ComfyFactorio/maps/scrapyard/burden.lua

local Event = require 'utils.event'
local Modifier = require "player_modifiers"
local Color = require 'utils.color_presets'

local function validate_player(player)
  if not player then return false end
  if not player.valid then return false end
  if not player.character then return false end
  if not player.connected then return false end
  if not game.players[player.name] then return false end
  return true
end

local function compute_fullness(player)
    local inv = player.get_inventory(defines.inventory.character_main)
    local max_stacks = #inv
    local num_stacks = 0

    local contents = inv.get_contents()
    for item, count in pairs(contents) do
        local stack_size = 1
        if game.item_prototypes[item].stackable then
            stack_size = game.item_prototypes[item].stack_size
        end

        num_stacks = num_stacks + count / stack_size
    end

    return num_stacks / max_stacks
end

local function check_burden(event)
    local player_modifiers = Modifier.get_table()
    local player = game.players[event.player_index]
    validate_player(player)
    local fullness = compute_fullness(player)
    player_modifiers[player.index].character_running_speed_modifier["scrapyard"] = 0.3  - fullness
    player_modifiers[player.index].character_mining_speed_modifier["scrapyard"] = 0.3 - fullness
    Modifier.update_player_modifiers(player)
    if fullness >= 0.3 and fullness <= 0.301 then
        player.print("You feel all of a sudden burden.", Color.yellow)
    elseif fullness >= 0.5 and fullness <= 0.501 then
         player.print("Maybe you should drop some of that inventory to lessen the burden.", Color.red)
    end
end


local function on_init(event)
    script.on_event(defines.events.on_player_main_inventory_changed, check_burden)
end

local function on_load(event)
    script.on_event(defines.events.on_player_main_inventory_changed, check_burden)
end

Event.on_init(on_init)
Event.on_load(on_load)