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from abc import ABC, abstractmethod
from typing import List

from gravitino.api.rel.expressions.expression import Expression
from gravitino.api.rel.expressions.sorts.null_ordering import NullOrdering
from gravitino.api.rel.expressions.sorts.sort_direction import SortDirection


class SortOrder(Expression, ABC):
    """Represents a sort order in the public expression API."""

    @abstractmethod
    def expression(self) -> Expression:
        """Returns the sort expression."""
        pass

    @abstractmethod
    def direction(self) -> SortDirection:
        """Returns the sort direction."""
        pass

    @abstractmethod
    def null_ordering(self) -> NullOrdering:
        """Returns the null ordering."""
        pass

    def children(self) -> List[Expression]:
        """Returns the children expressions of this sort order."""
        return [self.expression()]
