chore: run the app from a venv and read configuration from a dotenv (#95)

photo_pipeline/config.py

@@ -18,6 +18,61 @@ from typing import Mapping
 from pydantic import BaseModel, ConfigDict, SecretStr
 
 ENV_PREFIX = "PHOTO_PIPELINE_"
+ENV_FILE_VAR = f"{ENV_PREFIX}ENV_FILE"
+DEFAULT_ENV_FILE = Path(".env")
+
+# The archived CLI's variable names, so the configuration file an operator already
+# has keeps working. The vision provider reads the OpenAI SDK's names, and the
+# library root is configuration here rather than a bare path (US07-01 donor).
+LEGACY_ALIASES = {
+    "LLM_API_KEY": "OPENAI_API_KEY",
+    "GEMINI_API_KEY": "OPENAI_API_KEY",
+    "LLM_BASE_URL": "OPENAI_BASE_URL",
+    "LIBRARY": f"{ENV_PREFIX}LIBRARY_ROOTS",
+}
+
+
+def parse_env_file(text: str) -> dict[str, str]:
+    """``KEY=value`` lines into a mapping. Comments, blanks, and quotes handled.
+
+    Deliberately not a shell: no interpolation, no ``export``, no multi-line values.
+    A configuration file that can run code is a configuration file that can be a
+    vulnerability.
+    """
+    values: dict[str, str] = {}
+    for line in text.splitlines():
+        line = line.strip()
+        if not line or line.startswith("#") or "=" not in line:
+            continue
+        key, _, raw = line.partition("=")
+        key = key.strip()
+        if not key or key.startswith("#"):
+            continue
+        value = raw.strip().strip('"').strip("'")
+        values[key] = value
+        alias = LEGACY_ALIASES.get(key)
+        if alias:
+            values.setdefault(alias, value)
+    return values
+
+
+def load_env_file(path: Path | str | None = None) -> dict[str, str]:
+    """Load ``PHOTO_PIPELINE_ENV_FILE`` (or ``./.env``) into the environment.
+
+    Anything already exported wins: a file is the standing configuration, the shell
+    is what you meant *this time*. Returns what it applied, which is what the CLI
+    prints — names only, never values.
+    """
+    candidate = path or os.environ.get(ENV_FILE_VAR) or DEFAULT_ENV_FILE
+    candidate = Path(candidate)
+    if not candidate.is_file():
+        return {}
+    applied = {}
+    for key, value in parse_env_file(candidate.read_text()).items():
+        if key not in os.environ:
+            os.environ[key] = value
+            applied[key] = value
+    return applied
 
 
 class Config(BaseModel):
@@ -68,6 +123,9 @@ class Config(BaseModel):
     @classmethod
     def from_env(cls, environ: Mapping[str, str] | None = None) -> "Config":
         env = os.environ if environ is None else environ
+        if environ is None:
+            load_env_file()  # a file never overrides what the shell already set
+            env = os.environ
         data: dict = {}
         for name in cls.model_fields:
             raw = env.get(ENV_PREFIX + name.upper())