using System;
using UnityEngine;

namespace GravityFunctionality
{
	/// <summary>
	/// Available types of gravity.
	/// Need to match the existing functions!
	/// </summary>
	public enum Gravity
	{
		DownGravity = 0, UpGravity = 1, NoGravity = 2, InwardsGravity = 3, OutwardsGravity = 4
	}

	/// <summary>
	/// Serializable mapping of a color to a gravity.
	/// </summary>
	[Serializable]
	public class GravityColorEntry
	{
		public Gravity gravity;
		public Color color;
	}

	public static class GravityHelpers
	{
		/// <summary>
		/// Function which returns a gravity zero vector.
		/// </summary>
		private static readonly Func<Transform, Transform, Vector3> _noGravity =
			new((gravitySource, target) => new Vector3());

		/// <summary>
		/// Function which returns a gravity vector downwards, depending
		/// on the parent transforms rotation. 
		/// The parenting transform for a ship is the arena it's in.
		/// </summary>
		private static readonly Func<Transform, Transform, Vector3> _downGravity =
			new((gravitySource, target) =>
				 gravitySource.rotation * Vector3.down);

		/// <summary>
		/// Function which returns a gravity vector upwards, depending
		/// on the parent transforms rotation. 
		/// The parenting transform for a ship is the arena it's in.
		/// </summary>
		private static readonly Func<Transform, Transform, Vector3> _upGravity =
			new((gravitySource, target) =>
				 gravitySource.rotation * Vector3.up);

		/// <summary>
		/// Function which returns a gravity vector towards the center of the parenting transform.
		/// The parenting transform for a ship is the arena it's in.
		/// </summary>
		private static readonly Func<Transform, Transform, Vector3> _inwardsGravity =
			new((gravitySource, target) =>
				 (-target.position + gravitySource.position).normalized);

		/// <summary>
		/// Function which returns a gravity vector outwards from the center of the parenting transform.
		/// The parenting transform for a ship is the arena it's in.
		/// </summary>
		private static readonly Func<Transform, Transform, Vector3> _outwardsGravity =
		new((gravitySource, target) =>
				(target.position - gravitySource.position).normalized);

		/// <summary>
		/// Gets the gravity function belonging to the supplied gravity enum.
		/// </summary>
		/// <param name="gravity">Enum for the gravity function to get.</param>
		/// <returns>A gravity function</returns>
		public static Func<Transform, Transform, Vector3> GetGravityFunction(Gravity gravity)
		{
			switch (gravity)
			{
				case Gravity.DownGravity:
					return _downGravity;
				case Gravity.UpGravity:
					return _upGravity;
				case Gravity.NoGravity:
					return _noGravity;
				case Gravity.OutwardsGravity:
					return _outwardsGravity;
				case Gravity.InwardsGravity:
					return _inwardsGravity;
				default:
					return null;
			}
		}
	}
}