package pov
type myArc struct {
	from string
	to   string
}
type Graph struct {
	nodes []string
	arcs  []myArc
}
func New() *Graph {
	return &Graph{}
}
func (g *Graph) AddNode(nodeLabel string) {
	g.nodes = append(g.nodes, nodeLabel)
}
func (g *Graph) AddArc(from, to string) {
	g.arcs = append(g.arcs, myArc{from, to})
}
func (g *Graph) ArcList() []string {
	var ret []string
	for _, a := range g.arcs {
		ret = append(ret, a.from+" -> "+a.to)
	}
	return ret
}
func (g *Graph) ChangeRoot(oldRoot, newRoot string) *Graph {
	// copy the original graph nodes
	ret := &Graph{}
	for _, node := range g.nodes {
		ret.nodes = append(ret.nodes, node)
	}
	// reparenting
	route := make(chan string, 1)
	for _, a := range g.arcs {
		if a.to == newRoot {
			route <- a.from
			a.from, a.to = a.to, a.from
		}
		ret.arcs = append(ret.arcs, a)
	}
	for {
		select {
		case elem := <-route:
			if elem == oldRoot {
				break
			}
			for i, a := range g.arcs {
				if a.to == elem {
					route <- a.from
					a.to, a.from = a.from, a.to
					ret.arcs[i] = a
				}
			}
		default:
			return ret
		}
	}
}