# Copyright 2010-2025 The pygit2 contributors
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from collections.abc import Callable

from ._pygit2 import FilterSource


class Filter:
    """
    Base filter class to be used with libgit2 filters.

    Inherit from this class and override the `check()`, `write()` and `close()`
    methods to define a filter which can then be registered via
    `pygit2.filter_register()`.

    A new Filter instance will be instantiated for each stream which needs to
    be filtered. For each stream, filter methods will be called in this order:

        - `check()`
        - `write()` (may be called multiple times)
        - `close()`

    Filtered output data should be written to the next filter in the chain
    during `write()` and `close()` via the `write_next` method. All output data
    must be written to the next filter before returning from `close()`.

    If a filter is dependent on reading the complete input data stream, the
    filter should only write output data in `close()`.
    """

    #: Space-separated string list of attributes to be used in `check()`
    attributes: str = ''

    @classmethod
    def nattrs(cls) -> int:
        return len(cls.attributes.split())

    def check(self, src: FilterSource, attr_values: list[str | None]) -> None:
        """
        Check whether this filter should be applied to the given source.

        `check` will be called once per stream.

        If `Passthrough` is raised, the filter will not be applied.

        Parameters:

        src: The source of the filtered blob.

        attr_values: The values of each attribute for the blob being filtered.
            `attr_values` will be a sorted list containing attributes in the
            order they were defined in ``cls.attributes``.
        """

    def write(
        self, data: bytes, src: FilterSource, write_next: Callable[[bytes], None]
    ) -> None:
        """
        Write input `data` to this filter.

        `write()` may be called multiple times per stream.

        Parameters:

        data: Input data.

        src: The source of the filtered blob.

        write_next: The ``write()`` method of the next filter in the chain.
            Filtered output data should be written to `write_next` whenever it is
            available.
        """
        write_next(data)

    def close(self, write_next: Callable[[bytes], None]) -> None:
        """
        Close this filter.

        `close()` will be called once per stream whenever all writes() to this
        stream have been completed.

        Parameters:
            write_next: The ``write()`` method of the next filter in the chain.
                Any remaining filtered output data must be written to
                `write_next` before returning.
        """
