local function create_particles(surface, position, amount)
	if not surface.valid then return end
	local math_random = math.random
	for i = 1, amount, 1 do 
		local m = math_random(6, 12)
		local m2 = m * 0.005
		
		surface.create_particle({
			name = "stone-particle",
			position = position,
			frame_speed = 0.1,
			vertical_speed = 0.1,
			height = 0.1,
			movement = {m2 - (math_random(0, m) * 0.01), m2 - (math_random(0, m) * 0.01)}
		})
	end	
end

local function spawn_biter(surface, position, evolution)
	if not surface.valid then return end
	local evo = math.floor(evolution * 1000)
	
	local biter_chances = {
		{name = "small-biter", chance = math.floor(1000 - (evo * 1.6))},
		{name = "small-spitter", chance = math.floor(500 - evo * 0.8)},
		{name = "medium-biter", chance = -150 + evo},
		{name = "medium-spitter", chance = -75 + math.floor(evo * 0.5)},
		{name = "big-biter", chance = math.floor((evo - 500) * 3)},
		{name = "big-spitter", chance = math.floor((evo - 500) * 2)},
		{name = "behemoth-biter", chance = math.floor((evo - 800) * 6)},
		{name = "behemoth-spitter", chance = math.floor((evo - 800) * 4)}
	}
	
	local max_chance = 0	
	for i = 1, 8, 1 do
		if biter_chances[i].chance < 0 then biter_chances[i].chance = 0 end
		max_chance = max_chance + biter_chances[i].chance
	end
	local r = math.random(1, max_chance)	
	local current_chance = 0
	for i = 1, 8, 1 do
		current_chance = current_chance + biter_chances[i].chance
		if r <= current_chance then
			local biter_name = biter_chances[i].name
			local p = surface.find_non_colliding_position(biter_name, position, 10, 1)
			if not p then return end
			surface.create_entity({name = biter_name, position = p, force = "enemy"})
			return
		end
	end
end

local function unearthing_biters(surface, position, amount)
	if not surface then return end
	if not position then return end
	if not position.x then return end
	if not position.y then return end	
	
	local evolution = game.forces.enemy.evolution_factor
	
	local ticks = amount * 30
	ticks = ticks + 90
	for t = 1, ticks, 1 do
		if not global.on_tick_schedule[game.tick + t] then global.on_tick_schedule[game.tick + t] = {} end
				
		global.on_tick_schedule[game.tick + t][#global.on_tick_schedule[game.tick + t] + 1] = {
			func = create_particles,
			args = {surface, {x = position.x, y = position.y}, 4}
		}										
		
		if t > 90 then
			if t % 30 == 29 then			
				global.on_tick_schedule[game.tick + t][#global.on_tick_schedule[game.tick + t] + 1] = {
					func = spawn_biter,
					args = {surface, {x = position.x, y = position.y}, evolution}
				}
			end
		end
	end		
end

return unearthing_biters