feat: bootstrap FastAPI configuration

app/config.py

@@ -0,0 +1,36 @@
+from functools import lru_cache
+from pathlib import Path
+
+from pydantic import Field, PositiveInt, model_validator
+from pydantic_settings import BaseSettings, SettingsConfigDict
+
+
+class Settings(BaseSettings):
+    model_config = SettingsConfigDict(env_file=".env", extra="ignore", case_sensitive=False)
+
+    admin_password: str = Field(alias="ADMIN_PASSWORD", min_length=1)
+    secret_key: str = Field(alias="SECRET_KEY", min_length=16)
+    credential_encryption_key: str = Field(alias="CREDENTIAL_ENCRYPTION_KEY", min_length=1)
+    data_dir: Path = Field(default=Path("/data"), alias="DATA_DIR")
+    database_url: str | None = Field(default=None, alias="DATABASE_URL")
+    sync_interval_minutes: PositiveInt = Field(default=5, alias="SYNC_INTERVAL_MINUTES")
+
+    @model_validator(mode="after")
+    def derive_paths(self) -> "Settings":
+        self.data_dir = self.data_dir.expanduser().resolve()
+        if self.database_url is None:
+            self.database_url = f"sqlite:///{self.data_dir / 'app.db'}"
+        return self
+
+    @property
+    def tokens_dir(self) -> Path:
+        return self.data_dir / "tokens"
+
+    @property
+    def activities_dir(self) -> Path:
+        return self.data_dir / "activities"
+
+
+@lru_cache
+def get_settings() -> Settings:
+    return Settings()