feat: add applyAffix and Elites.eligible

src/elites.lua

@@ -0,0 +1,162 @@
+-- Elite monsters: rare, affixed variants of the ordinary bestiary. Builder
+-- rolls promotion once a floor's entities are already fully placed (appended
+-- dead last in Builder.build, after every other placement - artifacts, the
+-- boss, the quest board - so it can never perturb an earlier system's rng
+-- sequence, exactly like those do for their own rolls). An elite still rides
+-- the same ai.lua/abilities.lua dispatch and scheduler as any other creature;
+-- only its stats, its name, and the on-hit/on-death/lifesteal hooks Game
+-- wires in separately set it apart from a plain spawn of the same species.
+-- A floor deep enough for a second affix ("champion") draws it from the
+-- remaining pool, so a champion never doubles up on the same one.
+
+local Resistances = require("resistances")
+
+local Elites = {}
+
+Elites.MIN_DEPTH = 3
+Elites.CHAMPION_DEPTH = 7
+
+Elites.affixes = {
+  { key = "brutal",       name = "brutal",       hpMult = 1.2, attack = 3 },
+  { key = "armored",      name = "armored",      hpMult = 1.3, defense = 3 },
+  { key = "swift",        name = "swift",        speed = 30 },
+  { key = "regenerating", name = "regenerating", regen = 3 },
+  { key = "warded",       name = "warded",       resist = Resistances.RESIST },
+  { key = "vampiric",     name = "vampiric",     lifesteal = 0.5 },
+  { key = "chilling",     name = "chilling",     onHit = { status = "slow", duration = 3, potency = 1 } },
+  { key = "volatile",     name = "volatile",     onDeathDamage = 8, onDeathType = Resistances.FIRE },
+}
+
+Elites.byKey = {}
+for _, affix in ipairs(Elites.affixes) do
+  Elites.byKey[affix.key] = affix
+end
+
+-- Elemental types a "warded" roll can pick from - physical is excluded since
+-- every hit already respects the plain attack/defense floor in combat.lua.
+local RESISTABLE = {
+  Resistances.FIRE, Resistances.COLD, Resistances.POISON,
+  Resistances.LIGHTNING, Resistances.ARCANE,
+}
+
+local function applyAffix(entity, affix, rng)
+  entity.eliteAffixes[#entity.eliteAffixes + 1] = affix.key
+  if affix.hpMult then
+    local bonus = math.floor(entity.maxHp * (affix.hpMult - 1))
+    entity.maxHp = entity.maxHp + bonus
+    entity.hp = entity.hp + bonus
+  end
+  if affix.attack then
+    entity.attack = entity.attack + affix.attack
+    entity.baseAttack = entity.baseAttack + affix.attack
+  end
+  if affix.defense then
+    entity.defense = entity.defense + affix.defense
+    entity.baseDefense = entity.baseDefense + affix.defense
+  end
+  if affix.speed then entity.speed = entity.speed + affix.speed end
+  if affix.regen then entity.regen = (entity.regen or 0) + affix.regen end
+  if affix.resist then
+    local element = RESISTABLE[rng:range(1, #RESISTABLE)]
+    entity.resist = entity.resist or {}
+    if entity.resist[element] ~= Resistances.IMMUNE then
+      entity.resist[element] = affix.resist
+    end
+  end
+  entity.name = affix.name .. " " .. entity.name
+end
+
+-- Eligible for promotion: a plain bestiary spawn, never a boss (already the
+-- rarer, sturdier variant) or the passive shopkeeper.
+function Elites.eligible(entity)
+  return entity.kind == "monster" and not entity.isBoss and entity.ai ~= "vend"
+end
+
+-- Rolled once per eligible monster after a floor's entities are already
+-- placed. Mutates `entity` in place; a no-op below Elites.MIN_DEPTH, on an
+-- ineligible entity, or when the roll simply misses.
+function Elites.maybePromote(rng, entity, depth)
+  if depth < Elites.MIN_DEPTH or not Elites.eligible(entity) then return end
+  if not rng:chance(1, 6) then return end
+  entity.elite = true
+  entity.eliteAffixes = {}
+  local pool = {}
+  for i, affix in ipairs(Elites.affixes) do pool[i] = affix end
+  local rolls = 1
+  if depth >= Elites.CHAMPION_DEPTH and rng:chance(1, 3) then rolls = 2 end
+  for _ = 1, rolls do
+    if #pool == 0 then break end
+    local idx = rng:range(1, #pool)
+    applyAffix(entity, pool[idx], rng)
+    table.remove(pool, idx)
+  end
+  entity.eliteTier = #entity.eliteAffixes >= 2 and "champion" or "elite"
+end
+
+-- The first volatile affix on `entity`, if any - the death burst
+-- Game:awardKill triggers right after Abilities.onDeath.
+function Elites.explosionFor(entity)
+  if not entity.eliteAffixes then return nil end
+  for _, key in ipairs(entity.eliteAffixes) do
+    local affix = Elites.byKey[key]
+    if affix and affix.onDeathDamage then return affix end
+  end
+  return nil
+end
+
+-- The status rider (if any) a hit landed by `entity` should apply to its
+-- victim - same shape as a weapon affix's onHit (see affixes.lua), so Game
+-- can hand it straight to Status.apply.
+function Elites.onHitRider(entity)
+  if not entity.eliteAffixes then return nil end
+  for _, key in ipairs(entity.eliteAffixes) do
+    local affix = Elites.byKey[key]
+    if affix and affix.onHit then return affix.onHit end
+  end
+  return nil
+end
+
+-- Fraction of dealt damage `entity` heals back on a hit it lands, summed
+-- across its affixes (never more than one vampiric roll in practice).
+function Elites.lifestealFraction(entity)
+  if not entity.eliteAffixes then return 0 end
+  local total = 0
+  for _, key in ipairs(entity.eliteAffixes) do
+    local affix = Elites.byKey[key]
+    if affix and affix.lifesteal then total = total + affix.lifesteal end
+  end
+  return total
+end
+
+-- Bonus xp a felled elite is worth on top of its plain species reward: half
+-- again for a single-affix elite, a full second helping for a champion.
+function Elites.xpBonus(entity, baseXp)
+  if not entity.elite then return 0 end
+  local mult = entity.eliteTier == "champion" and 1.0 or 0.5
+  return math.floor(baseXp * mult)
+end
+
+-- Fired from Game:awardKill right after Abilities.onDeath: a volatile
+-- elite's corpse bursts, scorching the player and any companion or monster
+-- adjacent to it (itself excluded) for its cataloged damage and type.
+function Elites.onDeath(game, monster)
+  local affix = Elites.explosionFor(monster)
+  if not affix then return nil end
+  local hit = {}
+  local targets = { game.player }
+  for _, other in ipairs(game:currentEntities()) do targets[#targets + 1] = other end
+  for _, victim in ipairs(targets) do
+    if victim ~= monster and victim:isAlive()
+      and math.abs(victim.x - monster.x) <= 1 and math.abs(victim.y - monster.y) <= 1 then
+      local dealt = Resistances.apply(victim, affix.onDeathDamage, affix.onDeathType)
+      if dealt > 0 then
+        victim.hp = victim.hp - dealt
+        hit[#hit + 1] = string.format("%s for %d", victim.name, dealt)
+      end
+    end
+  end
+  if #hit == 0 then return nil end
+  return string.format("%s bursts, scorching %s", monster.name, table.concat(hit, ", "))
+end
+
+return Elites