base.py

# Copyright (C) 2010, 2011 Sebastian Thiel (byronimo@gmail.com) and contributors
#
# This module is part of GitDB and is released under
# the New BSD License: http://www.opensource.org/licenses/bsd-license.php
"""Module with basic data structures - they are designed to be lightweight and fast"""
from util import (
    bin_to_hex,
    zlib
)

from fun import (
    type_id_to_type_map,
    type_to_type_id_map
)

__all__ = ('OInfo', 'OPackInfo', 'ODeltaPackInfo',
           'OStream', 'OPackStream', 'ODeltaPackStream',
           'IStream', 'InvalidOInfo', 'InvalidOStream')

#{ ODB Bases


class OInfo(tuple):

    """Carries information about an object in an ODB, provding information 
    about the binary sha of the object, the type_string as well as the uncompressed size
    in bytes.

    It can be accessed using tuple notation and using attribute access notation::

        assert dbi[0] == dbi.binsha
        assert dbi[1] == dbi.type
        assert dbi[2] == dbi.size

    The type is designed to be as lighteight as possible."""
    __slots__ = tuple()

    def __new__(cls, sha, type, size):
        return tuple.__new__(cls, (sha, type, size))

    def __init__(self, *args):
        tuple.__init__(self)

    #{ Interface
    @property
    def binsha(self):
        """:return: our sha as binary, 20 bytes"""
        return self[0]

    @property
    def hexsha(self):
        """:return: our sha, hex encoded, 40 bytes"""
        return bin_to_hex(self[0])

    @property
    def type(self):
        return self[1]

    @property
    def type_id(self):
        return type_to_type_id_map[self[1]]

    @property
    def size(self):
        return self[2]
    #} END interface


class OPackInfo(tuple):

    """As OInfo, but provides a type_id property to retrieve the numerical type id, and 
    does not include a sha.

    Additionally, the pack_offset is the absolute offset into the packfile at which 
    all object information is located. The data_offset property points to the abosolute
    location in the pack at which that actual data stream can be found."""
    __slots__ = tuple()

    def __new__(cls, packoffset, type, size):
        return tuple.__new__(cls, (packoffset, type, size))

    def __init__(self, *args):
        tuple.__init__(self)

    #{ Interface

    @property
    def pack_offset(self):
        return self[0]

    @property
    def type(self):
        return type_id_to_type_map[self[1]]

    @property
    def type_id(self):
        return self[1]

    @property
    def size(self):
        return self[2]

    #} END interface


class ODeltaPackInfo(OPackInfo):

    """Adds delta specific information, 
    Either the 20 byte sha which points to some object in the database, 
    or the negative offset from the pack_offset, so that pack_offset - delta_info yields
    the pack offset of the base object"""
    __slots__ = tuple()

    def __new__(cls, packoffset, type, size, delta_info):
        return tuple.__new__(cls, (packoffset, type, size, delta_info))

    #{ Interface
    @property
    def delta_info(self):
        return self[3]
    #} END interface


class OStream(OInfo):

    """Base for object streams retrieved from the database, providing additional 
    information about the stream.
    Generally, ODB streams are read-only as objects are immutable"""
    __slots__ = tuple()

    def __new__(cls, sha, type, size, stream, *args, **kwargs):
        """Helps with the initialization of subclasses"""
        return tuple.__new__(cls, (sha, type, size, stream))

    def __init__(self, *args, **kwargs):
        tuple.__init__(self)

    #{ Stream Reader Interface

    def read(self, size=-1):
        return self[3].read(size)

    @property
    def stream(self):
        return self[3]

    #} END stream reader interface


class ODeltaStream(OStream):

    """Uses size info of its stream, delaying reads"""

    def __new__(cls, sha, type, size, stream, *args, **kwargs):
        """Helps with the initialization of subclasses"""
        return tuple.__new__(cls, (sha, type, size, stream))

    #{ Stream Reader Interface

    @property
    def size(self):
        return self[3].size

    #} END stream reader interface


class OPackStream(OPackInfo):

    """Next to pack object information, a stream outputting an undeltified base object
    is provided"""
    __slots__ = tuple()

    def __new__(cls, packoffset, type, size, stream, *args):
        """Helps with the initialization of subclasses"""
        return tuple.__new__(cls, (packoffset, type, size, stream))

    #{ Stream Reader Interface
    def read(self, size=-1):
        return self[3].read(size)

    @property
    def stream(self):
        return self[3]
    #} END stream reader interface


class ODeltaPackStream(ODeltaPackInfo):

    """Provides a stream outputting the uncompressed offset delta information"""
    __slots__ = tuple()

    def __new__(cls, packoffset, type, size, delta_info, stream):
        return tuple.__new__(cls, (packoffset, type, size, delta_info, stream))

    #{ Stream Reader Interface
    def read(self, size=-1):
        return self[4].read(size)

    @property
    def stream(self):
        return self[4]
    #} END stream reader interface


class IStream(list):

    """Represents an input content stream to be fed into the ODB. It is mutable to allow 
    the ODB to record information about the operations outcome right in this instance.

    It provides interfaces for the OStream and a StreamReader to allow the instance
    to blend in without prior conversion.

    The only method your content stream must support is 'read'"""
    __slots__ = tuple()

    def __new__(cls, type, size, stream, sha=None):
        return list.__new__(cls, (sha, type, size, stream, None))

    def __init__(self, type, size, stream, sha=None):
        list.__init__(self, (sha, type, size, stream, None))

    #{ Interface
    @property
    def hexsha(self):
        """:return: our sha, hex encoded, 40 bytes"""
        return bin_to_hex(self[0])

    def _error(self):
        """:return: the error that occurred when processing the stream, or None"""
        return self[4]

    def _set_error(self, exc):
        """Set this input stream to the given exc, may be None to reset the error"""
        self[4] = exc

    error = property(_error, _set_error)

    #} END interface

    #{ Stream Reader Interface

    def read(self, size=-1):
        """Implements a simple stream reader interface, passing the read call on 
            to our internal stream"""
        return self[3].read(size)

    #} END stream reader interface

    #{  interface

    def _set_binsha(self, binsha):
        self[0] = binsha

    def _binsha(self):
        return self[0]

    binsha = property(_binsha, _set_binsha)

    def _type(self):
        return self[1]

    def _set_type(self, type):
        self[1] = type

    type = property(_type, _set_type)

    def _size(self):
        return self[2]

    def _set_size(self, size):
        self[2] = size

    size = property(_size, _set_size)

    def _stream(self):
        return self[3]

    def _set_stream(self, stream):
        self[3] = stream

    stream = property(_stream, _set_stream)

    #} END odb info interface


class InvalidOInfo(tuple):

    """Carries information about a sha identifying an object which is invalid in 
    the queried database. The exception attribute provides more information about
    the cause of the issue"""
    __slots__ = tuple()

    def __new__(cls, sha, exc):
        return tuple.__new__(cls, (sha, exc))

    def __init__(self, sha, exc):
        tuple.__init__(self, (sha, exc))

    @property
    def binsha(self):
        return self[0]

    @property
    def hexsha(self):
        return bin_to_hex(self[0])

    @property
    def error(self):
        """:return: exception instance explaining the failure"""
        return self[1]


class InvalidOStream(InvalidOInfo):

    """Carries information about an invalid ODB stream"""
    __slots__ = tuple()

#} END ODB Bases