"""The FAT format analyzer helper implementation."""

from dfvfs.analyzer import analyzer
from dfvfs.analyzer import analyzer_helper
from dfvfs.analyzer import specification
from dfvfs.lib import definitions


class FATAnalyzerHelper(analyzer_helper.AnalyzerHelper):
    """FAT analyzer helper."""

    FORMAT_CATEGORIES = frozenset([definitions.FORMAT_CATEGORY_FILE_SYSTEM])

    TYPE_INDICATOR = definitions.TYPE_INDICATOR_FAT

    def GetFormatSpecification(self):
        """Retrieves the format specification.

        Returns:
          FormatSpecification: format specification or None if the format cannot
              be defined by a specification object.
        """
        format_specification = specification.FormatSpecification(self.type_indicator)

        # Boot sector signature.
        format_specification.AddNewSignature(b"\x55\xaa", offset=510)

        # FAT-12 and FAT-16 file system hint.
        format_specification.AddNewSignature(b"FAT12   ", offset=54)
        format_specification.AddNewSignature(b"FAT16   ", offset=54)

        # FAT-32 file system hint.
        format_specification.AddNewSignature(b"FAT32   ", offset=82)

        # exFAT file system signature.
        format_specification.AddNewSignature(b"EXFAT   ", offset=3)

        return format_specification

    def IsEnabled(self):
        """Determines if the analyzer helper is enabled.

        Returns:
          bool: True if the analyzer helper is enabled.
        """
        return definitions.PREFERRED_FAT_BACK_END == self.TYPE_INDICATOR


analyzer.Analyzer.RegisterHelper(FATAnalyzerHelper())
