GRAV_CONSTANT = 1e+1
MAX_PATH_TRACK_POINT = 1000

class PhysObj
	attr_accessor :world, :saved_pos, :pos, :vel, :accel, :x, :y, :show_info, :angle, :parent_orbit, :accel_vecs
	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 = []
		@show_info = false
		@angle = 0
		@parent_orbit = ""
		@accel_vecs = []
	end

	private def apply_accel_vecs
		@accel_vecs.each do |vec|
			@accel += vec
		end
		@accel_vecs = []
	end

	def tick
		@x, @y = @pos[0], @pos[1]
		@angle %= 360

		self.apply_accel_vecs
		if( !world.freeze ) then
			if( @accel.magnitude != 0 ) then
				@vel += @accel
			end

			if( @vel.magnitude != 0 ) then
				@pos += @vel
			end
			@saved_pos << @pos

			if(@saved_pos.length > MAX_PATH_TRACK_POINT) then
				@saved_pos = @saved_pos[1..-1]
			end
		end
	end

	def render_path(x_offset=0, y_offset=0)
		@saved_pos.each do |pos|
			Gosu.draw_rect(pos[0] + x_offset, pos[1] + y_offset, 1, 1, Gosu::Color.argb(0xaa_ccccff))
		end
	end

	private def debug_string
		return "\n#{self.name} - #{self.parent_orbit.name}\nVel: #{self.vel.magnitude.round(1)} #{self.vel.round(4)}\nAccel: #{self.accel.magnitude.round(4)} #{self.accel.round(4)}\nPos: #{self.pos.round(4)}\nAngle: #{self.angle.round(1)} deg\n"
	end

	def render(x_offset=0, y_offset=0, color=Gosu::Color.argb(0xaa_2222ff))
		if( @show_info ) then
			self.world.fonts[:normal].draw_text(self.debug_string, self.pos[0] + x_offset, self.pos[1] + y_offset, 1, 1.0, 1.0, color)
		end
	end

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

			scaled_vec = vec*scale

			pos1 = Vector[x_offset, y_offset] + 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

	def draw_direction(x_offset=0, y_offset=0)
		rads = (self.angle * Math::PI) / 180
		dir_vec = Vector[Math::cos(rads), Math::sin(rads)]
		self.draw_vector(dir_vec, 25, 0xaf_aaaaff, x_offset, y_offset)
	end
end


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

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

	def render(offset_x=0, offset_y=0)
		super offset_x, offset_y, @color
		x, y = offset_x + self.pos[0], offset_y + 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
end


class Planet < PhysObj
	attr_reader :color, :mass, :radius, :circle_thickness
	def initialize(name, world, color, mass=1e+2, radius=20, circle_thickness=4)
		super name, world

		@color = color
		@mass = mass

		@radius = radius
		@circle_thickness = circle_thickness
	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[@radius/2, @radius/2]
		return (dir_vec/dir_vec.magnitude) * calculate_gravity_scalar(obj, dir_vec)  
	end

	def orbit(physobjs)
		if( !self.world.freeze ) then
			physobjs.each do |obj|
				grav_vec = self.calculate_gravity_vector(obj)
				obj.accel_vecs << grav_vec
			end
		end
	end

	private def debug_string
		return "\n#{self.name}\nPos: #{self.pos.round(4)}\nMass: #{self.mass.round(4)}\nRadius: #{self.radius.round(4)} p\nGravity: #{(self.mass*GRAV_CONSTANT).round(2)} p/r^2"
	end

	def render(x_offset=0, y_offset=0)
		super @radius*3, @radius*3, Gosu::Color.argb(0xff_ffffff)
		Gosu.draw_circle(self.pos[0] + x_offset, self.pos[1] + y_offset, @radius, @color, 0, @circle_thickness)
	end
end