// Copyright (c) 2014-2015 Robert Rouhani <robert.rouhani@gmail.com> and other contributors (see CONTRIBUTORS file).
// Licensed under the MIT License - https://raw.github.com/Robmaister/SharpNav/master/LICENSE

using System.Runtime.InteropServices;

using SharpNav.Geometry;

#if MONOGAME
using Vector3 = Microsoft.Xna.Framework.Vector3;
#elif OPENTK
using Vector3 = OpenTK.Vector3;
#elif SHARPDX
using Vector3 = SharpDX.Vector3;
#endif

namespace SharpNav
{
	/// <summary>
	/// A <see cref="ContourVertex"/> is a vertex that stores 3 integer coordinates and a region ID, and is used to build <see cref="Contour"/>s.
	/// </summary>
	[StructLayout(LayoutKind.Sequential)]
	public struct ContourVertex
	{
		/// <summary>
		/// The X coordinate.
		/// </summary>
		public int X;

		/// <summary>
		/// The Y coordinate.
		/// </summary>
		public int Y;

		/// <summary>
		/// The Z coordinate.
		/// </summary>
		public int Z;

		/// <summary>
		/// The region that the vertex belongs to.
		/// </summary>
		public RegionId RegionId;

		/// <summary>
		/// Initializes a new instance of the <see cref="ContourVertex"/> struct.
		/// </summary>
		/// <param name="x">The X coordinate.</param>
		/// <param name="y">The Y coordinate.</param>
		/// <param name="z">The Z coordinate.</param>
		/// <param name="region">The region ID.</param>
		public ContourVertex(int x, int y, int z, RegionId region)
		{
			this.X = x;
			this.Y = y;
			this.Z = z;
			this.RegionId = region;
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="SharpNav.ContourVertex"/> struct.
		/// </summary>
		/// <param name="vec">The array of X,Y,Z coordinates.</param>
		/// <param name="region">The Region ID.</param>
		public ContourVertex(Vector3 vec, RegionId region)
		{
			this.X = (int)vec.X;
			this.Y = (int)vec.Y;
			this.Z = (int)vec.Z;
			this.RegionId = region;
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="ContourVertex"/> struct as a copy.
		/// </summary>
		/// <param name="vert">The original vertex.</param>
		/// <param name="index">The index of the original vertex, which is temporarily stored in the <see cref="RegionId"/> field.</param>
		public ContourVertex(ContourVertex vert, int index)
		{
			this.X = vert.X;
			this.Y = vert.Y;
			this.Z = vert.Z;
			this.RegionId = new RegionId(index);
		}

		/// <summary>
		/// Initializes a new instance of the <see cref="ContourVertex"/> struct as a copy.
		/// </summary>
		/// <param name="vert">The original vertex.</param>
		/// <param name="region">The region that the vertex belongs to.</param>
		public ContourVertex(ContourVertex vert, RegionId region)
		{
			this.X = vert.X;
			this.Y = vert.Y;
			this.Z = vert.Z;
			this.RegionId = region;
		}

		/// <summary>
		/// Gets the leftness of a triangle formed from 3 contour vertices.
		/// </summary>
		/// <param name="a">The first vertex.</param>
		/// <param name="b">The second vertex.</param>
		/// <param name="c">The third vertex.</param>
		/// <returns>A value indicating the leftness of the triangle.</returns>
		public static bool IsLeft(ref ContourVertex a, ref ContourVertex b, ref ContourVertex c)
		{
			int area;
			Area2D(ref a, ref b, ref c, out area);
			return area < 0;
		}

		/// <summary>
		/// Gets the 2D area of the triangle ABC.
		/// </summary>
		/// <param name="a">Point A of triangle ABC.</param>
		/// <param name="b">Point B of triangle ABC.</param>
		/// <param name="c">Point C of triangle ABC.</param>
		/// <param name="area">The 2D area of the triangle.</param>
		public static void Area2D(ref ContourVertex a, ref ContourVertex b, ref ContourVertex c, out int area)
		{
			area = (b.X - a.X) * (c.Z - a.Z) - (c.X - a.X) * (b.Z - a.Z);
		}
	}
}