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

namespace NTERA.Engine
{
	public class Variable : IEnumerable<KeyValuePair<int[], Value>>
	{
		public string Name { get; }

		public ValueType Type { get; }

		protected Dictionary<int[], Value> Dictionary { get; } = new Dictionary<int[], Value>(new ZeroIntegerArrayEqualityComparer());
		
		public Variable(string name, ValueType type)
		{
			Name = name;
			Type = type;
		}

		public virtual Value this[params int[] index]
		{
			get
			{
				if (Dictionary.TryGetValue(index, out var value))
					return value;

				return Type == ValueType.String ? new Value("") : new Value(0d);
			}
			set => Dictionary[index] = value;
		}

		public IEnumerator<KeyValuePair<int[], Value>> GetEnumerator()
		{
			return Dictionary.GetEnumerator();
		}

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

	public class ZeroIntegerArrayEqualityComparer : IEqualityComparer<int[]>
	{
		public bool Equals(int[] x, int[] y)
		{
			if (x == null && y != null
				|| y == null && x != null)
				return false;

			if (x == null || x.Length == 0)
				x = new[] { 0 };

			if (y == null || y.Length == 0)
				y = new[] { 0 };

			int xNonZeroLength = x.Length;
			int yNonZeroLength = y.Length;

			for (; xNonZeroLength > 0; xNonZeroLength--)
			{
				if (x[xNonZeroLength - 1] != 0)
					break;
			}

			for (; yNonZeroLength > 0; yNonZeroLength--)
			{
				if (y[yNonZeroLength - 1] != 0)
					break;
			}

			if (xNonZeroLength != yNonZeroLength)
			{
				return false;
			}

			for (int i = 0; i < xNonZeroLength; i++)
			{
				if (x[i] != y[i])
				{
					return false;
				}
			}

			return true;
		}

		public int GetHashCode(int[] obj)
		{
			if (obj.Length == 0)
				return 17 * 23; //equal to int[] { 0 }

			int nonZeroLength = obj.Length;

			for (; nonZeroLength > 0; nonZeroLength--)
			{
				if (obj[nonZeroLength - 1] != 0)
					break;
			}

			int result = 17;
			for (int i = 0; i < nonZeroLength; i++)
			{
				unchecked
				{
					result = result * 23 + obj[i];
				}
			}

			return result;
		}
	}
}