VILLASnode/common/include/villas/graph/directed.hpp

/* A directed graph.
 *
 * @file
 * @author Daniel Krebs <github@daniel-krebs.net>
 * @copyright 2014-2022, Institute for Automation of Complex Power Systems, EONERC
 * @license Apache License 2.0
 */

#pragma once

#include <map>
#include <list>
#include <memory>
#include <sstream>
#include <string>
#include <fstream>
#include <stdexcept>
#include <algorithm>

#include <villas/log.hpp>
#include <villas/graph/vertex.hpp>
#include <villas/graph/edge.hpp>

namespace villas {
namespace graph {

template<typename VertexType = Vertex, typename EdgeType = Edge>
class DirectedGraph {
public:

	using VertexIdentifier = Vertex::Identifier;
	using EdgeIdentifier = Edge::Identifier;
	using Path = std::list<EdgeIdentifier>;

	DirectedGraph(const std::string &name = "DirectedGraph") :
	    lastVertexId(0),
	    lastEdgeId(0),
	    logger(logging.get(name))
	{ }

	std::shared_ptr<VertexType> getVertex(VertexIdentifier vertexId) const
	{
		// Cannot use [] operator, because creates non-existing elements
		// at() will throw std::out_of_range if element does not exist
		return vertices.at(vertexId);
	}

	template<class UnaryPredicate>
	VertexIdentifier findVertex(UnaryPredicate p)
	{
		for (auto &v : vertices) {
			auto &vertexId = v.first;
			auto &vertex = v.second;

			if (p(vertex)) {
				return vertexId;
			}
		}

		throw std::out_of_range("vertex not found");
	}

	std::shared_ptr<EdgeType> getEdge(EdgeIdentifier edgeId) const
	{
		if (edgeId >= lastEdgeId)
			throw std::invalid_argument("edge doesn't exist");

		// Cannot use [] operator, because creates non-existing elements
		// at() will throw std::out_of_range if element does not exist
		return edges.at(edgeId);
	}

	std::size_t getEdgeCount() const
	{
		return edges.size();
	}

	std::size_t getVertexCount() const
	{
		return vertices.size();
	}

	VertexIdentifier addVertex(std::shared_ptr<VertexType> vertex)
	{
		vertex->id = lastVertexId++;

		logger->debug("New vertex: {}", vertex->toString());
		vertices[vertex->id] = vertex;

		return vertex->id;
	}

	EdgeIdentifier addEdge(std::shared_ptr<EdgeType> edge,
	                       VertexIdentifier fromVertexId,
	                       VertexIdentifier toVertexId)
	{
		// Allocate edge id
		edge->id = lastEdgeId++;

		// Connect it
		edge->from = fromVertexId;
		edge->to = toVertexId;

		logger->debug("New edge {}: {} -> {}", edge->toString(), edge->from, edge->to);

		// This is a directed graph, so only push edge to starting vertex
		getVertex(edge->from)->edges.push_back(edge->id);

		// Add new edge to graph
		edges[edge->id] = edge;

		return edge->id;
	}

	EdgeIdentifier addDefaultEdge(VertexIdentifier fromVertexId,
	                              VertexIdentifier toVertexId)
	{
		// Create a new edge
		std::shared_ptr<EdgeType> edge(new EdgeType);

		return addEdge(edge, fromVertexId, toVertexId);
	}

	void removeEdge(EdgeIdentifier edgeId)
	{
		auto edge = getEdge(edgeId);
		auto startVertex = getVertex(edge->from);

		// Remove edge only from starting vertex (this is a directed graph)
		logger->debug("Remove edge {} from vertex {}", edgeId, edge->from);
		startVertex->edges.remove(edgeId);

		logger->debug("Remove edge {}", edgeId);
		edges.erase(edgeId);
	}

	void removeVertex(VertexIdentifier vertexId)
	{
		// Delete every edge that start or ends at this vertex
		auto it = edges.begin();
		while (it != edges.end()) {
			auto &edgeId = it->first;
			auto &edge = it->second;

			bool removeEdge = false;

			if (edge->to == vertexId) {
				logger->debug("Remove edge {} from vertex {}'s edge list",
				              edgeId, edge->from);

				removeEdge = true;

				auto startVertex = getVertex(edge->from);
				startVertex->edges.remove(edge->id);

			}

			if ((edge->from == vertexId) or removeEdge) {
				logger->debug("Remove edge {}", edgeId);
				// Remove edge from global edge list
				it = edges.erase(it);
			}
			else
				++it;
		}

		logger->debug("Remove vertex {}", vertexId);
		vertices.erase(vertexId);
		lastVertexId--;
	}

	const std::list<EdgeIdentifier>& vertexGetEdges(VertexIdentifier vertexId) const
	{
		return getVertex(vertexId)->edges;
	}

	using check_path_fn = std::function<bool(const Path&)>;

	static
	bool checkPath(const Path&)
	{
		return true;
	}

	bool getPath(VertexIdentifier fromVertexId,
	             VertexIdentifier toVertexId,
	             Path &path,
	             check_path_fn pathCheckFunc = checkPath)
	{
		if (fromVertexId == toVertexId)
			// Arrived at the destination
			return true;
		else {
			auto fromVertex = getVertex(fromVertexId);

			for (auto &edgeId : fromVertex->edges) {
				auto edgeOfFromVertex = getEdge(edgeId);

				// Loop detection
				bool loop = false;
				for (auto &edgeIdInPath : path) {
					auto edgeInPath = getEdge(edgeIdInPath);
					if (edgeInPath->from == edgeOfFromVertex->to) {
						loop = true;
						break;
					}
				}

				if (loop) {
					logger->debug("Loop detected via edge {}", edgeId);
					continue;
				}

				// Remember the path we're investigating to detect loops
				path.push_back(edgeId);

				// Recursive, depth-first search
				if (getPath(edgeOfFromVertex->to, toVertexId, path, pathCheckFunc) and pathCheckFunc(path))
					// Path found, we're done
					return true;
				else
					// Tear down path that didn't lead to the destination
					path.pop_back();
			}
		}

		return false;
	}

	void dump(const std::string &fileName = "") const
	{
		logger->info("Vertices:");
		for (auto &v : vertices) {
			auto &vertex = v.second;

			// Format connected vertices into a list
			std::stringstream ssEdges;
			for (auto &edge : vertex->edges) {
				ssEdges << getEdge(edge)->to << " ";
			}

			logger->info("  {} connected to: {}", vertex->toString(), ssEdges.str());
		}

		std::fstream s(fileName, s.out | s.trunc);
		if (s.is_open()) {
			s << "digraph memgraph {" << std::endl;
		}

		logger->info("Edges:");
		for (auto &e : edges) {
			auto &edge = e.second;

			logger->info("  {}: {} -> {}", edge->toString(), edge->from, edge->to);
			if (s.is_open()) {
				auto from = getVertex(edge->from);
				auto to = getVertex(edge->to);

				s << std::dec;
				s << "  \"" << *from << "\" -> \"" << *to << "\""
				  << " [label=\"" << *edge << "\"];" << std::endl;
			}
		}

		if (s.is_open()) {
			s << "}" << std::endl;
			s.close();
		}
	}

protected:
	VertexIdentifier lastVertexId;
	EdgeIdentifier lastEdgeId;

	std::map<VertexIdentifier, std::shared_ptr<VertexType>> vertices;
	std::map<EdgeIdentifier, std::shared_ptr<EdgeType>> edges;

	Logger logger;
};

} // namespace graph
} // namespace villas