package sort

// Node is a generic interface representing a graph node.
type Node[T any] interface {
	// Value returns the value of the node.
	Value() T
	// Adjacencies returns a slice of nodes adjacent to this node
	Adjacencies() []Node[T]
}

// Topo performs a topological sort on a slice of nodes in place.
func TopoSort[T any](nodes []Node[T]) {
	v := make(map[Node[T]]bool)
	pos := 0
	var dfs func(Node[T])
	dfs = func(n Node[T]) {
		v[n] = true
		for _, e := range n.Adjacencies() {
			if !v[e] {
				dfs(e)
			}
		}
		nodes[pos] = n
		pos++
	}

	for _, n := range nodes {
		if !v[n] {
			dfs(n)
		}
	}
}

// RTopoSort performs a reverse topological sort on a slice of nodes in place.
func RTopoSort[T any](nodes []Node[T]) {
	TopoSort(nodes)

	for i, j := 0, len(nodes)-1; i < j; i, j = i+1, j-1 {
		nodes[i], nodes[j] = nodes[j], nodes[i]
	}
}