/*
   AMU: Custom simple markup language
   Copyright (C) 2021 Arsen Musayelyan

   This program is free software: you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation, either version 3 of the License, or
   (at your option) any later version.

   This program is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

// Package stack implements a simple stack using go slices.
package stack

import "reflect"

// Stack is a LIFO stack using slices for storage
type Stack struct {
	items []interface{}
}

// Create a new stack
func New() *Stack {
	return &Stack{}
}

// Add a value to the end of the stack
func (s *Stack) Push(val interface{}) {
	// Add element to slice
	s.items = append(s.items, val)
}

// Remove the value on the end of the stack and return it.
func (s *Stack) Pop() interface{} {
	// Get index of last element
	n := s.Size() - 1
	// Get last item in slice
	item := s.items[n]
	// Set element to zero value
	s.items[n] = reflect.Zero(reflect.TypeOf(item)).Interface()
	// Remove element
	s.items = s.items[:n]
	return item
}

// Return value on the end of the stack without removing
func (s *Stack) Peek() interface{} {
	// Get index of last element
	n := s.Size() - 1
	// Return last element
	return s.items[n]
}

// Get the amount of items on the stack
func (s *Stack) Size() int {
	return len(s.items)
}