feat(items): add item catalog and equipment stats

src/items.lua

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+-- Items are plain data tables so they serialize without metatable handling.
+-- Potions and scrolls carry an effect key resolved by the effects module; gear
+-- modifies effective stats when equipped and may carry an affix. Potion and
+-- scroll type catalogs drive the identification system.
+
+local Items = {}
+
+Items.POTION = "potion"
+Items.SCROLL = "scroll"
+Items.WEAPON = "weapon"
+Items.ARMOR = "armor"
+Items.RING = "ring"
+Items.FOOD = "food"
+Items.KEY = "key"
+
+-- Catalogs list every distinct type in a fixed order; identification assigns a
+-- random appearance to each entry, so the order here must stay stable.
+Items.potionTypes = {
+  { effect = "heal",     name = "potion of healing",   power = 10 },
+  { effect = "poison",   name = "potion of poison",    power = 3 },
+  { effect = "strength", name = "potion of strength",  power = 0 },
+  { effect = "haste",    name = "potion of speed",     power = 0 },
+}
+
+Items.scrollTypes = {
+  { effect = "teleport", name = "scroll of teleportation" },
+  { effect = "identify", name = "scroll of identify" },
+  { effect = "mapping",  name = "scroll of magic mapping" },
+  { effect = "fireball", name = "scroll of fireball" },
+}
+
+function Items.typeId(item)
+  return item.kind .. "/" .. (item.effect or "")
+end
+
+function Items.potion(power)
+  return { kind = Items.POTION, effect = "heal", name = "potion of healing", glyph = "!", power = power }
+end
+
+function Items.potionOf(effect, power)
+  local spec
+  for _, entry in ipairs(Items.potionTypes) do
+    if entry.effect == effect then spec = entry end
+  end
+  return { kind = Items.POTION, effect = effect, name = spec.name, glyph = "!", power = power or spec.power }
+end
+
+function Items.scroll(effect)
+  local spec
+  for _, entry in ipairs(Items.scrollTypes) do
+    if entry.effect == effect then spec = entry end
+  end
+  return { kind = Items.SCROLL, effect = effect, name = spec.name, glyph = "?" }
+end
+
+function Items.weapon(name, power)
+  return { kind = Items.WEAPON, name = name, glyph = "/", power = power }
+end
+
+function Items.armor(name, power)
+  return { kind = Items.ARMOR, name = name, glyph = "[", power = power }
+end
+
+function Items.ring(name, attack, defense)
+  return { kind = Items.RING, name = name, glyph = "=", attack = attack or 0, defense = defense or 0 }
+end
+
+function Items.food(name, nutrition)
+  return { kind = Items.FOOD, name = name, glyph = "%", nutrition = nutrition }
+end
+
+function Items.key(name)
+  return { kind = Items.KEY, name = name or "iron key", glyph = "*" }
+end
+
+function Items.equipWeapon(item, entity)
+  if entity.weapon then
+    entity.attack = entity.attack - entity.weapon.power
+    entity.inventory[#entity.inventory + 1] = entity.weapon
+  end
+  entity.weapon = item
+  entity.attack = entity.attack + item.power
+  return item.power
+end
+
+function Items.equipArmor(item, entity)
+  if entity.armor then
+    entity.defense = entity.defense - entity.armor.power
+    entity.inventory[#entity.inventory + 1] = entity.armor
+  end
+  entity.armor = item
+  entity.defense = entity.defense + item.power
+  return item.power
+end
+
+function Items.equipRing(item, entity)
+  if entity.ring then
+    entity.attack = entity.attack - entity.ring.attack
+    entity.defense = entity.defense - entity.ring.defense
+    entity.inventory[#entity.inventory + 1] = entity.ring
+  end
+  entity.ring = item
+  entity.attack = entity.attack + item.attack
+  entity.defense = entity.defense + item.defense
+  return item.attack + item.defense
+end
+
+-- Applies a self-contained item to an entity and returns the magnitude of its
+-- effect. Effects that need the wider world (teleport, mapping, fireball) are
+-- routed through the effects module by the game instead.
+function Items.use(item, entity)
+  if item.kind == Items.POTION and item.effect == "heal" then
+    local before = entity.hp
+    entity.hp = math.min(entity.maxHp, entity.hp + item.power)
+    return entity.hp - before
+  elseif item.kind == Items.WEAPON then
+    return Items.equipWeapon(item, entity)
+  elseif item.kind == Items.ARMOR then
+    return Items.equipArmor(item, entity)
+  elseif item.kind == Items.RING then
+    return Items.equipRing(item, entity)
+  end
+  return 0
+end
+
+function Items.useFromInventory(entity, index)
+  local item = table.remove(entity.inventory, index)
+  local effect = Items.use(item, entity)
+  return item, effect
+end
+
+return Items