local min = math.min
local abs = math.abs

function steampunk_blimp.physics(self)
    local friction = 0.996
	local vel=self.object:get_velocity()
		-- dumb friction
	if self.isonground and not self.isinliquid then
        --minetest.chat_send_all("with friction")
		vel = {x=vel.x*friction,
								y=vel.y,
								z=vel.z*friction}
        self.object:set_velocity(vel)
	end
	
	-- bounciness
	if self.springiness and self.springiness > 0 then
		local vnew = vector.new(vel)
		
		if not self.collided then						-- ugly workaround for inconsistent collisions
			for _,k in ipairs({'y','z','x'}) do
				if vel[k]==0 and abs(self.lastvelocity[k])> 0.1 then
					vnew[k]=-self.lastvelocity[k]*self.springiness
				end
			end
		end
		
		if not vector.equals(vel,vnew) then
			self.collided = true
		else
			if self.collided then
				vnew = vector.new(self.lastvelocity)
			end
			self.collided = false
		end
		--minetest.chat_send_all("vnew")
		self.object:set_velocity(vnew)
    end
    --[[else
        self.object:set_pos(self.object:get_pos())
        if not self.isonground then
            --minetest.chat_send_all("test")
            self.object:set_velocity(vel)
        end
	end]]--

	--buoyancy
	local surface = nil
	local surfnodename = nil
	local spos = airutils.get_stand_pos(self)
	spos.y = spos.y+0.01
	-- get surface height
	local snodepos = airutils.get_node_pos(spos)
	local surfnode = airutils.nodeatpos(spos)
	while surfnode and (surfnode.drawtype == 'liquid' or surfnode.drawtype == 'flowingliquid') do
		surfnodename = surfnode.name
		surface = snodepos.y +0.5
		if surface > spos.y+self.height then break end
		snodepos.y = snodepos.y+1
		surfnode = airutils.nodeatpos(snodepos)
	end

    local new_velocity = nil

    local accell = {x=0, y=0, z=0}
    self.water_drag = 0.1
    self.object:move_to(self.object:get_pos())
    local time_correction = (self.dtime/steampunk_blimp.ideal_step)
    local y_accel = self._baloon_buoyancy*time_correction
    local max_y_acell = 0.6
    if y_accel > max_y_acell then y_accel = max_y_acell end
    if y_accel < (-1*max_y_acell) then y_accel = -1*max_y_acell end


    if surface then
        self.isinliquid = true
        local height = self.height
		local submergence = min(surface-spos.y,height)/height
--		local balance = self.buoyancy*self.height
		local buoyacc = airutils.gravity*(self.buoyancy-submergence)
        --local buoyacc = self._baloon_buoyancy*(self.buoyancy-submergence)
        accell = {x=-vel.x*self.water_drag,y=buoyacc-(vel.y*abs(vel.y)*0.4),z=-vel.z*self.water_drag}
        --local v_accell = {x=0,y=buoyacc-(vel.y*abs(vel.y)*0.4),z=0}
        airutils.set_acceleration(self.object,accell)
        if self._baloon_buoyancy > 0 then
            airutils.set_acceleration(self.object,{x=0,y=y_accel,z=0})
        end
	else
        self.isinliquid = false
        if self._baloon_buoyancy == 0 then
            local velocity = vector.new(vel)
            velocity.y = velocity.y - (velocity.y/100)
            self.object:set_velocity(velocity)
        end
        --minetest.chat_send_all("_baloon_buoyancy: "..self._baloon_buoyancy.." - dtime: "..self.dtime.." - ideal: "..steampunk_blimp.ideal_step)
        airutils.set_acceleration(self.object,{x=0,y=y_accel,z=0})
    end
    
end