Mini Shell

"""Implements the functionality of an undirected graph."""

import copy

from .directed_graph import DirectedGraph
from ..exceptions import NonexistentNodeError, NonexistentEdgeError


class UndirectedGraph(DirectedGraph):
    def __deepcopy__(self, memo=None):
        graph = UndirectedGraph()
        graph.nodes = copy.deepcopy(self.nodes)
        graph.edges = copy.deepcopy(self.edges)
        graph.next_node_id = self.next_node_id
        graph.next_edge_id = self.next_edge_id
        graph._num_nodes = self._num_nodes
        graph._num_edges = self._num_edges
        return graph

    def new_edge(self, node_a, node_b, cost=1):
        """Adds a new, undirected edge between node_a and node_b with a cost.
        Returns the edge id of the new edge."""
        edge_id = super(UndirectedGraph, self).new_edge(node_a, node_b, cost)
        self.nodes[node_b]['edges'].append(edge_id)
        return edge_id

    def neighbors(self, node_id):
        """Find all the nodes where there is an edge from the specified node to that node.
        Returns a list of node ids."""
        node = self.get_node(node_id)
        flattened_nodes_list = []
        for a, b in [self.get_edge(edge_id)['vertices'] for edge_id in node['edges']]:
            flattened_nodes_list.append(a)
            flattened_nodes_list.append(b)
        node_set = set(flattened_nodes_list)
        if node_id in node_set:
            node_set.remove(node_id)
        return [nid for nid in node_set]

    def delete_edge_by_id(self, edge_id):
        """Removes the edge identified by "edge_id" from the graph."""
        edge = self.get_edge(edge_id)

        # Remove the edge from the "from node"
        # --Determine the from node
        from_node_id = edge['vertices'][0]
        from_node = self.get_node(from_node_id)

        # --Remove the edge from it
        from_node['edges'].remove(edge_id)

        # Remove the edge from the "to node"
        to_node_id = edge['vertices'][1]
        to_node = self.get_node(to_node_id)

        # --Remove the edge from it
        to_node['edges'].remove(edge_id)

        # Remove the edge from the edge list
        del self.edges[edge_id]

        self._num_edges -= 1

    def move_edge_target(self, edge_id, node_a):
        """Moves an edge so that it targets node_a."""
        # Grab the edge
        edge = self.get_edge(edge_id)

        # Remove the edge from the original "target node"
        original_target_node_id = edge['vertices'][1]
        original_target_node = self.get_node(original_target_node_id)
        original_target_node['edges'].remove(edge_id)

        # Add the edge to the new target node
        new_target_node_id = node_a
        new_target_node = self.get_node(new_target_node_id)
        new_target_node['edges'].append(edge_id)

        # Alter the vertices on the edge
        edge['vertices'] = (edge['vertices'][0], node_a)

    def get_edge_ids_by_node_ids(self, node_a, node_b):
        """Returns a list of edge ids connecting node_a to node_b."""
        # Check if the nodes are adjacent
        if not self.adjacent(node_a, node_b):
            return []

        # They're adjacent, so pull the list of edges from node_a and determine which ones point to node_b
        node = self.get_node(node_a)
        return [edge_id for edge_id in node['edges'] \
                if (self.get_edge(edge_id)['vertices'][1] == node_b or self.get_edge(edge_id)['vertices'][0] == node_b)]