app/backend/app/core/config.py

import secrets
import warnings
from pathlib import Path
from typing import Annotated, Any, Literal

from pydantic import (
    AnyUrl,
    BeforeValidator,
    EmailStr,
    HttpUrl,
    PostgresDsn,
    computed_field,
    model_validator,
)
from pydantic_settings import BaseSettings, SettingsConfigDict
from typing_extensions import Self


def parse_cors(v: Any) -> list[str] | str:
    if isinstance(v, str) and not v.startswith("["):
        return [i.strip() for i in v.split(",") if i.strip()]
    elif isinstance(v, list | str):
        return v
    raise ValueError(v)


class Settings(BaseSettings):
    model_config = SettingsConfigDict(
        # Use top level .env file (one level above ./backend/)
        env_file="../.env",
        env_ignore_empty=True,
        extra="ignore",
    )
    API_V1_STR: str = "/api/v1"
    SECRET_KEY: str = secrets.token_urlsafe(32)
    # 60 minutes * 24 hours * 8 days = 8 days
    ACCESS_TOKEN_EXPIRE_MINUTES: int = 60 * 24 * 8
    FRONTEND_HOST: str = "http://localhost:5173"
    ENVIRONMENT: Literal["local", "staging", "production"] = "local"

    # Flows live on disk as a git repository; secrets stay outside it.
    FLOWS_DIR: Path = Path("flow-data/flows")
    SECRETS_FILE: Path = Path("flow-data/secrets.enc")
    # The MCP endpoint, and the OAuth server agents authenticate against. Off
    # until someone asks for it: it opens client registration to the network.
    MCP_ENABLED: bool = False
    DOMAIN: str = "localhost"
    OAUTH_PRIVATE_KEY_FILE: Path = Path("flow-data/oauth-key.pem")
    OAUTH_CODE_EXPIRE_SECONDS: int = 60
    # Short, because an agent's token is a bearer secret held by a program
    # rather than a person, and it can refresh unattended.
    MCP_TOKEN_EXPIRE_MINUTES: int = 60
    MCP_REFRESH_EXPIRE_DAYS: int = 30
    FLOW_MAX_WORKERS: int = 4
    # Without a Redis host the engine keeps its state in memory.
    REDIS_HOST: str | None = None
    REDIS_PORT: int = 6379

    BACKEND_CORS_ORIGINS: Annotated[
        list[AnyUrl] | str, BeforeValidator(parse_cors)
    ] = []

    @computed_field  # type: ignore[prop-decorator]
    @property
    def oauth_issuer(self) -> str:
        """Who issues MCP tokens — this app, on its API host.

        Kept separate from the app's own URL because a hosted deployment can
        later point agents at a different issuer without the resource server
        changing: it validates whatever issuer it is configured to trust.
        """
        scheme = "http" if self.ENVIRONMENT == "local" else "https"
        return f"{scheme}://api.{self.DOMAIN}"

    @computed_field  # type: ignore[prop-decorator]
    @property
    def mcp_resource(self) -> str:
        """The resource an MCP token is issued for (RFC 8707)."""
        return f"{self.oauth_issuer}/mcp"

    @computed_field  # type: ignore[prop-decorator]
    @property
    def all_cors_origins(self) -> list[str]:
        return [str(origin).rstrip("/") for origin in self.BACKEND_CORS_ORIGINS] + [
            self.FRONTEND_HOST
        ]

    PROJECT_NAME: str
    SENTRY_DSN: HttpUrl | None = None
    POSTGRES_SERVER: str
    POSTGRES_PORT: int = 5432
    POSTGRES_USER: str
    POSTGRES_PASSWORD: str = ""
    POSTGRES_DB: str = ""

    @computed_field  # type: ignore[prop-decorator]
    @property
    def SQLALCHEMY_DATABASE_URI(self) -> PostgresDsn:
        return PostgresDsn.build(
            scheme="postgresql+psycopg",
            username=self.POSTGRES_USER,
            password=self.POSTGRES_PASSWORD,
            host=self.POSTGRES_SERVER,
            port=self.POSTGRES_PORT,
            path=self.POSTGRES_DB,
        )

    SMTP_TLS: bool = True
    SMTP_SSL: bool = False
    SMTP_PORT: int = 587
    SMTP_HOST: str | None = None
    SMTP_USER: str | None = None
    SMTP_PASSWORD: str | None = None
    EMAILS_FROM_EMAIL: EmailStr | None = None
    EMAILS_FROM_NAME: str | None = None

    @model_validator(mode="after")
    def _set_default_emails_from(self) -> Self:
        if not self.EMAILS_FROM_NAME:
            self.EMAILS_FROM_NAME = self.PROJECT_NAME
        return self

    EMAIL_RESET_TOKEN_EXPIRE_HOURS: int = 48

    @computed_field  # type: ignore[prop-decorator]
    @property
    def emails_enabled(self) -> bool:
        return bool(self.SMTP_HOST and self.EMAILS_FROM_EMAIL)

    EMAIL_TEST_USER: EmailStr = "test@example.com"
    FIRST_SUPERUSER: EmailStr
    FIRST_SUPERUSER_PASSWORD: str

    def _check_default_secret(self, var_name: str, value: str | None) -> None:
        if value == "changethis":
            message = (
                f'The value of {var_name} is "changethis", '
                "for security, please change it, at least for deployments."
            )
            if self.ENVIRONMENT == "local":
                warnings.warn(message, stacklevel=1)
            else:
                raise ValueError(message)

    @model_validator(mode="after")
    def _enforce_non_default_secrets(self) -> Self:
        self._check_default_secret("SECRET_KEY", self.SECRET_KEY)
        self._check_default_secret("POSTGRES_PASSWORD", self.POSTGRES_PASSWORD)
        self._check_default_secret(
            "FIRST_SUPERUSER_PASSWORD", self.FIRST_SUPERUSER_PASSWORD
        )

        return self


settings = Settings()  # type: ignore