268 lines
6.6 KiB
Go
268 lines
6.6 KiB
Go
// Package graph implements an immutable unidirectional graph.
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package graph
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import (
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"crypto/rand"
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"encoding/hex"
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"fmt"
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)
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// Value wraps a go value in a way such that it will be uniquely identified
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// within any Graph and between Graphs. Use NewValue to create a Value instance.
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// You can create an instance manually as long as ID is globally unique.
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type Value struct {
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ID string
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V interface{}
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}
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// Void is the absence of any value.
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var Void Value
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// NewValue returns a Value instance wrapping any go value. The Value returned
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// will be independent of the passed in go value. So if the same go value is
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// passed in twice then the two returned Value instances will be treated as
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// being different values by Graph.
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func NewValue(V interface{}) Value {
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b := make([]byte, 8)
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if _, err := rand.Read(b); err != nil {
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panic(err)
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}
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return Value{
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ID: hex.EncodeToString(b),
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V: V,
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}
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}
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// Edge is a directional edge connecting two values in a Graph, the Tail and the
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// Head.
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type Edge struct {
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Tail, Head Value
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}
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func (e Edge) id() string {
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return fmt.Sprintf("%q->%q", e.Tail, e.Head)
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}
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// an edgeIndex maps valueIDs to a set of edgeIDs. Graph keeps two edgeIndex's,
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// one for input edges and one for output edges.
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type edgeIndex map[string]map[string]struct{}
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func (ei edgeIndex) cp() edgeIndex {
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if ei == nil {
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return edgeIndex{}
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}
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ei2 := make(edgeIndex, len(ei))
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for valID, edgesM := range ei {
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edgesM2 := make(map[string]struct{}, len(edgesM))
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for id := range edgesM {
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edgesM2[id] = struct{}{}
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}
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ei2[valID] = edgesM2
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}
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return ei2
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}
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func (ei edgeIndex) add(valID, edgeID string) {
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edgesM, ok := ei[valID]
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if !ok {
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edgesM = map[string]struct{}{}
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ei[valID] = edgesM
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}
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edgesM[edgeID] = struct{}{}
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}
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func (ei edgeIndex) del(valID, edgeID string) {
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edgesM, ok := ei[valID]
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if !ok {
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return
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}
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delete(edgesM, edgeID)
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if len(edgesM) == 0 {
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delete(ei, valID)
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}
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}
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// Graph implements an immutable, unidirectional graph which can hold generic
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// values. All methods are thread-safe as they don't modify the Graph in any
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// way.
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//
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// The Graph's zero value is the initial empty graph.
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//
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// The Graph does not keep track of Edge ordering. Assume that all slices of
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// Edges are in random order.
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type Graph struct {
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m map[string]Edge
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// these are indices mapping Value IDs to all the in/out edges for that
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// Value in the Graph.
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vIns, vOuts edgeIndex
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}
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func (g Graph) cp() Graph {
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g2 := Graph{
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m: make(map[string]Edge, len(g.m)),
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vIns: g.vIns.cp(),
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vOuts: g.vOuts.cp(),
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}
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for id, e := range g.m {
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g2.m[id] = e
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}
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return g2
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}
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// Add returns a new Graph instance with the given Edge added to it. If the
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// original Graph already had that Edge this returns the original Graph.
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func (g Graph) Add(e Edge) Graph {
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id := e.id()
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if _, ok := g.m[id]; ok {
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return g
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}
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g2 := g.cp()
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g2.m[id] = e
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g2.vIns.add(e.Head.ID, id)
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g2.vOuts.add(e.Tail.ID, id)
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return g2
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}
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// Del returns a new Graph instance without the given Edge in it. If the
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// original Graph didn't have that Edge this returns the original Graph.
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func (g Graph) Del(e Edge) Graph {
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id := e.id()
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if _, ok := g.m[id]; !ok {
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return g
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}
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g2 := g.cp()
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delete(g2.m, id)
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g2.vIns.del(e.Head.ID, id)
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g2.vOuts.del(e.Tail.ID, id)
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return g2
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}
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// Edges returns all Edges which are part of the Graph
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func (g Graph) Edges() []Edge {
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edges := make([]Edge, 0, len(g.m))
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for _, e := range g.m {
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edges = append(edges, e)
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}
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return edges
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}
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// NOTE the Node type exists primarily for convenience. As far as Graph's
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// internals are concerned it doesn't _really_ exist, and no Graph method should
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// ever take Node as a parameter (except the callback functions like in
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// Traverse, where it's not really being taken in).
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// Node wraps a Value in a Graph to include that Node's input and output Edges
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// in that Graph.
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type Node struct {
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Value
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// All Edges in the Graph with this Node's Value as their Head and Tail,
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// respectively.
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Ins, Outs []Edge
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}
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// Node returns the Node for the given Value, or false if the Graph doesn't
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// contain the Value.
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func (g Graph) Node(v Value) (Node, bool) {
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n := Node{Value: v}
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for edgeID := range g.vIns[v.ID] {
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n.Ins = append(n.Ins, g.m[edgeID])
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}
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for edgeID := range g.vOuts[v.ID] {
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n.Outs = append(n.Outs, g.m[edgeID])
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}
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return n, len(n.Ins) > 0 || len(n.Outs) > 0
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}
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// Nodes returns a Node for each Value which has at least one Edge in the Graph,
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// with the Nodes mapped by their Value's ID.
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func (g Graph) Nodes() map[string]Node {
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nodesM := make(map[string]Node, len(g.m)*2)
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for _, edge := range g.m {
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// if head and tail are modified at the same time it messes up the case
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// where they are the same node
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{
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head := nodesM[edge.Head.ID]
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head.Value = edge.Head
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head.Ins = append(head.Ins, edge)
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nodesM[head.ID] = head
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}
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{
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tail := nodesM[edge.Tail.ID]
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tail.Value = edge.Tail
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tail.Outs = append(tail.Outs, edge)
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nodesM[tail.ID] = tail
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}
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}
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return nodesM
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}
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// Has returns true if the Graph contains at least one Edge with a Head or Tail
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// of Value.
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func (g Graph) Has(v Value) bool {
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if _, ok := g.vIns[v.ID]; ok {
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return true
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} else if _, ok := g.vOuts[v.ID]; ok {
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return true
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}
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return false
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}
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// Traverse is used to traverse the Graph until a stopping point is reached.
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// Traversal starts with the cursor at the given start Value. Each hop is
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// performed by passing the cursor Value's Node into the next function. The
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// cursor moves to the returned Value and next is called again, and so on.
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//
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// If the boolean returned from the next function is false traversal stops and
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// this method returns.
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//
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// If start has no Edges in the Graph, or a Value returned from next doesn't,
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// this will still call next, but the Node will be the zero value.
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func (g Graph) Traverse(start Value, next func(n Node) (Value, bool)) {
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curr := start
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for {
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currNode, ok := g.Node(curr)
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if ok {
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curr, ok = next(currNode)
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} else {
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curr, ok = next(Node{})
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}
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if !ok {
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return
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}
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}
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}
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func (g Graph) edgesShared(g2 Graph) bool {
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for id := range g2.m {
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if _, ok := g.m[id]; !ok {
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return false
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}
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}
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return true
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}
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// SubGraph returns true if the given Graph shares all of its Edges with this
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// Graph.
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func (g Graph) SubGraph(g2 Graph) bool {
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// as a quick check before iterating through the edges, if g has fewer edges
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// than g2 then g2 can't possibly be a sub-graph of it
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if len(g.m) < len(g2.m) {
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return false
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}
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return g.edgesShared(g2)
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}
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// Equal returns true if the given Graph and this Graph have exactly the same
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// Edges.
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func (g Graph) Equal(g2 Graph) bool {
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if len(g.m) != len(g2.m) {
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return false
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}
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return g.edgesShared(g2)
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}
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