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package cdc.graphs.core;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import cdc.graphs.EdgeDirection;
import cdc.graphs.EdgeTip;
import cdc.graphs.GraphAdapter;
import cdc.graphs.impl.ExtensionSubGraph;

/**
 * Utility dedicated to computation of connected components of a graph.
 *
 * @author Damien Carbonne
 *
 * @param  Node class
 * @param  Edge class
 */
public class GraphConnectedComponents extends GraphBase {
    public GraphConnectedComponents(GraphAdapter adapter) {
        super(adapter);
    }

    /**
     * Computes the connected components containing a particular node.
     *
     * @param node The node whose connected components subgraph must be
     *            computed.
     * @return The connected components containing node.
     */
    public GraphAdapter computeConnectedComponents(N node) {
        if (adapter.containsNode(node)) {
            final ExtensionSubGraph result = new ExtensionSubGraph<>(adapter);
            // Nodes to process. Initialized with node
            final Set todo = new HashSet<>();
            todo.add(node);
            // Nodes that have been processed
            final Set done = new HashSet<>();

            while (!todo.isEmpty()) {
                // Process next node
                final N next = todo.iterator().next();
                todo.remove(next);
                done.add(next);
                // Add node to result graph
                result.addNode(next);

                // Add outgoing edges to result graph
                for (final E edge : adapter.getEdges(next, EdgeDirection.OUTGOING)) {
                    result.addEdge(edge);
                    final N target = adapter.getTip(edge, EdgeTip.TARGET);
                    if (!done.contains(target)) {
                        todo.add(target);
                    }
                }

                // Add ingoing edges to result graph
                for (final E edge : adapter.getEdges(next, EdgeDirection.INGOING)) {
                    result.addEdge(edge);
                    final N source = adapter.getTip(edge, EdgeTip.SOURCE);
                    if (!done.contains(source)) {
                        todo.add(source);
                    }
                }
            }
            return result;
        } else {
            throw new IllegalArgumentException("Node (" + node + ") does not belong to delegate");
        }
    }

    /**
     * Computes all connected components of a graph.
     *
     * @return A list of all connected components subgraphs.
     */
    public List> computeConnectedComponents() {
        final List> result = new ArrayList<>();
        final Set todo = new HashSet<>();
        for (final N node : adapter.getNodes()) {
            todo.add(node);
        }

        while (!todo.isEmpty()) {
            final N node = todo.iterator().next();
            final GraphAdapter subgraph = computeConnectedComponents(node);
            result.add(subgraph);
            for (final N n : subgraph.getNodes()) {
                todo.remove(n);
            }
        }

        return result;
    }
}