package tree

import "fmt" // debug

// FindOrder determines the correct order according to these rules:
// 1. A node cannot come before all of its parents have been included.
// 2. At any given time, the lowest-lettered step must be executed.
func FindOrder(root *Node) []*Node {
	seen := make(map[rune]bool)
	return findOrderR(root, seen)
}

func findOrderR(node *Node, seen map[rune]bool) []*Node {
	order := []*Node{}

	// debug
	fmt.Printf("In node: %c | Children: ", node.Name)
	for _, child := range node.Children {
		fmt.Printf("%c ", child.Name)
	}
	fmt.Printf("| Parents: ")
	for _, parent := range node.Parents {
		fmt.Printf("%c ", parent.Name)
	}
	fmt.Println()
	// end debug

	// add the node, but only if all its parents have been seen
	if len(node.Parents) == 0 {
		seen[node.Name] = true
	} else {
		for _, parent := range node.Parents {
			if _, ok := seen[parent.Name]; !ok {
				return order
			}
		}

		if _, ok := seen[node.Name]; !ok {
			order = append(order, node)
			fmt.Printf("Added node: %c\n", node.Name)
			seen[node.Name] = true
		}
	}

	// recurse
	for _, child := range node.Children {
		order = append(order, findOrderR(child, seen)...)
	}

	return order
}