# Source code for canlib.kvadblib.node

    import ctypes as ct

    from .attribute import Attribute
    from .exceptions import KvdNoAttribute, KvdWrongOwner
    from .enums import AttributeOwner
    from .wrapper import dll

    class Node(object):
        """Database Node"""
        def __init__(self, db, handle, name=None, comment=None):
            self._handle = handle
            self._db = db  # used to lookup attribute definitions
            if name is not None:
                self.name = name
            if comment is not None:
                self.comment = comment

        def __eq__(self, other):
            if self.name != other.name:
                return False
            if self.comment != other.comment:
                return False
            return True

        def __ne__(self, other):
            return not self == other

        def __repr__(self):
            return ("Node(name='{}, comment={}')".format(self.name, self.comment))

        def attributes(self):
            """Return a generator over all message attributes."""
            ah = None
            nah = ct.c_void_p()
            try:
                dll.kvaDbGetFirstNodeAttribute(self._handle, ct.byref(nah))
            except KvdNoAttribute:
                return
            while nah.value is not None:
                ah, nah = nah, ct.c_void_p()
                yield Attribute(self, ah)
                try:
                    dll.kvaDbGetNextAttribute(ah, ct.byref(nah))
                except KvdNoAttribute:
                    return

        def delete_attribute(self, name):
            """Delete attribute from node."""
            ah = ct.c_void_p()
            dll.kvaDbGetNodeAttributeByName(
                self._handle, name.encode('utf-8'), ct.byref(ah))
            dll.kvaDbDeleteNodeAttribute(self._handle, ah)

        def get_attribute_value(self, name):
            """Return attribute value

            If the attribute is not set on the message, we return the attribute
            definition default value.

            """
            ah = ct.c_void_p()

            # Try and find attribute on node
            try:
                dll.kvaDbGetNodeAttributeByName(
                    self._handle, name.encode('utf-8'), ct.byref(ah))
            except KvdNoAttribute:
                # Lookup the attribute definition
                atr_def = self._db.get_attribute_definition_by_name(name)

                # only attributes with node as owner are valid, name is also
                # unique accross all attributes so it is enough to check this one
                # for owner
                if atr_def.owner != AttributeOwner.NODE:
                    raise KvdWrongOwner()
                value = atr_def.definition.default
            else:
                attribute = Attribute(self._db, ah)
                value = attribute.value
            return value

        def set_attribute_value(self, name, value):
            """Set value of attribute 'name' on node.

            If no attribute called 'name' is set on node, attach a node
            attribute from the database attribute definition first.

            """
            ah = ct.c_void_p()

            # Try and find attribute on node
            try:
                dll.kvaDbGetNodeAttributeByName(
                    self._handle, name.encode('utf-8'), ct.byref(ah))
            except KvdNoAttribute:
                # If no attribute was found, lookup the attribute definition and
                # add a new attribute to the node
                attrib_def = self._db.get_attribute_definition_by_name(name)
                dll.kvaDbAddNodeAttribute(
                    self._handle, attrib_def._handle, ct.byref(ah))
            # Set the value in the node attribute
            attribute = Attribute(self._db, ah)
            attribute.value = value

        @property
        def comment(self):
            """`str`: The node's comment"""
            buf = ct.create_string_buffer(255)
            dll.kvaDbGetNodeComment(self._handle, buf, ct.sizeof(buf))
            return buf.value.decode('utf-8')

        @comment.setter
        def comment(self, value):
            dll.kvaDbSetNodeComment(self._handle, value.encode('utf-8'))

        @property
        def name(self):
            """`str`: The node's name"""
            buf = ct.create_string_buffer(255)
            dll.kvaDbGetNodeName(self._handle, buf, ct.sizeof(buf))
            return buf.value.decode('utf-8')

        @name.setter
        def name(self, value):
            dll.kvaDbSetNodeName(self._handle, value.encode('utf-8'))