package main

const EPS = 0.001

type SDF interface {
	Distance(Vector3) float64
}

func Gradient(sdf SDF, p Vector3, eps float64) Vector3 {
	dx := (sdf.Distance(p.Add(Vector3{X: eps})) - sdf.Distance(p.Add(Vector3{X: -eps}))) / (2 * eps)
	dy := (sdf.Distance(p.Add(Vector3{Y: eps})) - sdf.Distance(p.Add(Vector3{Y: -eps}))) / (2 * eps)
	dz := (sdf.Distance(p.Add(Vector3{Z: eps})) - sdf.Distance(p.Add(Vector3{Z: -eps}))) / (2 * eps)
	return Vector3{X: dx, Y: dy, Z: dz}
}

// Some transformations see https://iquilezles.org/articles/distfunctions/

type translatedSDF struct {
	primitive SDF
	translate Vector3
}

func (s translatedSDF) Distance(p Vector3) float64 {
	return s.primitive.Distance(p.Sub(s.translate))
}

type rotatedSDF struct {
	primitive SDF
	rotVector Vector3
	angle     float64
}

func (s rotatedSDF) Distance(p Vector3) float64 {
	rotated_p := rotate(p, s.rotVector, s.angle)
	return s.primitive.Distance(rotated_p)
}

type scaledSDF struct {
	primitive SDF
	scale     float64
}

func (s scaledSDF) Distance(p Vector3) float64 {
	return s.primitive.Distance(p.Scale(1/s.scale)) * s.scale
}

type infiniteRep struct {
	primitive SDF
	cellSize  Vector3
}

// TODO
// func (s infiniteRep) Distance(p Vector3) float64 {
// 	x, y, z := p.Unpack()
// 	sx, sy, sz := s.cellSize.Unpack()
// }

// Sphere

type Sphere struct {
	center Vector3
	radius float64
}

func (s Sphere) Distance(p Vector3) float64 {
	return p.Sub(s.center).Length()
}