import io
import struct
import olefile
from .record_decoder import ParseError, binary_records, ascii_records, detect_format

MAX_STREAM_BYTES = 32 * 1024 * 1024
MAX_TOTAL_BYTES = 64 * 1024 * 1024

def read_document(data):
    fmt=detect_format(data)
    if fmt=='ascii':
        return fmt,[],ascii_records(data),[]
    try:
        with olefile.OleFileIO(io.BytesIO(data),raise_defects=olefile.DEFECT_INCORRECT) as ole:
            entries=ole.listdir(streams=True,storages=False)
            if len(entries)>256: raise ParseError('Too many OLE streams')
            streams=[{'name':'/'.join(p),'size':ole.get_size(p)} for p in entries]
            if any(s['size']>MAX_STREAM_BYTES for s in streams) or sum(s['size'] for s in streams)>MAX_TOTAL_BYTES:
                raise ParseError('OLE stream size limit exceeded')
            if not ole.exists('FileHeader') or ole.get_type('FileHeader')!=2:
                raise ParseError('OLE container has no FileHeader stream')
            main=binary_records(ole.openstream('FileHeader').read(),'FileHeader')
            extra=[]
            if ole.exists('Additional') and ole.get_type('Additional')==2:
                extra=binary_records(ole.openstream('Additional').read(),'Additional')
            return fmt,streams,main,extra
    except (OSError,IOError,ValueError,IndexError,struct.error) as exc:
        raise ParseError(f'Invalid OLE schematic: {exc}') from exc