ComfyFactorio/modules/rocks_broken_paint_tiles.lua

--Mining or breaking a rock paints the tiles underneath
local event = require 'utils.event'

local valid_entities = {
	["rock-big"] = true,
	["rock-huge"] = true,
	["sand-rock-big"] = true	
}

local replacement_tiles = {
	["nuclear-ground"] = "dirt-7",
	["dirt-7"] = "dirt-6",
	["dirt-6"] = "dirt-5",
	["dirt-5"] = "dirt-4",
	["dirt-4"] = "dirt-3",	
	["dirt-3"] = "dirt-2"
}

local coords = {
		{x = 0, y = 0},{x = -1, y = -1},{x = 1, y = -1},
		{x = 0, y = -1},{x = -1, y = 0},{x = -1, y = 1},
		{x = 0, y = 1},{x = 1, y = 1},{x = 1, y = 0},
		{x = 2, y = 0},{x = -2, y = 0},{x = 0, y = 2},{x = 0, y = -2}
	}

local function on_pre_player_mined_item(event)
	local entity = event.entity
	if not valid_entities[entity.name] then return end	
	
	local tiles = {}
	for _, p in pairs(coords) do
		local pos = {x = entity.position.x + p.x, y = entity.position.y + p.y}
		local tile = entity.surface.get_tile(pos)		
		if not tile.collides_with("player-layer") then
			if replacement_tiles[tile.name] and math.random(1,2) == 1 then
				table.insert(tiles, {name = replacement_tiles[tile.name], position = pos})
			end
		end			
	end
	if #tiles == 0 then return end		
	entity.surface.set_tiles(tiles, true)
end

local function on_entity_died(event)	
	if not event.entity.valid then return end
	on_pre_player_mined_item(event)
end

event.add(defines.events.on_entity_died, on_entity_died)
event.add(defines.events.on_pre_player_mined_item, on_pre_player_mined_item)