terraform/dag/graph.go

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package dag
import (
"bytes"
"fmt"
"sort"
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"sync"
)
// Graph is used to represent a dependency graph.
type Graph struct {
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vertices []Vertex
edges []Edge
downEdges map[Vertex]*set
upEdges map[Vertex]*set
once sync.Once
}
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// Vertex of the graph.
type Vertex interface{}
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// NamedVertex is an optional interface that can be implemented by Vertex
// to give it a human-friendly name that is used for outputting the graph.
type NamedVertex interface {
Vertex
Name() string
}
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// Vertices returns the list of all the vertices in the graph.
func (g *Graph) Vertices() []Vertex {
return g.vertices
}
// Edges returns the list of all the edges in the graph.
func (g *Graph) Edges() []Edge {
return g.edges
}
// Add adds a vertex to the graph. This is safe to call multiple time with
// the same Vertex.
func (g *Graph) Add(v Vertex) Vertex {
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g.once.Do(g.init)
g.vertices = append(g.vertices, v)
return v
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}
// Connect adds an edge with the given source and target. This is safe to
// call multiple times with the same value. Note that the same value is
// verified through pointer equality of the vertices, not through the
// value of the edge itself.
func (g *Graph) Connect(edge Edge) {
g.once.Do(g.init)
source := edge.Source()
target := edge.Target()
// Do we have this already? If so, don't add it again.
if s, ok := g.downEdges[source]; ok && s.Include(target) {
return
}
// TODO: add all edges
g.edges = append(g.edges, edge)
// Add the down edge
s, ok := g.downEdges[source]
if !ok {
s = new(set)
g.downEdges[source] = s
}
s.Add(target)
// Add the up edge
s, ok = g.upEdges[target]
if !ok {
s = new(set)
g.upEdges[target] = s
}
s.Add(source)
}
// String outputs some human-friendly output for the graph structure.
func (g *Graph) String() string {
var buf bytes.Buffer
// Build the list of node names and a mapping so that we can more
// easily alphabetize the output to remain deterministic.
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names := make([]string, 0, len(g.vertices))
mapping := make(map[string]Vertex, len(g.vertices))
for _, v := range g.vertices {
name := vertName(v)
names = append(names, name)
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mapping[name] = v
}
sort.Strings(names)
// Write each node in order...
for _, name := range names {
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v := mapping[name]
targets := g.downEdges[v]
buf.WriteString(fmt.Sprintf("%s\n", name))
// Alphabetize dependencies
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deps := make([]string, 0, targets.Len())
for _, target := range targets.List() {
deps = append(deps, vertName(target))
}
sort.Strings(deps)
// Write dependencies
for _, d := range deps {
buf.WriteString(fmt.Sprintf(" %s\n", d))
}
}
return buf.String()
}
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func (g *Graph) init() {
g.vertices = make([]Vertex, 0, 5)
g.edges = make([]Edge, 0, 2)
g.downEdges = make(map[Vertex]*set)
g.upEdges = make(map[Vertex]*set)
}
func vertName(raw Vertex) string {
switch v := raw.(type) {
case NamedVertex:
return v.Name()
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case fmt.Stringer:
return fmt.Sprintf("%s", v)
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default:
return fmt.Sprintf("%v", v)
}
}