pgraph: Add logic functions for adding subgraphs

These are helper functions to merge in existing graphs into a main graph
with or without adding an edge relationship between a vertex and the new
graph. These are particularly useful if using mgmt as a lib to break
apart units of work into functions that create sub graphs, which are
then added to the main graph when they're returned.

pgraph/subgraph.go

@@ -0,0 +1,106 @@
+// Mgmt
+// Copyright (C) 2013-2017+ James Shubin and the project contributors
+// Written by James Shubin <james@shubin.ca> and the project contributors
+//
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Affero General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// 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 Affero General Public License for more details.
+//
+// You should have received a copy of the GNU Affero General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+package pgraph
+
+// AddGraph adds the set of edges and vertices of a graph to the existing graph.
+func (g *Graph) AddGraph(graph *Graph) {
+	g.addEdgeVertexGraphHelper(nil, graph, nil, false, false)
+}
+
+// AddEdgeVertexGraph adds a directed edge to the graph from a vertex.
+// This is useful for flattening the relationship between a subgraph and an
+// existing graph, without having to run the subgraph recursively. It adds the
+// maximum number of edges, creating a relationship to every vertex.
+func (g *Graph) AddEdgeVertexGraph(vertex Vertex, graph *Graph, edgeGenFn func(v1, v2 Vertex) Edge) {
+	g.addEdgeVertexGraphHelper(vertex, graph, edgeGenFn, false, false)
+}
+
+// AddEdgeVertexGraphLight adds a directed edge to the graph from a vertex.
+// This is useful for flattening the relationship between a subgraph and an
+// existing graph, without having to run the subgraph recursively. It adds the
+// minimum number of edges, creating a relationship to the vertices with
+// indegree equal to zero.
+func (g *Graph) AddEdgeVertexGraphLight(vertex Vertex, graph *Graph, edgeGenFn func(v1, v2 Vertex) Edge) {
+	g.addEdgeVertexGraphHelper(vertex, graph, edgeGenFn, false, true)
+}
+
+// AddEdgeGraphVertex adds a directed edge to the vertex from a graph.
+// This is useful for flattening the relationship between a subgraph and an
+// existing graph, without having to run the subgraph recursively. It adds the
+// maximum number of edges, creating a relationship from every vertex.
+func (g *Graph) AddEdgeGraphVertex(graph *Graph, vertex Vertex, edgeGenFn func(v1, v2 Vertex) Edge) {
+	g.addEdgeVertexGraphHelper(vertex, graph, edgeGenFn, true, false)
+}
+
+// AddEdgeGraphVertexLight adds a directed edge to the vertex from a graph.
+// This is useful for flattening the relationship between a subgraph and an
+// existing graph, without having to run the subgraph recursively. It adds the
+// minimum number of edges, creating a relationship from the vertices with
+// outdegree equal to zero.
+func (g *Graph) AddEdgeGraphVertexLight(graph *Graph, vertex Vertex, edgeGenFn func(v1, v2 Vertex) Edge) {
+	g.addEdgeVertexGraphHelper(vertex, graph, edgeGenFn, true, true)
+}
+
+// addEdgeVertexGraphHelper is a helper function to add a directed edges to the
+// graph from a vertex, or vice-versa. It operates in this reverse direction by
+// specifying the reverse argument as true. It is useful for flattening the
+// relationship between a subgraph and an existing graph, without having to run
+// the subgraph recursively. It adds the maximum number of edges, creating a
+// relationship to or from every vertex if the light argument is false, and if
+// it is true, it adds the minimum number of edges, creating a relationship to
+// or from the vertices with an indegree or outdegree equal to zero depending on
+// if we specified reverse or not.
+func (g *Graph) addEdgeVertexGraphHelper(vertex Vertex, graph *Graph, edgeGenFn func(v1, v2 Vertex) Edge, reverse, light bool) {
+
+	var degree map[Vertex]int // compute all of the in/outdegree's if needed
+	if light && reverse {
+		degree = graph.OutDegree()
+	} else if light { // && !reverse
+		degree = graph.InDegree()
+	}
+	for _, v := range graph.VerticesSorted() { // sort to help out edgeGenFn
+
+		// forward:
+		// we only want to add edges to indegree == 0, because every
+		// other vertex is a dependency of at least one of those
+
+		// reverse:
+		// we only want to add edges to outdegree == 0, because every
+		// other vertex is a pre-requisite to at least one of these
+		if light && degree[v] != 0 {
+			continue
+		}
+
+		g.AddVertex(v) // ensure vertex is part of the graph
+
+		if vertex != nil && reverse {
+			edge := edgeGenFn(v, vertex) // generate a new unique edge
+			g.AddEdge(v, vertex, edge)
+		} else if vertex != nil { // && !reverse
+			edge := edgeGenFn(vertex, v)
+			g.AddEdge(vertex, v, edge)
+		}
+	}
+
+	// also remember to suck in all of the graph's edges too!
+	for v1 := range graph.Adjacency() {
+		for v2, e := range graph.Adjacency()[v1] {
+			g.AddEdge(v1, v2, e)
+		}
+	}
+}