package main

import "fmt" // for IO and standard library
import "os" // for handling the progress bar
import "math" // for maths
import "unsafe" // for fast inverse square pointers
import "math/rand" // for random
import "time" // for random


func init() {
    rand.Seed(time.Now().UnixNano())
}

// ================ 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
}

func RandomInUnitSphere() Vec3 {
	for true {
		p := RandomVec3(-1, 1)
		if (p.Length_squared() < 1) {
			return p
		}
	}
	return NewVec3(0,0,0)
}

func RandomUnitVector() Vec3 {
	return Unit_vector(RandomInUnitSphere())
}

func RandomOnHemisphere(normal Vec3) Vec3 {
	var on_unit_sphere Vec3 = RandomUnitVector()
	if (Dot(on_unit_sphere, normal) > 0.0) {
		return on_unit_sphere
	} else {
		return on_unit_sphere.Neg()
	}
}

const pi float32 = 3.1415926535897932385

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

func RandomDouble() float32 {
    // Returns a random real in [0,1).
    return rand.Float32()
}

func RandomDoubleInRange(min, max float32) float32 {
    // Returns a random real in [min,max).
    return min + (max-min)*RandomDouble()
}

func RandomVec3(borders ...float32) Vec3 {
	if (len(borders) == 2) {
		return NewVec3(RandomDoubleInRange(borders[0], borders[1]),RandomDoubleInRange(borders[0], borders[1]),RandomDoubleInRange(borders[0], borders[1]))
	} else {
		return NewVec3(RandomDouble(),RandomDouble(),RandomDouble())
	}
}
// ============== COLOUR CLASS ==============

func Write_color(v Vec3, samples_per_pixel int) {
	// Averaging

	r := v.X() / float32(samples_per_pixel)
	g := v.Y() / float32(samples_per_pixel)
	b := v.Z() / float32(samples_per_pixel)

	// Write the translate [0, 255] value of each color component
	intensity := NewInterval(0.000, 0.999)
	fmt.Println(int(intensity.Clamp(r)* 256.0), int(intensity.Clamp(g)* 256.0), int(intensity.Clamp(b)* 256.0))
}

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(),
		},
	}
}

// =============== INTERVAL =================

type Interval struct {
	min, max float32
}

func NewInterval(borders ...float32) *Interval {
	if (len(borders) == 2) {
		return &Interval{
			min: borders[0],
			max: borders[1],
		}
	} else {
		return &Interval{
			min: float32(math.Inf(1)),
			max: float32(math.Inf(-1)),
		}
	}
}

func (i *Interval) Contains(x float32) bool {
	return i.min <= x && x <= i.max
}

func (i *Interval) Surrounds(x float32) bool {
	return i.min < x && x < i.max
}

func (i *Interval) Clamp(x float32) float32 {
	if (x < i.min) {
		return i.min
	} else if (x > i.max) {
		return i.max
	}
	return x
}

var Empty *Interval = NewInterval()
var Universe *Interval = NewInterval(float32(math.Inf(-1)), float32(math.Inf(1)))


// =============== 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_t *Interval, 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 (!ray_t.Surrounds(root)) {
		root = (sqrtd-half_b) / a
		if (!ray_t.Surrounds(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_t Interval, rec *Hit_record) bool {
	var temp_rec Hit_record
	var hit_anything bool = false
	var closest_so_far float32 = ray_t.max

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

// =============== CAMERA ===================

type Camera struct {
	aspect_ratio float32
	image_width int
	image_height int
	center Vec3
	pixel00_loc Vec3
	pixel_delta_u Vec3
	pixel_delta_v Vec3
	samples_per_pixel int
	max_depth int
} 

func NewCamera() *Camera {
	return &Camera{}
}

func Ray_color(r Ray, depth int, world *Hittable) Vec3 {
	var rec Hit_record

	if (depth <= 0) {
		return NewColor(0,0,0)
	}
	if (world.Hit(&r, *NewInterval(0.001, float32(math.Inf(1))), &rec)) {
		//direction := RandomOnHemisphere(rec.normal)
		direction := rec.normal.Add(RandomUnitVector())
		return Ray_color(*((NewRay(rec.p, direction))), depth-1, world).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))
}

func (cam *Camera) Initialize() {
    // Calculate the image height
    cam.image_height = int(float32(cam.image_width) / cam.aspect_ratio)
    if cam.image_height < 1 {
        cam.image_height = 1
    }
    // Viewport
    var focal_length float32 = 1.0
    var viewport_height float32 = 2.0
    var viewport_width float32 = viewport_height * float32(cam.image_width)/float32(cam.image_height)
    cam.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
    cam.pixel_delta_u = viewport_u.Div(float32(cam.image_width))
    cam.pixel_delta_v = viewport_v.Div(float32(cam.image_height))

    // Calculate the location of the upper left pixel
    viewport_upper_left := cam.center.Sub(cam.center).Sub(NewVec3(0, 0, focal_length)).Sub(viewport_u.Div(2)).Sub(viewport_v.Div(2))
    cam.pixel00_loc = viewport_upper_left.Add((cam.pixel_delta_u.Add(cam.pixel_delta_v)).Div(2))
}

func (cam *Camera) Render(world *Hittable) {
    cam.Initialize()

    // Rendering
    fmt.Println("P3")
    fmt.Println(cam.image_width, " ", cam.image_height, "\n255")
    for j := 0; j < cam.image_height; j++ {
        fmt.Fprintf(os.Stderr, "\rScanlines remaining: %d ", cam.image_height-j)
        for i := 0; i < cam.image_width; i++ {
			pixel_color := NewColor(0,0,0)
			for sample := 0; sample < cam.samples_per_pixel; sample++ {
				r := cam.GetRay(i, j)
				pixel_color = pixel_color.Add(Ray_color(*r, cam.max_depth, world))
			}
			Write_color(pixel_color, cam.samples_per_pixel)
        }
    }
}

func (cam *Camera) GetRay(i, j int) *Ray {
	// Get a randomly sampled camera ray for the pixel at location i,j
	pixel_center := cam.pixel00_loc.Add(cam.pixel_delta_u.Mult(float32(i))).Add(cam.pixel_delta_v.Mult(float32(j)))
	pixel_sample := pixel_center.Add(cam.Pixel_sample_square())

	ray_direction := pixel_sample.Sub(cam.center)
	return NewRay(cam.center, ray_direction)
}

func (cam *Camera) Pixel_sample_square() Vec3 {
	// Returns a random point in the square surrounding a pixel at the origin
	px := -0.5 + RandomDouble()
	py := -0.5 + RandomDouble()
	return (cam.pixel_delta_u.Mult(px).Add(cam.pixel_delta_v.Mult(py)))
}



// =============== MAIN =====================
func main() {
	// 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,
	})
	// Image

	cam := NewCamera()
	cam.aspect_ratio = 16.0 / 9.0
    cam.image_width = 400
	cam.samples_per_pixel = 100
	cam.max_depth = 50
	cam.Render(world)
	// INFO: The pixels are written out in rows.
	// Image file can be created with
	// go run main.go > image.ppm
}