require "matrix"
load "gosu_plugin.rb"

GRAV_CONSTANT = 1e+1

class PhysObj
	attr_accessor :world, :saved_pos, :pos, :vel, :accel, :x, :y
	attr_reader :name
	def initialize(name, world)
		@name = name
		@world = world
		@pos = Vector.zero(2)
		@vel = Vector.zero(2)
		@accel = Vector.zero(2)
		@x, @y = 0, 0
		@saved_pos = []
	end

	def tick
		if( @accel.magnitude != 0 ) then
			@vel += @accel
		end

		if( @vel.magnitude != 0 ) then
			@pos += @vel
		end
		@x, @y = @pos[0], @pos[1]
		@saved_pos << @pos
	end

	def render_path
		@saved_pos.each do |pos|
			Gosu.draw_rect(pos[0], pos[1], 1, 1, Gosu::Color.argb(0x44_ccccff))
		end
	end

end


class PhysCube < PhysObj
	attr_reader :width, :height
	def initialize(name, world, width, height, color=0xff_ffffff, ela=-0.8)
		super name, world

		@width, @height = width, height
		@color = Gosu::Color.argb(color)
		@ela = ela
	end

	def render
		x, y = self.pos[0], self.pos[1]
		Gosu.draw_quad(x, y, @color, x + self.width, y, @color, x, y + self.height, @color, x + self.width, y + self.height, @color)
	end

	def physics
		self.tick
	end

	def draw_vector(vec, scale=2, color=0xaf_ffaaaa)
		if( vec.magnitude != 0 ) then
			clr = Gosu::Color.argb(color)

			scaled_vec = vec*scale

			pos1 = self.pos + Vector[self.width/2, self.height/2]
			pos2 = pos1 + scaled_vec
			
			x1 = pos1[0]
			y1 = pos1[1]

			x2 = pos2[0]
			y2 = pos2[1]

			Gosu.draw_line(x1, y1, clr, x2, y2, clr)
		end
	end

end


class Planet < PhysCube
	attr_reader :mass
	def initialize(name, world, color, mass=1e+2)
		super name, world, 40, 40, color
		@mass = mass
	end

	private def calculate_gravity_scalar(obj, dir_vec)
		grav = GRAV_CONSTANT * (self.mass/(dir_vec.magnitude**2))
		return grav
	end

	private def calculate_gravity_vector(obj)
		dir_vec = self.pos - obj.pos + Vector[self.width/2, self.height/2]
		return (dir_vec/dir_vec.magnitude) * calculate_gravity_scalar(obj, dir_vec)  
	end

	def orbit(physobjs)
		physobjs.each do |obj|
			grav_vec = self.calculate_gravity_vector(obj)
			obj.accel = grav_vec
		end
	end

	def render
		Gosu.draw_circle(self.pos[0], self.pos[1], 20, @color)
	end
end