symuid/symuid/library/cmus.py

import re
import sys


def _int_from_bytes_sys(data_bytes):
    return int.from_bytes(data_bytes, byteorder=sys.byteorder)


class Track:

    RESERVED_PAD_REGEX = rb'\xff{16,}'
    STRING_TERMINATOR = b'\x00'

    def __init__(self, cache_size, cache_bytes):
        """
        struct cache_entry {
            // size of this struct including size itself
            uint32_t size;
            int32_t play_count;
            int64_t mtime;
            int32_t duration;
            int32_t bitrate;
            int32_t bpm; // CACHE_VERSION 0x0d (commit 976c10d0e42c9ecd7389b28dd7c5b560a1702821)
            uint8_t _reserved[CACHE_ENTRY_RESERVED_SIZE];
            // filename, codec, codec_profile and N * (key, val)
            char strings[];
        };
        """
        assert len(cache_bytes) + 4 == cache_size
        self._play_count = _int_from_bytes_sys(cache_bytes[0:4])
        # self._mtime = _int_from_bytes_sys(cache_bytes[4:12])
        # self._duration_seconds = _int_from_bytes_sys(cache_bytes[12:16])
        # self._bitrate = _int_from_bytes_sys(cache_bytes[16:20])
        # self._bpm = _int_from_bytes_sys(cache_bytes[20:24])
        strings = re.split(self.RESERVED_PAD_REGEX, cache_bytes)[1] \
            .split(self.STRING_TERMINATOR)
        self._path = strings[0]

    @property
    def path(self):
        return self._path

    @property
    def play_count(self):
        return self._play_count


class Cache:

    # pylint: disable=too-few-public-methods

    FILE_PREFIX = b'CTC'
    VERSION_LENGTH = 1
    SUPPORTED_VERSIONS = [b'\x0c', b'\x0d']
    # always big endian, see cache_init()
    FLAGS_BYTEORDER = 'big'
    FLAGS_LENGTH = 4
    FLAG_64_BIT = 0x01

    HEADER_LENGTH = len(FILE_PREFIX) + VERSION_LENGTH + FLAGS_LENGTH

    def __init__(self, path):
        self._path = path
        with open(self._path, 'rb') as stream:
            # see cache.c cache_init()
            assert stream.read(len(self.FILE_PREFIX)) == self.FILE_PREFIX
            cache_version = stream.read(self.VERSION_LENGTH)
            assert cache_version in self.SUPPORTED_VERSIONS, cache_version
            flags = int.from_bytes(
                stream.read(self.FLAGS_LENGTH),
                byteorder=self.FLAGS_BYTEORDER,  # persistent
            )
            assert flags & self.FLAG_64_BIT
            # support no other flags
            assert flags & ~self.FLAG_64_BIT == 0, flags

    def get_tracks(self):
        with open(self._path, 'rb') as stream:
            stream.seek(self.HEADER_LENGTH)
            # size includes size itself
            while True:
                size = _int_from_bytes_sys(stream.read(4))
                if size == 0:
                    break
                yield Track(size, stream.read(size - 4))
                # see cache.c write_ti ALIGN
                stream.read((-size) % 8)