# Source code for tables.link

    # -*- coding: utf-8 -*-

    ########################################################################
    #
    # License: BSD
    # Created: November 25, 2009
    # Author: Francesc Alted - faltet@pytables.com
    #
    # $Id$
    #
    ########################################################################

    """Create links in the HDF5 file.

    This module implements containers for soft and external links.  Hard
    links doesn't need a container as such as they are the same as regular
    nodes (groups or leaves).

    Classes:

        SoftLink
        ExternalLink

    Functions:

    Misc variables:

    """

    import os
    import tables
    from tables import linkextension
    from tables.node import Node
    from tables.utils import lazyattr
    from tables.attributeset import AttributeSet
    import tables.file
    from tables._past import previous_api, previous_api_property

    def _g_get_link_class(parent_id, name):
        """Guess the link class."""

        return linkextension._get_link_class(parent_id, name)

    _g_getLinkClass = previous_api(_g_get_link_class)

    class Link(Node):
        """Abstract base class for all PyTables links.

        A link is a node that refers to another node.  The Link class inherits from
        Node class and the links that inherits from Link are SoftLink and
        ExternalLink.  There is not a HardLink subclass because hard links behave
        like a regular Group or Leaf.  Contrarily to other nodes, links cannot have
        HDF5 attributes.  This is an HDF5 library limitation that might be solved
        in future releases.

        See :ref:`LinksTutorial` for a small tutorial on how to work with links.

        .. rubric:: Link attributes

        .. attribute:: target

            The path string to the pointed node.

        """

        # Properties
        @lazyattr
        def _v_attrs(self):
            """
            A *NoAttrs* instance replacing the typical *AttributeSet* instance of
            other node objects.  The purpose of *NoAttrs* is to make clear that
            HDF5 attributes are not supported in link nodes.
            """
            class NoAttrs(AttributeSet):
                def __getattr__(self, name):
                    raise KeyError("you cannot get attributes from this "
                                   "`%s` instance" % self.__class__.__name__)

                def __setattr__(self, name, value):
                    raise KeyError("you cannot set attributes to this "
                                   "`%s` instance" % self.__class__.__name__)

                def _g_close(self):
                    pass
            return NoAttrs(self)

        def __init__(self, parentnode, name, target=None, _log=False):
            self._v_new = target is not None
            self.target = target
            """The path string to the pointed node."""

            super(Link, self).__init__(parentnode, name, _log)

        # Public and tailored versions for copy, move, rename and remove methods
        def copy(self, newparent=None, newname=None,
                 overwrite=False, createparents=False):
            """Copy this link and return the new one.

            See :meth:`Node._f_copy` for a complete explanation of the arguments.
            Please note that there is no recursive flag since links do not have
            child nodes.

            """

            newnode = self._f_copy(newparent=newparent, newname=newname,
                                   overwrite=overwrite,
                                   createparents=createparents)
            # Insert references to a `newnode` via `newname`
            newnode._v_parent._g_refnode(newnode, newname, True)
            return newnode

        def move(self, newparent=None, newname=None, overwrite=False):
            """Move or rename this link.

            See :meth:`Node._f_move` for a complete explanation of the arguments.

            """

            return self._f_move(newparent=newparent, newname=newname,
                                overwrite=overwrite)

        def remove(self):
            """Remove this link from the hierarchy."""

            return self._f_remove()

        def rename(self, newname=None, overwrite=False):
            """Rename this link in place.

            See :meth:`Node._f_rename` for a complete explanation of the arguments.

            """

            return self._f_rename(newname=newname, overwrite=overwrite)

        def __repr__(self):
            return str(self)

    class SoftLink(linkextension.SoftLink, Link):
        """Represents a soft link (aka symbolic link).

        A soft link is a reference to another node in the *same* file hierarchy.
        Provided that the target node exists, its attributes and methods can be
        accessed directly from the softlink using the normal `.` syntax.

        Softlinks also have the following public methods/attributes:

            * `target`
            * `dereference()`
            * `copy()`
            * `move()`
            * `remove()`
            * `rename()`
            * `is_dangling()`

        Note that these will override any correspondingly named methods/attributes
        of the target node.

        For backwards compatibility, it is also possible to obtain the target node
        via the `__call__()` special method (this action is called *dereferencing*;
        see below)

        Examples
        --------

        ::
            >>> f = tables.open_file('/tmp/test_softlink.h5', 'w')
            >>> a = f.create_array('/', 'A', np.arange(10))
            >>> link_a = f.create_soft_link('/', 'link_A', target='/A')

            # transparent read/write access to a softlinked node
            >>> link_a[0] = -1
            >>> print(link_a[:], link_a.dtype)
            (array([-1,  1,  2,  3,  4,  5,  6,  7,  8,  9]), dtype('int64'))

            # dereferencing a softlink using the __call__() method
            >>> print(link_a() is a)
            True

            # SoftLink.remove() overrides Array.remove()
            >>> link_a.remove()
            >>> print(link_a)
            <closed tables.link.SoftLink at 0x7febe97186e0>
            >>> print(a[:], a.dtype)
            (array([-1,  1,  2,  3,  4,  5,  6,  7,  8,  9]), dtype('int64'))

        """

        # Class identifier.
        _c_classid = 'SOFTLINK'

        _c_classId = previous_api_property('_c_classid')

        # attributes with these names/prefixes are treated as attributes of the
        # SoftLink rather than the target node
        _link_attrnames = ('target', 'dereference', 'is_dangling', 'copy', 'move',
                           'remove', 'rename', '__init__', '__str__', '__repr__',
                           '__class__', '__dict__')
        _link_attrprefixes = ('_f_', '_c_', '_g_', '_v_')

        def __call__(self):
            """Dereference `self.target` and return the object.

            Examples
            --------

            ::

                >>> f=tables.open_file('data/test.h5')
                >>> print(f.root.link0)
                /link0 (SoftLink) -> /another/path
                >>> print(f.root.link0())
                /another/path (Group) ''

            """
            return self.dereference()

        def dereference(self):

            if self._v_isopen:
                target = self.target
                # Check for relative pathnames
                if not self.target.startswith('/'):
                    target = self._v_parent._g_join(self.target)
                return self._v_file._get_node(target)
            else:
                return None

        def __getattribute__(self, attrname):

            # get attribute of the SoftLink itself
            if (attrname in SoftLink._link_attrnames
                or attrname[:3] in SoftLink._link_attrprefixes):
                return object.__getattribute__(self, attrname)

            # get attribute of the target node
            elif not self._v_isopen:
                raise tables.ClosedNodeError('the node object is closed')
            elif self.is_dangling():
                return None
            else:
                target_node = self.dereference()
                try:
                    # __getattribute__() fails to get children of Groups
                    return target_node.__getattribute__(attrname)
                except AttributeError:
                    # some node classes (e.g. Array) don't implement __getattr__()
                    return target_node.__getattr__(attrname)

        def __setattr__(self, attrname, value):

            # set attribute of the SoftLink itself
            if (attrname in SoftLink._link_attrnames
                or attrname[:3] in SoftLink._link_attrprefixes):
                object.__setattr__(self, attrname, value)

            # set attribute of the target node
            elif not self._v_isopen:
                raise tables.ClosedNodeError('the node object is closed')
            elif self.is_dangling():
                raise ValueError("softlink target does not exist")
            else:
                self.dereference().__setattr__(attrname, value)

        def __getitem__(self, key):
            """__getitem__ must be defined in the SoftLink class in order for array
            indexing syntax to work"""

            if not self._v_isopen:
                raise tables.ClosedNodeError('the node object is closed')
            elif self.is_dangling():
                raise ValueError("softlink target does not exist")
            else:
                return self.dereference().__getitem__(key)

        def __setitem__(self, key, value):
            """__setitem__ must be defined in the SoftLink class in order for array
            indexing syntax to work"""

            if not self._v_isopen:
                raise tables.ClosedNodeError('the node object is closed')
            elif self.is_dangling():
                raise ValueError("softlink target does not exist")
            else:
                self.dereference().__setitem__(key, value)

        def is_dangling(self):
            return not (self.dereference() in self._v_file)

        def __str__(self):
            """Return a short string representation of the link.

            Examples
            --------

            ::

                >>> f=tables.open_file('data/test.h5')
                >>> print(f.root.link0)
                /link0 (SoftLink) -> /path/to/node

            """

            classname = self.__class__.__name__
            target = str(self.target)
            # Check for relative pathnames
            if not self.target.startswith('/'):
                target = self._v_parent._g_join(self.target)
            if self._v_isopen:
                closed = ""
            else:
                closed = "closed "
            if target not in self._v_file:
                dangling = " (dangling)"
            else:
                dangling = ""
            return "%s%s (%s) -> %s%s" % (closed, self._v_pathname, classname,
                                          self.target, dangling)

    class ExternalLink(linkextension.ExternalLink, Link):
        """Represents an external link.

        An external link is a reference to a node in *another* file.
        Getting access to the pointed node (this action is called
        *dereferencing*) is done via the :meth:`__call__` special method
        (see below).

        .. rubric:: ExternalLink attributes

        .. attribute:: extfile

            The external file handler, if the link has been dereferenced.
            In case the link has not been dereferenced yet, its value is
            None.

        """

        # Class identifier.
        _c_classid = 'EXTERNALLINK'

        _c_classId = previous_api_property('_c_classid')

        def __init__(self, parentnode, name, target=None, _log=False):
            self.extfile = None
            """The external file handler, if the link has been dereferenced.
            In case the link has not been dereferenced yet, its value is
            None."""
            super(ExternalLink, self).__init__(parentnode, name, target, _log)

        def _get_filename_node(self):
            """Return the external filename and nodepath from `self.target`."""

            # This is needed for avoiding the 'C:\\file.h5' filepath notation
            filename, target = self.target.split(':/')
            return filename, '/' + target

        def __call__(self, **kwargs):
            """Dereference self.target and return the object.

            You can pass all the arguments supported by the :func:`open_file`
            function (except filename, of course) so as to open the referenced
            external file.

            Examples
            --------

            ::

                >>> f=tables.open_file('data1/test1.h5')
                >>> print(f.root.link2)
                /link2 (ExternalLink) -> data2/test2.h5:/path/to/node
                >>> plink2 = f.root.link2('a')  # open in 'a'ppend mode
                >>> print(plink2)
                /path/to/node (Group) ''
                >>> print(plink2._v_filename)
                'data2/test2.h5'        # belongs to referenced file

            """

            filename, target = self._get_filename_node()

            if not os.path.isabs(filename):
                # Resolve the external link with respect to the this
                # file's directory.  See #306.
                base_directory = os.path.dirname(self._v_file.filename)
                filename = os.path.join(base_directory, filename)

            if self.extfile is None or not self.extfile.isopen:
                self.extfile = tables.open_file(filename, **kwargs)
            else:
                # XXX: implement better consistency checks
                assert self.extfile.filename == filename
                assert self.extfile.mode == kwargs.get('mode', 'r')

            return self.extfile._get_node(target)

        def umount(self):
            """Safely unmount self.extfile, if opened."""

            extfile = self.extfile
            # Close external file, if open
            if extfile is not None and extfile.isopen:
                extfile.close()
                self.extfile = None

        def _f_close(self):
            """Especific close for external links."""

            self.umount()
            super(ExternalLink, self)._f_close()

        def __str__(self):
            """Return a short string representation of the link.

            Examples
            --------

            ::

                >>> f=tables.open_file('data1/test1.h5')
                >>> print(f.root.link2)
                /link2 (ExternalLink) -> data2/test2.h5:/path/to/node

            """

            classname = self.__class__.__name__
            return "%s (%s) -> %s" % (self._v_pathname, classname, self.target)

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