Add from_cache_dir class method.

Add testing.

src/abc_atlas_access/abc_atlas_cache/abc_project_cache.py

@@ -1,12 +1,14 @@
 from typing import Optional, Union, List
 from pathlib import Path
 import logging
+import os
 import pandas as pd
+import warnings
+
 from abc_atlas_access.abc_atlas_cache.cloud_cache import (
     S3CloudCache,
     LocalCache
 )
-import warnings
 
 
 class AbcProjectCacheVersionException(Exception):
@@ -136,6 +138,35 @@ def from_local_cache(
         )
         return cls(cache, local=True)
 
+    @classmethod
+    def from_cache_dir(
+            cls,
+            cache_dir: Union[str, Path],
+    ) -> "ProjectCloudApiBase":
+        """Instantiate either a local_cache or s3_cache instance of the class.
+
+        Tests if user has write access to the directory, instantiate a s3_cache
+        else instantiate a local_cache.
+
+        Parameters
+        ----------
+        cache_dir: str or pathlib.Path
+            Path to the directory where data will be stored on the local system
+
+        Returns
+        -------
+        ProjectCloudApiBase instance
+        """
+        cache_dir = Path(cache_dir)
+        # If the directory does not exist or we have write access to it
+        # we will use the s3 cache. Else we will use the local cache.
+        if not cache_dir.exists() or os.access(cache_dir, os.W_OK):
+            return cls.from_s3_cache(cache_dir)
+        elif cache_dir.exists() and not os.access(cache_dir, os.W_OK):
+            return cls.from_local_cache(cache_dir)
+        else:
+            raise RuntimeError("Could not access or create cache directory.")
+
     def compare_manifests(self,
                           manifest_newer_name: str,
                           manifest_older_name: str

tests/abc_atlas_cache/test_abc_project_cache.py

@@ -1,6 +1,9 @@
 import json
-import pytest
 from moto import mock_aws
+import os
+from unittest.mock import patch
+import pytest
+
 from .utils import (
     BaseCacheTestCase,
     create_manifest_dict,
@@ -11,6 +14,10 @@
 from abc_atlas_access.abc_atlas_cache.abc_project_cache import AbcProjectCache
 from abc_atlas_access.abc_atlas_cache.file_attributes import \
     CacheFileAttributes
+from abc_atlas_access.abc_atlas_cache.cloud_cache import (
+    LocalCache,
+    S3CloudCache
+)
 
 
 @mock_aws
@@ -249,3 +256,28 @@ def test_abc_project_cache_local_cache(self):
             directory="test_directory"
         )
         assert metadata_paths == [self.cache_dir / self.new_metadata_path]
+
+    def test_abc_project_cache_from_cache_dir(self):
+        """Run test that caches are initialized from the cache directory
+        correctly as either a S3CloudCache or LocalCache object when
+        appropreate.
+        """
+        AbcProjectCache._bucket_name = self.test_bucket_name
+        cache = AbcProjectCache.from_cache_dir(self.cache_dir)
+        assert isinstance(cache.cache, S3CloudCache)
+
+        # Download data into the local cache.
+        cache.get_data_path(directory="second_dir",
+                            file_name=self.new_file)
+        cache.get_data_path(directory="test_directory",
+                            file_name=self.data_file)
+        cache.get_metadata_path(directory="test_directory",
+                                file_name="metadata_file")
+
+        # Remove the previous cache object.
+        del cache
+
+        # Initialize a new read only object from the local cache.
+        with patch('os.access', return_value=False):
+            cache = AbcProjectCache.from_cache_dir(self.cache_dir)
+        assert isinstance(cache.cache, LocalCache)