using MoonWorks.Math.Fixed;
using System.Runtime.CompilerServices;

namespace MoonWorks.Collision.Fixed
{
	public static class NarrowPhase
	{
		private struct Edge
		{
			public Fix64 Distance;
			public Vector2 Normal;
			public int Index;
		}

		public static bool TestCollision<T, U>(Collider<T> colliderA, in Transform2D transformA, Collider<U> colliderB, in Transform2D transformB) where T : struct, IShape2D where U : struct, IShape2D
		{
			foreach (var shapeA in colliderA)
			{
				foreach (var shapeB in colliderB)
				{
					if (TestCollision(shapeA, transformA, shapeB, transformB))
					{
						return true;
					}
				}
			}

			return false;
		}

		public static bool TestCollision<T, U>(Collider<T> collider, in Transform2D transformA, U shape, in Transform2D transformB) where T : struct, IShape2D where U : struct, IShape2D
		{
			foreach (var colliderShape in collider)
			{
				if (TestCollision(colliderShape, transformA, shape, transformB))
				{
					return true;
				}
			}

			return false;
		}

		public static bool TestCollision<T, U>(U shape, in Transform2D transformA, Collider<T> collider, in Transform2D transformB) where T : struct, IShape2D where U : struct, IShape2D
		{
			return TestCollision(collider, transformB, shape, transformA);
		}

		public static bool TestCollision<T, U>(in T shapeA, in Transform2D transformA, in U shapeB, in Transform2D transformB) where T : struct, IShape2D where U : struct, IShape2D
		{
			if (shapeA is Circle circle)
			{
				if (shapeB is Circle circleB)
				{
					return TestCollision(circle, transformA, circleB, transformB);
				}
				else if (shapeB is Point pointB)
				{
					return TestCollision(circle, transformA, pointB, transformB);
				}
				else if (shapeB is Rectangle rectangleB)
				{
					return TestCollision(circle, transformA, rectangleB, transformB);
				}
			}
			else if (shapeA is Point point)
			{
				if (shapeB is Circle circleB)
				{
					return TestCollision(point, transformA, circleB, transformB);
				}
				else if (shapeB is Point pointB)
				{
					return TestCollision(point, transformA, pointB, transformB);
				}
				else if (shapeB is Rectangle rectangleB)
				{
					return TestCollision(point, transformA, rectangleB, transformB);
				}
			}
			else if (shapeA is Rectangle rectangle)
			{
				if (shapeB is Circle circleB)
				{
					return TestCollision(rectangle, transformA, circleB, transformB);
				}
				else if (shapeB is Point pointB)
				{
					return TestCollision(rectangle, transformA, pointB, transformB);
				}
				else if (shapeB is Rectangle rectangleB)
				{
					return TestCollision(rectangle, transformA, rectangleB, transformB);
				}
			}
			else if (shapeA is Line line)
			{
				if (shapeB is Line lineB)
				{
					return TestCollision(line, transformA, lineB, transformB);
				}
			}

			return FindCollisionSimplex(shapeA, transformA, shapeB, transformB).Item1;
		}

		public static bool TestCollision(in Rectangle rectangleA, in Transform2D transformA, in Rectangle rectangleB, in Transform2D transformB)
		{
			if (transformA.IsAxisAligned && transformB.IsAxisAligned)
			{
				return TestRectangleOverlap(rectangleA, transformA, rectangleB, transformB);
			}
			else
			{
				return FindCollisionSimplex(rectangleA, transformA, rectangleB, transformB).Item1;
			}
		}

		public static bool TestCollision(in Point point, in Transform2D transformA, in Rectangle rectangle, in Transform2D transformB)
		{
			if (transformB.IsAxisAligned)
			{
				return TestPointRectangleOverlap(point, transformA, rectangle, transformB);
			}
			else
			{
				return FindCollisionSimplex(point, transformA, rectangle, transformB).Item1;
			}
		}

		public static bool TestCollision(in Rectangle rectangle, in Transform2D transformA, in Point point, in Transform2D transformB)
		{
			return TestCollision(point, transformB, rectangle, transformA);
		}

		public static bool TestCollision(in Rectangle rectangle, in Transform2D transformA, in Circle circle, in Transform2D transformB)
		{
			if (transformA.IsAxisAligned && transformB.IsUniformScale)
			{
				return TestCircleRectangleOverlap(circle, transformB, rectangle, transformA);
			}
			else
			{
				return FindCollisionSimplex(rectangle, transformA, circle, transformB).Item1;
			}
		}

		public static bool TestCollision(in Circle circle, in Transform2D transformA, in Rectangle rectangle, in Transform2D transformB)
		{
			return TestCollision(rectangle, transformB, circle, transformA);
		}

		public static bool TestCollision(in Circle circle, in Transform2D transformA, in Point point, in Transform2D transformB)
		{
			if (transformA.IsUniformScale)
			{
				return TestCirclePointOverlap(circle, transformA, point, transformB);
			}
			else
			{
				return FindCollisionSimplex(circle, transformA, point, transformB).Item1;
			}
		}

		public static bool TestCollision(in Point point, in Transform2D transformA, in Circle circle, in Transform2D transformB)
		{
			return TestCollision(circle, transformB, point, transformA);
		}

		public static bool TestCollision(in Circle circleA, in Transform2D transformA, in Circle circleB, in Transform2D transformB)
		{
			if (transformA.IsUniformScale && transformB.IsUniformScale)
			{
				return TestCircleOverlap(circleA, transformA, circleB, transformB);
			}
			else
			{
				return FindCollisionSimplex(circleA, transformA, circleB, transformB).Item1;
			}
		}

		public static bool TestCollision(in Line lineA, in Transform2D transformA, in Line lineB, in Transform2D transformB)
		{
			return TestLineOverlap(lineA, transformA, lineB, transformB);
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestRectangleOverlap(in Rectangle rectangleA, in Transform2D transformA, in Rectangle rectangleB, in Transform2D transformB)
		{
			var firstAABB = rectangleA.TransformedAABB(transformA);
			var secondAABB = rectangleB.TransformedAABB(transformB);

			return firstAABB.Left < secondAABB.Right && firstAABB.Right > secondAABB.Left && firstAABB.Top < secondAABB.Bottom && firstAABB.Bottom > secondAABB.Top;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestPointRectangleOverlap(in Point point, in Transform2D pointTransform, in Rectangle rectangle, in Transform2D rectangleTransform)
		{
			var transformedPoint = pointTransform.Position;
			var AABB = rectangle.TransformedAABB(rectangleTransform);

			return transformedPoint.X > AABB.Left && transformedPoint.X < AABB.Right && transformedPoint.Y < AABB.Bottom && transformedPoint.Y > AABB.Top;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestCirclePointOverlap(in Circle circle, in Transform2D circleTransform, in Point point, in Transform2D pointTransform)
		{
			var circleCenter = circleTransform.Position;
			var circleRadius = circle.Radius * circleTransform.Scale.X;

			var distanceX = circleCenter.X - pointTransform.Position.X;
			var distanceY = circleCenter.Y - pointTransform.Position.Y;

			return (distanceX * distanceX) + (distanceY * distanceY) < (circleRadius * circleRadius);
		}

		/// <summary>
		/// NOTE: The rectangle must be axis aligned, and the scaling of the circle must be uniform.
		/// </summary>
		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestCircleRectangleOverlap(in Circle circle, in Transform2D circleTransform, in Rectangle rectangle, in Transform2D rectangleTransform)
		{
			var circleCenter = circleTransform.Position;
			var circleRadius = circle.Radius * circleTransform.Scale.X;
			var AABB = rectangle.TransformedAABB(rectangleTransform);

			var closestX = Fix64.Clamp(circleCenter.X, AABB.Left, AABB.Right);
			var closestY = Fix64.Clamp(circleCenter.Y, AABB.Top, AABB.Bottom);

			var distanceX = circleCenter.X - closestX;
			var distanceY = circleCenter.Y - closestY;

			var distanceSquared = (distanceX * distanceX) + (distanceY * distanceY);
			return distanceSquared < (circleRadius * circleRadius);
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestCircleOverlap(in Circle circleA, in Transform2D transformA, in Circle circleB, in Transform2D transformB)
		{
			var radiusA = circleA.Radius * transformA.Scale.X;
			var radiusB = circleB.Radius * transformB.Scale.Y;

			var centerA = transformA.Position;
			var centerB = transformB.Position;

			var distanceSquared = (centerA - centerB).LengthSquared();
			var radiusSumSquared = (radiusA + radiusB) * (radiusA + radiusB);

			return distanceSquared < radiusSumSquared;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		public static bool TestLineOverlap(in Line lineA, in Transform2D transformA, in Line lineB, in Transform2D transformB)
		{
			var b = lineA.End - lineA.Start;
			var d = lineB.End - lineB.Start;
			var bDotDPerp = b.X * d.Y - b.Y * d.X;

			if (bDotDPerp == Fix64.Zero)
			{
				return false;
			}

			var c = lineB.Start - lineA.Start;
			var t = (c.X * d.Y - c.Y * d.X) / bDotDPerp;
			if (t < 0 || t > 1)
			{
				return false;
			}

			var u = (c.X * b.Y - c.Y * b.X) / bDotDPerp;
			if (u < 0 || u > 1)
			{
				return false;
			}

			return true;
		}

		public static bool TestLineOverlap(in Line lineA, in Transform2D transformA, in Line lineB, in Transform2D transformB, out Vector2 intersection)
		{
			intersection = Vector2.Zero;

			var b = lineA.End - lineA.Start;
			var d = lineB.End - lineB.Start;
			var bDotDPerp = b.X * d.Y - b.Y * d.X;

			if (bDotDPerp == Fix64.Zero)
			{
				return false;
			}

			var c = lineB.Start - lineA.Start;
			var t = (c.X * d.Y - c.Y * d.X) / bDotDPerp;
			if (t < 0 || t > 1)
			{
				return false;
			}

			var u = (c.X * b.Y - c.Y * b.X) / bDotDPerp;
			if (u < 0 || u > 1)
			{
				return false;
			}

			intersection = lineA.Start + t * b;
			return true;
		}

		public static bool TestLineAABBOverlap(in Line line, in AABB2D aabb, out Fix64 entry, out Fix64 exit)
		{
			entry = Fix64.MinValue;
			exit = Fix64.MaxValue;

			var lineDirection = line.End - line.Start;

			if (lineDirection.X != Fix64.Zero)
			{
				var tx1 = (aabb.Min.X - line.Start.X) / lineDirection.X;
				var tx2 = (aabb.Max.X - line.Start.X) / lineDirection.X;

				entry = Fix64.Max(entry, Fix64.Min(tx1, tx2));
				exit = Fix64.Min(exit, Fix64.Max(tx1, tx2));
			}

			if (lineDirection.Y != Fix64.Zero)
			{
				var ty1 = (aabb.Min.Y - line.Start.Y) / lineDirection.Y;
				var ty2 = (aabb.Max.Y - line.Start.Y) / lineDirection.Y;

				entry = Fix64.Max(entry, Fix64.Min(ty1, ty2));
				exit = Fix64.Min(exit, Fix64.Max(ty1, ty2));
			}

			return exit >= entry;
		}

		public static bool TestPointOverlap(in Point pointA, in Transform2D transformA, in Point pointB, in Transform2D transformB)
		{
			return transformA.Position == transformB.Position;
		}

		public static (bool, Simplex2D) FindCollisionSimplex<T, U>(T shapeA, Transform2D transformA, U shapeB, Transform2D transformB) where T : IShape2D where U : IShape2D
		{
			var minkowskiDifference = new MinkowskiDifference<T, U>(shapeA, transformA, shapeB, transformB);
			var c = minkowskiDifference.Support(Vector2.UnitX);
			var b = minkowskiDifference.Support(-Vector2.UnitX);
			return Check(minkowskiDifference, c, b);
		}

		public unsafe static Vector2 Intersect(IShape2D shapeA, Transform2D Transform2DA, IShape2D shapeB, Transform2D Transform2DB, Simplex2D simplex)
		{
			if (shapeA == null) { throw new System.ArgumentNullException(nameof(shapeA)); }
			if (shapeB == null) { throw new System.ArgumentNullException(nameof(shapeB)); }
			if (!simplex.TwoSimplex) { throw new System.ArgumentException("Simplex must be a 2-Simplex.", nameof(simplex)); }

			var epsilon = Fix64.FromFraction(1, 10000);

			var a = simplex.A;
			var b = simplex.B.Value;
			var c = simplex.C.Value;

			Vector2 intersection = default;

			for (var i = 0; i < 32; i++)
			{
				var edge = FindClosestEdge(simplex);
				var support = CalculateSupport(shapeA, Transform2DA, shapeB, Transform2DB, edge.Normal);
				var distance = Vector2.Dot(support, edge.Normal);

				intersection = edge.Normal;
				intersection *= distance;

				if (Fix64.Abs(distance - edge.Distance) <= epsilon)
				{
					return intersection;
				}
				else
				{
					simplex.Insert(support, edge.Index);
				}
			}

			return intersection; // close enough
		}

		private static unsafe Edge FindClosestEdge(Simplex2D simplex)
		{
			var closestDistance = Fix64.MaxValue;
			var closestNormal = Vector2.Zero;
			var closestIndex = 0;

			for (var i = 0; i < 4; i += 1)
			{
				var j = (i + 1 == 3) ? 0 : i + 1;

				var a = simplex[i];
				var b = simplex[j];

				var e = b - a;

				var oa = a;

				var n = Vector2.Normalize(TripleProduct(e, oa, e));

				var d = Vector2.Dot(n, a);

				if (d < closestDistance)
				{
					closestDistance = d;
					closestNormal = n;
					closestIndex = j;
				}
			}

			return new Edge
			{
				Distance = closestDistance,
				Normal = closestNormal,
				Index = closestIndex
			};
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private static Vector2 CalculateSupport<T, U>(T shapeA, Transform2D Transform2DA, U shapeB, Transform2D Transform2DB, Vector2 direction) where T : IShape2D where U : IShape2D
		{
			return shapeA.Support(direction, Transform2DA) - shapeB.Support(-direction, Transform2DB);
		}

		private static (bool, Simplex2D) Check<T, U>(MinkowskiDifference<T, U> minkowskiDifference, Vector2 c, Vector2 b) where T : IShape2D where U : IShape2D
		{
			var cb = c - b;
			var c0 = -c;
			var d = Direction(cb, c0);
			return DoSimplex(minkowskiDifference, new Simplex2D(b, c), d);
		}

		private static (bool, Simplex2D) DoSimplex<T, U>(MinkowskiDifference<T, U> minkowskiDifference, Simplex2D simplex, Vector2 direction) where T : IShape2D where U : IShape2D
		{
			var a = minkowskiDifference.Support(direction);
			var notPastOrigin = Vector2.Dot(a, direction) < Fix64.Zero;
			var (intersects, newSimplex, newDirection) = EnclosesOrigin(a, simplex);

			if (notPastOrigin)
			{
				return (false, default(Simplex2D));
			}
			else if (intersects)
			{
				return (true, new Simplex2D(simplex.A, simplex.B.Value, a));
			}
			else
			{
				return DoSimplex(minkowskiDifference, newSimplex, newDirection);
			}
		}

		private static (bool, Simplex2D, Vector2) EnclosesOrigin(Vector2 a, Simplex2D simplex)
		{
			if (simplex.ZeroSimplex)
			{
				return HandleZeroSimplex(a, simplex.A);
			}
			else if (simplex.OneSimplex)
			{
				return HandleOneSimplex(a, simplex.A, simplex.B.Value);
			}
			else
			{
				return (false, simplex, Vector2.Zero);
			}
		}

		private static (bool, Simplex2D, Vector2) HandleZeroSimplex(Vector2 a, Vector2 b)
		{
			var ab = b - a;
			var a0 = -a;
			var (newSimplex, newDirection) = SameDirection(ab, a0) ? (new Simplex2D(a, b), Perpendicular(ab, a0)) : (new Simplex2D(a), a0);
			return (false, newSimplex, newDirection);
		}

		private static (bool, Simplex2D, Vector2) HandleOneSimplex(Vector2 a, Vector2 b, Vector2 c)
		{
			var a0 = -a;
			var ab = b - a;
			var ac = c - a;
			var abp = Perpendicular(ab, -ac);
			var acp = Perpendicular(ac, -ab);

			if (SameDirection(abp, a0))
			{
				if (SameDirection(ab, a0))
				{
					return (false, new Simplex2D(a, b), abp);
				}
				else
				{
					return (false, new Simplex2D(a), a0);
				}
			}
			else if (SameDirection(acp, a0))
			{
				if (SameDirection(ac, a0))
				{
					return (false, new Simplex2D(a, c), acp);
				}
				else
				{
					return (false, new Simplex2D(a), a0);
				}
			}
			else
			{
				return (true, new Simplex2D(b, c), a0);
			}
		}

		private static Vector2 TripleProduct(Vector2 a, Vector2 b, Vector2 c)
		{
			var A = new Vector3(a.X, a.Y, Fix64.Zero);
			var B = new Vector3(b.X, b.Y, Fix64.Zero);
			var C = new Vector3(c.X, c.Y, Fix64.Zero);

			var first = Vector3.Cross(A, B);
			var second = Vector3.Cross(first, C);

			return new Vector2(second.X, second.Y);
		}

		private static Vector2 Direction(Vector2 a, Vector2 b)
		{
			var d = TripleProduct(a, b, a);
			var collinear = d == Vector2.Zero;
			return collinear ? new Vector2(a.Y, -a.X) : d;
		}

		[MethodImpl(MethodImplOptions.AggressiveInlining)]
		private static bool SameDirection(Vector2 a, Vector2 b)
		{
			return Vector2.Dot(a, b) > Fix64.Zero;
		}

		private static Vector2 Perpendicular(Vector2 a, Vector2 b)
		{
			return TripleProduct(a, b, a);
		}
	}
}