from sqlalchemy.engine import URL, make_url
from sqlalchemy.exc import ArgumentError


_DEFAULT_DATABASE_PORTS = {
    "mysql": 3306,
    "postgresql": 5432,
}
_PLATFORM_MIGRATION_BACKENDS = frozenset({"postgresql", "sqlite"})

DatabaseTarget = tuple[str, str, int | None, str]


def database_target(value: str | URL | None) -> DatabaseTarget | None:
    """Return a credential-free physical database identity."""

    if not value:
        return None
    try:
        url = make_url(value)
    except (ArgumentError, TypeError, ValueError):
        return None
    backend = url.get_backend_name().lower()
    return (
        backend,
        str(url.host or "").casefold(),
        url.port or _DEFAULT_DATABASE_PORTS.get(backend),
        str(url.database or ""),
    )


def database_password(value: str | URL | None) -> str | None:
    """Return a configured password without including it in diagnostics."""

    if not value:
        return None
    try:
        password = make_url(value).password
    except (ArgumentError, TypeError, ValueError):
        return None
    return str(password) if password is not None else None


def validate_platform_migration_target(
    database_url: str | URL,
    legacy_database_url: str | None,
) -> DatabaseTarget:
    """Fail closed before Alembic can connect to an unsafe database target."""

    platform = database_target(database_url)
    if platform is None:
        raise RuntimeError("DATABASE_URL is not a valid platform database URL")
    if platform[0] not in _PLATFORM_MIGRATION_BACKENDS:
        raise RuntimeError(
            "Platform migrations are supported only for PostgreSQL or local SQLite"
        )
    legacy = database_target(legacy_database_url)
    if legacy is not None and platform == legacy:
        raise RuntimeError(
            "Refusing to migrate DATABASE_URL because it matches LEGACY_DATABASE_URL"
        )
    return platform