package analyzer

import (
	"go/ast"
)

// A visitFunc visits a node of the Go AST. The function can use stack to
// retrieve AST nodes on the path from the node up to the root.  If the return
// value is true, the children of node are also visited; otherwise they are
// skipped.
type visitFunc func(node ast.Node, stack stackFunc) bool

// A stackFunc returns the ith stack entry above of an AST node, where 0
// denotes the node itself. If the ith entry does not exist, the function
// returns nil.
type stackFunc func(i int) ast.Node

// astVisitor implements ast.Visitor, passing each visited node to a callback
// function.
type astVisitor struct {
	stack []ast.Node
	visit visitFunc
}

func newASTVisitor(f visitFunc) ast.Visitor { return &astVisitor{visit: f} }

// Visit implements the required method of the ast.Visitor interface.
func (w *astVisitor) Visit(node ast.Node) ast.Visitor {
	if node == nil {
		w.stack = w.stack[:len(w.stack)-1] // pop
		return w
	}

	w.stack = append(w.stack, node) // push
	if !w.visit(node, w.parent) {
		return nil
	}
	return w
}

func (w *astVisitor) parent(i int) ast.Node {
	if i >= len(w.stack) {
		return nil
	}
	return w.stack[len(w.stack)-1-i]
}