graph/iterator: implement edge and line based lazy node iterator

graph/iterator/nodes.go

@@ -178,3 +178,100 @@ func (n *Nodes) Reset() {
 	n.pos = 0
 	n.iter = n.nodes.MapRange()
 }
+
+// NodesByEdge implements the graph.Nodes interfaces.
+// The iteration order of Nodes is randomized.
+type NodesByEdge struct {
+	nodes map[int64]graph.Node
+	edges reflect.Value
+	iter  *reflect.MapIter
+	pos   int
+	curr  graph.Node
+}
+
+// NewNodesByEdge returns a NodesByEdge initialized with the
+// provided nodes, a map of node IDs to graph.Nodes, and the set
+// of edges, a map of to-node IDs to graph.Edge, that can be
+// traversed to reach the nodes that the NodesByEdge will iterate
+// over. No check is made that the keys match the graph.Node IDs,
+// and the map keys are not used.
+//
+// Behavior of the NodesByEdge is unspecified if nodes or edges
+// is mutated after the call the NewNodes.
+func NewNodesByEdge(nodes map[int64]graph.Node, edges map[int64]graph.Edge) *NodesByEdge {
+	rv := reflect.ValueOf(edges)
+	return &NodesByEdge{nodes: nodes, edges: rv, iter: rv.MapRange()}
+}
+
+// NewNodesByWeightedEdge returns a NodesByEdge initialized with the
+// provided nodes, a map of node IDs to graph.Nodes, and the set
+// of edges, a map of to-node IDs to graph.WeightedEdge, that can be
+// traversed to reach the nodes that the NodesByEdge will iterate
+// over. No check is made that the keys match the graph.Node IDs,
+// and the map keys are not used.
+//
+// Behavior of the NodesByEdge is unspecified if nodes or edges
+// is mutated after the call the NewNodes.
+func NewNodesByWeightedEdge(nodes map[int64]graph.Node, edges map[int64]graph.WeightedEdge) *NodesByEdge {
+	rv := reflect.ValueOf(edges)
+	return &NodesByEdge{nodes: nodes, edges: rv, iter: rv.MapRange()}
+}
+
+// NewNodesByLines returns a NodesByEdge initialized with the
+// provided nodes, a map of node IDs to graph.Nodes, and the set
+// of lines, a map to-node IDs to map of graph.Line, that can be
+// traversed to reach the nodes that the NodesByEdge will iterate
+// over. No check is made that the keys match the graph.Node IDs,
+// and the map keys are not used.
+//
+// Behavior of the NodesByEdge is unspecified if nodes or lines
+// is mutated after the call the NewNodes.
+func NewNodesByLines(nodes map[int64]graph.Node, lines map[int64]map[int64]graph.Line) *NodesByEdge {
+	rv := reflect.ValueOf(lines)
+	return &NodesByEdge{nodes: nodes, edges: rv, iter: rv.MapRange()}
+}
+
+// NewNodesByWeightedLines returns a NodesByEdge initialized with the
+// provided nodes, a map of node IDs to graph.Nodes, and the set
+// of lines, a map to-node IDs to map of graph.WeightedLine, that can be
+// traversed to reach the nodes that the NodesByEdge will iterate
+// over. No check is made that the keys match the graph.Node IDs,
+// and the map keys are not used.
+//
+// Behavior of the NodesByEdge is unspecified if nodes or lines
+// is mutated after the call the NewNodes.
+func NewNodesByWeightedLines(nodes map[int64]graph.Node, lines map[int64]map[int64]graph.WeightedLine) *NodesByEdge {
+	rv := reflect.ValueOf(lines)
+	return &NodesByEdge{nodes: nodes, edges: rv, iter: rv.MapRange()}
+}
+
+// Len returns the remaining number of nodes to be iterated over.
+func (n *NodesByEdge) Len() int {
+	return n.edges.Len() - n.pos
+}
+
+// Next returns whether the next call of Node will return a valid node.
+func (n *NodesByEdge) Next() bool {
+	if n.pos >= n.edges.Len() {
+		return false
+	}
+	ok := n.iter.Next()
+	if ok {
+		n.pos++
+		n.curr = n.nodes[n.iter.Key().Int()]
+	}
+	return ok
+}
+
+// Node returns the current node of the iterator. Next must have been
+// called prior to a call to Node.
+func (n *NodesByEdge) Node() graph.Node {
+	return n.curr
+}
+
+// Reset returns the iterator to its initial state.
+func (n *NodesByEdge) Reset() {
+	n.curr = nil
+	n.pos = 0
+	n.iter = n.edges.MapRange()
+}