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# to you under the Apache License, Version 2.0 (the
# "License"); you may not use this file except in compliance
# with the License.  You may obtain a copy of the License at
#
#   http://www.apache.org/licenses/LICENSE-2.0
#
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# KIND, either express or implied.  See the License for the
# specific language governing permissions and limitations
# under the License.

"""
Provides compatibility patches for fastavro on Python 3.6,
specifically for handling zstd-compressed Avro files.

The main issue addressed is:
- On Python 3.6, fastavro's zstd decompression may fail with:
  "zstd.ZstdError: could not determine content size in frame header"
  
This module patches fastavro's zstd handling to use a more compatible
decompression method that works on Python 3.6.
"""

import sys

_patch_applied = False


def _apply_zstd_patch():
    global _patch_applied
    if _patch_applied or sys.version_info[:2] != (3, 6):
        return

    try:
        import fastavro._read as fastavro_read
        import zstandard as zstd
        from io import BytesIO
    except (ImportError, AttributeError):
        return

    def _fixed_zstandard_read_block(decoder):
        from fastavro._read import read_long
        
        length = read_long(decoder)
        
        if hasattr(decoder, 'read_fixed'):
            data = decoder.read_fixed(length)
        elif hasattr(decoder, 'read'):
            data = decoder.read(length)
        else:
            from fastavro._read import read_fixed
            data = read_fixed(decoder, length)

        decompressor = zstd.ZstdDecompressor()
        with decompressor.stream_reader(BytesIO(data)) as reader:
            decompressed = reader.read()
            return BytesIO(decompressed)

    if hasattr(fastavro_read, 'BLOCK_READERS'):
        block_readers = fastavro_read.BLOCK_READERS
        block_readers['zstandard'] = _fixed_zstandard_read_block
        block_readers['zstd'] = _fixed_zstandard_read_block
        _patch_applied = True


if sys.version_info[:2] == (3, 6):
    try:
        _apply_zstd_patch()
    except ImportError:
        pass
