feat(pems_data): define a basic Cache class

uses an underlying redis connection

Author: thekaveman

pems_data/pyproject.toml

@@ -3,7 +3,7 @@ name = "pems_data"
 description = "Common data access library for PeMS."
 dynamic = ["version"]
 requires-python = ">=3.12"
-dependencies = ["boto3==1.39.7", "pandas==2.3.0"]
+dependencies = ["boto3==1.39.7", "pandas==2.3.0", "redis==6.2.0"]
 
 [build-system]
 requires = ["setuptools>=75", "setuptools_scm>=8"]

pems_data/src/pems_data/cache.py

@@ -0,0 +1,26 @@
+import os
+
+import redis
+
+
+def redis_connection() -> redis.Redis:
+    hostname = os.environ.get("REDIS_HOSTNAME", "redis")
+    port = int(os.environ.get("REDIS_PORT", "6379"))
+
+    return redis.Redis(host=hostname, port=port)
+
+
+class Cache:
+    """Basic caching interface for `pems_data`."""
+
+    def __init__(self):
+        self.r = redis_connection()
+
+    def is_available(self) -> bool:
+        return self.r.ping() is True
+
+    def get(self, key):
+        return self.r.get(key)
+
+    def set(self, key, value):
+        self.r.set(key, value)

tests/pytest/pems_data/test_cache.py

@@ -0,0 +1,63 @@
+import redis
+import pytest
+
+from pems_data.cache import Cache, redis_connection
+
+
+class TestRedisConnection:
+    @pytest.fixture(autouse=True)
+    def mock_redis(self, mocker):
+        return mocker.patch("redis.Redis")
+
+    def test_redis_connection_default_values(self, mock_redis):
+        redis_connection()
+        mock_redis.assert_called_once_with(host="redis", port=6379)
+
+    def test_redis_connection_custom_values(self, mock_redis, monkeypatch):
+        monkeypatch.setenv("REDIS_HOSTNAME", "custom-host")
+        monkeypatch.setenv("REDIS_PORT", "1234")
+
+        redis_connection()
+        mock_redis.assert_called_once_with(host="custom-host", port=1234)
+
+
+class TestCache:
+    @pytest.fixture
+    def mock_redis_connection(self, mocker):
+        mock_redis = mocker.patch("pems_data.cache.redis_connection")
+        mock_redis.return_value = mocker.Mock(spec=redis.Redis)
+        return mock_redis.return_value
+
+    @pytest.fixture
+    def cache(self, mock_redis_connection):
+        return Cache()
+
+    def test_init_creates_redis_connection(self, mock_redis_connection):
+        cache = Cache()
+        assert cache.r == mock_redis_connection
+
+    def test_is_available_true(self, cache, mock_redis_connection):
+        mock_redis_connection.ping.return_value = True
+
+        assert cache.is_available() is True
+        mock_redis_connection.ping.assert_called_once()
+
+    def test_is_available_false(self, cache, mock_redis_connection):
+        mock_redis_connection.ping.return_value = False
+
+        assert cache.is_available() is False
+        mock_redis_connection.ping.assert_called_once()
+
+    def test_get(self, cache, mock_redis_connection):
+        expected = b"test-value"
+        mock_redis_connection.get.return_value = expected
+
+        result = cache.get("test-key")
+
+        assert result == expected
+        mock_redis_connection.get.assert_called_once_with("test-key")
+
+    def test_set(self, cache, mock_redis_connection):
+        cache.set("test-key", "test-value")
+
+        mock_redis_connection.set.assert_called_once_with("test-key", "test-value")