// Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements.  See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file to You under the Apache License, Version 2.0
// (the "License"); you may not use this file except in compliance with
// the License.  You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

package lexer

type runeNode struct {
	r    rune
	next *runeNode
}

type runeStack struct {
	start *runeNode
}

func newRuneStack() runeStack {
	return runeStack{}
}

func (s *runeStack) push(r rune) {
	node := &runeNode{r: r}
	if s.start == nil {
		s.start = node
	} else {
		node.next = s.start
		s.start = node
	}
}

func (s *runeStack) pop() rune {
	if s.start == nil {
		return EOFRune
	} else {
		n := s.start
		s.start = n.next
		return n.r
	}
}

func (s *runeStack) clear() {
	s.start = nil
}