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"""Sequence-field type rules shared by validation and Python comparators."""

from pypaimon.schema.data_types import AtomicType, DataField, Keyword


def _base_type_name(field: DataField) -> str:
    """Base type keyword of a field, stripping any ``(precision[, scale])``
    parameters and the ``NOT NULL`` suffix. E.g. ``DECIMAL(10, 2)`` and
    ``TIMESTAMP(6)`` map to ``DECIMAL`` / ``TIMESTAMP``.
    """
    return field.type.type.split('(')[0].split(' ')[0]


_COMPARABLE_TYPE_NAMES = frozenset(
    member.value for member in Keyword if member is not Keyword.VARIANT)


def is_comparable_seq_field(field: DataField) -> bool:
    """Whether ``field`` can serve as a ``sequence.field`` for pypaimon's
    atomic comparator: it must be an ``AtomicType`` whose base type name is
    orderable. Complex types (ARRAY / MAP / ROW / ...) and the atomic-but-
    unorderable VARIANT both return ``False``. Used by the read-builder
    guard to reject unsupported sequence fields up front.
    """
    return (isinstance(field.type, AtomicType)
            and _base_type_name(field) in _COMPARABLE_TYPE_NAMES)