using System;
using System.Runtime.CompilerServices;
using UnityEngine;

public readonly struct Rotation2D
{
	public Rotation2D(Angle angle)
	{
		Sin = Mathf.Sin(angle.Radians);
		OneMinusCos = 1f - Mathf.Cos(angle.Radians);
	}

	private Rotation2D(float sin, float oneMinusCos)
	{
		Sin = sin;
		OneMinusCos = oneMinusCos;
	}

	public float Sin { get; }

	public float OneMinusCos { get; }

	public float Cos => 1f - OneMinusCos;

	public Angle CounterclockwiseAngle => Angle.FromRadians(Mathf.Atan2(Sin, Cos));

	public Angle ClockwiseAngle => -CounterclockwiseAngle;

	public Vector2 UpAxis => new Vector2(-Sin, Cos);

	public Vector2 RightAxis => new Vector2(Cos, Sin);

	public Rotation2D Inverse => new Rotation2D(-Sin, OneMinusCos);

	public static Rotation2D Identity => new Rotation2D();

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static Vector2 operator *(Rotation2D rotation2D, Vector2 vector)
	{
		float sin = rotation2D.Sin;
		float cos = rotation2D.Cos;
		return new Vector2(
			vector.x * cos - vector.y * sin,
			vector.x * sin + vector.y * cos
		);
	}

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static Rotation2D operator *(Rotation2D a, Rotation2D b)
	{
		float sinA = a.Sin;
		float cosA = a.Cos;
		float sinB = b.Sin;
		float cosB = b.Cos;

		float cos = cosA * cosB - sinA * sinB;
		float sin = sinA * cosB + cosA * sinB;

		return new Rotation2D(sin, 1f - cos);
	}

	[MethodImpl(MethodImplOptions.AggressiveInlining)]
	public static Rotation2D FromToRotation(Vector2 fromDirection, Vector2 toDirection)
	{
		float angleRadians = Mathf.Atan2(toDirection.y, toDirection.x) - Mathf.Atan2(fromDirection.y, fromDirection.x);
		return new Rotation2D(Angle.FromRadians(angleRadians));
	}
}