// Copyright ©2019 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package r3

import "math"

// Vec is a 3D vector.
type Vec struct {
	X, Y, Z float64
}

// Add returns the vector sum of p and q.
func Add(p, q Vec) Vec {
	return Vec{
		X: p.X + q.X,
		Y: p.Y + q.Y,
		Z: p.Z + q.Z,
	}
}

// Sub returns the vector sum of p and -q.
func Sub(p, q Vec) Vec {
	return Vec{
		X: p.X - q.X,
		Y: p.Y - q.Y,
		Z: p.Z - q.Z,
	}
}

// Scale returns the vector p scaled by f.
func Scale(f float64, p Vec) Vec {
	return Vec{
		X: f * p.X,
		Y: f * p.Y,
		Z: f * p.Z,
	}
}

// Dot returns the dot product p·q.
func Dot(p, q Vec) float64 {
	return p.X*q.X + p.Y*q.Y + p.Z*q.Z
}

// Cross returns the cross product p×q.
func Cross(p, q Vec) Vec {
	return Vec{
		p.Y*q.Z - p.Z*q.Y,
		p.Z*q.X - p.X*q.Z,
		p.X*q.Y - p.Y*q.X,
	}
}

// Rotate returns a new vector, rotated by alpha around the provided axis.
func Rotate(p Vec, alpha float64, axis Vec) Vec {
	return NewRotation(alpha, axis).Rotate(p)
}

// Norm returns the Euclidean norm of p
//  |p| = sqrt(p_x^2 + p_y^2 + p_z^2).
func Norm(p Vec) float64 {
	return math.Hypot(p.X, math.Hypot(p.Y, p.Z))
}

// Norm2 returns the Euclidean squared norm of p
//  |p|^2 = p_x^2 + p_y^2 + p_z^2.
func Norm2(p Vec) float64 {
	return p.X*p.X + p.Y*p.Y + p.Z*p.Z
}

// Unit returns the unit vector colinear to p.
// Unit returns {NaN,NaN,NaN} for the zero vector.
func Unit(p Vec) Vec {
	if p.X == 0 && p.Y == 0 && p.Z == 0 {
		return Vec{X: math.NaN(), Y: math.NaN(), Z: math.NaN()}
	}
	return Scale(1/Norm(p), p)
}

// Cos returns the cosine of the opening angle between p and q.
func Cos(p, q Vec) float64 {
	return Dot(p, q) / (Norm(p) * Norm(q))
}

// Box is a 3D bounding box.
type Box struct {
	Min, Max Vec
}