package physics

import (
	"math"
)

type Position Point
type Velocity Vector
type Acceleration Vector

var Gravity = Acceleration{
	X: 0,
	Y: 9.81,
}

type Motion struct {
	pos Position
	vel Velocity
	acc Acceleration
}

type Physics struct {
	current Motion
	initial Motion
	fps     float64
}

type Vector struct {
	X float64
	Y float64
}

type Point struct {
	X float64
	Y float64
}

// Distance calculates the euclidean distance between two points
func (a Point) Distance(b Point) float64 {
	return math.Sqrt(math.Pow(b.X-a.X, 2) + math.Pow(b.Y-a.Y, 2))
}

func New(pos Point, vel, acc Vector, fps float64) *Physics {
	motion := Motion{
		pos: Position(pos),
		vel: Velocity(vel),
		acc: Acceleration(acc),
	}
	return &Physics{
		initial: motion,
		current: motion,
		fps:     fps,
	}
}

func (p *Physics) Reset() {
	p.current = p.initial
}

func (p *Physics) Update() {
	p.current.pos.X += p.current.vel.X / p.fps
	p.current.pos.Y += p.current.vel.Y / p.fps

	p.current.vel.X += p.current.acc.X / p.fps
	p.current.vel.Y += p.current.acc.Y / p.fps
}

func (p Physics) Displacement() float64 {
	return Point(p.initial.pos).Distance(Point(p.current.pos))
}

func (p Physics) PosX() int {
	return int(math.Round(p.current.pos.X))
}

func (p Physics) PosY() int {
	return int(math.Round(p.current.pos.Y))
}