feat: add Artifacts.create and Artifacts.lifestealAmount

src/artifacts.lua

@@ -0,0 +1,133 @@
+-- Unique named gear. Unlike a rolled affix (affixes.lua), which stacks a
+-- small power bump onto an ordinary base item, an artifact is a fixed,
+-- always-on mechanic attached to a fixed item - lifesteal, thorns, a passive
+-- regen aura, an armour-ignoring shot. Artifacts are never masked by
+-- identification: identify.isConcealable only conceals potions and scrolls,
+-- so a found artifact shows its real name and effect immediately.
+--
+-- Builder places at most one per floor from depth 5 on, its rarity roll
+-- appended after every other placement (see builder.lua) so it can never
+-- perturb an earlier system's rng sequence. Per-floor rng is independent
+-- (dungeon.lua reseeds fresh per depth), so this is a per-floor rarity, not a
+-- tracked one-per-run guarantee the way the amulet is.
+
+local Items = require("items")
+
+local Artifacts = {}
+
+Artifacts.LIFESTEAL = "lifesteal"
+Artifacts.THORNS = "thorns"
+Artifacts.REGEN = "regen"
+Artifacts.PIERCING = "piercing"
+
+Artifacts.catalog = {
+  {
+    key = "bloodfang", slot = "weapon", name = "Bloodfang", power = 4,
+    unique = Artifacts.LIFESTEAL, value = 0.5,
+  },
+  {
+    key = "aegis_of_embers", slot = "armor", name = "Aegis of Embers", power = 2,
+    unique = Artifacts.THORNS, value = 0.5,
+  },
+  {
+    key = "ring_of_the_tide", slot = "ring", name = "Ring of the Tide", attack = 1, defense = 1,
+    unique = Artifacts.REGEN, value = 2,
+  },
+  {
+    key = "gale_bow", slot = "bow", name = "Gale Bow", power = 3, range = 6,
+    unique = Artifacts.PIERCING, value = 3,
+  },
+  {
+    key = "cinderplate", slot = "armor", name = "Cinderplate", power = 2,
+    resist = { fire = "resist" },
+  },
+  {
+    key = "frostband", slot = "ring", name = "Frostband", attack = 0, defense = 1,
+    resist = { cold = "resist" },
+  },
+
+  -- Boss-exclusive drops (bosses.lua): stronger versions of an existing
+  -- unique mechanic, flagged bossOnly so the loop below keeps them out of
+  -- Artifacts.order and therefore out of builder.lua's ordinary per-floor
+  -- roll. The only way to obtain one is felling the boss that guarantees it.
+  {
+    key = "warlords_cleaver", slot = "weapon", name = "the Warlord's Cleaver", power = 6,
+    unique = Artifacts.LIFESTEAL, value = 0.75, bossOnly = true,
+  },
+  {
+    key = "lich_phylactery", slot = "ring", name = "the Lich's Phylactery", attack = 1, defense = 2,
+    unique = Artifacts.REGEN, value = 4, bossOnly = true,
+  },
+  {
+    key = "bone_queen_carapace", slot = "armor", name = "the Bone Queen's Carapace", power = 4,
+    unique = Artifacts.THORNS, value = 0.9, bossOnly = true,
+  },
+}
+
+Artifacts.byKey = {}
+Artifacts.order = {}
+for _, spec in ipairs(Artifacts.catalog) do
+  Artifacts.byKey[spec.key] = spec
+  if not spec.bossOnly then
+    Artifacts.order[#Artifacts.order + 1] = spec.key
+  end
+end
+
+-- Builds the dropped item for `key` in the same shape items.lua's own
+-- constructors return for that slot, tagged with the fields the equip
+-- callers below key their special-case behaviour off (`unique` and `value`).
+function Artifacts.create(key)
+  local spec = Artifacts.byKey[key]
+  if not spec then return nil end
+  local item
+  if spec.slot == "weapon" then
+    item = Items.weapon(spec.name, spec.power)
+  elseif spec.slot == "armor" then
+    item = Items.armor(spec.name, spec.power)
+  elseif spec.slot == "ring" then
+    item = Items.ring(spec.name, spec.attack, spec.defense)
+  elseif spec.slot == "bow" then
+    item = Items.bow(spec.name, spec.power, spec.range)
+  end
+  item.artifact = key
+  item.unique = spec.unique
+  item.value = spec.value
+  item.resist = spec.resist
+  return item
+end
+
+-- Hp returned to `attacker` from a lifesteal weapon's hit, or 0 without one.
+function Artifacts.lifestealAmount(attacker, damage)
+  local weapon = attacker.weapon
+  if weapon and weapon.unique == Artifacts.LIFESTEAL then
+    return math.max(1, math.floor(damage * weapon.value))
+  end
+  return 0
+end
+
+-- Damage reflected back at whoever just landed a melee hit on `defender`, or
+-- 0 without thorned armour worn.
+function Artifacts.thornsAmount(defender, damage)
+  local armor = defender.armor
+  if armor and armor.unique == Artifacts.THORNS then
+    return math.max(1, math.floor(damage * armor.value))
+  end
+  return 0
+end
+
+-- Hp `entity` regenerates this turn from a worn ring, or 0 without one.
+function Artifacts.ringRegen(entity)
+  local ring = entity.ring
+  if ring and ring.unique == Artifacts.REGEN then return ring.value end
+  return 0
+end
+
+-- Flat defense `entity`'s readied bow ignores on its next shot, or 0 without
+-- a piercing bow.
+function Artifacts.bowPierce(entity)
+  local bow = entity.bow
+  if bow and bow.unique == Artifacts.PIERCING then return bow.value end
+  return 0
+end
+
+return Artifacts