#region Copyright & License Information
/*
 * Copyright (c) The OpenRA Developers and Contributors
 * This file is part of OpenRA, which is free software. It is made
 * available to you 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. For more
 * information, see COPYING.
 */
#endregion

using System;
using OpenRA.Primitives;

namespace OpenRA
{
	// Represents a layer of "something" that covers the map
	public sealed class CellLayer<T> : CellLayerBase<T>
	{
		public event Action<CPos> CellEntryChanged = null;

		public CellLayer(Map map)
			: base(map) { }

		public CellLayer(MapGridType gridType, Size size)
			: base(gridType, size) { }

		public override void CopyValuesFrom(CellLayerBase<T> anotherLayer)
		{
			if (CellEntryChanged != null)
				throw new InvalidOperationException(
					$"Cannot copy values when there are listeners attached to the {nameof(CellEntryChanged)} event.");

			base.CopyValuesFrom(anotherLayer);
		}

		public override void Clear()
		{
			if (CellEntryChanged != null)
				throw new InvalidOperationException(
					$"Cannot clear values when there are listeners attached to the {nameof(CellEntryChanged)} event.");

			base.Clear();
		}

		public override void Clear(T clearValue)
		{
			if (CellEntryChanged != null)
				throw new InvalidOperationException(
					$"Cannot clear values when there are listeners attached to the {nameof(CellEntryChanged)} event.");

			base.Clear(clearValue);
		}

		// Resolve an array index from cell coordinates
		int Index(CPos cell)
		{
			// PERF: Inline CPos.ToMPos to avoid MPos allocation
			var x = cell.X;
			var y = cell.Y;
			if (GridType == MapGridType.Rectangular)
				return y * Size.Width + x;

			var u = (x - y) / 2;
			var v = x + y;
			return v * Size.Width + u;
		}

		// Resolve an array index from map coordinates
		int Index(MPos uv)
		{
			return uv.V * Size.Width + uv.U;
		}

		/// <summary>Gets or sets the <see cref="CellLayer"/> using cell coordinates.</summary>
		public T this[CPos cell]
		{
			get => Entries[Index(cell)];

			set
			{
				Entries[Index(cell)] = value;

				CellEntryChanged?.Invoke(cell);
			}
		}

		/// <summary>Gets or sets the layer contents using raw map coordinates (not CPos!).</summary>
		public T this[MPos uv]
		{
			get => Entries[Index(uv)];

			set
			{
				Entries[Index(uv)] = value;

				CellEntryChanged?.Invoke(uv.ToCPos(GridType));
			}
		}

		public bool TryGetValue(CPos cell, out T value)
		{
			// .ToMPos() returns the same result if the X and Y coordinates
			// are switched. X < Y is invalid in the RectangularIsometric coordinate system,
			// so we pre-filter these to avoid returning the wrong result
			if (GridType == MapGridType.RectangularIsometric && cell.X < cell.Y)
			{
				value = default;
				return false;
			}

			var uv = cell.ToMPos(GridType);
			if (Bounds.Contains(uv.U, uv.V))
			{
				value = Entries[Index(uv)];
				return true;
			}

			value = default;
			return false;
		}

		public bool Contains(CPos cell)
		{
			// .ToMPos() returns the same result if the X and Y coordinates
			// are switched. X < Y is invalid in the RectangularIsometric coordinate system,
			// so we pre-filter these to avoid returning the wrong result
			if (GridType == MapGridType.RectangularIsometric && cell.X < cell.Y)
				return false;

			return Contains(cell.ToMPos(GridType));
		}

		public bool Contains(MPos uv)
		{
			return Bounds.Contains(uv.U, uv.V);
		}

		public CPos Clamp(CPos uv)
		{
			return Clamp(uv.ToMPos(GridType)).ToCPos(GridType);
		}

		public MPos Clamp(MPos uv)
		{
			return uv.Clamp(new Rectangle(0, 0, Size.Width - 1, Size.Height - 1));
		}
	}

	// Helper functions
	public static class CellLayer
	{
		/// <summary>Create a new layer by resizing another layer. New cells are filled with defaultValue.</summary>
		public static CellLayer<T> Resize<T>(CellLayer<T> layer, Size newSize, T defaultValue)
		{
			var result = new CellLayer<T>(layer.GridType, newSize);
			var width = Math.Min(layer.Size.Width, newSize.Width);
			var height = Math.Min(layer.Size.Height, newSize.Height);

			result.Clear(defaultValue);
			for (var j = 0; j < height; j++)
				for (var i = 0; i < width; i++)
					result[new MPos(i, j)] = layer[new MPos(i, j)];

			return result;
		}
	}
}