DEMI-PROJECT-PACKAGE
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Serializable stack and equipment state. Item definitions and gameplay effects
are supplied by the game as validated data assets.
local Inventory = {}
Inventory.__index = Inventory

function Inventory.new(events, capacity)
  return setmetatable({ events = assert(events), capacity = capacity or 20, stacks = {}, equipment = {} }, Inventory)
end

function Inventory:add(item, count, maximum)
  count, maximum = count or 1, maximum or math.huge
  if count <= 0 then return 0 end
  local current = self.stacks[item] or 0
  local added = math.min(count, maximum - current)
  if current == 0 and added > 0 then
    local unique = 0; for _ in pairs(self.stacks) do unique = unique + 1 end
    if unique >= self.capacity then return 0 end
  end
  if added > 0 then self.stacks[item] = current + added; self.events:emit("inventory_changed", { item = item, count = self.stacks[item] }) end
  return added
end

function Inventory:remove(item, count)
  local current = self.stacks[item] or 0; local removed = math.min(current, math.max(0, count or 1))
  local left = current - removed; self.stacks[item] = left > 0 and left or nil
  if removed > 0 then self.events:emit("inventory_changed", { item = item, count = left }) end
  return removed
end

function Inventory:equip(slot, item)
  if item and not self.stacks[item] then return false end
  self.equipment[slot] = item; self.events:emit("equipment_changed", { slot = slot, item = item }); return true
end

function Inventory:save() return { stacks = self.stacks, equipment = self.equipment, capacity = self.capacity } end
function Inventory:load(value)
  if type(value) ~= "table" or type(value.stacks) ~= "table" then return false end
  self.stacks, self.equipment, self.capacity = value.stacks, value.equipment or {}, value.capacity or self.capacity
  return true
end

return Inventory
local Events = require("demi.gameplay.events")
local Inventory = require("demi.gameplay.inventory")

Test.case("capacity and stacks clamp", function()
  local inventory = Inventory.new(Events.new(), 1)
  Test.equal(inventory:add("coin", 8, 5), 5); Test.equal(inventory:add("key", 1), 0)
  Test.equal(inventory:remove("coin", 99), 5); Test.equal(inventory.stacks.coin, nil)
end)

Test.case("save load keeps equipment", function()
  local first = Inventory.new(Events.new()); first:add("sword"); first:equip("hand", "sword")
  local second = Inventory.new(Events.new()); Test.equal(second:load(first:save()), true)
  Test.equal(second.equipment.hand, "sword")
end)