"""The Mac OS disk image (MODI) 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 MODIAnalyzerHelper(analyzer_helper.AnalyzerHelper):
    """Mac OS disk image (MODI) analyzer helper."""

    FORMAT_CATEGORIES = frozenset([definitions.FORMAT_CATEGORY_STORAGE_MEDIA_IMAGE])

    TYPE_INDICATOR = definitions.TYPE_INDICATOR_MODI

    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)

        # Sparse disk image (.sparseimage) signature in header.
        format_specification.AddNewSignature(b"sprs", offset=0)

        # Universal Disk Image Format (UDIF) (.dmg) signature in footer.
        format_specification.AddNewSignature(b"koly", offset=-512)

        return format_specification


analyzer.Analyzer.RegisterHelper(MODIAnalyzerHelper())
