namespace HeuristicLab.Problems.ProgramSynthesis {
  using System;
  using System.Collections;
  using System.Collections.Generic;
  using System.Linq;

  /// <summary>
  ///     While Push's Stacks are generally treated as genuine Stacks---that is, inclassions take their arguments from the
  ///     tops of
  ///     the Stacks and push their results onto the tops of the Stacks---a few inclassions (like YANK and SHOVE) do allow
  ///     direct access
  ///     to "deep" stack elements by means of integer indices. To this extent the Stacks can be used as general, random
  ///     access memory
  ///     classures. This is one of the features that ensures the Turing-completeness of Push (another being the arbitrary
  ///     name/value
  ///     bindings supported by the NAME data type and DEFINE methods; see below).
  /// </summary>
  /// <typeparam name="T">The item type of the collection.</typeparam>
  public class PushStack<T> : IPushStack<T> {
    private const string Delimiter = " ";

    private readonly List<T> data;

    public PushStack(int capacity = 0) {
      data = new List<T>(capacity);
      IsEnabled = true;
    }

    public bool IsEnabled { get; set; }

    public int Capacity
    {
      get
      {
        return data.Capacity;
      }
    }

    public T Top
    {
      get
      {
        return data[Count - 1];
      }

      set
      {
        data[Count - 1] = value;
      }
    }

    public T TopOrDefault
    {
      get
      {
        return Count > 0 ? Top : default(T);
      }
    }

    public T Bottom
    {
      get
      {
        return data[0];
      }
    }

    public T BottomOrDefault
    {
      get
      {
        return Count > 0 ? Bottom : default(T);
      }
    }

    public int Count
    {
      get
      {
        return data.Count;
      }
    }

    public bool IsEmpty
    {
      get
      {
        return Count == 0;
      }
    }

    public bool IsReadOnly
    {
      get
      {
        return false;
      }
    }

    public void Add(T item) {
      Push(item);
    }

    public void Clear() {
      data.Clear();
    }

    public bool Contains(T item) {
      return data.Contains(item);
    }

    public void CopyTo(T[] array, int arrayIndex) {
      data.CopyTo(array, arrayIndex);
    }

    public IEnumerator<T> GetEnumerator() {
      return data.GetEnumerator();
    }

    public T ElementAt(int index) {
      return data[index];
    }

    public T this[int index]
    {
      get { return data[Count - 1 - index]; }
      set { data[Count - 1 - index] = value; }
    }

    public void Swap(int count) {
      var top = Top;
      var bottomIndex = Count - count;

      for (var i = Count - 1; i > bottomIndex; i--)
        data[i] = data[i - 1];

      data[bottomIndex] = top;
    }

    public void Yank(int index) {
      if (index == Count - 1) return;

      var item = data[index];
      data.RemoveAt(index);
      data.Add(item);
    }

    public T Pop() {
      var top = Top;
      data.RemoveAt(Count - 1);

      return top;
    }

    public IReadOnlyList<T> Pop(int count) {
      var items = Peek(count);
      Remove(count);

      return items;
    }

    public IReadOnlyList<T> Peek(int count) {
      var startIndex = Count - count;

      var items = new T[count];
      data.CopyTo(startIndex, items, 0, count);

      return items;
    }

    public void Push(T item) {
      if (!IsEnabled) return;

      data.Add(item);
    }

    public void Push(T item1, T item2) {
      if (!IsEnabled) return;

      data.Add(item1);
      data.Add(item2);
    }

    public void Push(T item1, T item2, T item3) {
      if (!IsEnabled) return;

      data.Add(item1);
      data.Add(item2);
      data.Add(item3);
    }

    public void Push(T item1, T item2, T item3, T item4) {
      if (!IsEnabled) return;

      data.Add(item1);
      data.Add(item2);
      data.Add(item3);
      data.Add(item4);
    }

    public void Push(IReadOnlyList<T> items, int startIndex) {
      if (!IsEnabled) return;

      for (var i = startIndex; i < items.Count; i++) data.Add(items[i]);
    }

    public void Push(IReadOnlyList<T> items) {
      if (!IsEnabled) return;

      data.AddRange(items);
    }

    public void Push(IEnumerable<T> items) {
      if (!IsEnabled) return;

      data.AddRange(items);
    }

    public void Insert(int index, T item) {
      if (!IsEnabled) return;

      data.Insert(Count - index, item);
    }

    public bool Remove(T item) {
      return data.Remove(item);
    }

    public void RemoveTop() {
      data.RemoveAt(Count - 1);
    }

    public void Remove(int count) {
      data.RemoveRange(Count - count, count);
    }

    public void RemoveAt(int index) {
      data.RemoveAt(index);
    }

    public void RemoveAt(int index, int count) {
      data.RemoveRange(index, count);
    }

    public bool TryPop(out T item) {
      if (Count > 0) {
        item = Pop();
        return true;
      }
      item = default(T);
      return false;
    }

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

    public override string ToString() {
      return string.Join(Delimiter, data.Select(x => x.ToString()).Reverse());
    }

    IEnumerable<string> IPushStack.AsStrings() {
      return data.Select(x => x.ToString());
    }

    IEnumerable<object> IPushStack.AsObjects() {
      return data.OfType<object>();
    }
  }
}