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"""DNS nodes.  A node is a set of rdatasets."""

import StringIO

import dns.rdataset
import dns.rdatatype
import dns.renderer

class Node(object):
    """A DNS node.
    
    A node is a set of rdatasets

    @ivar rdatasets: the node's rdatasets
    @type rdatasets: list of dns.rdataset.Rdataset objects"""

    __slots__ = ['rdatasets']
    
    def __init__(self):
        """Initialize a DNS node.
        """
        
        self.rdatasets = [];

    def to_text(self, name, **kw):
        """Convert a node to text format.

        Each rdataset at the node is printed.  Any keyword arguments
        to this method are passed on to the rdataset's to_text() method.
        @param name: the owner name of the rdatasets
        @type name: dns.name.Name object
        @rtype: string
        """
        
        s = StringIO.StringIO()
        for rds in self.rdatasets:
            print >> s, rds.to_text(name, **kw)
        return s.getvalue()[:-1]

    def __repr__(self):
        return '<DNS node ' + str(id(self)) + '>'
    
    def __eq__(self, other):
        """Two nodes are equal if they have the same rdatasets.

        @rtype: bool
        """
        #
        # This is inefficient.  Good thing we don't need to do it much.
        #
        for rd in self.rdatasets:
            if rd not in other.rdatasets:
                return False
        for rd in other.rdatasets:
            if rd not in self.rdatasets:
                return False
        return True

    def __ne__(self, other):
        return not self.__eq__(other)
        
    def __len__(self):
        return len(self.rdatasets)

    def __iter__(self):
        return iter(self.rdatasets)

    def find_rdataset(self, rdclass, rdtype, covers=dns.rdatatype.NONE,
                      create=False):
        """Find an rdataset matching the specified properties in the
        current node.

        @param rdclass: The class of the rdataset
        @type rdclass: int
        @param rdtype: The type of the rdataset
        @type rdtype: int
        @param covers: The covered type.  Usually this value is
        dns.rdatatype.NONE, but if the rdtype is dns.rdatatype.SIG or
        dns.rdatatype.RRSIG, then the covers value will be the rdata
        type the SIG/RRSIG covers.  The library treats the SIG and RRSIG
        types as if they were a family of
        types, e.g. RRSIG(A), RRSIG(NS), RRSIG(SOA).  This makes RRSIGs much
        easier to work with than if RRSIGs covering different rdata
        types were aggregated into a single RRSIG rdataset.
        @type covers: int
        @param create: If True, create the rdataset if it is not found.
        @type create: bool
        @raises KeyError: An rdataset of the desired type and class does
        not exist and I{create} is not True.
        @rtype: dns.rdataset.Rdataset object
        """

        for rds in self.rdatasets:
            if rds.match(rdclass, rdtype, covers):
                return rds
        if not create:
            raise KeyError
        rds = dns.rdataset.Rdataset(rdclass, rdtype)
        self.rdatasets.append(rds)
        return rds

    def get_rdataset(self, rdclass, rdtype, covers=dns.rdatatype.NONE,
                     create=False):
        """Get an rdataset matching the specified properties in the
        current node.

        None is returned if an rdataset of the specified type and
        class does not exist and I{create} is not True.

        @param rdclass: The class of the rdataset
        @type rdclass: int
        @param rdtype: The type of the rdataset
        @type rdtype: int
        @param covers: The covered type.
        @type covers: int
        @param create: If True, create the rdataset if it is not found.
        @type create: bool
        @rtype: dns.rdataset.Rdataset object or None
        """

        try:
            rds = self.find_rdataset(rdclass, rdtype, covers, create)
        except KeyError:
            rds = None
        return rds

    def delete_rdataset(self, rdclass, rdtype, covers=dns.rdatatype.NONE):
        """Delete the rdataset matching the specified properties in the
        current node.

        If a matching rdataset does not exist, it is not an error.

        @param rdclass: The class of the rdataset
        @type rdclass: int
        @param rdtype: The type of the rdataset
        @type rdtype: int
        @param covers: The covered type.
        @type covers: int
        """

        rds = self.get_rdataset(rdclass, rdtype, covers)
        if not rds is None:
            self.rdatasets.remove(rds)

    def replace_rdataset(self, replacement):
        """Replace an rdataset.
        
        It is not an error if there is no rdataset matching I{replacement}.

        Ownership of the I{replacement} object is transferred to the node;
        in other words, this method does not store a copy of I{replacement}
        at the node, it stores I{replacement} itself.
        """

        self.delete_rdataset(replacement.rdclass, replacement.rdtype,
                             replacement.covers)
        self.rdatasets.append(replacement)