using Sandbox;
using System;

namespace VeloX;


[GameResource( "Wheel Friction", "tire", "Wheel Friction", Category = "VeloX", Icon = "radio_button_checked" )]
public class TirePreset : GameResource
{

	[Property] public Pacejka Pacejka { get; set; }

	public float RollResistanceLin { get; set; } = 1E-3f;
	public float RollResistanceQuad { get; set; } = 1E-6f;

	public float GetRollingResistance( float velocity, float resistance_factor )
	{   // surface influence on rolling resistance
		float resistance = resistance_factor * RollResistanceLin;

		// heat due to tire deformation increases rolling resistance
		// approximate by quadratic function
		resistance += velocity * velocity * RollResistanceQuad;

		return resistance;
	}

	public void ComputeSlip( float vlon, float vlat, float vrot, out float slip_ratio, out float slip_angle )
	{
		float rvlon = 1 / MathF.Max( MathF.Abs( vlon ), 1E-3f );
		float vslip = vrot - vlon;
		slip_ratio = vslip * rvlon;
		slip_angle = -MathF.Atan( vlat * rvlon );
	}

	/// approximate asin(x) = x + x^3/6 for +-18 deg range
	public static float ComputeCamberAngle( float sin_camber )
	{
		float sc = Math.Clamp( sin_camber, -0.3f, 0.3f );
		return ((1 / 6.0f) * (sc * sc) + 1) * sc;
	}

	public struct TireState
	{
		public float friction = 0;  // surface friction coefficient
		public float camber = 0;  // tire camber angle relative to track surface
		public float vcam = 0;  // camber thrust induced lateral slip velocity
		public float slip = 0;  // ratio of tire contact patch speed to road speed
		public float slip_angle = 0;  // the angle between the wheel heading and the wheel velocity
		public float ideal_slip = 0;  // peak force slip ratio
		public float ideal_slip_angle = 0;  // peak force slip angle
		public float fx = 0;  // positive during traction
		public float fy = 0;  // positive in a right turn
		public float mz = 0;  // positive in a left turn

		public TireState()
		{
		}
	};

	public void ComputeState(
		float normal_force,
		float rot_velocity,
		float lon_velocity,
		float lat_velocity,
		float camber_angle,
		out TireState s
	)
	{
		s = new TireState
		{
			camber = camber_angle,
			friction = 1.0f
		};

		if ( normal_force * s.friction < 1E-6f )
		{
			s.slip = s.slip_angle = 0;
			s.fx = s.fy = s.mz = 0;
			return;
		}

		float Fz = Math.Min( normal_force * 1E-3f, 30f );
		ComputeSlip( lon_velocity, lat_velocity, rot_velocity, out float slip, out float slip_angle );
		float sigma = slip;
		float alpha = slip_angle.RadianToDegree();
		float gamma = s.camber.RadianToDegree();
		float Fx = Pacejka.PacejkaFx( sigma, Fz, s.friction );
		float Fy = Pacejka.PacejkaFy( alpha, Fz, gamma, s.friction, out float camber_alpha );
		s.vcam = ComputeCamberVelocity( camber_alpha.DegreeToRadian(), lon_velocity );
		s.slip = slip;
		s.slip_angle = slip_angle;
		s.fx = Fx;
		s.fy = Fy;
	}

	public static float ComputeCamberVelocity( float sa, float vx )
	{
		float tansa = (1 / 3.0f * (sa * sa) + 1) * sa;
		return tansa * vx;
	}
}