
+CACHE_PATH = relpath('writecache')
+HISTORICAL_PATTERN = '{date}_{base}_cache.json'
+
+class TestCacheFile(oxrlib.cache.WriteCacheFile):
+    def __init__(self, path, *args, **kwargs):
+        self.path = path
+        assert args[0].startswith('w')
+
+    def open(self):
+        open_file = io.StringIO()
+        open_file.name = self.path.as_posix()
+        return open_file
+
+
+@pytest.fixture
+def dummycache():
+    cache = oxrlib.cache.CacheWriter(CACHE_PATH, file_class=TestCacheFile)
+    cache.setup(historical=HISTORICAL_PATTERN)
+    return cache
+
+def test_cache_success(dummycache, any_date):
+    base = 'USD'
+    expect_name = CACHE_PATH / HISTORICAL_PATTERN.format(date=any_date.isoformat(), base=base)
+    with dummycache.historical(any_date, base) as cache_file:
+        assert pathlib.Path(cache_file.name) == expect_name