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# Source code for astropy.timeseries.core

    # Licensed under a 3-clause BSD style license - see LICENSE.rst

    from contextlib import contextmanager
    from functools import wraps
    from types import FunctionType

    from astropy.table import QTable

    __all__ = ["BaseTimeSeries", "autocheck_required_columns"]

    COLUMN_RELATED_METHODS = [
        "add_column",
        "add_columns",
        "keep_columns",
        "remove_column",
        "remove_columns",
        "rename_column",
    ]

    def autocheck_required_columns(cls):
        """
        This is a decorator that ensures that the table contains specific
        methods indicated by the _required_columns attribute. The aim is to
        decorate all methods that might affect the columns in the table and check
        for consistency after the methods have been run.
        """

        def decorator_method(method):
            @wraps(method)
            def wrapper(self, *args, **kwargs):
                result = method(self, *args, **kwargs)
                self._check_required_columns()
                return result

            return wrapper

        for name in COLUMN_RELATED_METHODS:
            if not hasattr(cls, name) or not isinstance(getattr(cls, name), FunctionType):
                raise ValueError(f"{name} is not a valid method")
            setattr(cls, name, decorator_method(getattr(cls, name)))

        return cls

    class BaseTimeSeries(QTable):
        _required_columns = None
        _required_columns_enabled = True

        # If _required_column_relax is True, we don't require the columns to be
        # present but we do require them to be the correct ones IF present. Note
        # that this is a temporary state - as soon as the required columns
        # are all present, we toggle this to False
        _required_columns_relax = False

        def _check_required_columns(self):
            def as_scalar_or_list_str(obj):
                if not hasattr(obj, "__len__"):
                    return f"'{obj}'"
                elif len(obj) == 1:
                    return f"'{obj[0]}'"
                else:
                    return str(obj)

            if not self._required_columns_enabled:
                return

            if self._required_columns is not None:
                if self._required_columns_relax:
                    required_columns = self._required_columns[: len(self.colnames)]
                else:
                    required_columns = self._required_columns

                plural = "s" if len(required_columns) > 1 else ""

                if not self._required_columns_relax and len(self.colnames) == 0:
                    raise ValueError(
                        f"{self.__class__.__name__} object is invalid - expected"
                        f" '{required_columns[0]}' as the first column{plural} but time"
                        " series has no columns"
                    )

                elif self.colnames[: len(required_columns)] != required_columns:
                    raise ValueError(
                        f"{self.__class__.__name__} object is invalid - expected"
                        f" {as_scalar_or_list_str(required_columns)} as the first"
                        f" column{plural} but found"
                        f" {as_scalar_or_list_str(self.colnames[: len(required_columns)])}"
                    )

                if (
                    self._required_columns_relax
                    and self._required_columns
                    == self.colnames[: len(self._required_columns)]
                ):
                    self._required_columns_relax = False

        @contextmanager
        def _delay_required_column_checks(self):
            self._required_columns_enabled = False
            yield
            self._required_columns_enabled = True
            self._check_required_columns()