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package com.questdb.ql.parser;

import com.questdb.ex.ParserException;
import com.questdb.ql.model.ExprNode;
import com.questdb.std.IntStack;

import java.util.ArrayDeque;

final class PostOrderTreeTraversalAlgo {
    private final ArrayDeque stack = new ArrayDeque<>();
    private final IntStack indexStack = new IntStack();

    void traverse(ExprNode node, Visitor visitor) throws ParserException {

        // post-order iterative tree traversal
        // see http://en.wikipedia.org/wiki/Tree_traversal

        stack.clear();
        indexStack.clear();

        ExprNode lastVisited = null;

        while (!stack.isEmpty() || node != null) {
            if (node != null) {
                stack.push(node);
                indexStack.push(0);
                node = node.rhs;
            } else {
                ExprNode peek = stack.peek();
                if (peek.paramCount < 3) {
                    if (peek.lhs != null && lastVisited != peek.lhs) {
                        node = peek.lhs;
                    } else {
                        visitor.visit(peek);
                        lastVisited = stack.poll();
                        indexStack.pop();
                    }
                } else {
                    int index = indexStack.peek();
                    if (index < peek.paramCount) {
                        node = peek.args.getQuick(index);
                        indexStack.update(index + 1);
                    } else {
                        visitor.visit(peek);
                        lastVisited = stack.poll();
                        indexStack.pop();
                    }
                }
            }
        }
    }

    public interface Visitor {
        void visit(ExprNode node) throws ParserException;
    }
}