import hashlib
import mimetypes

MEDIA_EXTS_CACHE = []


def media_exts():
    """ List of media file extensions from local system mimetypes """
    if not MEDIA_EXTS_CACHE:
        mimetypes.init()
        for ext in mimetypes.types_map:
            if mimetypes.types_map[ext].split('/')[0] in ('audio', 'video'):
                MEDIA_EXTS_CACHE.append(ext)
    return MEDIA_EXTS_CACHE


def is_media_file_ext(ext):
    """ Is the given extension a media file extension according to the local system mimetypes """
    return ext.lower().lstrip('.') in [e.lower().lstrip('.') for e in media_exts()]


def hash_file(filename):
    """ return a SHA256 hash for the given file """
    h = hashlib.sha256()
    b = bytearray(128 * 1024)
    mv = memoryview(b)
    with open(filename, 'rb', buffering=0) as f:
        for n in iter(lambda: f.readinto(mv), 0):
            h.update(mv[:n])
    return h.hexdigest()


def is_subdir_of(subject, other):
    """ is subject a subdirectory of other """
    if not subject.parent:
        return False
    if subject.parent == other:
        return True
    return is_subdir_of(subject.parent, other)