/*
 * Copyright (c) 2012-2026 Daniele Bartolini et al.
 * SPDX-License-Identifier: GPL-3.0-or-later
 */

namespace Crown
{
[Compact]
public struct Quaternion
{
	public double x;
	public double y;
	public double z;
	public double w;

	public Quaternion(double x, double y, double z, double w)
	{
		this.x = x;
		this.y = y;
		this.z = z;
		this.w = w;
	}

	public Quaternion.from_array(Gee.ArrayList<Value?> arr)
	{
		this.x = (double)arr[0];
		this.y = (double)arr[1];
		this.z = (double)arr[2];
		this.w = (double)arr[3];
	}

	public Quaternion.from_axis_angle(Vector3 axis, float angle)
	{
		double ha = angle * 0.5;
		double sa = Math.sin(ha);
		double ca = Math.cos(ha);
		this.x = axis.x * sa;
		this.y = axis.y * sa;
		this.z = axis.z * sa;
		this.w = ca;
	}

	public Quaternion.from_euler(double rx, double ry, double rz)
	{
		// http://www.euclideanspace.com/maths/geometry/rotations/conversions/eulerToQuaternion/
		double c1 = Math.cos(ry*0.5);
		double s1 = Math.sin(ry*0.5);
		double c2 = Math.cos(rz*0.5);
		double s2 = Math.sin(rz*0.5);
		double c3 = Math.cos(rx*0.5);
		double s3 = Math.sin(rx*0.5);
		double c1c2 = c1*c2;
		double s1s2 = s1*s2;

		double nw = c1c2*c3 - s1s2*s3;
		double nx = c1c2*s3 + s1s2*c3;
		double ny = s1*c2*c3 + c1*s2*s3;
		double nz = c1*s2*c3 - s1*c2*s3;

		this.x = nx;
		this.y = ny;
		this.z = nz;
		this.w = nw;
	}

	public Quaternion.from_matrix(Matrix4x4 m)
	{
		// http://www.euclideanspace.com/maths/geometry/rotations/conversions/matrixToQuaternion/
		double tr = m.x.x + m.y.y + m.z.z;

		if (tr > 0.0) {
			double sq = Math.sqrt(1.0 + tr) * 0.5;
			double inv = 0.25 / sq;
			this.w = sq;
			this.x = (m.y.z - m.z.y) * inv;
			this.y = (m.z.x - m.x.z) * inv;
			this.z = (m.x.y - m.y.x) * inv;
		} else if ((m.x.x > m.y.y) && (m.x.x > m.z.z)) {
			double sq = Math.sqrt(1.0 + m.x.x - m.y.y - m.z.z) * 0.5;
			double inv = 0.25 / sq;
			this.x = sq;
			this.w = (m.y.z - m.z.y) * inv;
			this.y = (m.x.y + m.y.x) * inv;
			this.z = (m.z.x + m.x.z) * inv;
		} else if (m.y.y > m.z.z) {
			double sq = Math.sqrt(1.0 + m.y.y - m.x.x - m.z.z) * 0.5;
			double inv = 0.25 / sq;
			this.y = sq;
			this.w = (m.z.x - m.x.z) * inv;
			this.x = (m.x.y + m.y.x) * inv;
			this.z = (m.y.z + m.z.y) * inv;
		} else {
			double sq = Math.sqrt(1.0 + m.z.z - m.x.x - m.y.y) * 0.5;
			double inv = 0.25 / sq;
			this.z = sq;
			this.w = (m.x.y - m.y.x) * inv;
			this.x = (m.z.x + m.x.z) * inv;
			this.y = (m.y.z + m.z.y) * inv;
		}
	}

	public Quaternion.look(Vector3 dir, Vector3 up)
	{
		Vector3 xaxis = dir.cross(up);
		Vector3 zaxis = xaxis.cross(dir);

		Matrix4x4 m = {};
		m.x.x = xaxis.x;
		m.x.y = xaxis.y;
		m.x.z = xaxis.z;
		m.x.w = 0.0;

		m.y.x = dir.x;
		m.y.y = dir.y;
		m.y.z = dir.z;
		m.y.w = 0.0;

		m.z.x = zaxis.x;
		m.z.y = zaxis.y;
		m.z.z = zaxis.z;
		m.z.w = 0.0;

		m.t.x = 0.0;
		m.t.y = 0.0;
		m.t.z = 0.0;
		m.t.w = 1.0;

		Quaternion q = Quaternion.from_matrix(m);
		q.normalize();
		this.x = q.x;
		this.y = q.y;
		this.z = q.z;
		this.w = q.w;
	}

	/// Returns the dot product between quaternions @a a and @a b.
	public double dot(Quaternion b)
	{
		return this.w * b.w + this.x * b.x + this.y * b.y + this.z * b.z;
	}

	/// Returns the length of @a q.
	public double length()
	{
		return Math.sqrt(dot(this));
	}

	public void normalize()
	{
		double len = length();
		double inv_len = 1.0f / len;
		this.x *= inv_len;
		this.y *= inv_len;
		this.z *= inv_len;
		this.w *= inv_len;
	}

	public Gee.ArrayList<Value?> to_array()
	{
		Gee.ArrayList<Value?> arr = new Gee.ArrayList<Value?>();
		arr.add(this.x);
		arr.add(this.y);
		arr.add(this.z);
		arr.add(this.w);
		return arr;
	}

	public Vector3 to_euler()
	{
		// http://www.euclideanspace.com/maths/geometry/rotations/conversions/quaternionToEuler/
		double test = x*y + z*w;
		if (test > 0.499) { // singularity at north pole
			double rx = 0.0;
			double ry = 2.0 * Math.atan2(x, w);
			double rz = Math.PI*0.5;
			return Vector3(rx, ry, rz);
		}
		if (test < -0.499) { // singularity at south pole
			double rx = +0.0;
			double ry = -2.0 * Math.atan2(x, w);
			double rz = -Math.PI*0.5;
			return Vector3(rx, ry, rz);
		}
		double xx = x*x;
		double yy = y*y;
		double zz = z*z;

		double rrx = Math.atan2(2.0*x*w - 2.0*y*z, 1.0 - 2.0*xx - 2.0*zz);
		double rry = Math.atan2(2.0*y*w - 2.0*x*z, 1.0 - 2.0*yy - 2.0*zz);
		double rrz = Math.asin(2.0*test);

		return Vector3(rrx, rry, rrz);
	}

	public string to_string()
	{
		return "%f, %f, %f, %f".printf(x, y, z, w);
	}

	public static bool equal_func(Quaternion? a, Quaternion? b)
	{
		return a.x == b.x
			&& a.y == b.y
			&& a.z == b.z
			&& a.w == b.w
			;
	}
}

public const Quaternion QUATERNION_IDENTITY = { 0.0, 0.0, 0.0, 1.0 };

} /* namespace Crown */