// -----------------------------------------------------------------------------
// file="RandomAccessibleStack"
// Project: StgSharp
// Copyright (c) Nitload.
// SPDX-License-Identifier: MIT
// -----------------------------------------------------------------------------

using System;
using System.Collections;
using System.Collections.Generic;

namespace StgSharp.Collections
{
    public class RandomAccessibleStack<T> : IEnumerable<T>
    {

        private const int DefaultCapacity = 4;

        private T[] _array;
        private int _size;
        private int _version;

        /// <summary>
        ///   Initializes a new instance of the RandomAccessStack class that is empty and has the
        ///   default initial capacity.
        /// </summary>
        public RandomAccessibleStack()
        {
            _array = new T[DefaultCapacity];
        }

        /// <summary>
        ///   Initializes a new instance of the RandomAccessStack class that is empty and has the
        ///   specified initial capacity.
        /// </summary>
        public RandomAccessibleStack(
               int capacity
        )
        {
            if (capacity < 0) {
                throw new ArgumentOutOfRangeException(
                    nameof(capacity), "Capacity must be non-negative.");
            }

            _array = new T[capacity];
        }

        /// <summary>
        ///   Gets or sets the element at the specified index in the stack (0 = bottom, Count-1 =
        ///   top).
        /// </summary>
        public T this[
                 int index
        ]
        {
            get
            {
                if (index < 0 || index >= _size) {
                    throw new ArgumentOutOfRangeException(nameof(index));
                }

                return _array[index];
            }
            /*
            set
            {
                if( index < 0 || index >= PrimSize ) {
                    throw new ArgumentOutOfRangeException( nameof( index ) );
                }
                _array[ index ] = value;
                _version++;
            }
            /**/
        }

        /// <summary>
        ///   Gets the number of elements contained in the stack.
        /// </summary>
        public int Count => _size;

        /// <summary>
        ///   Removes all objects from the stack.
        /// </summary>
        public void Clear()
        {
            Array.Clear(_array, 0, _size);
            _size = 0;
            _version++;
        }

        /// <summary>
        ///   Returns an enumerator that iterates through the stack from top to bottom. Throws if
        ///   the stack is modified during iteration.
        /// </summary>
        public IEnumerator<T> GetEnumerator()
        {
            int expectedVersion = _version;
            for (int i = _size - 1; i >= 0; i--)
            {
                if (expectedVersion != _version) {
                    throw new InvalidOperationException(
                        "Collection was modified during enumeration.");
                }

                yield return _array[i];
            }
        }

        /// <summary>
        ///   Returns the object at the top of the stack without removing it.
        /// </summary>
        public T Peek()
        {
            if (_size == 0) {
                throw new InvalidOperationException("Stack is empty.");
            }

            return _array[_size - 1];
        }

        /// <summary>
        ///   Removes and returns the object at the top of the stack.
        /// </summary>
        public T Pop()
        {
            if (_size == 0) {
                throw new InvalidOperationException("Stack is empty.");
            }

            T item = _array[--_size];
            _array[_size] = default!;
            _version++;
            return item;
        }

        /// <summary>
        ///   Adds an item to the top of the stack.
        /// </summary>
        public void Push(
                    T item
        )
        {
            if (_size == _array.Length) {
                EnsureCapacity(_size + 1);
            }

            _array[_size++] = item;
            _version++;
        }

        private void EnsureCapacity(
                     int min
        )
        {
            int newCapacity = _array.Length == 0 ? DefaultCapacity : _array.Length * 2;
            if (newCapacity < min) {
                newCapacity = min;
            }

            Array.Resize(ref _array, newCapacity);
        }

        IEnumerator IEnumerable.GetEnumerator()
        {
            return GetEnumerator();
        }

    }
}