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# Source code for fnss.netconfig.buffers

    """
    Provides function to assign and manipulate buffer sizes of network interfaces.
    """
    import networkx as nx
    from numpy import mean

    from fnss.units import capacity_units, time_units

    __all__ = [
        'set_buffer_sizes_bw_delay_prod',
        'set_buffer_sizes_link_bandwidth',
        'set_buffer_sizes_constant',
        'get_buffer_sizes',
        'clear_buffer_sizes',
               ]

    def set_buffer_sizes_bw_delay_prod(topology, buffer_unit='bytes',
                                       packet_size=1500):
        """
        Assign a buffer sizes proportionally to the product of link bandwidth and
        average network RTT. This is a rule of thumb according to which the buffers
        of Internet routers are generally configured.

        Parameters
        ----------
        topology : Topology or DirectedTopology
            The topology on which delays are applied.
        buffer_unit : string
            The unit of buffer sizes. Supported units are: *bytes* and *packets*
        packet_size : int, optional
            The average packet size (in bytes). It used only if *packets* is
            selected as buffer size to properly calculate buffer sizes given
            bandwidth and delay values.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.erdos_renyi_topology(50, 0.2)
        >>> fnss.set_capacities_constant(topology, 10, 'Mbps')
        >>> fnss.set_delays_constant(topology, 2, 'ms')
        >>> fnss.set_buffer_sizes_bw_delay_prod(topology)
        """
        try:
            assert all(('capacity' in topology.edge[u][v]
                        for u, v in topology.edges_iter()))
            assert all(('delay' in topology.edge[u][v]
                        for u, v in topology.edges_iter()))
            capacity_unit = topology.graph['capacity_unit']
            delay_unit = topology.graph['delay_unit']
        except (AssertionError, KeyError):
            raise ValueError('All links must have a capacity and delay attribute')
        topology.graph['buffer_unit'] = buffer_unit
        # this filters potential self-loops which would crash the function
        edges = [(u, v) for (u, v) in topology.edges_iter() if u != v]
        # dictionary listing all end-to-end routes in which a link appears
        route_presence = dict(zip(edges, [[] for _ in range(len(edges))]))
        # dictionary with all network routes
        route = nx.all_pairs_dijkstra_path(topology, weight='weight')
        # Dictionary storing end-to-end path delays for each OD pair
        e2e_delay = {}

        for orig in route:
            e2e_delay[orig] = {}
            for dest in route[orig]:
                path = route[orig][dest]
                if len(path) <= 1:
                    continue
                path_delay = 0
                for hop in range(len(path) - 1):
                    if 'delay' in topology.edge[path[hop]][path[hop + 1]]:
                        if (path[hop], path[hop + 1]) in route_presence:
                            route_presence[(path[hop], path[hop + 1])] \
                                          .append((orig, dest))
                        else:
                            route_presence[(path[hop + 1], path[hop])] \
                                          .append((orig, dest))
                        path_delay += \
                                topology.edge[path[hop]][path[hop + 1]]['delay']
                    else:
                        raise ValueError('No link delays available')
                e2e_delay[orig][dest] = path_delay

        # dict containing mean RTT experienced by flows traversing a specific link
        mean_rtt_dict = {}
        for (u, v), route in route_presence.items():
            if route:
                try:
                    mean_rtt = mean([e2e_delay[o][d] + e2e_delay[d][o]
                                     for (o, d) in route])
                except KeyError:
                    raise ValueError('Cannot assign buffer sizes because some '
                                     'paths do not have corresponding return path')
            else:
                # if this is the case, then this link is in any shortest path,
                # not even in the one between its endpoint because there is an
                # alternative route with lower cost.
                # In this case we arbitrarily set the RTT as the RTT between the
                # link endpoint if that link was used, i.e. twice the delay of the
                # link
                if (v, u) in edges:
                    mean_rtt = topology.edge[u][v]['delay'] + \
                               topology.edge[v][u]['delay']
                else:
                    try:
                        mean_rtt = topology.edge[u][v]['delay'] + e2e_delay[v][u]
                    except KeyError:
                        raise ValueError('Cannot assign buffer sizes because some '
                                     'paths do not have corresponding return path')
            mean_rtt_dict[(u, v)] = mean_rtt
        norm_factor = capacity_units[capacity_unit] * \
                      time_units[delay_unit] / 8000.0
        if buffer_unit == 'packets':
            norm_factor /= packet_size
        for u, v in edges:
            capacity = topology.edge[u][v]['capacity']
            buffer_size = int(mean_rtt_dict[(u, v)] * capacity * norm_factor)
            topology.edge[u][v]['buffer'] = buffer_size
        return

    def set_buffer_sizes_link_bandwidth(topology, k=1.0, default_size=None,
                                        buffer_unit='bytes', packet_size=1500):
        """
        Assign a buffer sizes proportionally to the bandwidth of the interface on
        which the flush. In particularly, the buffer size will be equal to
        :math:`k \times C`, where :math:`C` is the capacity of the link in bps.

        This assignment is equal to the bandwidth-delay product if :math:`k` is the
        average RTT in seconds.

        To use this function, all links of the topology must have a *capacity*
        attribute. If the length of a link cannot be determined, it is applied the
        delay equal *default_delay* if specified, otherwise an error is returned.

        Parameters
        ----------
        topology : Topology or DirectedTopology
            The topology on which delays are applied.
        k : float, optional
            The multiplicative constant applied to capacity to derive buffer size
        default_size : float, optional
            The buffer size to be applied to interfaces whose speed is unknown. If
            it is None and at least one link does not have a capacity attribute,
            return an error
        buffer_unit : string, unit
            The unit of buffer sizes. Supported units are: *bytes* and *packets*
        packet_size : int, optional
            The average packet size (in bytes). It used only if *packets* is
            selected as buffer size to properly calculate buffer sizes given
            bandwidth and delay values.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.erdos_renyi_topology(50, 0.1)
        >>> fnss.set_capacities_constant(topology, 10, 'Mbps')
        >>> fnss.set_delays_constant(topology, 2, 'ms')
        >>> fnss.set_buffer_sizes_link_bandwidth(topology, k=1.0)
        """
        if k <= 0:
            raise ValueError('k must be a positive number')
        if default_size is None:
            if 'capacity_unit' not in topology.graph \
                    or not all('capacity' in topology.edge[u][v]
                               for u, v in topology.edges_iter()):
                raise ValueError('All links must have a capacity attribute. '
                                 'Set capacity or specify a default buffer size')
        topology.graph['buffer_unit'] = buffer_unit
        # We further dived norm_factor by 8 because buffer unit is bytes
        norm_factor = capacity_units[topology.graph['capacity_unit']] / 8.0
        if buffer_unit == 'packets':
            norm_factor /= packet_size
        for u, v in topology.edges_iter():
            if 'capacity' in topology.edge[u][v]:
                capacity = topology.edge[u][v]['capacity']
                buffer_size = int(k * capacity * norm_factor)
            else:
                buffer_size = default_size
            topology.edge[u][v]['buffer'] = buffer_size

    def set_buffer_sizes_constant(topology, buffer_size, buffer_unit='bytes',
                                  interfaces=None):
        """
        Assign a constant buffer size to all selected interfaces

        Parameters
        ----------
        topology : Topology or DirectedTopology
            The topology on which buffer sizes are applied.
        buffer_size : int
            The constant buffer_size to be applied to all interface
        buffer_unit : string, unit
            The unit of buffer sizes. Supported units are: *bytes* and *packets*
        interfaces : iterable container of tuples, optional
            Iterable container of selected interfaces on which buffer sizes are
            applied.
            An interface is defined by the tuple (u,v) where u is the node on which
            the interface is located and (u,v) is the link to which the buffer
            flushes.

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.Topology()
        >>> topology.add_path([1, 2, 4, 5, 8])
        >>> fnss.set_buffer_sizes_constant(topology, 100000, buffer_unit='bytes', \
        ... interfaces=[(1,2), (5,8), (4,5)])
        """
        if buffer_size < 0:
            raise ValueError('The buffer_size argument cannot be negative')
        if interfaces is not None and 'buffer_unit' in topology.graph:
            curr_buffer_unit = topology.graph['buffer_unit']
            if curr_buffer_unit != buffer_unit:
                raise ValueError('The topology already contains buffer sizes ' \
                                 'expressed in %s. Use that unit instead of %s' \
                                 % (curr_buffer_unit, buffer_unit))
        topology.graph['buffer_unit'] = buffer_unit
        edges = topology.edges_iter() if interfaces is None else interfaces
        for u, v in edges:
            topology.edge[u][v]['buffer'] = buffer_size

    def get_buffer_sizes(topology):
        """
        Returns all the buffer sizes.

        Parameters
        ----------
        topology : Topology or DirectedTopology

        Returns
        -------
        buffer_sizes : dict
            Dictionary of buffer sizes keyed by (u, v) tuple. The key (u, v)
            represents a network interface where u is the node on which the
            interface is located and (u, v) is the link to which the buffer flushes

        Examples
        --------
        >>> import fnss
        >>> topology = fnss.Topology()
        >>> topology.add_path([1, 2, 3])
        >>> fnss.set_buffer_sizes_constant(topology, buffer_size=10)
        >>> buffer = fnss.get_buffer_sizes(topology)
        >>> buffer[(1,2)]
        10
        """
        return nx.get_edge_attributes(topology, 'buffer')

    def clear_buffer_sizes(topology):
        """
        Remove all buffer sizes from the topology.

        Parameters
        ----------
        topology : Topology or DirectedTopology
            The topology whose buffer sizes are cleared
        """
        if 'buffer_unit' in topology.graph:
            del topology.graph['buffer_unit']
        for u, v in topology.edges_iter():
            if 'buffer' in topology.edge[u][v]:
                del topology.edge[u][v]['buffer']

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