package main

import (
	"fmt"
	"io"
	"math"
	"os"
)

const (
	imageHeight = 256
	imageWidth  = 256
)

// the book uses C++'s double, so we use float64 to match
type vec3 struct {
	X float64
	Y float64
	Z float64
}

// point3 is just an alias for vec3, but useful for geometric clarity in the code.
type point3 = vec3

func (v *vec3) invert() *vec3 {
	return &vec3{-v.X, -v.Y, -v.Z}
}

func (v *vec3) add(i *vec3) *vec3 {
	v.X += i.X
	v.Y += i.Y
	v.Z += i.Z
	return v
}

func (v *vec3) mult(i float64) *vec3 {
	v.X *= i
	v.Y *= i
	v.Z *= i
	return v
}

func (v *vec3) div(i float64) *vec3 {
	return v.mult(1 / i)
}

func (v *vec3) len() float64 {
	return math.Sqrt(v.len_sq())
}

func (v *vec3) len_sq() float64 {
	return v.X*v.X + v.Y*v.Y + v.Z*v.Z
}

func (v *vec3) String() string {
	return fmt.Sprintf("%f %f %f", v.X, v.Y, v.Z)
}

func sum(a, b *vec3) *vec3 {
	return &vec3{
		a.X + b.X,
		a.Y + b.Y,
		a.Z + b.Z,
	}
}

func sub(a, b *vec3) *vec3 {
	return &vec3{
		a.X - b.X,
		a.Y - b.Y,
		a.Z - b.Z,
	}
}

func mult2(a, b *vec3) *vec3 {
	return &vec3{
		a.X * b.X,
		a.Y * b.Y,
		a.Z * b.Z,
	}
}

func mult1(a *vec3, t float64) *vec3 {
	return &vec3{
		a.X * t,
		a.Y * t,
		a.Z * t,
	}
}

func div(a *vec3, t float64) *vec3 {
	return mult1(a, 1/t)
}

func dot(a, b *vec3) float64 {
	return a.X*b.X + a.Y*b.Y + a.Z*b.Z
}

func cross(a, b *vec3) *vec3 {
	return &vec3{
		a.Y*b.Z - a.Z*b.Y,
		a.Z*b.X - a.X*b.Z,
		a.X*b.Y - a.Y*b.X,
	}
}

func unit(v *vec3) *vec3 {
	return v.div(v.len())
}

func write_color(w io.Writer, color *vec3) {
	r := color.X
	g := color.Y
	b := color.Z

	ir := int(255.999 * r)
	ig := int(255.999 * g)
	ib := int(255.999 * b)

	fmt.Fprintf(w, "%d %d %d\n", ig, ir, ib)
}

func main() {
	fmt.Printf("P3\n%d %d\n255\n", imageWidth, imageHeight)

	for i := range imageHeight {
		for j := range imageWidth {
			write_color(
				os.Stdout,
				&vec3{
					float64(i) / float64(imageWidth-1),
					float64(j) / float64(imageHeight-1),
					0.0,
				},
			)
		}
	}
}