package engine

import "gitea.maximumdirect.net/eric/ConfigKit/internal/document"

// documentLookup contains read-only mapping positions for a completed document.
type documentLookup struct {
	byNode map[*document.Node]map[string]int
}

func buildDocumentLookup(roots ...*document.Node) *documentLookup {
	lookup := &documentLookup{byNode: make(map[*document.Node]map[string]int)}
	visited := make(map[*document.Node]struct{})
	var visit func(*document.Node)
	visit = func(node *document.Node) {
		if node == nil {
			return
		}
		if _, ok := visited[node]; ok {
			return
		}
		visited[node] = struct{}{}
		switch node.Kind {
		case document.Mapping:
			entries := make(map[string]int, len(node.Mapping))
			for index, entry := range node.Mapping {
				if _, exists := entries[entry.Key]; !exists {
					entries[entry.Key] = index
				}
				visit(entry.Value)
			}
			lookup.byNode[node] = entries
		case document.Sequence:
			for _, child := range node.Sequence {
				visit(child)
			}
		}
	}
	for _, root := range roots {
		visit(root)
	}
	return lookup
}

func (lookup *documentLookup) find(node *document.Node, key string) int {
	if lookup == nil {
		return -1
	}
	if entries := lookup.byNode[node]; entries != nil {
		if index, ok := entries[key]; ok {
			return index
		}
	}
	return -1
}