package main

import "fmt" // for IO and standard library
import "os" // for handling the progress bar
import "math" // for maths
import "unsafe"

// ================ VEC3 CLASS =====================

type Vec3 struct {
	E [3]float32
}

//Basic vector functions

func NewVec3(e0, e1, e2 float32) Vec3 {
	return Vec3{E: [3]float32{e0, e1, e2}}
}

func (v Vec3) X() float32 {
	return v.E[0]
}

// can be executed as v.X() in main

func (v Vec3) Y() float32 {
	return v.E[1]
}

func (v Vec3) Z() float32 {
	return v.E[2]
}

func (v Vec3) Neg() Vec3 {
	return NewVec3(-v.E[0], -v.E[1], -v.E[2])
}

func (v Vec3) Get(i int) float32 {
	return v.E[i]
}

func (v *Vec3) Set(i int, val float32) {
	v.E[i] = val
}

func (v Vec3) Add(v2 Vec3) Vec3 {
	return NewVec3(v.E[0]+v2.E[0], v.E[1]+v2.E[1], v.E[2]+v2.E[2])
}

func (v Vec3) Mult(t float32) Vec3 {
	return NewVec3(v.E[0]*t, v.E[1]*t, v.E[2]*t)
}

func (v Vec3) Div(t float32) Vec3 {
	if t != 0 {
		return NewVec3(v.E[0] / t, v.E[1] / t, v.E[2] / t)
	}
	return v
}


func (v Vec3) Length() float32 {
	return float32(math.Sqrt(float64(v.E[0]*v.E[0] + v.E[1]*v.E[1] + v.E[2]*v.E[2])))
}

func (v Vec3) Length_squared() float32 {
	return v.E[0]*v.E[0] + v.E[1]*v.E[1] + v.E[2]*v.E[2]
}

// Vector utility functions

func (v Vec3) String() string {
	return fmt.Sprintf("%v %v %v", v.E[0], v.E[1], v.E[2])
}

func (v Vec3) Sub(v2 Vec3) Vec3 {
	return NewVec3(v.E[0]-v2.E[0], v.E[1]-v2.E[1], v.E[2]-v2.E[2])
}

func (v Vec3) MultVec(v2 Vec3) Vec3 {
	return NewVec3(v.E[0]*v2.E[0], v.E[1]*v2.E[1], v.E[2]*v2.E[2])
}

func (v Vec3) DivVec(v2 Vec3) Vec3 {
	if v2.E[0] != 0 && v2.E[1] != 0 && v2.E[2] != 0 {
		return NewVec3(v.E[0]/v2.E[0], v.E[1]/v2.E[1], v.E[2]/v2.E[2])
	}
	return v
}

func Dot(v1 Vec3, v2 Vec3) float32 {
	return (v1.E[0]*v2.E[0] + v1.E[1]*v2.E[1] + v1.E[2]*v2.E[2])
}

func Cross(v1 Vec3, v2 Vec3) Vec3 {
	return NewVec3(v1.E[1]*v2.E[2] - v1.E[2]*v2.E[1],
		v1.E[2]*v2.E[0] - v1.E[0]*v2.E[2],
		v1.E[0]*v2.E[1] - v1.E[1]*v2.E[0])
}

func q_rsqrt(v Vec3) float32 {
	var x float32 = v.E[0]*v.E[0] + v.E[1]*v.E[1] + v.E[2]*v.E[2]
	i := *(*int32)(unsafe.Pointer(&x)) // evil floating point bit level hacking
    i = 0x5f3759df - (i >> 1)          // what the fuck?
    y := *(*float32)(unsafe.Pointer(&i))
    return y
}

func Unit_vector(v Vec3) Vec3 {
	new_v := v.Mult(q_rsqrt(v))
    return new_v
}

const pi float32 = 3.1415926535897932385

func Degrees_to_radians(degrees float32) float32 {
	return (degrees * pi) / 180.0
}

// ============== COLOUR CLASS ==============

func Write_color(v Vec3) {
	fmt.Println(int(255.999*v.E[0]), int(255.999*v.E[1]), int(255.999*v.E[2]))
}

func NewColor(e0, e1, e2 float32) Vec3 {
	return Vec3{E: [3]float32{e0, e1, e2}}
}

// ============== RAY CLASS =================

func NewPoint3(e0, e1, e2 float32) Vec3 {
	return Vec3{E: [3]float32{e0, e1, e2}}
}
type Ray struct {
	Orig Vec3
	Dir Vec3
}

func NewRay(orig Vec3, dir Vec3) *Ray {
    return &Ray{Orig: orig, Dir: dir}
}

func (r *Ray) Origin() Vec3 {
	return r.Orig
}

func (r *Ray) Direction() Vec3 {
	return r.Dir
}

func (r *Ray) At(t float32) Vec3 {
	return Vec3{
		E: [3]float32{
			r.Orig.X() + t*r.Dir.X(),
			r.Orig.Y() + t*r.Dir.Y(),
			r.Orig.Z() + t*r.Dir.Z(),
		},
	}
}


// =============== HIT ======================

type Hit_record struct {
	p Vec3
	normal Vec3
	t float32
	front_face bool
}

func (rec *Hit_record) Set_face_normal(r *Ray, outward_normal Vec3) {
	if (Dot(r.Direction(), outward_normal) < 0) {
		rec.front_face = true
	}
	if (rec.front_face) {
		rec.normal = outward_normal
	} else {
		rec.normal = outward_normal.Neg()
	}
}

// =============== SPHERE ===================

type Sphere struct {
	center Vec3
	radius float32
}

func (s Sphere) Hit_sphere(r *Ray, ray_tmin float32, ray_tmax float32, rec *Hit_record) bool {
	oc := r.Origin().Sub(s.center)
	a := r.Direction().Length_squared()
	half_b := Dot(oc, r.Direction())
	c := oc.Length_squared() - s.radius*s.radius

	discriminant := half_b*half_b - a*c
	if (discriminant < 0) {
		return false
	}
	sqrtd := float32(math.Sqrt(float64(discriminant)))

	// find the nearest root that lies in the acceptable range
	root := (-half_b - sqrtd) / a
	if (root <= ray_tmin || ray_tmax<= root) {
		root = (sqrtd-half_b) / a
		if (root <= ray_tmin || ray_tmax <= root) {
			return false
		}
	}
	rec.t = root
	rec.p = r.At(rec.t)
	outward_normal := rec.p.Sub(s.center).Div(s.radius)
	rec.Set_face_normal(r, outward_normal)
	return true
}

// =============== HITTABLE ==================
type Hittable struct {
	spheres []Sphere
}

func NewHittable() *Hittable {
	return &Hittable{}
}

func (hl *Hittable) Add(s Sphere) {
	hl.spheres = append(hl.spheres, s)
}

func (hl *Hittable) Clear() {
	hl.spheres = []Sphere{}
}

func (hl Hittable) Hit(r *Ray, ray_tmin float32, ray_tmax float32, rec *Hit_record) bool {
	var temp_rec Hit_record
	var hit_anything bool = false
	var closest_so_far float32 = ray_tmax

	for _, sphere := range hl.spheres {
		if (sphere.Hit_sphere(r, ray_tmin, closest_so_far, &temp_rec)) {
			hit_anything = true
			closest_so_far = temp_rec.t
			*rec = temp_rec
		}
	}
	return hit_anything
}

func Ray_color(r Ray, world *Hittable) Vec3 {
	var rec Hit_record
	if (world.Hit(&r, 0, float32(math.Inf(1)), &rec)) {
		return rec.normal.Add(NewColor(1,1,1)).Mult(0.5)
	}
	unit_direction := Unit_vector(r.Direction())
	a := (unit_direction.Y() + 1.0)*0.5

	return NewColor(1.0,1.0,1.0).Mult(float32(1.0-a)).Add(NewColor(0.5,0.7,1.0).Mult(a))

}

// =============== MAIN =====================
func main() {

     // Image
	 aspect_ratio := 16.0 / 9.0;
     var image_width int = 400;

	 // Calculate the image height
     var image_height int = int(float64(image_width) / aspect_ratio)
	 if image_height < 1 {
		image_height = 1
	 }

	 // World

	 world := NewHittable()
	 world.Add(Sphere{
		 center: NewVec3(0, 0, -1),
		 radius: 0.5,
	 })
	 world.Add(Sphere{
		 center: NewVec3(0, -100.5, -1),
		 radius: 100,
	 })
	 
	 // Camera
	 var focal_length float32 = 1.0
	 var viewport_height float32 = 2.0
	 var viewport_width float32 = viewport_height * float32(image_width)/float32(image_height)
	 camera_center := NewVec3(0,0,0)

	 // Calculate the vectors across the horizontal and down the vertical viewport edges
	 viewport_u := NewVec3(viewport_width, 0, 0)
	 viewport_v := NewVec3(0, -viewport_height, 0)

	 //Calculate the horizontal and vertical delta vectors from pixel to pixel
	 pixel_delta_u := viewport_u.Div(float32(image_width))
	 pixel_delta_v := viewport_v.Div(float32(image_height))

	 // Calculate the location of the upper left pixel
	 viewport_upper_left := camera_center.Sub(camera_center).Sub(NewVec3(0, 0, focal_length)).Sub(viewport_u.Div(2)).Sub(viewport_v.Div(2))
     pixel00_loc := viewport_upper_left.Add((pixel_delta_u.Add(pixel_delta_v)).Div(2))
	 // Rendering
     fmt.Println("P3")
     fmt.Println(image_width, " ", image_height, "\n255")
     for j := 0; j < image_height; j++ {
          fmt.Fprintf(os.Stderr, "\rScanlines remaining: %d ", image_height-j)
          for i := 0; i < image_width; i++ {
			   pixel_center := pixel00_loc.Add(pixel_delta_u.Mult(float32(i))).Add(pixel_delta_v.Mult(float32(j)))
			   ray_direction := pixel_center.Sub(camera_center)
			   r := NewRay(camera_center, ray_direction)

			   pixel_color := Ray_color(*r, world)
			   Write_color(pixel_color)
          }
     }
     // INFO: The pixels are written out in rows.
     // Image file can be created with
     // go run main.go > image.ppm
}