-- Biters and Spitters gain additional health / resistance -- mewmew
-- Use global.biter_health_boost or global.biter_health_boost_forces to modify their health.
-- 1 = vanilla health, 2 = 200% vanilla health
-- do not use values below 1
local math_floor = math.floor
local math_round = math.round
local Public = {}

local function clean_table()
	--Perform a table cleanup every 1000 boosts
	global.biter_health_boost_count = global.biter_health_boost_count + 1
	if global.biter_health_boost_count % 1000 ~= 0 then return end

	local units_to_delete = {}

	--Mark all health boost entries for deletion
	for key, health in pairs(global.biter_health_boost_units) do
		units_to_delete[key] = true
	end

	--Remove valid health boost entries from deletion
	for _, surface in pairs(game.surfaces) do
		for _, unit in pairs(surface.find_entities_filtered({type = "unit"})) do
			units_to_delete[unit.unit_number] = nil
		end
	end

	--Remove abandoned health boost entries
	for key, _ in pairs(units_to_delete) do
		global.biter_health_boost_units[key] = nil
	end
end

local function create_boss_healthbar(entity, size)
	return rendering.draw_sprite({
		sprite="virtual-signal/signal-white",
		tint={0, 200, 0},
		x_scale=size * 15, y_scale=size, render_layer="light-effect",
		target=entity, target_offset={0, -2.5}, surface=entity.surface,
	})
end

local function set_boss_healthbar(health, max_health, healthbar_id)
	local m = health / max_health
	local x_scale = rendering.get_y_scale(healthbar_id) * 15
	rendering.set_x_scale(healthbar_id, x_scale * m)
	rendering.set_color(healthbar_id, {math_floor(255 - 255 * m), math_floor(200 * m), 0})
end

function Public.add_unit(unit, health_multiplier)
	if not health_multiplier then health_multiplier = global.biter_health_boost end
	global.biter_health_boost_units[unit.unit_number] = {
		math_floor(unit.prototype.max_health * health_multiplier),
		math_round(1 / health_multiplier, 5),
	}
	clean_table()
end

function Public.add_boss_unit(unit, health_multiplier, health_bar_size)
	if not health_multiplier then health_multiplier = global.biter_health_boost end
	if not health_bar_size then health_bar_size = 0.5 end
	local health = math_floor(unit.prototype.max_health * health_multiplier)
	global.biter_health_boost_units[unit.unit_number] = {
		health,
		math_round(1 / health_multiplier, 5),
		{max_health = health, healthbar_id = create_boss_healthbar(unit, health_bar_size), last_update = game.tick},
	}
	clean_table()
end

local function on_entity_damaged(event)
	local biter = event.entity
	if not (biter and biter.valid) then return end
	if biter.type ~= "unit" then return end
  if event.final_damage_amount == 0 then return end

	local biter_health_boost_units = global.biter_health_boost_units

	local unit_number = biter.unit_number

	--Create new health pool
	local health_pool = biter_health_boost_units[unit_number]
	if not health_pool then
		if global.biter_health_boost_forces[biter.force.index] then
			Public.add_unit(biter, global.biter_health_boost_forces[biter.force.index])
		else
			Public.add_unit(biter, global.biter_health_boost)
		end
		health_pool = biter_health_boost_units[unit_number]
	end

	--Process boss unit health bars
	local boss = health_pool[3]
	if boss then
		if boss.last_update + 10 < game.tick then
			set_boss_healthbar(health_pool[1], boss.max_health, boss.healthbar_id)
			boss.last_update = game.tick
		end
	end

  --Calculate current actual health, accounting for regeneration
  local current_health = biter.health * (1 / health_pool[2])

	--Reduce health pool
	health_pool[1] = current_health - event.final_damage_amount

	--Set entity health relative to health pool
	biter.health = health_pool[1] * health_pool[2]

	--Proceed to kill entity if health is 0
	if biter.health > 0 then return end

	if event.cause then
		if event.cause.valid then
			event.entity.die(event.cause.force, event.cause)
			return
		end
	end
	biter.die(biter.force)
end

local function on_init()
	global.biter_health_boost = 1
	global.biter_health_boost_forces = {}
	global.biter_health_boost_units = {}
	global.biter_health_boost_count = 0
end

local event = require 'utils.event'
event.on_init(on_init)
event.add(defines.events.on_entity_damaged, on_entity_damaged)

return Public