#!/usr/bin/python
# Copyright (C) 2013,2015  Codethink Limited
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; version 2 of the License.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program.  If not, see <http://www.gnu.org/licenses/>.

'''A Morph deployment configuration extension to handle /etc/network/interfaces

This extension prepares /etc/network/interfaces with the interfaces specified
during deployment.

If no network configuration is provided, eth0 will be configured for DHCP
with the hostname of the system.
'''


import os
import sys
import cliapp

import morphlib


class SimpleNetworkError(morphlib.Error):
    '''Errors associated with simple network setup'''
    pass


class SimpleNetworkConfigurationExtension(cliapp.Application):
    '''Configure /etc/network/interfaces

    Reading NETWORK_CONFIG, this extension sets up /etc/network/interfaces.
    '''

    def process_args(self, args):
        network_config = os.environ.get(
            "NETWORK_CONFIG", "lo:loopback;eth0:dhcp,hostname=$(hostname)")

        self.status(msg="Processing NETWORK_CONFIG=%(nc)s", nc=network_config)

        stanzas = self.parse_network_stanzas(network_config)
        iface_file = self.generate_iface_file(stanzas)

        with open(os.path.join(args[0], "etc/network/interfaces"), "w") as f:
            f.write(iface_file)

    def generate_iface_file(self, stanzas):
        """Generate an interfaces file from the provided stanzas.

        The interfaces will be sorted by name, with loopback sorted first.
        """

        def cmp_iface_names(a, b):
            a = a['name']
            b = b['name']
            if a == "lo":
                return -1
            elif b == "lo":
                return 1
            else:
                return cmp(a,b)

        return "\n".join(self.generate_iface_stanza(stanza)
                         for stanza in sorted(stanzas, cmp=cmp_iface_names))

    def generate_iface_stanza(self, stanza):
        """Generate an interfaces stanza from the provided data."""

        name = stanza['name']
        itype = stanza['type']
        lines  = ["auto %s" % name, "iface %s inet %s" % (name, itype)]
        lines += ["    %s %s" % elem for elem in stanza['args'].items()]
        lines += [""]
        return "\n".join(lines)


    def parse_network_stanzas(self, config):
        """Parse a network config environment variable into stanzas.

        Network config stanzas are semi-colon separated.
        """

        return [self.parse_network_stanza(s) for s in config.split(";")]

    def parse_network_stanza(self, stanza):
        """Parse a network config stanza into name, type and arguments.

        Each stanza is of the form name:type[,arg=value]...

        For example:
                   lo:loopback
                   eth0:dhcp
                   eth1:static,address=10.0.0.1,netmask=255.255.0.0
        """
        elements = stanza.split(",")
        lead = elements.pop(0).split(":")
        if len(lead) != 2:
            raise SimpleNetworkError("Stanza '%s' is missing its type" %
                                     stanza)
        iface = lead[0]
        iface_type = lead[1]

        if iface_type not in ['loopback', 'static', 'dhcp']:
            raise SimpleNetworkError("Stanza '%s' has unknown interface type"
                                     " '%s'" % (stanza, iface_type))

        argpairs = [element.split("=", 1) for element in elements]
        output_stanza = { "name": iface,
                          "type": iface_type,
                          "args": {} }
        for argpair in argpairs:
            if len(argpair) != 2:
                raise SimpleNetworkError("Stanza '%s' has bad argument '%r'"
                                         % (stanza, argpair.pop(0)))
            if argpair[0] in output_stanza["args"]:
                raise SimpleNetworkError("Stanza '%s' has repeated argument"
                                         " %s" % (stanza, argpair[0]))
            output_stanza["args"][argpair[0]] = argpair[1]

        return output_stanza

    def status(self, **kwargs):
        '''Provide status output.

        The ``msg`` keyword argument is the actual message,
        the rest are values for fields in the message as interpolated
        by %.

        '''

        self.output.write('%s\n' % (kwargs['msg'] % kwargs))

SimpleNetworkConfigurationExtension().run()