emmental: Add support for an application-specific temporary directory

And include a function to help extract embedded cover.jpg files.

Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

emmental/tmpdir.py

@@ -0,0 +1,21 @@
+# Copyright 2022 (c) Anna Schumaker.
+"""Special handling for temporary directories."""
+import tempfile
+import pathlib
+from . import gsetup
+
+TMP_DIR = pathlib.Path(tempfile.gettempdir()) / gsetup.APPLICATION_ID
+TMP_DIR.mkdir(exist_ok=True)
+
+
+def cover_jpg(data: bytes | None = None) -> pathlib.Path:
+    """Get the path to the temporary cover.jpg file.
+
+    If 'data' is provided, then the file will be created with the
+    contents initialized to 'data'.
+    """
+    cover = TMP_DIR / "cover.jpg"
+    if data is not None:
+        with cover.open("wb") as f:
+            f.write(data)
+    return cover

tests/test_tmpdir.py

@@ -0,0 +1,33 @@
+# Copyright 2022 (c) Anna Schumaker.
+"""Test our temporary directory handling code."""
+import tempfile
+import pathlib
+import unittest
+import emmental.tmpdir
+
+TMP_DIR = pathlib.Path(tempfile.gettempdir())
+
+
+class TestTmpDir(unittest.TestCase):
+    """Our teporary directory test case."""
+
+    def setUp(self):
+        """Prepare for testing."""
+        emmental.tmpdir.cover_jpg().unlink(missing_ok=True)
+
+    def test_tmpdir(self):
+        """Test TMP_DIR location and existence."""
+        self.assertEqual(emmental.tmpdir.TMP_DIR,
+                         TMP_DIR / emmental.gsetup.APPLICATION_ID)
+        self.assertTrue(emmental.tmpdir.TMP_DIR.is_dir())
+
+    def test_cover_jpg(self):
+        """Test temporary cover.jpg handling."""
+        cover = emmental.tmpdir.cover_jpg()
+        self.assertEqual(cover, emmental.tmpdir.TMP_DIR / "cover.jpg")
+        self.assertFalse(cover.is_file())
+
+        cover = emmental.tmpdir.cover_jpg("Test Text".encode("utf-8"))
+        self.assertTrue(cover.is_file())
+        with cover.open("rb") as f:
+            self.assertEqual(f.read(), "Test Text".encode("utf-8"))